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Effects of inescapable shock and shock-produced conflict on self selection of alcohol in rats
Pharmacology Biochemistry and Behavior, Vol. 2, pp. 2 7 - 3 3 . ANKHO International Inc., 1974. Printed in the U.S.A.
Effects of Inescapable Shock and Shock-Produced Conflict on Self Selection of Alcohol in Rats H Y M I E A N I S M A N A N D T. G A R Y W A L L E R
University o f Waterloo, Waterloo, Ontario, Canada
( R e c e i v e d 12 April 1 9 7 3 ) ANISMAN, H. AND T. G. WALLER. Effects of inescapable shock and shock-produced conflict on self selection of alcohol in rats. PHARMAC. BIOCHEM. BEHAV. 2(1) 2 7 - 3 3 , 1974. - In five experiments it was found that stress of inescapable unavoidable shock produced increased self selection of alcohol. These effects were maintained only so long as the shock schedule was continued. Factors such as predictability of shock, shock schedule and nutritional deficiency were found not to alter alcohol consumption substantially. In contrast to the effects of inescapable unavoidable stress, shock-produced conflict did not lead to the self selection of alcohol. Results were interpreted in terms of a Tension Reduction Hypothesis and the role of control over aversive stimulation. Inescapable shock
Conflict
Self selection of alcohol
d r i n k i n g b e h a v i o r c a n n o t be c o n s i d e r e d a defensive r e a c t i o n in t h e rats r e p e r t o i r e of responses [5 ] it is n o t at all surprising t h a t t h e t e n d e n c y to c o n s u m e alcohol is a c q u i r e d as slowly as it is. It would be e x p e c t e d t h a t if t h e p r o b a b i l i t y of alcohol b e i n g sampled were m a x i m i z e d while the organism were in t h e stressful s i t u a t i o n , t h e n t h e c o n s u m a t o r y r e s p o n s e s s h o u l d b e a c q u i r e d m o r e readily. P r e l i m i n a r y i n v e s t i g a t i o n s carried o u t at o u r l a b o r a t o r i e s i n d i c a t e d t h a t o n e m e t h o d w h i c h is f r u i t f u l in this respect is simply to c o n t i n u o u s l y h o u s e the a n i m a l in t h e stressful s i t u a t i o n w i t h b o t h a l c o h o l and w a t e r freely available. In each of t h e studies t o be r e p o r t e d this t e c h n i q u e was e m p l o y e d . The variables m a n i p u l a t e d in each o f the e x p e r i m e n t s essentially r e p r e s e n t e d a n a t t e m p t to f u r t h e r e n h a n c e t h e rates of self selection o f e t h a n o l in an aversive s i t u a t i o n .
S E V E R A L investigators have d e m o n s t r a t e d t h a t e t h y l a l c o h o l decreases t h e n u m b e r o f r e s p o n s e s m a d e in a n active a v o i d a n c e task [2,4] and increases t h e d i s t a n c e subjects will a p p r o a c h in an a p p r o a c h - a v o i d a n c e c o n f l i c t s i t u a t i o n [ 3, 12, 13 ]. On t h e basis o f t h e s e e x p e r i m e n t s , as well as a n u m b e r of o t h e r c o m p a r a b l e r e p o r t s [ 8 ] , it h a d b e e n suggested t h a t e t h a n o l reduces stress in aversively motivated situations (Tension Reduction Hypothesis). It follows t h a t if e t h a n o l r e d u c e s t e n s i o n associated with t h e stress o f electric s h o c k , t h e n v o l u n t a r y a l c o h o l cons u m p t i o n in an aversive s i t u a t i o n s h o u l d be r e i n f o r c i n g and, c o n s e q u e n t l y , s h o u l d increase in f r e q u e n c y . H o w e v e r , p a r a d o x i c a l results have b e e n r e p o r t e d c o n c e r n i n g this p r e d i c t i o n . Myers and H o l m a n [14] r e p o r t e d t h a t n e i t h e r a c c l i m a t i o n t o alcohol, or s h o c k p r e s e n t e d on a partial s c h e d u l e (variable or fixed i n t e r v a l ) resulted in i n c r e a s e d a l c o h o l c o n s u m p t i o n . Similarly, Casey [9] f o u n d t h a t a l c o h o l c o n s u m p t i o n did n o t increase u n t i l 16 days after a stress t r e a t m e n t was t e r m i n a t e d . In c o n t r a s t t o these r e p o r t s , several o t h e r investigators (e.g., [1, 11, 17] f o u n d t h a t v o l u n t a r y alcohol c o n s u m p t i o n increased as a result of stress p r o d u c e d b y electric shock. One f a c t o r w h i c h m i g h t a c c o u n t for these d i s c r e p a n t results c o n c e r n s t h e o p p o r t u n i t y animals have for s a m p l i n g the alcohol. Specifically, since v o l u n t a r y alcohol c o n s u m p t i o n in a stressful s i t u a t i o n is essentially a m o d e of escaping or avoiding stress, t h e rate o f acquiring t h e c o n s u m a t o r y r e s p o n s e s h o u l d be r e g a r d e d in t h e same f a s h i o n as w o u l d a r u n n i n g or b a r - p r e s s a v o i d a n c e response. Specifically, since
EXPERIMENT 1 One variable w h i c h m a y i n f l u e n c e the degree of volit i o n a l a l c o h o l c o n s u m p t i o n is the s t r e s s - r e s t s c h e d u l e to w h i c h a n i m a l s are s u b j e c t e d . Specifically, it has b e e n d e m o n s t r a t e d t h a t m o n k e y s [6,7] and rats [18] are m o r e p r o n e to gastric u l c e r a t i o n w h e n m a i n t a i n e d o n a 6 h r s t r e s s - 6 h r rest s c h e d u l e t h a n o n a 12 hr s t r e s s - 1 2 hr rest schedule, suggesting t h a t animals are less able to cope, via i n t e r n a l m e c h a n i s m s , w i t h stress p r e s e n t e d o n a 6 h r - 6 h r schedule. If t h e degree of stress, or the o r g a n i s m ' s ability to cope w i t h stress, is related to self s e l e c t i o n of alcohol, t h e n it s h o u l d follow t h a t alcohol c o n s u m p t i o n w o u l d be differentially a f f e c t e d b y t h e s t r e s s - r e s t s c h e d u l e e m p l o y e d .
The research was supported by a grant from Licensed Beverage Industric, Inc. Requests for reprints should be sent to Hymie Anisman, Department of Psychology, University of Waterloo, Waterloo, N2L 3G1, Ontario, Canada. 27
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ANISMAN AND WALLER
METHOD
Animals Twelve e x p e r i m e n t a l l y naive male H o l t z m a n rats weighing 2 3 0 - 2 5 0 g u p o n arrival f r o m t h e H o l t z m a n Co., Madison, Wisconsin were used. Rats were i n d i v i d u a l l y h o u s e d in s t a n d a r d wire cages w i t h ad lib f o o d a n d w a t e r for seven days p r i o r to a n y e x p e r i m e n t a l t r e a t m e n t . A t t h e start o f t h e e x p e r i m e n t rats weighed 2 6 0 - 2 8 0 g.
Apparatus During the course of the e x p e r i m e n t twelve Plexiglas c h a m b e r s (23 x 21 x 20 c m ) served as the a n i m a l s ' living quarters. T h e f l o o r of each c h a m b e r consisted of 0.16 cm stainless steel rods, spaced 1.25 cm apart ( c e n t e r to c e n t e r ) , t h r o u g h w h i c h electric s h o c k o f 1.0 m A ( c o n s t a n t c u r r e n t , 60 cycle AC) could be delivered. O c c u r e n c e s of s h o c k periods, d u r a t i o n o f s h o c k s a n d i n t e r s h o c k intervals were p r o g r a m m e d t h r o u g h a series o f timers, relays a n d a tape drive. Holes drilled in o n e wall of e a c h c h a m b e r , 8.0 cm a p a r t a n d 4.0 cm a b o v e t h e grid floor, p e r m i t t e d t h e insert i o n of d r i n k i n g s p o u t s o f 100 cc g r a d u a t e d cylinders. Size o f d r i n k i n g s p o u t s were u n i f o r m for all animals a n d p e r m i t ted a p p r o x i m a t e l y 1 - 3 cc of spillage or e v a p o r a t i o n over a 24 h r period.
Procedure Rats were r a n d o m l y assigned to t h r e e groups. Rats in one g r o u p received a single 2 sec signaled i n e s c a p a b l e s h o c k every 30 rain d u r i n g a l t e r n a t e 6 h r periods ( G r o u p 6 - 6 ) . A s e c o n d g r o u p similarly received s h o c k every 30 min. However, s h o c k periods o c c u r r e d d u r i n g a l t e r n a t e 12 hr periods ( G r o u p 1 2 - 1 2 ) . Finally, a t h i r d g r o u p received n o s h o c k e x p o s u r e ( G r o u p 0 - 0 ) . S h o c k periods in t h e 6 6 and 1 2 - 1 2 g r o u p s were c o u n t e r b a l a n c e d such t h a t , while s h o c k was o n for h a l f the animals, it was o f f for t h e r e m a i n i n g rats. T h e s h o c k b e g a n on the second day of the e x p e r i m e n t a n d c o n t i n u e d 11 days. Rats were m a i n t a i n e d in t h e c h a m b e r s for 4 a d d i t i o n a l days f o l l o w i n g t e r m i n a t i o n of t h e shock treatment. A l c o h o l a n d w a t e r were available ad lib t h r o u g h o u t t h e e x p e r i m e n t . On Day 1 ( w h e n n o s h o c k was p r e s e n t e d ) the c o n c e n t r a t i o n of alcohol was 2% (v/v). C o n s u m p t i o n of w a t e r and alcohol on this day served as t h e baseline cons u m p t i o n rate. On s u b s e q u e n t days the a l c o h o l c o n c e n t r a tion was increased daily in 1% i n c r e m e n t s until the c o n c e n t r a t i o n was 10% (v/v). The 10% c o n c e n t r a t i o n was m a i n t a i n e d for t h e d u r a t i o n of t h e e x p e r i m e n t . The posit i o n s o f the alcohol a n d w a t e r cylinders were varied twice daily ( 0 9 0 0 a n d 1700 Hr) o n a r a n d o m s c h e d u l e a n d fluid c o n s u m p t i o n was r e c o r d e d daily at 0 9 0 0 Hr. Only a single baseline day was e m p l o y e d , since t h e cons u m p t i o n o f a l c o h o l at the 2% c o n c e n t r a t i o n h a d previously n o t b e e n f o u n d to b e predictive of s u b s e q u e n t c o n s u m p t i o n w i t h increasing alcohol c o n c e n t r a t i o n s . T h e p u r p o s e o f t h e n o n s h o c k day was essentially to p e r m i t t h e animals to h a b i t u a t e to t h e novel e n v i r o n m e n t . A c c o r d i n g l y , t h e self s e l e c t i o n o f a l c o h o l a m o n g s h o c k groups w i t h i n the p r e s e n t i n v e s t i g a t i o n s h o u l d be c o n s i d e r e d w i t h respect t o n o n s h o c k groups r a t h e r t h a n the baseline measure. RESULTS
Figure 1 s h o w s the m e a n q u a n t i t y of a l c o h o l and w a t e r
c o n s u m e d daily by each of the groups. An analysis of variance of t h e fluid c o n s u m p t i o n yielded a signficiant S h o c k t r e a t m e n t x Fluid i n t e r a c t i o n ( F ( 2 , 9) = 4.72, p < 0 . 0 5 ) . S u b s e q u e n t m u l t i p l e c o m p a r i s o n s i n d i c a t e d t h a t rats in b o t h s h o c k groups c o n s u m e d m o r e alcohol t h a n did the n o n s h o c k group, h o w e v e r , alcohol c o n s u m p t i o n did n o t differ b e t w e e n the t w o s h o c k groups. A m o n g rats in G r o u p 6 - 6 a p r e f e r e n c e for alcohol was d e v e l o p e d w i t h i n 3 days o f t h e c o m m e n c e m e n t of the s h o c k schedule, whereas a m o n g rats in G r o u p 12--12 an alcohol p r e f e r e n c e was e v i d e n t as early as the first s h o c k day. It s h o u l d be n o t e d t h a t this p r e f e r e n c e was n o t e v i d e n t u n t i l the s h o c k schedule was c o m m e n c e d ; witness the lack o f an alcohol preference e x h i b i t e d b y all groups d u r i n g the n o n s h o c k day. I n s p e c t i o n of fluid c o n s u m p t i o n a m o n g the animals w i t h i n each g r o u p revealed for b o t h the 6 - 6 and 12 12 groups, 3 of t h e 4 animals s h o w e d s t r o n g p r e f e r e n c e s for alcohol over water, whereas a m o n g the animals in the 0 - 0 group only o n e rat s h o w e d a n y p r e f e r e n c e for alcohol, a n d this was restricted t o the first few days of t r a i n i n g where alcohol c o n c e n t r a t i o n s were relatively low. A l t h o u g h the Shock T r e a t m e n t x Fluid x Days Interact i o n was n o t significant, i n s p e c t i o n o f t h e data (see Fig. 1) i n d i c a t e d t h a t c o n s u m p t i o n of alcohol in the s h o c k groups decreased following the t e r m i n a t i o n of t h e s h o c k schedule. T h e decrease was m u c h m o r e e v i d e n t for G r o u p 6 - 6 t h a n G r o u p 12 12. Nevertheless, d i f f e r e n c e s b e t w e e n alcohol and w a t e r c o n s u m p t i o n a m o n g the 6 6 and 1 2 - 1 2 groups did n o t a p p r o a c h statistical significance. It is i n t e r e s t i n g to n o t e t h a t a l t h o u g h the v o l u n t a r y c o n s u m p t i o n of alcohol was d e p e n d e n t on t h e p r e s e n c e of shock, n o s y s t e m a t i c d i f f e r e n c e s in c o n s u m p t i o n were e v i d e n t d u r i n g stress and rest periods a m o n g e i t h e r of the s h o c k groups. A l t h o u g h c o n s t a n t i l l u m i n a t i o n was provided, animals t e n d e d to c o n s u m e m o s t of the fluid d u r i n g n i g h t h o u r s of the diurnal cycle (9 p . m . - 9 a.m.). The general t r e n d of t h e results were c o n s i s t e n t regardless of w h e t h e r the data was a n a l y z e d in t e r m s of t o t a l v o l u m e s of fluid c o n s u m e d or a b s o l u t e alcohol c o n s u m e d / k i l o g r a m b o d y weight (X a l c o h o l / k g d u r i n g s h o c k days = 3.04 ml/kg, 7 . 8 0 m l / k g , 6 . 1 6 m l / k g for the 0 - 0 , 6 - 6 and 1 2 - 1 2 groups respectively). I m m e d i a t e l y following the t e r m i n a t i o n of the experim e n t rats were disected and s t o m a c h e s e x a m i n e d for ulceration. N o n e of the rats were f o u n d to have gastric u l c e r a t i o n . DISCUSSION
In a c c o r d a n c e with earlier r e p o r t s (e.g. [1, 11, 1 7 ] , the results of E x p e r i m e n t 1 i n d i c a t e d t h a t stress o f electric s h o c k was effective in p r o d u c i n g volitional alcohol cons u m p t i o n to the e x t e n t t h a t alcohol, the originally n o n preferred fluid, b e c a m e the preferred one. Moreover, this was f o u n d to be the case regardless of w h e t h e r rats were shocked on a 6hr on-6hr off or 1 2 h r o n - 1 2 h r off schedule. While the p r o c e d u r e of m a i n t a i n i n g rats in the s h o c k c h a m b e r t h r o u g h o u t the e x p e r i m e n t a l t r e a t m e n t , and increasing the daily c o n c e n t r a t i o n of alcohol in small i n c r e m e n t s , m a y have p r o m p t e d v o l u n t a r y alcohol cons u m p t i o n , this p r o c e d u r e in itself was n o t sufficient to p r o m o t e s e l e c t i o n o f alcohol as the p r e f e r r e d beverage. Rather, the necessary c o n d i t i o n appears to be t h a t s h o c k be a d m i n i s t e r e d to animals. These data are c o n s i s t e n t w i t h the T e n s i o n R e d u c t i o n H y p o t h e s i s . Specifically, a l c o h o l pres u m a b l y reduces stress, is thus r e i n f o r c i n g and c o n s e q u e n t l y
EFFECTS
OF STRESS ON SELF SELECTION
GROUP
OF ALCOHOL
29
Alcohol Water
12-12
50
20 I0
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30 20 °
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3
4
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5 6 7 8 9 I0 I0 I0 I0 I0 I0 I0 I0 ALCOHOL CONCENTRATION PAD) 4
7
I0
13
16
DAYS FIG. 1. Mean and standard deviation of alcohol and water c o n s u m e d (ml) over sixteen days. Note: shock was not delivered on Days 1 3 - 1 6 .
30
ANISMAN AND WALLER
increases in f r e q u e n c y . T h e fact t h a t t h e v o l u m e o f a l c o h o l c o n s u m e d declined in t h e s h o c k g r o u p s w h e n the s h o c k t r e a t m e n t was t e r m i n a t e d suggests t h a t self selection is due t o p h y s i c a l stress ( s h o c k ) and n o t s e c o n d a r y s t i m u l i (i.e., i m p l i c i t a n d explicit cues of the s h o c k c h a m b e r ) .
TABLE 1 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF VARIABLE INTERVAL SHOCK AND FOOD DEPRIVATION (EXPERIMENT 2)
EXPERIMENT 2 A l t h o u g h t h e m o s t p a r s i m o n i o u s e x p l a n a t i o n of the data o b s e r v e d in E x p e r i m e n t 1 is in t e r m s of t h e T e n s i o n Reduct i o n H y p o t h e s i s , an a l t e r n a t i v e i n t e r p r e t a t i o n of these data does exist. Specifically, d u r i n g t h e first few days o f t h e s t r e s s s c h e d u l e s h o c k e d rats d e m o n s t r a t e d a m a r k e d decrease in weight ( m e a n weight loss b e i n g 14.5 gin). A c c o r d i n g l y , it can be argued t h a t b e c a u s e e t h a n o l has a greater n u t r i t i v e value [19] a n i m a l s are m o r e apt to c o n s u m e this fluid t h a n tap water. If this were t h e case, t h e n f o o d d e p r i v a t i o n s h o u l d increase self s e l e c t i o n of a l c o h o l even a m o n g n o n s h o c k e d rats. O n e p u r p o s e of E x p e r i m e n t 2 was t o test such a possibility. A s e c o n d p o i n t of i n t e r e s t w i t h respect t o E x p e r i m e n t 1 is the fact t h a t unsignaled s h o c k p r o d u c e d v o l i t i o n a l cons u m p t i o n of alcohol. Previous r e p o r t s [10] h a d i n d i c a t e d t h a t a necessary requisite for alcohol c o m s u m p t i ' o n to increase is t h a t a signal b e i m p l i c i t l y paired w i t h t h e shock. While the results of E x p e r i m e n t 1 are clearly i n c o m p a t i b l e w i t h t h e findings r e p o r t e d b y Cicero et al. [ 1 0 ] , it is possible t h a t t e m p o r a l cues served as a w a r n i n g signal for s h o c k , since s h o c k was p r e s e n t e d at fixed intervals. Were this the case, t h e n v o l i t i o n a l a l c o h o l c o n s u m p t i o n s h o u l d n o t increase if unsignaled s h o c k were p r e s e n t e d at r a n d o m intervals. E x p e r i m e n t 2 was designed t o test s u c h a prediction. METHOD T h e a p p a r a t u s and strain of rats was the same as t h a t used in E x p e r i m e n t 1. Twelve rats were r a n d o m l y assigned to o n e of t h r e e t r e a t m e n t c o n d i t i o n s . Rats in o n e group received ad lib food, a n d s h o c k o n a r a n d o m s c h e d u l e ( t w o 1.0mA 2sec shocks/hr) on a 6hr on-6hr off basis. A s e c o n d group received t h e same s h o c k t r e a t m e n t b u t received o n l y one h r of feeding t i m e per day. Finally rats in a t h i r d g r o u p received n o s h o c k b u t were p e r m i t t e d f o o d o n t h e same s c h e d u l e as t h e d e p r i v e d group. A l c o h o l and w a t e r were p r e s e n t e d t o rats in e a c h g r o u p on t h e same r e g i m e n as described in E x p e r i m e n t 1. Rats were m a i n t a i n e d on this s c h e d u l e over a 22 day period.
Fluid Alcohol
Water
8.7
29.8
Shocked food deprived
19.5
19.4
Shocked non-deprived
23.5
26.7
Group
Non-shocked food deprived
As in E x p e r i m e n t 1, n o n s h o c k e d animals c o n s u m e d significantly more w a t e r t h a n alcohol. In fact in Experim e n t 1, n o n s h o c k e d rats c o n s u m e d a m e a n of 14.2 cc w a t e r and 24.4 cc alcohol daily, while in E x p e r i m e n t 2 n o n s h o c k e d a n i m a l s c o n s u m e d an average of 8.7 cc of alcohol, and 29.8 cc of w a t e r daily. Thus it seems t h a t n o t o n l y did d e p r i v a t i o n n o t increase alcohol c o n s u m p t i o n , b u t r a t h e r it r e d u c e d the q u a n t i t y c o n s u m e d . Clearly, food d e p r i v a t i o n was n o t r e s p o n s i b l e for the self s e l e c t i o n of alcohol o b s e r v e d in s h o c k e d rats in Experim e n t 1 or 2. However, it was n o t e d in E x p e r i m e n t 2 (see Table 1) t h a t a l t h o u g h s h o c k e d rats c o n s u m e d m o r e a l c o h o l t h a n did n o n s h o c k e d rats, n o p r e f e r e n c e for alcohol over w a t e r was d e m o n s t r a t e d by the s h o c k e d groups. Since it is u n c l e a r w h e t h e r this was due to the r a n d o m s h o c k schedule, or simply a s p u r i o u s result, a subs e q u e n t e x p e r i m e n t e m p l o y i n g n o n s h o c k e d (n = 4) and r a n d o m l y s h o c k e d animals (n = 4) was carried out. Table 2 s h o w s t h e m e a n t o t a l w a t e r and alcohol c o n s u m p t i o n of these groups over the 13 day test period. It is e v i d e n t t h a t rats w h i c h received s h o c k on a r a n d o m s c h e d u l e c o n s u m e d m o r e alcohol t h a n did n o n s h o c k e d rats, a n d also d e m o n s t r a t e d a p r e f e r e n c e for alcohol over w a t e r as h a d b e e n seen in E x p e r i m e n t 1. In each of t h e s e t w o studies, e x a m i n a t i o n of the s t o m a c h e s yielded n o evidence of u l c e r a t i o n . This was also f o u n d to b e the case in several a d d i t i o n a l and similar studies w h e r e rats received s h o c k and were p e r m i t t e d access only to water. It appears t h a t u l c e r a t i o n was n o t a b y p r o d u c t of t h e stress t r e a t m e n t e m p l o y e d .
RESULTS AND DISCUSSION T a b l e 1 s h o w s t h e m e a n daily v o l u m e s of w a t e r a n d of alcohol s o l u t i o n c o n s u m e d over t h e 22 day t e s t i n g period. An analysis of variance of t h e fluid v o l u m e s c o n s u m e d yielded a significant T r e a t m e n t x Fluid i n t e r a c t i o n ( F ( 2 , 3) = 5.22, p < 0 . 0 5 ) . C o m p a r i s o n s b e t w e e n the m e a n s involved in the i n t e r a c t i o n i n d i c a t e d t h a t b o t h s h o c k groups c o n s u m e d m o r e alcohol t h a n did the food d e p r i v e d n o n s h o c k g r o u p ( p < 0 . 0 5 ) . Moreover, t h e shockf o o d d e p r i v e d g r o u p c o n s u m e d less alcohol t h a n did t h e s h o c k n o n d e p r i v e d group. It is unclear, h o w e v e r , w h e t h e r this was a result of f o o d d e p r i v a t i o n resulting in t h e a l c c h o l b e i n g more effective as a stress r e d u c e r , or w h e t h e r it is s i m p l y a m a t t e r of t h e n o n d e p r i v e d group consuming more fluid (as was the case for w a t e r consumption),
TABLE 2 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF SHOCK PRESENTED ON A VARIABLE INTERVAL SCHEDULE (EXPERIMENT 2)
Fluid Group
Alcohol
Water
Shock
26.6
13.6
Non-shock
18.0
22.1
E F F E C T S O F S T R E S S ON S E L F S E L E C T I O N O F A L C O H O L
EXPERIMENT 3 In each of the previous e x p e r i m e n t s the rats had no control over the occurence of shock. Under these conditions alcohol c o n s u m p t i o n was reliably found to increase, but in no case was ulceration found in any of the animals. Given these findings it would be interesting to determine whether some degree of control over shock would produce ulceration and w h e t h e r this procedure would also produce v o l u n t a r y alcohol c o n s u m p t i o n . As previously indicated, alcohol has typically been found to reduce avoidance behavior in a conflict situation [ 3 , 1 2 ] , presumably because of its tension-reducing properties. It follows then, that in a conflict situation where free choice alcohol and water are available, the probability of alcohol being consumed should increase. Moreover, because of the animals partial control over shock in such a situation it is likely that ulceration may occur as indicated by Brady (1958). Since strain differences have been found to be an i m p o r t a n t variable in alcohol self selection studies [20] and in studies on gastric ulceration [ 1 6 ] , two strains of rats, H o l t z m a n and S p r a g u e - D a w l e y , were e m p l o y e d in the present investigations. Preliminary unpublished studies indicated that, although stress increased alcohol consumption in H o l t z m a n rats, S p r a g u e - D a w l e y rats e x h i b i t e d a distinct aversion towards alcohol, and a preference for alcohol was not increased through stress. If stress in a conflict situation is more aversive than that of inescapable shock, it might be e x p e c t e d that S p r a g u e - D a w l e y rats would d e m o n s t r a t e increased c o n s u m p t i o n of alcohol.
31
intervals six times an hour, with each shock being 1.0 mA and 2 min in duration. Accordingly, shock was present in one side of the chambers 20% of the time. This t r e a t m e n t was continued for 10 consecutive days. Percentages of alcohol in the daily solutions, and the r a n d o m i z a t i o n of drinking tubes was the same as in E x p e r i m e n t 1. RESULTS AND DISCUSSION Table 3 shows the mean daily volumes of water and of alcohol solution consumed. An analysis of variance of the c o n s u m p t i o n scores did not yield any significant main effects or interactions involving the shock t r e a t m e n t or for strain of rats. In fact, subjects in the conflict group c o n s u m e d slightly less alcohol than did the isolated group. This difference, however, did not approach statistical significance. The analyses o f variance of the absolute alcohol c o n s u m e d / k g b o d y weight and volume of alcohol/ water ratio yielded similar results. Moreoever, inspection of the c o n s u m p t i o n scores over days revealed no systema t i c c h a n g e s in the volumes of alcohol consumed. E x a m i n a t i o n of the animals stomachs again revealed no signs of ulceration in any of the groups.
TABLE 3 MEAN DAILY VOLUME (ml) OF WATER AND ALCOHOL CONSUMED AS A FUNCTION OF STRESS TREATMENT (EXPERIMENT 3)
METHOD
Animals Animals were 24 male rats weighing 2 3 0 - 2 5 0 gm u p o n arrival from the supplier. Half the rats were of the H o l t z m a n strain and obtained f r o m the H o l t z m a n Co., Madison, Wisconsin, while the remaining rats were of the Sprague-Dawley strain procured from the S p r a g u e Dawley Co., Madison, Wisconsin.
Fluid Group
Alcohol
Water
Non-shock
16.3
27.9
Conflict
16.9
23.2
Isolated
20.8
20.6
Apparatus The testing chambers were the same as those described in E x p e r i m e n t 1. The wiring of the grid floor in the eight shock chambers was modified. For half the chambers the part of the grid floor which could be electrified was that nearer the drinking spouts, while for the remaining chambers the grid floor which could be electrified was on the side opposite the drinking spouts.
Procedure Rats of each strain were r a n d o m l y assigned to one of three t r e a t m e n t groups. Unlike E x p e r i m e n t s 1 and 2 the shock schedule was maintained continuously through each 24 hr period. One group received no shock, a second group received shock only on the side of the chamber where the drinking spouts were located (conflict group), and a third group received shock only on the side of the chamber opposite the drinking spouts (isolated group). The third group was included to control for learning to stay on one side of the chamber, and to control for possible effects of restricted m o v e m e n t experienced by the conflict group. Electric shock was presented at r a n d o m
While these data appear inconsistent with a tension reduction hypothesis, there are several factors which may have been influential in producing these effects. Specifically, since shock occurred only 20% of the time, rats may often have avoided the shock and were thus not sufficiently stressed. Thus in E x p e r i m e n t 4 the probability of shock being present was increased from 20% to 80%. EXPERIMENT 4
Apparatus and Procedure The apparatus and procedure were the same as in E x p e r i m e n t 3 e x c e p t that shock was presented r a n d o m l y on 24 occasions during each h o u r (each shock being 2 min in duration), thus resulting in the grid floor being electrified 80% of the time. Unlike E x p e r i m e n t 3, this study e m p l o y e d only H o l t z m a n rats (n = 12) since differences in alcohol c o n s u m p t i o n were in fact not evident b e t w e e n the strains.
32
ANISMAN AND WALLER RESULTS AND DISCUSSION
Table 4 s h o w s t h e m e a n v o l u m e s o f a l c o h o l a n d w a t e r c o n s u m e d b y each of t h e t r e a t m e n t groups. An analysis o f v a r i a n c e of t h e fluid v o l u m e s c o n s u m e d yielded n o significant m a i n effects or i n t e r a c t i o n s . If t h e d a t a were a n a l y z e d in t e r m s of a b s o l u t e alcohol c o n s u m e d / k g b o d y weight, a significant T r e a t m e n t s m a i n e f f e c t was o b t a i n e d ( F ( 2 , 9) = 4.65, p < 0 . 0 5 ) . C o m p a r i s o n s b e t w e e n the m e a n s involved in this m a i n effect i n d i c a t e d t h a t the c o n f l i c t g r o u p c o n s u m e d significantly less a l c o h o l t h a n did t h e r e m a i n i n g t w o groups. T h e m a i n source for this d i f f e r e n c e , as seen in Table 4, seems t o be a result o f t h e c o n f l i c t g r o u p c o n s u m i n g less t o t a l fluid ( a l c o h o l a n d w a t e r ) t h a n t h e r e m a i n i n g groups. TABLE 4 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF STRESS TREATMENT (EXPERIMENT 4)
effective in p r o d u c i n g u l c e r a t i o n . If rats received m o r e or less days o n t h e conflict t r e a t m e n t t h e n u l c e r a t i o n was n o t observed. EXPERIMENT 5 E x p e r i m e n t 5 was a f u r t h e r i n q u i r y i n t o the role of s h o c k p r o d u c e d c o n f l i c t o n v o l u n t a r y alcohol c o n s u m p t i o n . E x p e r i m e n t s 1 - 4 i n d i c a t e d t h a t while unsignaled inescapable s h o c k increases t h e self selection of alcohol, s h o c k p r o d u c e d c o n f l i c t does n o t . As previously suggested, rats in the c o n f l i c t g r o u p c o n s u m e d little fluid ( a l c o h o l or w a t e r ) d u r i n g t h e first few days of t r a i n i n g and t h u s m a y n o t have h a d t h e o p p o r t u n i t y to a d a p t to t h e aversive taste of t h e a l c o h o l s o l u t i o n . C o n s e q u e n t l y , w h e n t h e rats in t h e conflict g r o u p did c o m m e n c e c o n s u m i n g fluid, the increased c o n c e n t r a t i o n o f alcohol p r e s e n t m a y have b e e n relatively m o r e aversive t h a n it was in t h e n o n s h o c k e d or isolated groups, a n d as a result the a l c o h o l was n o t c o n s u m e d in a p p r e c i a b l e q u a n t i t i e s . It follows t h a t if the c o n c e n t r a t i o n o f a l c o h o l were m a i n t a i n e d at a c o n s t a n t weak c o n c e n t r a t i o n , t h a n t h e conflict g r o u p w o u l d d e m o n s t r a t e increased volitional alcohol c o n s u m p t i o n relative to n o n s h o c k e d rats.
Fluid Group
Alcohol
Water
Non-shock
22.0
23.7
Conflict
13.5
14.1
Isolated
21.5
21.2
T h e fact t h a t c o n f l i c t did n o t increase v o l u n t a r y a l c o h o l c o n s u m p t i o n is i n c o m p a t i b l e w i t h a T e n s i o n R e d u c t i o n H y p o t h e s i s . T h e r e are, h o w e v e r , t h r e e d i s t i n c t a l t e r n a t i v e e x p l a n a t i o n s w h i c h m a y a c c o u n t for the o b s e r v e d c o n s u m p t i o n rates a m o n g the c o n f l i c t rats. (a) While the a n i m a l is in t h e c o n f l i c t s i t u a t i o n a d m i n i s t r a t i o n o f alcohol m a y r e d u c e stress. However, w h e n the o r g a n i s m is r e q u i r e d to select t h e a l c o h o l freely, the r e s p o n s e of crossing i n t o the s h o c k side o f t h e c h a m b e r ( p r e s u m a b l y w h e n t h e s h o c k is a b s e n t ) results in t h e conflict b e i n g resolved (at least t e m p o r a r i l y ) , a n d as a result t h e r e is n o n e e d for t h e alcohol. ( b ) Given t h a t t h e o r g a n i s m has some c o n t r o l over the o c c u r r e n c e of s h o c k t h r o u g h e x t e r n a l m e a n s (i.e., crossing or n o t crossing i n t o the s h o c k side), t h e necessity for seeking o t h e r m e a n s o f r e d u c i n g stress, in this case c o n s u m p t i o n of alcohol, are r e d u c e d . (c) Finally, it was n o t e d t h a t d u r i n g t h e first few days of the c o n f l i c t t r e a t m e n t rats m a d e few crossing i n t o t h e s h o c k c h a m b e r a n d c o n s u m e d very little fluid ( w a t e r as well as alcohol). A c c o r d i n g l y , t h e a n i m a l s h a d little o p p o r t u n i t y to sample t h e a l c o h o l and to learn of its t e n s i o n r e d u c i n g p r o p e r t i e s . Moreover, the rats did n o t have the o p p o r t u n i t y to a d a p t to the aversive taste of the alcohol at low c o n c e n t r a t i o n s . Perhaps w h e n animals finally did comm e n c e d r i n k i n g larger a m o u n t s of fluid, the relatively s t r o n g a l c o h o l s o l u t i o n was t o o aversive for the animal. A l t h o u g h c o n f l i c t did n o t p r o d u c e v o l i t i o n a l c o n s u m p t i o n of alcohol, t w o of t h e f o u r c o n f l i c t rats did have gastric u l c e r a t i o n . In a g r e e m e n t w i t h earlier r e p o r t s [ 1 6 ] , s u b s e q u e n t pilot studies c o n f i r m e d this same effect a n d i n d i c a t e d t h a t conflict t r e a t m e n t ranging f r o m 5 - 1 2 days is
Apparatus and Procedure T h e a p p a r a t u s , p r o c e d u r e a n d strain of rats (n = 12) were t h e same as in E x p e r i m e n t 4 e x c e p t t h a t the alcohol c o n c e n t r a t i o n was k e p t c o n s t a n t at 3% (v/v). The experim e n t a l t r e a t m e n t was m a i n t a i n e d for seven c o n s e c u t i v e days. RESULTS AND DISCUSSION Since t h e c o n f l i c t g r o u p c o n s u m e d c o n s i d e r a b l y less fluid t h a n the o t h e r t w o groups d u r i n g the first few days of training, the data were a n a l y z e d in t e r m s of the t o t a l v o l u m e of alcohol s o l u t i o n c o n s u m e d m i n u s total v o l u m e of w a t e r c o n s u m e d . T h e analysis of variance of these scores y i e l d e d a significant T r e a t m e n t s e f f e c t ( F ( 2 , 9) = 8.08, p < 0 . 0 5 ) . S u b s e q u e n t m u l t i p l e c o m p a r i s o n s revealed t h a t t h e i s o l a t e d g r o u p c o n s u m e d relatively m o r e alcohol (X alcohol X w a t e r c o n s u m e d = 2 2 . 1 0 ml) t h a n the conflict or n o n s h o c k groups (X a l c o h o l - X w a t e r c o n s u m e d = 3.32 a n d 7.00 ml respectively). These d i f f e r e n c e s were c o n s i s t e n t during 6 o f the 7 t r e a t m e n t days. Moreover, a d d i t i o n a l studies revealed c o m p a r a b l e results w h e n alcohol was maint a i n e d at e i t h e r a 5% or 3% (v/v) s o l u t i o n . Once again it a p p e a r e d t h a t conflict did n o t increase volitional a l c o h o l c o n s u m p t i o n . This was n o t a f u n c t i o n of alcohol t a s t i n g relatively m o r e aversive for the c o n f l i c t t h a n t h e n o n s h o c k e d or isolated groups since the c o n c e n t r a t i o n of a l c o h o l was k e p t c o n s t a n t t h r o u g h o u t the e x p e r i m e n t . Moreover, t h e fact t h a t the n o n s h o c k e d a n d conflict groups c o n s u m e d m o r e liquid f r o m the alcohol s o l u t i o n t h a n f r o m t h e water, attests to the fact t h a t t h e c o n c e n t r a t i o n of alcohol used was in itself n o t aversive. It is i n t e r e s t i n g t h a t the isolate g r o u p c o n s u m e d greater a m o u n t s of alcohol t h a n the o t h e r t w o groups, a l t h o u g h t h e y could passively avoid t h e shock. This finding is n o t really surprising since the t r e a t m e n t was a p p a r e n t l y a n aversive one in t h a t rats in t h e isolate g r o u p e x h i b i t e d weight loss c o m p a r a b l e to t h a t of the c o n f l i c t g r o u p b e t w e e n t h e first a n d second days of t r a i n i n g (X weight loss = 15.5 gm). Unlike the conflict group, weight increased following the s e c o n d day of training a m o n g t h e isolated rats. It seems t h a t partial c o n t r o l
E F F E C T S O F S T R E S S ON S E L F S E L E C T I O N O F A L C O H O L
over the o c c u r e n c e o f s h o c k (i.e., i n h i b i t o r y r e s p o n s e s precluded the o c c u r e n c e o f s h o c k in the isolate group) did lead to increased v o l u n t a r y alcohol c o n s u m p t i o n . The reliability o f this finding is q u e s t i o n a b l e , h o w e v e r , in t h a t the isolate group was n o t f o u n d to c o n s u m e m o r e a l c o h o l t h a n the n o n s h o c k group in E x p e r i m e n t s 3 and 4. Were this f i n d i n g f o u n d to be a replicable one it w o u l d suggest t h a t lack of c o n t r o l over s h o c k is relatively u n i m p o r t a n t in p r o d u c i n g volitional alcohol c o n s u m p t i o n . Given r e c e n t r e p o r t s in w h i c h avoidance training increased v o l u n t a r y alcohol cons u m p t i o n [ 1 5 ] , this possibility b e c o m e s an increasingly c o m p e l l i n g one. All factors c o n s i d e r e d the h y p o t h e s i s t h a t o n c e t h e animals in the c o n f l i c t group cross into the s h o c k side of the c h a m b e r the conflict is resolved and the necessity for a l c o h o l c o n s u m p t i o n is mitigated, appears to be the m o s t viable e x p l a n a t i o n o f the lack of c o n s u m p t i o n o f alcohol on the part of the conflict group. G E N E R A L DISCUSSION It is a p p a r e n t f r o m the results of the p r e s e n t series o f e x p e r i m e n t s t h a t e x p o s u r e to inescapable s h o c k effectively increases volitional alcohol c o n s u m p t i o n . Moreover, the self-selection was n o t due to n u t r i t i o n a l deficiencies (see also [ 2 0 ] ) , or to specific stimulus factors as previously suggested by Cicero et al. [ 1 0 ] . Specifically, the p r e s e n t e x p e r i m e n t s e m p l o y e d unsignalled s h o c k p r e s e n t e d on either a fixed or variable interval schedule, thus p r e c l u d i n g t e m p o r a l factors as being a signal for shock. It appears t h a t the stress per se was responsible for the self s e l e c t i o n o f
33
alcohol. Moreover, m a i n t e n a n c e of the c o n s u m a t o r y r e s p o n s e was also d e p e n d a n t on the presence o f the primary aversive stimulus. Witness the f i n d i n g that t e r m i n a t i o n o f the stress schedule quickly resulted in rats decreasing their c o n s u m p t i o n o f alcohol. Of course, it is n o t unlikely that if an explicit cue had b e e n paired w i t h shock, s u b s e q u e n t p r e s e n t a t i o n o f this cue alone may have m a i n t a i n e d the self selection o f alcohol. The i m p o r t a n t p o i n t here is that the necessary and sufficient c o n d i t i o n for v o l u n t a r y selection is t h a t a p r i m a r y stressor be i n t r o d u c e d . While an e x t e r n a l cue could possibly sustain the c o n s u m a t o r y r e s p o n s e even w h e n stress is t e r m i n a t e d , it is n o t a necessary c o n d i t i o n to initially establish the p r e f e r e n c e for alcohol. It is i n t e r e s t i n g t h a t a l t h o u g h a Tension R e d u c t i o n H y p o t h e s i s w o u l d p r e d i c t that conflict, as inescapable shock, s h o u l d increase v o l u n t a r y alcohol c o n s u m p t i o n , this was n o t the case in the present investigation. A l t h o u g h conflict was f o u n d to p r o d u c e a d r a m a t i c weight loss, c o m p a r a b l e to t h a t p r o d u c e d by inescapable shock, and on o c c a s i o n was also f o u n d to p r o d u c e gastric ulceration, n o sign of increased selection of alcohol was a p p a r e n t . It seems t h a t c o n t r o l over s h o c k may be an i m p o r t a n t d e t e r m i n a n t o f alcohol c o n s u m p t i o n . U n d e r t h o s e c o n d i t i o n s where an e x t e r n a l source o f coping with stress is available, the necessity o f c o n s u m i n g alcohol for possible stress r e d u c t i o n is m i n i m i z e d . In c o n t r a s t , where an e x t e r n a l source of coping with stress is n o t available, the i m p o r t a n c e of alcohol as a stress r e d u c e r is m a x i m i z e d . Quite possibly, the f e e d b a c k of stress r e d u c t i o n in the latter situation is less ambiguous, and t h e r e f o r e m o r e reinforcing.
REFERENCES 1~ Adamson, R. and R. Black. Volitional drinking and avoidance learning in the white rat. J. comp. physiol. Psychol. 52: 734 736, 1959. 2. Anisman, H. Fear reduction and active avoidance learning following administration of alcohol during prior CS-shock exposure. Q. Jl Stud. Alcohol 33: 783-793, 1972. 3. Barry, H. and N. E. Miller. Effects of drugs on approachavoidance conflict tested repeatedly by means of a telescope alley. J. comp. physiol. Psychol. 55:201 210, 1972. 4. Berger, H. J. Chlorpromazine and ethanol combination: Effects on respiration, random motor activity and conditioned avoidance escape in mice. Q. Jl Stud. Alcohol 30: 862-869, 1960. 5. Bolles, R. C. Species specific defense reactions and avoidance learning. Psychol. Rev. 77:32 48, 1970. 6. Brady, J. V. Ulcers in "executive Monkeys", Scient. Am. 199: 95-103, 1958. 7. Brady, J. V., R. W. Porter, D. C. Conrad and J. W. Mason. Avoidance behavior and the development of Gastroduodenal ulcers. J. exp. Analysis Behav. 1: 69-72, 1958. 8. Capell, H. and C. P. Herman. Alcohol and tension reduction: A review. Q. Jl Stud. Alcohol 33: 33-64, 1972. 9. Casey, A. The effect of stress on the consumption of alcohol and reserpine. Q. JlStud. Alcohol 21:208 216, 1960. 10. Cicero, T. J., R. D. Myers and W. C. Black. Increase in volitional ethanol consumption following interferences with a learned avoidance response. Physiol. Behav. 3: 657-660, 1968.
11. Clay, M. L. Conditions affecting voluntary alcohol consumption in rats. Q. Jl Stud. Alcohol 25:36 55, 1964. 12. Conger, J. J. The effects of 'alcohol on conflict behavior in the albino rat. Q. Jl Stud. Alcohol 12: 1-29, 1951. 13. Freed, E. X. The effect of alcohol on approach-avoidance conflict in the white rat. Q. Jl Stud. Alcohol 2 3 : 2 3 6 254, 1967. 14. Myers, R. D. and R. B. Holman. Failure of stress of electric shock to increase ethanol intake in rats. Q. J1 Stud. Alcohol 30: 132-137, 1969. 15. Opsahl, C. A. and G. I. Hatton. Volitional ethanol increases during acquisition and extinction of avoidance responding. Physiol. Behav. 8: 87-93, 1972. 16. Pare, W. P. Conflict duration, feeding schedule, and strain differences in conflict induced gastric ulcers. Physiol. Behav. 8: 165 171, 1971. 17. Powell, B. J., K. K. Kamano and L. K. Martin. Multiple factors affecting volitional consumption of alcohol in the Abrams Wistar rats. Q. JlStud. Alcohol 27:7 15, 1966. 18. Rice, H. K. The responding rest ratio in the production of gastric ulcers in the rat. PsychoL Rec. 1 3 : 1 1 - 1 4 , 1963. 19. Ritchie, J. M. The aliphatic alcohols. In: The Pharmacological Basis of Therapeutics, edited by L. S. Goodman and A. Gilman. Toronto: Collier-MacMillan, 1971. 20. Satinder, K. P. Behavior genetic-dependent self-selection of alcohol in rats. J. comp. physioL Psychol. 80: 422-434, 1972. 21. Weiss, J. M. Effects of coping behavior in different warning signal conditions on stress pathology in rats. J. comp. physiol. Psychol. 77:1 14, 1971.
Effects of Inescapable Shock and Shock-Produced Conflict on Self Selection of Alcohol in Rats H Y M I E A N I S M A N A N D T. G A R Y W A L L E R
University o f Waterloo, Waterloo, Ontario, Canada
( R e c e i v e d 12 April 1 9 7 3 ) ANISMAN, H. AND T. G. WALLER. Effects of inescapable shock and shock-produced conflict on self selection of alcohol in rats. PHARMAC. BIOCHEM. BEHAV. 2(1) 2 7 - 3 3 , 1974. - In five experiments it was found that stress of inescapable unavoidable shock produced increased self selection of alcohol. These effects were maintained only so long as the shock schedule was continued. Factors such as predictability of shock, shock schedule and nutritional deficiency were found not to alter alcohol consumption substantially. In contrast to the effects of inescapable unavoidable stress, shock-produced conflict did not lead to the self selection of alcohol. Results were interpreted in terms of a Tension Reduction Hypothesis and the role of control over aversive stimulation. Inescapable shock
Conflict
Self selection of alcohol
d r i n k i n g b e h a v i o r c a n n o t be c o n s i d e r e d a defensive r e a c t i o n in t h e rats r e p e r t o i r e of responses [5 ] it is n o t at all surprising t h a t t h e t e n d e n c y to c o n s u m e alcohol is a c q u i r e d as slowly as it is. It would be e x p e c t e d t h a t if t h e p r o b a b i l i t y of alcohol b e i n g sampled were m a x i m i z e d while the organism were in t h e stressful s i t u a t i o n , t h e n t h e c o n s u m a t o r y r e s p o n s e s s h o u l d b e a c q u i r e d m o r e readily. P r e l i m i n a r y i n v e s t i g a t i o n s carried o u t at o u r l a b o r a t o r i e s i n d i c a t e d t h a t o n e m e t h o d w h i c h is f r u i t f u l in this respect is simply to c o n t i n u o u s l y h o u s e the a n i m a l in t h e stressful s i t u a t i o n w i t h b o t h a l c o h o l and w a t e r freely available. In each of t h e studies t o be r e p o r t e d this t e c h n i q u e was e m p l o y e d . The variables m a n i p u l a t e d in each o f the e x p e r i m e n t s essentially r e p r e s e n t e d a n a t t e m p t to f u r t h e r e n h a n c e t h e rates of self selection o f e t h a n o l in an aversive s i t u a t i o n .
S E V E R A L investigators have d e m o n s t r a t e d t h a t e t h y l a l c o h o l decreases t h e n u m b e r o f r e s p o n s e s m a d e in a n active a v o i d a n c e task [2,4] and increases t h e d i s t a n c e subjects will a p p r o a c h in an a p p r o a c h - a v o i d a n c e c o n f l i c t s i t u a t i o n [ 3, 12, 13 ]. On t h e basis o f t h e s e e x p e r i m e n t s , as well as a n u m b e r of o t h e r c o m p a r a b l e r e p o r t s [ 8 ] , it h a d b e e n suggested t h a t e t h a n o l reduces stress in aversively motivated situations (Tension Reduction Hypothesis). It follows t h a t if e t h a n o l r e d u c e s t e n s i o n associated with t h e stress o f electric s h o c k , t h e n v o l u n t a r y a l c o h o l cons u m p t i o n in an aversive s i t u a t i o n s h o u l d be r e i n f o r c i n g and, c o n s e q u e n t l y , s h o u l d increase in f r e q u e n c y . H o w e v e r , p a r a d o x i c a l results have b e e n r e p o r t e d c o n c e r n i n g this p r e d i c t i o n . Myers and H o l m a n [14] r e p o r t e d t h a t n e i t h e r a c c l i m a t i o n t o alcohol, or s h o c k p r e s e n t e d on a partial s c h e d u l e (variable or fixed i n t e r v a l ) resulted in i n c r e a s e d a l c o h o l c o n s u m p t i o n . Similarly, Casey [9] f o u n d t h a t a l c o h o l c o n s u m p t i o n did n o t increase u n t i l 16 days after a stress t r e a t m e n t was t e r m i n a t e d . In c o n t r a s t t o these r e p o r t s , several o t h e r investigators (e.g., [1, 11, 17] f o u n d t h a t v o l u n t a r y alcohol c o n s u m p t i o n increased as a result of stress p r o d u c e d b y electric shock. One f a c t o r w h i c h m i g h t a c c o u n t for these d i s c r e p a n t results c o n c e r n s t h e o p p o r t u n i t y animals have for s a m p l i n g the alcohol. Specifically, since v o l u n t a r y alcohol c o n s u m p t i o n in a stressful s i t u a t i o n is essentially a m o d e of escaping or avoiding stress, t h e rate o f acquiring t h e c o n s u m a t o r y r e s p o n s e s h o u l d be r e g a r d e d in t h e same f a s h i o n as w o u l d a r u n n i n g or b a r - p r e s s a v o i d a n c e response. Specifically, since
EXPERIMENT 1 One variable w h i c h m a y i n f l u e n c e the degree of volit i o n a l a l c o h o l c o n s u m p t i o n is the s t r e s s - r e s t s c h e d u l e to w h i c h a n i m a l s are s u b j e c t e d . Specifically, it has b e e n d e m o n s t r a t e d t h a t m o n k e y s [6,7] and rats [18] are m o r e p r o n e to gastric u l c e r a t i o n w h e n m a i n t a i n e d o n a 6 h r s t r e s s - 6 h r rest s c h e d u l e t h a n o n a 12 hr s t r e s s - 1 2 hr rest schedule, suggesting t h a t animals are less able to cope, via i n t e r n a l m e c h a n i s m s , w i t h stress p r e s e n t e d o n a 6 h r - 6 h r schedule. If t h e degree of stress, or the o r g a n i s m ' s ability to cope w i t h stress, is related to self s e l e c t i o n of alcohol, t h e n it s h o u l d follow t h a t alcohol c o n s u m p t i o n w o u l d be differentially a f f e c t e d b y t h e s t r e s s - r e s t s c h e d u l e e m p l o y e d .
The research was supported by a grant from Licensed Beverage Industric, Inc. Requests for reprints should be sent to Hymie Anisman, Department of Psychology, University of Waterloo, Waterloo, N2L 3G1, Ontario, Canada. 27
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ANISMAN AND WALLER
METHOD
Animals Twelve e x p e r i m e n t a l l y naive male H o l t z m a n rats weighing 2 3 0 - 2 5 0 g u p o n arrival f r o m t h e H o l t z m a n Co., Madison, Wisconsin were used. Rats were i n d i v i d u a l l y h o u s e d in s t a n d a r d wire cages w i t h ad lib f o o d a n d w a t e r for seven days p r i o r to a n y e x p e r i m e n t a l t r e a t m e n t . A t t h e start o f t h e e x p e r i m e n t rats weighed 2 6 0 - 2 8 0 g.
Apparatus During the course of the e x p e r i m e n t twelve Plexiglas c h a m b e r s (23 x 21 x 20 c m ) served as the a n i m a l s ' living quarters. T h e f l o o r of each c h a m b e r consisted of 0.16 cm stainless steel rods, spaced 1.25 cm apart ( c e n t e r to c e n t e r ) , t h r o u g h w h i c h electric s h o c k o f 1.0 m A ( c o n s t a n t c u r r e n t , 60 cycle AC) could be delivered. O c c u r e n c e s of s h o c k periods, d u r a t i o n o f s h o c k s a n d i n t e r s h o c k intervals were p r o g r a m m e d t h r o u g h a series o f timers, relays a n d a tape drive. Holes drilled in o n e wall of e a c h c h a m b e r , 8.0 cm a p a r t a n d 4.0 cm a b o v e t h e grid floor, p e r m i t t e d t h e insert i o n of d r i n k i n g s p o u t s o f 100 cc g r a d u a t e d cylinders. Size o f d r i n k i n g s p o u t s were u n i f o r m for all animals a n d p e r m i t ted a p p r o x i m a t e l y 1 - 3 cc of spillage or e v a p o r a t i o n over a 24 h r period.
Procedure Rats were r a n d o m l y assigned to t h r e e groups. Rats in one g r o u p received a single 2 sec signaled i n e s c a p a b l e s h o c k every 30 rain d u r i n g a l t e r n a t e 6 h r periods ( G r o u p 6 - 6 ) . A s e c o n d g r o u p similarly received s h o c k every 30 min. However, s h o c k periods o c c u r r e d d u r i n g a l t e r n a t e 12 hr periods ( G r o u p 1 2 - 1 2 ) . Finally, a t h i r d g r o u p received n o s h o c k e x p o s u r e ( G r o u p 0 - 0 ) . S h o c k periods in t h e 6 6 and 1 2 - 1 2 g r o u p s were c o u n t e r b a l a n c e d such t h a t , while s h o c k was o n for h a l f the animals, it was o f f for t h e r e m a i n i n g rats. T h e s h o c k b e g a n on the second day of the e x p e r i m e n t a n d c o n t i n u e d 11 days. Rats were m a i n t a i n e d in t h e c h a m b e r s for 4 a d d i t i o n a l days f o l l o w i n g t e r m i n a t i o n of t h e shock treatment. A l c o h o l a n d w a t e r were available ad lib t h r o u g h o u t t h e e x p e r i m e n t . On Day 1 ( w h e n n o s h o c k was p r e s e n t e d ) the c o n c e n t r a t i o n of alcohol was 2% (v/v). C o n s u m p t i o n of w a t e r and alcohol on this day served as t h e baseline cons u m p t i o n rate. On s u b s e q u e n t days the a l c o h o l c o n c e n t r a tion was increased daily in 1% i n c r e m e n t s until the c o n c e n t r a t i o n was 10% (v/v). The 10% c o n c e n t r a t i o n was m a i n t a i n e d for t h e d u r a t i o n of t h e e x p e r i m e n t . The posit i o n s o f the alcohol a n d w a t e r cylinders were varied twice daily ( 0 9 0 0 a n d 1700 Hr) o n a r a n d o m s c h e d u l e a n d fluid c o n s u m p t i o n was r e c o r d e d daily at 0 9 0 0 Hr. Only a single baseline day was e m p l o y e d , since t h e cons u m p t i o n o f a l c o h o l at the 2% c o n c e n t r a t i o n h a d previously n o t b e e n f o u n d to b e predictive of s u b s e q u e n t c o n s u m p t i o n w i t h increasing alcohol c o n c e n t r a t i o n s . T h e p u r p o s e o f t h e n o n s h o c k day was essentially to p e r m i t t h e animals to h a b i t u a t e to t h e novel e n v i r o n m e n t . A c c o r d i n g l y , t h e self s e l e c t i o n o f a l c o h o l a m o n g s h o c k groups w i t h i n the p r e s e n t i n v e s t i g a t i o n s h o u l d be c o n s i d e r e d w i t h respect t o n o n s h o c k groups r a t h e r t h a n the baseline measure. RESULTS
Figure 1 s h o w s the m e a n q u a n t i t y of a l c o h o l and w a t e r
c o n s u m e d daily by each of the groups. An analysis of variance of t h e fluid c o n s u m p t i o n yielded a signficiant S h o c k t r e a t m e n t x Fluid i n t e r a c t i o n ( F ( 2 , 9) = 4.72, p < 0 . 0 5 ) . S u b s e q u e n t m u l t i p l e c o m p a r i s o n s i n d i c a t e d t h a t rats in b o t h s h o c k groups c o n s u m e d m o r e alcohol t h a n did the n o n s h o c k group, h o w e v e r , alcohol c o n s u m p t i o n did n o t differ b e t w e e n the t w o s h o c k groups. A m o n g rats in G r o u p 6 - 6 a p r e f e r e n c e for alcohol was d e v e l o p e d w i t h i n 3 days o f t h e c o m m e n c e m e n t of the s h o c k schedule, whereas a m o n g rats in G r o u p 12--12 an alcohol p r e f e r e n c e was e v i d e n t as early as the first s h o c k day. It s h o u l d be n o t e d t h a t this p r e f e r e n c e was n o t e v i d e n t u n t i l the s h o c k schedule was c o m m e n c e d ; witness the lack o f an alcohol preference e x h i b i t e d b y all groups d u r i n g the n o n s h o c k day. I n s p e c t i o n of fluid c o n s u m p t i o n a m o n g the animals w i t h i n each g r o u p revealed for b o t h the 6 - 6 and 12 12 groups, 3 of t h e 4 animals s h o w e d s t r o n g p r e f e r e n c e s for alcohol over water, whereas a m o n g the animals in the 0 - 0 group only o n e rat s h o w e d a n y p r e f e r e n c e for alcohol, a n d this was restricted t o the first few days of t r a i n i n g where alcohol c o n c e n t r a t i o n s were relatively low. A l t h o u g h the Shock T r e a t m e n t x Fluid x Days Interact i o n was n o t significant, i n s p e c t i o n o f t h e data (see Fig. 1) i n d i c a t e d t h a t c o n s u m p t i o n of alcohol in the s h o c k groups decreased following the t e r m i n a t i o n of t h e s h o c k schedule. T h e decrease was m u c h m o r e e v i d e n t for G r o u p 6 - 6 t h a n G r o u p 12 12. Nevertheless, d i f f e r e n c e s b e t w e e n alcohol and w a t e r c o n s u m p t i o n a m o n g the 6 6 and 1 2 - 1 2 groups did n o t a p p r o a c h statistical significance. It is i n t e r e s t i n g to n o t e t h a t a l t h o u g h the v o l u n t a r y c o n s u m p t i o n of alcohol was d e p e n d e n t on t h e p r e s e n c e of shock, n o s y s t e m a t i c d i f f e r e n c e s in c o n s u m p t i o n were e v i d e n t d u r i n g stress and rest periods a m o n g e i t h e r of the s h o c k groups. A l t h o u g h c o n s t a n t i l l u m i n a t i o n was provided, animals t e n d e d to c o n s u m e m o s t of the fluid d u r i n g n i g h t h o u r s of the diurnal cycle (9 p . m . - 9 a.m.). The general t r e n d of t h e results were c o n s i s t e n t regardless of w h e t h e r the data was a n a l y z e d in t e r m s of t o t a l v o l u m e s of fluid c o n s u m e d or a b s o l u t e alcohol c o n s u m e d / k i l o g r a m b o d y weight (X a l c o h o l / k g d u r i n g s h o c k days = 3.04 ml/kg, 7 . 8 0 m l / k g , 6 . 1 6 m l / k g for the 0 - 0 , 6 - 6 and 1 2 - 1 2 groups respectively). I m m e d i a t e l y following the t e r m i n a t i o n of the experim e n t rats were disected and s t o m a c h e s e x a m i n e d for ulceration. N o n e of the rats were f o u n d to have gastric u l c e r a t i o n . DISCUSSION
In a c c o r d a n c e with earlier r e p o r t s (e.g. [1, 11, 1 7 ] , the results of E x p e r i m e n t 1 i n d i c a t e d t h a t stress o f electric s h o c k was effective in p r o d u c i n g volitional alcohol cons u m p t i o n to the e x t e n t t h a t alcohol, the originally n o n preferred fluid, b e c a m e the preferred one. Moreover, this was f o u n d to be the case regardless of w h e t h e r rats were shocked on a 6hr on-6hr off or 1 2 h r o n - 1 2 h r off schedule. While the p r o c e d u r e of m a i n t a i n i n g rats in the s h o c k c h a m b e r t h r o u g h o u t the e x p e r i m e n t a l t r e a t m e n t , and increasing the daily c o n c e n t r a t i o n of alcohol in small i n c r e m e n t s , m a y have p r o m p t e d v o l u n t a r y alcohol cons u m p t i o n , this p r o c e d u r e in itself was n o t sufficient to p r o m o t e s e l e c t i o n o f alcohol as the p r e f e r r e d beverage. Rather, the necessary c o n d i t i o n appears to be t h a t s h o c k be a d m i n i s t e r e d to animals. These data are c o n s i s t e n t w i t h the T e n s i o n R e d u c t i o n H y p o t h e s i s . Specifically, a l c o h o l pres u m a b l y reduces stress, is thus r e i n f o r c i n g and c o n s e q u e n t l y
EFFECTS
OF STRESS ON SELF SELECTION
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5 6 7 8 9 I0 I0 I0 I0 I0 I0 I0 I0 ALCOHOL CONCENTRATION PAD) 4
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DAYS FIG. 1. Mean and standard deviation of alcohol and water c o n s u m e d (ml) over sixteen days. Note: shock was not delivered on Days 1 3 - 1 6 .
30
ANISMAN AND WALLER
increases in f r e q u e n c y . T h e fact t h a t t h e v o l u m e o f a l c o h o l c o n s u m e d declined in t h e s h o c k g r o u p s w h e n the s h o c k t r e a t m e n t was t e r m i n a t e d suggests t h a t self selection is due t o p h y s i c a l stress ( s h o c k ) and n o t s e c o n d a r y s t i m u l i (i.e., i m p l i c i t a n d explicit cues of the s h o c k c h a m b e r ) .
TABLE 1 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF VARIABLE INTERVAL SHOCK AND FOOD DEPRIVATION (EXPERIMENT 2)
EXPERIMENT 2 A l t h o u g h t h e m o s t p a r s i m o n i o u s e x p l a n a t i o n of the data o b s e r v e d in E x p e r i m e n t 1 is in t e r m s of t h e T e n s i o n Reduct i o n H y p o t h e s i s , an a l t e r n a t i v e i n t e r p r e t a t i o n of these data does exist. Specifically, d u r i n g t h e first few days o f t h e s t r e s s s c h e d u l e s h o c k e d rats d e m o n s t r a t e d a m a r k e d decrease in weight ( m e a n weight loss b e i n g 14.5 gin). A c c o r d i n g l y , it can be argued t h a t b e c a u s e e t h a n o l has a greater n u t r i t i v e value [19] a n i m a l s are m o r e apt to c o n s u m e this fluid t h a n tap water. If this were t h e case, t h e n f o o d d e p r i v a t i o n s h o u l d increase self s e l e c t i o n of a l c o h o l even a m o n g n o n s h o c k e d rats. O n e p u r p o s e of E x p e r i m e n t 2 was t o test such a possibility. A s e c o n d p o i n t of i n t e r e s t w i t h respect t o E x p e r i m e n t 1 is the fact t h a t unsignaled s h o c k p r o d u c e d v o l i t i o n a l cons u m p t i o n of alcohol. Previous r e p o r t s [10] h a d i n d i c a t e d t h a t a necessary requisite for alcohol c o m s u m p t i ' o n to increase is t h a t a signal b e i m p l i c i t l y paired w i t h t h e shock. While the results of E x p e r i m e n t 1 are clearly i n c o m p a t i b l e w i t h t h e findings r e p o r t e d b y Cicero et al. [ 1 0 ] , it is possible t h a t t e m p o r a l cues served as a w a r n i n g signal for s h o c k , since s h o c k was p r e s e n t e d at fixed intervals. Were this the case, t h e n v o l i t i o n a l a l c o h o l c o n s u m p t i o n s h o u l d n o t increase if unsignaled s h o c k were p r e s e n t e d at r a n d o m intervals. E x p e r i m e n t 2 was designed t o test s u c h a prediction. METHOD T h e a p p a r a t u s and strain of rats was the same as t h a t used in E x p e r i m e n t 1. Twelve rats were r a n d o m l y assigned to o n e of t h r e e t r e a t m e n t c o n d i t i o n s . Rats in o n e group received ad lib food, a n d s h o c k o n a r a n d o m s c h e d u l e ( t w o 1.0mA 2sec shocks/hr) on a 6hr on-6hr off basis. A s e c o n d group received t h e same s h o c k t r e a t m e n t b u t received o n l y one h r of feeding t i m e per day. Finally rats in a t h i r d g r o u p received n o s h o c k b u t were p e r m i t t e d f o o d o n t h e same s c h e d u l e as t h e d e p r i v e d group. A l c o h o l and w a t e r were p r e s e n t e d t o rats in e a c h g r o u p on t h e same r e g i m e n as described in E x p e r i m e n t 1. Rats were m a i n t a i n e d on this s c h e d u l e over a 22 day period.
Fluid Alcohol
Water
8.7
29.8
Shocked food deprived
19.5
19.4
Shocked non-deprived
23.5
26.7
Group
Non-shocked food deprived
As in E x p e r i m e n t 1, n o n s h o c k e d animals c o n s u m e d significantly more w a t e r t h a n alcohol. In fact in Experim e n t 1, n o n s h o c k e d rats c o n s u m e d a m e a n of 14.2 cc w a t e r and 24.4 cc alcohol daily, while in E x p e r i m e n t 2 n o n s h o c k e d a n i m a l s c o n s u m e d an average of 8.7 cc of alcohol, and 29.8 cc of w a t e r daily. Thus it seems t h a t n o t o n l y did d e p r i v a t i o n n o t increase alcohol c o n s u m p t i o n , b u t r a t h e r it r e d u c e d the q u a n t i t y c o n s u m e d . Clearly, food d e p r i v a t i o n was n o t r e s p o n s i b l e for the self s e l e c t i o n of alcohol o b s e r v e d in s h o c k e d rats in Experim e n t 1 or 2. However, it was n o t e d in E x p e r i m e n t 2 (see Table 1) t h a t a l t h o u g h s h o c k e d rats c o n s u m e d m o r e a l c o h o l t h a n did n o n s h o c k e d rats, n o p r e f e r e n c e for alcohol over w a t e r was d e m o n s t r a t e d by the s h o c k e d groups. Since it is u n c l e a r w h e t h e r this was due to the r a n d o m s h o c k schedule, or simply a s p u r i o u s result, a subs e q u e n t e x p e r i m e n t e m p l o y i n g n o n s h o c k e d (n = 4) and r a n d o m l y s h o c k e d animals (n = 4) was carried out. Table 2 s h o w s t h e m e a n t o t a l w a t e r and alcohol c o n s u m p t i o n of these groups over the 13 day test period. It is e v i d e n t t h a t rats w h i c h received s h o c k on a r a n d o m s c h e d u l e c o n s u m e d m o r e alcohol t h a n did n o n s h o c k e d rats, a n d also d e m o n s t r a t e d a p r e f e r e n c e for alcohol over w a t e r as h a d b e e n seen in E x p e r i m e n t 1. In each of t h e s e t w o studies, e x a m i n a t i o n of the s t o m a c h e s yielded n o evidence of u l c e r a t i o n . This was also f o u n d to b e the case in several a d d i t i o n a l and similar studies w h e r e rats received s h o c k and were p e r m i t t e d access only to water. It appears t h a t u l c e r a t i o n was n o t a b y p r o d u c t of t h e stress t r e a t m e n t e m p l o y e d .
RESULTS AND DISCUSSION T a b l e 1 s h o w s t h e m e a n daily v o l u m e s of w a t e r a n d of alcohol s o l u t i o n c o n s u m e d over t h e 22 day t e s t i n g period. An analysis of variance of t h e fluid v o l u m e s c o n s u m e d yielded a significant T r e a t m e n t x Fluid i n t e r a c t i o n ( F ( 2 , 3) = 5.22, p < 0 . 0 5 ) . C o m p a r i s o n s b e t w e e n the m e a n s involved in the i n t e r a c t i o n i n d i c a t e d t h a t b o t h s h o c k groups c o n s u m e d m o r e alcohol t h a n did the food d e p r i v e d n o n s h o c k g r o u p ( p < 0 . 0 5 ) . Moreover, t h e shockf o o d d e p r i v e d g r o u p c o n s u m e d less alcohol t h a n did t h e s h o c k n o n d e p r i v e d group. It is unclear, h o w e v e r , w h e t h e r this was a result of f o o d d e p r i v a t i o n resulting in t h e a l c c h o l b e i n g more effective as a stress r e d u c e r , or w h e t h e r it is s i m p l y a m a t t e r of t h e n o n d e p r i v e d group consuming more fluid (as was the case for w a t e r consumption),
TABLE 2 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF SHOCK PRESENTED ON A VARIABLE INTERVAL SCHEDULE (EXPERIMENT 2)
Fluid Group
Alcohol
Water
Shock
26.6
13.6
Non-shock
18.0
22.1
E F F E C T S O F S T R E S S ON S E L F S E L E C T I O N O F A L C O H O L
EXPERIMENT 3 In each of the previous e x p e r i m e n t s the rats had no control over the occurence of shock. Under these conditions alcohol c o n s u m p t i o n was reliably found to increase, but in no case was ulceration found in any of the animals. Given these findings it would be interesting to determine whether some degree of control over shock would produce ulceration and w h e t h e r this procedure would also produce v o l u n t a r y alcohol c o n s u m p t i o n . As previously indicated, alcohol has typically been found to reduce avoidance behavior in a conflict situation [ 3 , 1 2 ] , presumably because of its tension-reducing properties. It follows then, that in a conflict situation where free choice alcohol and water are available, the probability of alcohol being consumed should increase. Moreover, because of the animals partial control over shock in such a situation it is likely that ulceration may occur as indicated by Brady (1958). Since strain differences have been found to be an i m p o r t a n t variable in alcohol self selection studies [20] and in studies on gastric ulceration [ 1 6 ] , two strains of rats, H o l t z m a n and S p r a g u e - D a w l e y , were e m p l o y e d in the present investigations. Preliminary unpublished studies indicated that, although stress increased alcohol consumption in H o l t z m a n rats, S p r a g u e - D a w l e y rats e x h i b i t e d a distinct aversion towards alcohol, and a preference for alcohol was not increased through stress. If stress in a conflict situation is more aversive than that of inescapable shock, it might be e x p e c t e d that S p r a g u e - D a w l e y rats would d e m o n s t r a t e increased c o n s u m p t i o n of alcohol.
31
intervals six times an hour, with each shock being 1.0 mA and 2 min in duration. Accordingly, shock was present in one side of the chambers 20% of the time. This t r e a t m e n t was continued for 10 consecutive days. Percentages of alcohol in the daily solutions, and the r a n d o m i z a t i o n of drinking tubes was the same as in E x p e r i m e n t 1. RESULTS AND DISCUSSION Table 3 shows the mean daily volumes of water and of alcohol solution consumed. An analysis of variance of the c o n s u m p t i o n scores did not yield any significant main effects or interactions involving the shock t r e a t m e n t or for strain of rats. In fact, subjects in the conflict group c o n s u m e d slightly less alcohol than did the isolated group. This difference, however, did not approach statistical significance. The analyses o f variance of the absolute alcohol c o n s u m e d / k g b o d y weight and volume of alcohol/ water ratio yielded similar results. Moreoever, inspection of the c o n s u m p t i o n scores over days revealed no systema t i c c h a n g e s in the volumes of alcohol consumed. E x a m i n a t i o n of the animals stomachs again revealed no signs of ulceration in any of the groups.
TABLE 3 MEAN DAILY VOLUME (ml) OF WATER AND ALCOHOL CONSUMED AS A FUNCTION OF STRESS TREATMENT (EXPERIMENT 3)
METHOD
Animals Animals were 24 male rats weighing 2 3 0 - 2 5 0 gm u p o n arrival from the supplier. Half the rats were of the H o l t z m a n strain and obtained f r o m the H o l t z m a n Co., Madison, Wisconsin, while the remaining rats were of the Sprague-Dawley strain procured from the S p r a g u e Dawley Co., Madison, Wisconsin.
Fluid Group
Alcohol
Water
Non-shock
16.3
27.9
Conflict
16.9
23.2
Isolated
20.8
20.6
Apparatus The testing chambers were the same as those described in E x p e r i m e n t 1. The wiring of the grid floor in the eight shock chambers was modified. For half the chambers the part of the grid floor which could be electrified was that nearer the drinking spouts, while for the remaining chambers the grid floor which could be electrified was on the side opposite the drinking spouts.
Procedure Rats of each strain were r a n d o m l y assigned to one of three t r e a t m e n t groups. Unlike E x p e r i m e n t s 1 and 2 the shock schedule was maintained continuously through each 24 hr period. One group received no shock, a second group received shock only on the side of the chamber where the drinking spouts were located (conflict group), and a third group received shock only on the side of the chamber opposite the drinking spouts (isolated group). The third group was included to control for learning to stay on one side of the chamber, and to control for possible effects of restricted m o v e m e n t experienced by the conflict group. Electric shock was presented at r a n d o m
While these data appear inconsistent with a tension reduction hypothesis, there are several factors which may have been influential in producing these effects. Specifically, since shock occurred only 20% of the time, rats may often have avoided the shock and were thus not sufficiently stressed. Thus in E x p e r i m e n t 4 the probability of shock being present was increased from 20% to 80%. EXPERIMENT 4
Apparatus and Procedure The apparatus and procedure were the same as in E x p e r i m e n t 3 e x c e p t that shock was presented r a n d o m l y on 24 occasions during each h o u r (each shock being 2 min in duration), thus resulting in the grid floor being electrified 80% of the time. Unlike E x p e r i m e n t 3, this study e m p l o y e d only H o l t z m a n rats (n = 12) since differences in alcohol c o n s u m p t i o n were in fact not evident b e t w e e n the strains.
32
ANISMAN AND WALLER RESULTS AND DISCUSSION
Table 4 s h o w s t h e m e a n v o l u m e s o f a l c o h o l a n d w a t e r c o n s u m e d b y each of t h e t r e a t m e n t groups. An analysis o f v a r i a n c e of t h e fluid v o l u m e s c o n s u m e d yielded n o significant m a i n effects or i n t e r a c t i o n s . If t h e d a t a were a n a l y z e d in t e r m s of a b s o l u t e alcohol c o n s u m e d / k g b o d y weight, a significant T r e a t m e n t s m a i n e f f e c t was o b t a i n e d ( F ( 2 , 9) = 4.65, p < 0 . 0 5 ) . C o m p a r i s o n s b e t w e e n the m e a n s involved in this m a i n effect i n d i c a t e d t h a t the c o n f l i c t g r o u p c o n s u m e d significantly less a l c o h o l t h a n did t h e r e m a i n i n g t w o groups. T h e m a i n source for this d i f f e r e n c e , as seen in Table 4, seems t o be a result o f t h e c o n f l i c t g r o u p c o n s u m i n g less t o t a l fluid ( a l c o h o l a n d w a t e r ) t h a n t h e r e m a i n i n g groups. TABLE 4 MEAN DAILY VOLUME (ml) OF ALCOHOL AND WATER CONSUMED AS A FUNCTION OF STRESS TREATMENT (EXPERIMENT 4)
effective in p r o d u c i n g u l c e r a t i o n . If rats received m o r e or less days o n t h e conflict t r e a t m e n t t h e n u l c e r a t i o n was n o t observed. EXPERIMENT 5 E x p e r i m e n t 5 was a f u r t h e r i n q u i r y i n t o the role of s h o c k p r o d u c e d c o n f l i c t o n v o l u n t a r y alcohol c o n s u m p t i o n . E x p e r i m e n t s 1 - 4 i n d i c a t e d t h a t while unsignaled inescapable s h o c k increases t h e self selection of alcohol, s h o c k p r o d u c e d c o n f l i c t does n o t . As previously suggested, rats in the c o n f l i c t g r o u p c o n s u m e d little fluid ( a l c o h o l or w a t e r ) d u r i n g t h e first few days of t r a i n i n g and t h u s m a y n o t have h a d t h e o p p o r t u n i t y to a d a p t to t h e aversive taste of t h e a l c o h o l s o l u t i o n . C o n s e q u e n t l y , w h e n t h e rats in t h e conflict g r o u p did c o m m e n c e c o n s u m i n g fluid, the increased c o n c e n t r a t i o n o f alcohol p r e s e n t m a y have b e e n relatively m o r e aversive t h a n it was in t h e n o n s h o c k e d or isolated groups, a n d as a result the a l c o h o l was n o t c o n s u m e d in a p p r e c i a b l e q u a n t i t i e s . It follows t h a t if the c o n c e n t r a t i o n o f a l c o h o l were m a i n t a i n e d at a c o n s t a n t weak c o n c e n t r a t i o n , t h a n t h e conflict g r o u p w o u l d d e m o n s t r a t e increased volitional alcohol c o n s u m p t i o n relative to n o n s h o c k e d rats.
Fluid Group
Alcohol
Water
Non-shock
22.0
23.7
Conflict
13.5
14.1
Isolated
21.5
21.2
T h e fact t h a t c o n f l i c t did n o t increase v o l u n t a r y a l c o h o l c o n s u m p t i o n is i n c o m p a t i b l e w i t h a T e n s i o n R e d u c t i o n H y p o t h e s i s . T h e r e are, h o w e v e r , t h r e e d i s t i n c t a l t e r n a t i v e e x p l a n a t i o n s w h i c h m a y a c c o u n t for the o b s e r v e d c o n s u m p t i o n rates a m o n g the c o n f l i c t rats. (a) While the a n i m a l is in t h e c o n f l i c t s i t u a t i o n a d m i n i s t r a t i o n o f alcohol m a y r e d u c e stress. However, w h e n the o r g a n i s m is r e q u i r e d to select t h e a l c o h o l freely, the r e s p o n s e of crossing i n t o the s h o c k side o f t h e c h a m b e r ( p r e s u m a b l y w h e n t h e s h o c k is a b s e n t ) results in t h e conflict b e i n g resolved (at least t e m p o r a r i l y ) , a n d as a result t h e r e is n o n e e d for t h e alcohol. ( b ) Given t h a t t h e o r g a n i s m has some c o n t r o l over the o c c u r r e n c e of s h o c k t h r o u g h e x t e r n a l m e a n s (i.e., crossing or n o t crossing i n t o the s h o c k side), t h e necessity for seeking o t h e r m e a n s o f r e d u c i n g stress, in this case c o n s u m p t i o n of alcohol, are r e d u c e d . (c) Finally, it was n o t e d t h a t d u r i n g t h e first few days of the c o n f l i c t t r e a t m e n t rats m a d e few crossing i n t o t h e s h o c k c h a m b e r a n d c o n s u m e d very little fluid ( w a t e r as well as alcohol). A c c o r d i n g l y , t h e a n i m a l s h a d little o p p o r t u n i t y to sample t h e a l c o h o l and to learn of its t e n s i o n r e d u c i n g p r o p e r t i e s . Moreover, the rats did n o t have the o p p o r t u n i t y to a d a p t to the aversive taste of the alcohol at low c o n c e n t r a t i o n s . Perhaps w h e n animals finally did comm e n c e d r i n k i n g larger a m o u n t s of fluid, the relatively s t r o n g a l c o h o l s o l u t i o n was t o o aversive for the animal. A l t h o u g h c o n f l i c t did n o t p r o d u c e v o l i t i o n a l c o n s u m p t i o n of alcohol, t w o of t h e f o u r c o n f l i c t rats did have gastric u l c e r a t i o n . In a g r e e m e n t w i t h earlier r e p o r t s [ 1 6 ] , s u b s e q u e n t pilot studies c o n f i r m e d this same effect a n d i n d i c a t e d t h a t conflict t r e a t m e n t ranging f r o m 5 - 1 2 days is
Apparatus and Procedure T h e a p p a r a t u s , p r o c e d u r e a n d strain of rats (n = 12) were t h e same as in E x p e r i m e n t 4 e x c e p t t h a t the alcohol c o n c e n t r a t i o n was k e p t c o n s t a n t at 3% (v/v). The experim e n t a l t r e a t m e n t was m a i n t a i n e d for seven c o n s e c u t i v e days. RESULTS AND DISCUSSION Since t h e c o n f l i c t g r o u p c o n s u m e d c o n s i d e r a b l y less fluid t h a n the o t h e r t w o groups d u r i n g the first few days of training, the data were a n a l y z e d in t e r m s of the t o t a l v o l u m e of alcohol s o l u t i o n c o n s u m e d m i n u s total v o l u m e of w a t e r c o n s u m e d . T h e analysis of variance of these scores y i e l d e d a significant T r e a t m e n t s e f f e c t ( F ( 2 , 9) = 8.08, p < 0 . 0 5 ) . S u b s e q u e n t m u l t i p l e c o m p a r i s o n s revealed t h a t t h e i s o l a t e d g r o u p c o n s u m e d relatively m o r e alcohol (X alcohol X w a t e r c o n s u m e d = 2 2 . 1 0 ml) t h a n the conflict or n o n s h o c k groups (X a l c o h o l - X w a t e r c o n s u m e d = 3.32 a n d 7.00 ml respectively). These d i f f e r e n c e s were c o n s i s t e n t during 6 o f the 7 t r e a t m e n t days. Moreover, a d d i t i o n a l studies revealed c o m p a r a b l e results w h e n alcohol was maint a i n e d at e i t h e r a 5% or 3% (v/v) s o l u t i o n . Once again it a p p e a r e d t h a t conflict did n o t increase volitional a l c o h o l c o n s u m p t i o n . This was n o t a f u n c t i o n of alcohol t a s t i n g relatively m o r e aversive for the c o n f l i c t t h a n t h e n o n s h o c k e d or isolated groups since the c o n c e n t r a t i o n of a l c o h o l was k e p t c o n s t a n t t h r o u g h o u t the e x p e r i m e n t . Moreover, t h e fact t h a t the n o n s h o c k e d a n d conflict groups c o n s u m e d m o r e liquid f r o m the alcohol s o l u t i o n t h a n f r o m t h e water, attests to the fact t h a t t h e c o n c e n t r a t i o n of alcohol used was in itself n o t aversive. It is i n t e r e s t i n g t h a t the isolate g r o u p c o n s u m e d greater a m o u n t s of alcohol t h a n the o t h e r t w o groups, a l t h o u g h t h e y could passively avoid t h e shock. This finding is n o t really surprising since the t r e a t m e n t was a p p a r e n t l y a n aversive one in t h a t rats in t h e isolate g r o u p e x h i b i t e d weight loss c o m p a r a b l e to t h a t of the c o n f l i c t g r o u p b e t w e e n t h e first a n d second days of t r a i n i n g (X weight loss = 15.5 gm). Unlike the conflict group, weight increased following the s e c o n d day of training a m o n g t h e isolated rats. It seems t h a t partial c o n t r o l
E F F E C T S O F S T R E S S ON S E L F S E L E C T I O N O F A L C O H O L
over the o c c u r e n c e o f s h o c k (i.e., i n h i b i t o r y r e s p o n s e s precluded the o c c u r e n c e o f s h o c k in the isolate group) did lead to increased v o l u n t a r y alcohol c o n s u m p t i o n . The reliability o f this finding is q u e s t i o n a b l e , h o w e v e r , in t h a t the isolate group was n o t f o u n d to c o n s u m e m o r e a l c o h o l t h a n the n o n s h o c k group in E x p e r i m e n t s 3 and 4. Were this f i n d i n g f o u n d to be a replicable one it w o u l d suggest t h a t lack of c o n t r o l over s h o c k is relatively u n i m p o r t a n t in p r o d u c i n g volitional alcohol c o n s u m p t i o n . Given r e c e n t r e p o r t s in w h i c h avoidance training increased v o l u n t a r y alcohol cons u m p t i o n [ 1 5 ] , this possibility b e c o m e s an increasingly c o m p e l l i n g one. All factors c o n s i d e r e d the h y p o t h e s i s t h a t o n c e t h e animals in the c o n f l i c t group cross into the s h o c k side of the c h a m b e r the conflict is resolved and the necessity for a l c o h o l c o n s u m p t i o n is mitigated, appears to be the m o s t viable e x p l a n a t i o n o f the lack of c o n s u m p t i o n o f alcohol on the part of the conflict group. G E N E R A L DISCUSSION It is a p p a r e n t f r o m the results of the p r e s e n t series o f e x p e r i m e n t s t h a t e x p o s u r e to inescapable s h o c k effectively increases volitional alcohol c o n s u m p t i o n . Moreover, the self-selection was n o t due to n u t r i t i o n a l deficiencies (see also [ 2 0 ] ) , or to specific stimulus factors as previously suggested by Cicero et al. [ 1 0 ] . Specifically, the p r e s e n t e x p e r i m e n t s e m p l o y e d unsignalled s h o c k p r e s e n t e d on either a fixed or variable interval schedule, thus p r e c l u d i n g t e m p o r a l factors as being a signal for shock. It appears t h a t the stress per se was responsible for the self s e l e c t i o n o f
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alcohol. Moreover, m a i n t e n a n c e of the c o n s u m a t o r y r e s p o n s e was also d e p e n d a n t on the presence o f the primary aversive stimulus. Witness the f i n d i n g that t e r m i n a t i o n o f the stress schedule quickly resulted in rats decreasing their c o n s u m p t i o n o f alcohol. Of course, it is n o t unlikely that if an explicit cue had b e e n paired w i t h shock, s u b s e q u e n t p r e s e n t a t i o n o f this cue alone may have m a i n t a i n e d the self selection o f alcohol. The i m p o r t a n t p o i n t here is that the necessary and sufficient c o n d i t i o n for v o l u n t a r y selection is t h a t a p r i m a r y stressor be i n t r o d u c e d . While an e x t e r n a l cue could possibly sustain the c o n s u m a t o r y r e s p o n s e even w h e n stress is t e r m i n a t e d , it is n o t a necessary c o n d i t i o n to initially establish the p r e f e r e n c e for alcohol. It is i n t e r e s t i n g t h a t a l t h o u g h a Tension R e d u c t i o n H y p o t h e s i s w o u l d p r e d i c t that conflict, as inescapable shock, s h o u l d increase v o l u n t a r y alcohol c o n s u m p t i o n , this was n o t the case in the present investigation. A l t h o u g h conflict was f o u n d to p r o d u c e a d r a m a t i c weight loss, c o m p a r a b l e to t h a t p r o d u c e d by inescapable shock, and on o c c a s i o n was also f o u n d to p r o d u c e gastric ulceration, n o sign of increased selection of alcohol was a p p a r e n t . It seems t h a t c o n t r o l over s h o c k may be an i m p o r t a n t d e t e r m i n a n t o f alcohol c o n s u m p t i o n . U n d e r t h o s e c o n d i t i o n s where an e x t e r n a l source o f coping with stress is available, the necessity o f c o n s u m i n g alcohol for possible stress r e d u c t i o n is m i n i m i z e d . In c o n t r a s t , where an e x t e r n a l source of coping with stress is n o t available, the i m p o r t a n c e of alcohol as a stress r e d u c e r is m a x i m i z e d . Quite possibly, the f e e d b a c k of stress r e d u c t i o n in the latter situation is less ambiguous, and t h e r e f o r e m o r e reinforcing.
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