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Ethanol consumption under conditions of psychogenic polydipsia
Pkysiology and Bekavlor. Vol. 3, pp. 369-371. Pergamon Press, D68. Printed in Great Britain
Ethanol Consumption under Conditions of Psychogenic Polydipsia' R. B R U C E H O L M A N 2 A N D R O B E R T D. M Y E R S
Laboratory of Neuropschology, Purdue University, Lafayette, Indiana (Received 6 October 1967) HOt.b~N, R. B. and R. D. MYEIgS.Ethanol consumption under conditions of psychogenic polyd~sia. PHYSIOL.BEHAV. 3 (3) 369-371, 1968.--Psycholg~c polydipsia, produced by a fixed interval 90 sec reinforcement schedule, was used to determine whether excesive ethanol consumption could be induced in the rat. By offering increasing concentrations of ethanol to each rat during a sequence of test sessions, an alcohol selection-rejection curve was obtained under the regimen of psychol~nic polydipsia. A significant increase in ethanol intake occurred only at concentrations within a rat's normal prefe~er~e range. At concentrations above 8 per cent the noxious taste of the ethanol apparently blocked significant consumption of this fluid. However, the small volumes of ethanol which were consumed at the higher concentrations may have reflected the additional source of calories present in this fluid. Polydipsia in rats Taste of ethanol Schedule-induced ethanol polydipsia
Alcohol consumption Psychogenic polydipsia and ethanol Drinking of ethanol Fluid intake
MOST animals will not drink ethanol in the range of concentrations analogous to human consumption and hence will not become what might be termed "intoxicated". For this reason experimental investigations of the etiology of volitional ethanol consumption have met with fimited success. The phenomenon of schedule-induced (psychogenic) polydipsia as described by Falk [1] appears to offer a behavioral paradigm for simulating in an animal the compulsive drinking behavior of the human alcoholic. In Falk's original experiment, the food deprived rats maintained at 70-80 per cent of normal body weight, worked for food pellets in a Skinner box on a variable l-rain interval reinforcement schedule (VI-I) in which a bar press produced a food pellet on the average of one per rain. Under these conditions a typical rat drank 3-4 times more water during a 3.17 hr test session than the average volume consumed in its home cage over a 24-hr period. Rats on a psychogenic polydipsia regimen will also ingest sufficient volumes of 5.6 per cent ethyl alcohol to become "intoxicated" as defined by blood alcohol levels [4]. Can the behavioral situation associated with psychogenic polydipsia truly create a "drive" for ethanol ? This research was carried out to determine whether the rat's acceptance of ethanol in concentrations within and above its normal range of preference would be affected by the conditions of scheduleinduced polydipsia. Since the factors of taste and calories are significantly related to an animal's selection of ethanol, one group of rats was offered ethanol throughout the experiment, i.e., in the experimental test chamber and in the home cage; in contrast, a second group was also given ethanol in the experimental chamber but water in the home cage. These two treatments provided the means by which the ethanol and polydipsia variables could be delineated.
METHOD
Subjects and Apparatus Six male rats of the Long-Evans hooded strain (Windsor Biology Gardens) ranging from 250-300 g and 90-100 days old at the beginning of the experiments were used. Each animal was individually housed under constant light conditions and maintained on a diet of Wayne Lab Blox and ad libitum fluids. The chambers used for the polydipsia measurements were similar to those described by Falk [1] and were approximately 9.5 × 9 x 9 in. Figure 1 illustrates diagrammatically one of the experimental chambers which was enclosed in a polystyrene box to attenuate sound. All reinforcement schedules were remotely programmed by standard relay systems. Counters and cumulative recorders were employed to monitor the number of responses and reinforcements.
Procedure All rats were trained in the experimental chambers to press a Scientific Prototype lever to obtain 45 mg food pellets (P. J. Noyes, Co.). Stable bar pressing rates were obtained by reinforcing each lever response. To elicit psychogenic polydipsia for water, each rat was tested at the same time every day for 3.5 hr each on a fixed interval (FI)-90-sec reinforcement schedule. That is, a bar press would produce a food pellet only after a 90-sec interval elapsed following the delivery of the previous pellet. At the conclusion of each test session the animal was returned to its home cage where water and supplementary food (8--14 g per day) were available so that its body weight could be maintained between 70-80 per cent of the pre-experimental level. After a stable level of polydipsia
XThisresearch was supported in part by Grant GB 3874 from the National Science Foundation and by a grant from the Wallace Laboratories. ~IIH Fellow in Neurobiology. 369
370
H()[ MAN AND MYERS 1.4"
I ~-olydip:~o i Con)roi
z Food Cup
1
o
--
~
i=[J
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Lo+er
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Q2"
,pout
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u
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~
25-
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• +" Potydips+a - Control
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15FIG. I. Schematic diagram of experimental chamber showing the positions of the lever, food cup, light and partition. The graduated cylinder containing water or an ethanol solution is mounted on the side of the sound-proof box.
.........~ . . ~ .
:~
+
+
.
.
.
developed, ethanol selection testing in the experimental chamber was begun. In the home cage, half of the rats (n = 3) were offered water (termed hereafter "ethanol/water group") whereas the other half received the same concentration of ethanol in the home cage as offered in the experimental chamber (termed hereafter "ethanol/ethanol group"). The ethanol concentrations, prepared volumetrically with tap water, were increased daily in 1 per cent steps from 3-13 per cent and in 2 per cent steps from 14-20 per cent. At the completion of the 3-20 per cent ethanol selection sequence, all animals received only water and their entire food supplement in the home cage for a 5-day rest period. As a control for the effects of the FI schedule on ethanol consumption, the same 3-20 per cent testing procedure was repeated, except that the lever was removed and the average number of pellets (i.e., 135) normally obtained by the rat on previous polydipsia sessions was placed in the food cup prior to the start of each 3.5-hr session. RESULTS
1'0'
.
ETOH
' f4
"
Concenfralion
FIG. 2. Mean intakes of ethanol in g (top) and ml (bottom) for six rats tested under polydipsia and control conditions. Ethanol concentrations (abscissa) were increased daily at the beginning of each 3.5 hr test session in 1 per cent Steps from 3-14 percent and in 2 per cent steps through 20 per cent. except for elevations at the 3 and 4 per cent concentrations (Fig. 2, bottom). Figure 3 separates the total daily consumption at each concentration for the "ethanol/ethanol group" and "ethanol/ 60. '
Elhanol/Ethanol Group(n:3) '
3(]
+ • Total • '. . . . . . . . Exp. Chamber ""~'~'~'"~'\'~'~'" ,, .. , .'--" Hame Cage
._c 1~ c+~ :..o._+
The results clearly indicate that overall ethanol consumption was elevated under the regimen of psychogenic polydipsia in comparison to the control period. However, this difference occurred only at the lower concentrations. Figure 2 presents the mean intakes in terms of volume (ml) and weight (g) of ethanol for the six rats at all ethanol concentrations offered under polydipsia and control conditions. These data are independent of the home cage treatments, since the water or ethanol in the home cage had no significant effect on ethanol intakes in the experimental chamber [3]. Significant differences in the volumes consumed between polydipsia and control conditions were noted (Fig. 2, bottom) only between the 3 and 7 per cent concentrations inclusive (F = 17.34, 6.68, 25.66, 12.21, 6,19, respectively; df= 1/60, p < 0.05). Also, the g of ethanol ingested were similarly greater at the lower concentrations and peaked at the 11 per cent level (Fig. 2, top). For all animals under the polydipsia regimen, the volumes consumed from 3 through 7 per cent differed significantly from those at the higher concentrations, 13-20 per cent. However, under the control conditions the intake of ethanol was stable
2"0
(%)
E ~= 50.
i
l
.
.
.
.
i
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•
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.+
+. . . . . . .
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i
Ethanol/Water Group(n=3) \,
3(3
o
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'
.G . . . .
• ... + .
lb'
....., +.-~ -.-=
'
'1'4
ETOH Concentration (%)
'
'
~/o
FIG. 3. Mean fluid intakes for 3 rats (top) offered ethanol in both the experimental chamber and home cage (ethanol/ethanol group) and for 3 rats (bottom) offered ethanol in the experimental chamber hut water in the home cage (ethanol/water group). The functions represent the total fluid ingested at each increasing concentration, (as in Fig. 2) as well as the breakdown of the fluids consumed in the experimental chamher and home cage.
SCHEDULE-INDUCED ETHANOL POLYDIPSIA
371
water group" into the two component parts: ml consumed in the home cage vs. ml consumed in the experimental chamber, Above the 4 per cent concentration, the home cage intake of the "ethanol/ethanol group" (Fig. 3, top) was greater than in any test session. On the other hand, the intake of the "ethanol/water group" (Fig. 3, bottom) was much lower in the home cage than in the experimental chamber until the 14 per cent concentration was offered.
DISCUSSION
The behavioral conditions associated with scheduleinduced polydipsia caused rats to drink significantly larger volumes of ethanol than in a control situation. Although these results confirm Lester's earlier finding [4] with ethanol, the increase in intake occurred only at the lower concentrations, which parallels Falk's report [2] with increasing NaCI solutions. It would appear that the taste of ethanol above the 8 per cent caused a reduction in the amounts ingested. Richter and Campbell [8], Lester and Greenberg [5] and Myers [6] have demonstrated that the taste of this fluid is an important factor in terms of a rat's ethanol consumption. In the present study the evidence for the importance of taste with respect to psychogenic polydipsia is three-fold. First, in the "ethanol/ethanol group" the magnitude of polydipsia in the experimental chamber began to decline even at the 4 per cent concentration and most of the daily ethanol was then obtained in the home cage. This result suggests that the noxious tasting solutions were ingested at intervals distributed over the 20.5-hr home cage period. Second, the relatively high daily consumption of ethanol in the home cage decreased in the "ethanol/ethanol group" as the concentrations became higher. This is in contrast to the magnitude of water consumed by the "ethanol/water group". Third, in considering g of ethanol ingested under control conditions, peak consumption occurred at 18 per cent; however, on the polydipsia regimen, the maximum intake occurred at the 11 per cent level. Above this concentration the taste of the
solutions apparently inhibited any further increase in the number of g of ethanol ingested at the higher concentrations. In fact, the magnitude of consumption (g) in this range under the polydipsia regimen decreased to a level similar to that of the control. The lack of any significant change in activity level as reflected by lever pressing rates as well as the number of pellets consumed per test session indicate that the rat's decrease in ethanol intake was not due to the pharmacological actions of this drug. Another important feature of these results pertains to the influence of the caloric value of ethanol on the magnitude of polydipsia. F o o d deprivation as well as nutritional deficiencies have been shown to modify a rat's normal ethanol preference [7,9, 10]. The food-deprived animal in this study may have increased its ethanol consumption to supplement its restricted daily caloric intake, particularly at the lower concentrations when taste was not a major factor. In addition, for rats offered only ethanol, the diuretic action of this substance even in low concentrations could have elevated the requirements for fluid so that normal water balance was maintained. Both these factors could explain why the "ethanol/ethanol group" drank more fluid in the home cage than the "ethanol/water group." On the other hand, the "ethanol]water group", with ethanol available only during the test sessions continued to drink in the experimental chamber through 12 per cent to obtain additional calories. At this concentration, a reversal occurred and the caloric drive was ostensibly overridden by the noxious taste of the fluid. These results clearly show that taste and caloric value cannot easily be dismissed in an analysis of psychogenic polydipsia in which ethanol is the test fluid. Surely, the strength of the "drive" for fluids is seriously diminished by taste in the higher percent range, although taste does not appear to be the sole determinant of a rat's selection of a given ethanol solution. Ultimately, the magnitude of ethanol which may be voluntarily ingested under these behavioral conditions will be determined when the factor of taste is circumvented.
REFERENCES
1. Falk, J. Studies on schedule-induced polydipsia. In: Thirst edited by M. Wayner, London: Pergamon Press, pp. 95-116, 1964. 2. Falk, J. Analysis of water and NaCI solution acceptance by schedule-induced polydipsia. J. exp. Analysis. Behav. 9: 111-118, 1966. 3. Holman, R. B. The effect of psychogenic polydipsia on volitional ethanol consumption in the rat. Master of Science Thesis, Purdue University, 1967. 4. I..ester, D. Sclf-maintenance of intoxication in the rat. Q. JI. Stud. Alcohol 22: 223-231, 1961. 5. I.ester, D. and L. Greenberg. Nutrition and the etiology of alcoholism: The effect of sucrose, fat and saccharin on the self-selection of alcohol by rats. Q. JI. Stud. Alcohol. 13: 553-560, 1952. 6. Myers, R. D. Changes in learning, extinction and fluid preferences as a function of chronic alcohol consumption in rats. J. comp. physiol. Psychoi. $4: 510-516, 1961.
7. Myers, R. D. Voluntary alcohol consumption in animals: Peripheral and intraccrcbral factors. Psychosom. Med. 28: 484-497, 1966. 8. Richter, C. and K. Campbell. Alcohol taste thresholds and concentration of solution preferred by rats. Science 91: 507, 1940. 9. Segovia-Riqu©lme, N., A. Hederra, M. Anex, O. Barnier, I. Figuerola-Camps,I. Campos-Hoppe, N. Jara and J. Mardones. Influencia de factores geneticos y nutrimentales sobre la apetancia de etanol. Paper presented at the International Symposium on Alcohol and Alcoholism, Santiago de Chile, 1966. 10. Westerfeld, W. and J. Lawrow. The effect of caloric restriction and thiamin deficiency on the voluntary consumption of alcohol by rats. Q. Jl. Stud. Alcohol 14: 378-384, 1953.
Ethanol Consumption under Conditions of Psychogenic Polydipsia' R. B R U C E H O L M A N 2 A N D R O B E R T D. M Y E R S
Laboratory of Neuropschology, Purdue University, Lafayette, Indiana (Received 6 October 1967) HOt.b~N, R. B. and R. D. MYEIgS.Ethanol consumption under conditions of psychogenic polyd~sia. PHYSIOL.BEHAV. 3 (3) 369-371, 1968.--Psycholg~c polydipsia, produced by a fixed interval 90 sec reinforcement schedule, was used to determine whether excesive ethanol consumption could be induced in the rat. By offering increasing concentrations of ethanol to each rat during a sequence of test sessions, an alcohol selection-rejection curve was obtained under the regimen of psychol~nic polydipsia. A significant increase in ethanol intake occurred only at concentrations within a rat's normal prefe~er~e range. At concentrations above 8 per cent the noxious taste of the ethanol apparently blocked significant consumption of this fluid. However, the small volumes of ethanol which were consumed at the higher concentrations may have reflected the additional source of calories present in this fluid. Polydipsia in rats Taste of ethanol Schedule-induced ethanol polydipsia
Alcohol consumption Psychogenic polydipsia and ethanol Drinking of ethanol Fluid intake
MOST animals will not drink ethanol in the range of concentrations analogous to human consumption and hence will not become what might be termed "intoxicated". For this reason experimental investigations of the etiology of volitional ethanol consumption have met with fimited success. The phenomenon of schedule-induced (psychogenic) polydipsia as described by Falk [1] appears to offer a behavioral paradigm for simulating in an animal the compulsive drinking behavior of the human alcoholic. In Falk's original experiment, the food deprived rats maintained at 70-80 per cent of normal body weight, worked for food pellets in a Skinner box on a variable l-rain interval reinforcement schedule (VI-I) in which a bar press produced a food pellet on the average of one per rain. Under these conditions a typical rat drank 3-4 times more water during a 3.17 hr test session than the average volume consumed in its home cage over a 24-hr period. Rats on a psychogenic polydipsia regimen will also ingest sufficient volumes of 5.6 per cent ethyl alcohol to become "intoxicated" as defined by blood alcohol levels [4]. Can the behavioral situation associated with psychogenic polydipsia truly create a "drive" for ethanol ? This research was carried out to determine whether the rat's acceptance of ethanol in concentrations within and above its normal range of preference would be affected by the conditions of scheduleinduced polydipsia. Since the factors of taste and calories are significantly related to an animal's selection of ethanol, one group of rats was offered ethanol throughout the experiment, i.e., in the experimental test chamber and in the home cage; in contrast, a second group was also given ethanol in the experimental chamber but water in the home cage. These two treatments provided the means by which the ethanol and polydipsia variables could be delineated.
METHOD
Subjects and Apparatus Six male rats of the Long-Evans hooded strain (Windsor Biology Gardens) ranging from 250-300 g and 90-100 days old at the beginning of the experiments were used. Each animal was individually housed under constant light conditions and maintained on a diet of Wayne Lab Blox and ad libitum fluids. The chambers used for the polydipsia measurements were similar to those described by Falk [1] and were approximately 9.5 × 9 x 9 in. Figure 1 illustrates diagrammatically one of the experimental chambers which was enclosed in a polystyrene box to attenuate sound. All reinforcement schedules were remotely programmed by standard relay systems. Counters and cumulative recorders were employed to monitor the number of responses and reinforcements.
Procedure All rats were trained in the experimental chambers to press a Scientific Prototype lever to obtain 45 mg food pellets (P. J. Noyes, Co.). Stable bar pressing rates were obtained by reinforcing each lever response. To elicit psychogenic polydipsia for water, each rat was tested at the same time every day for 3.5 hr each on a fixed interval (FI)-90-sec reinforcement schedule. That is, a bar press would produce a food pellet only after a 90-sec interval elapsed following the delivery of the previous pellet. At the conclusion of each test session the animal was returned to its home cage where water and supplementary food (8--14 g per day) were available so that its body weight could be maintained between 70-80 per cent of the pre-experimental level. After a stable level of polydipsia
XThisresearch was supported in part by Grant GB 3874 from the National Science Foundation and by a grant from the Wallace Laboratories. ~IIH Fellow in Neurobiology. 369
370
H()[ MAN AND MYERS 1.4"
I ~-olydip:~o i Con)roi
z Food Cup
1
o
--
~
i=[J
,+-Partition
Lo+er
Q6-
Fan
Q2"
,pout
-i -?
u
35-
~
25-
\
• +" Potydips+a - Control
Cylinder
15FIG. I. Schematic diagram of experimental chamber showing the positions of the lever, food cup, light and partition. The graduated cylinder containing water or an ethanol solution is mounted on the side of the sound-proof box.
.........~ . . ~ .
:~
+
+
.
.
.
developed, ethanol selection testing in the experimental chamber was begun. In the home cage, half of the rats (n = 3) were offered water (termed hereafter "ethanol/water group") whereas the other half received the same concentration of ethanol in the home cage as offered in the experimental chamber (termed hereafter "ethanol/ethanol group"). The ethanol concentrations, prepared volumetrically with tap water, were increased daily in 1 per cent steps from 3-13 per cent and in 2 per cent steps from 14-20 per cent. At the completion of the 3-20 per cent ethanol selection sequence, all animals received only water and their entire food supplement in the home cage for a 5-day rest period. As a control for the effects of the FI schedule on ethanol consumption, the same 3-20 per cent testing procedure was repeated, except that the lever was removed and the average number of pellets (i.e., 135) normally obtained by the rat on previous polydipsia sessions was placed in the food cup prior to the start of each 3.5-hr session. RESULTS
1'0'
.
ETOH
' f4
"
Concenfralion
FIG. 2. Mean intakes of ethanol in g (top) and ml (bottom) for six rats tested under polydipsia and control conditions. Ethanol concentrations (abscissa) were increased daily at the beginning of each 3.5 hr test session in 1 per cent Steps from 3-14 percent and in 2 per cent steps through 20 per cent. except for elevations at the 3 and 4 per cent concentrations (Fig. 2, bottom). Figure 3 separates the total daily consumption at each concentration for the "ethanol/ethanol group" and "ethanol/ 60. '
Elhanol/Ethanol Group(n:3) '
3(]
+ • Total • '. . . . . . . . Exp. Chamber ""~'~'~'"~'\'~'~'" ,, .. , .'--" Hame Cage
._c 1~ c+~ :..o._+
The results clearly indicate that overall ethanol consumption was elevated under the regimen of psychogenic polydipsia in comparison to the control period. However, this difference occurred only at the lower concentrations. Figure 2 presents the mean intakes in terms of volume (ml) and weight (g) of ethanol for the six rats at all ethanol concentrations offered under polydipsia and control conditions. These data are independent of the home cage treatments, since the water or ethanol in the home cage had no significant effect on ethanol intakes in the experimental chamber [3]. Significant differences in the volumes consumed between polydipsia and control conditions were noted (Fig. 2, bottom) only between the 3 and 7 per cent concentrations inclusive (F = 17.34, 6.68, 25.66, 12.21, 6,19, respectively; df= 1/60, p < 0.05). Also, the g of ethanol ingested were similarly greater at the lower concentrations and peaked at the 11 per cent level (Fig. 2, top). For all animals under the polydipsia regimen, the volumes consumed from 3 through 7 per cent differed significantly from those at the higher concentrations, 13-20 per cent. However, under the control conditions the intake of ethanol was stable
2"0
(%)
E ~= 50.
i
l
.
.
.
.
i
•
•
•
.+
+. . . . . . .
+-----o
)
i
Ethanol/Water Group(n=3) \,
3(3
o
%...
'
.G . . . .
• ... + .
lb'
....., +.-~ -.-=
'
'1'4
ETOH Concentration (%)
'
'
~/o
FIG. 3. Mean fluid intakes for 3 rats (top) offered ethanol in both the experimental chamber and home cage (ethanol/ethanol group) and for 3 rats (bottom) offered ethanol in the experimental chamber hut water in the home cage (ethanol/water group). The functions represent the total fluid ingested at each increasing concentration, (as in Fig. 2) as well as the breakdown of the fluids consumed in the experimental chamher and home cage.
SCHEDULE-INDUCED ETHANOL POLYDIPSIA
371
water group" into the two component parts: ml consumed in the home cage vs. ml consumed in the experimental chamber, Above the 4 per cent concentration, the home cage intake of the "ethanol/ethanol group" (Fig. 3, top) was greater than in any test session. On the other hand, the intake of the "ethanol/water group" (Fig. 3, bottom) was much lower in the home cage than in the experimental chamber until the 14 per cent concentration was offered.
DISCUSSION
The behavioral conditions associated with scheduleinduced polydipsia caused rats to drink significantly larger volumes of ethanol than in a control situation. Although these results confirm Lester's earlier finding [4] with ethanol, the increase in intake occurred only at the lower concentrations, which parallels Falk's report [2] with increasing NaCI solutions. It would appear that the taste of ethanol above the 8 per cent caused a reduction in the amounts ingested. Richter and Campbell [8], Lester and Greenberg [5] and Myers [6] have demonstrated that the taste of this fluid is an important factor in terms of a rat's ethanol consumption. In the present study the evidence for the importance of taste with respect to psychogenic polydipsia is three-fold. First, in the "ethanol/ethanol group" the magnitude of polydipsia in the experimental chamber began to decline even at the 4 per cent concentration and most of the daily ethanol was then obtained in the home cage. This result suggests that the noxious tasting solutions were ingested at intervals distributed over the 20.5-hr home cage period. Second, the relatively high daily consumption of ethanol in the home cage decreased in the "ethanol/ethanol group" as the concentrations became higher. This is in contrast to the magnitude of water consumed by the "ethanol/water group". Third, in considering g of ethanol ingested under control conditions, peak consumption occurred at 18 per cent; however, on the polydipsia regimen, the maximum intake occurred at the 11 per cent level. Above this concentration the taste of the
solutions apparently inhibited any further increase in the number of g of ethanol ingested at the higher concentrations. In fact, the magnitude of consumption (g) in this range under the polydipsia regimen decreased to a level similar to that of the control. The lack of any significant change in activity level as reflected by lever pressing rates as well as the number of pellets consumed per test session indicate that the rat's decrease in ethanol intake was not due to the pharmacological actions of this drug. Another important feature of these results pertains to the influence of the caloric value of ethanol on the magnitude of polydipsia. F o o d deprivation as well as nutritional deficiencies have been shown to modify a rat's normal ethanol preference [7,9, 10]. The food-deprived animal in this study may have increased its ethanol consumption to supplement its restricted daily caloric intake, particularly at the lower concentrations when taste was not a major factor. In addition, for rats offered only ethanol, the diuretic action of this substance even in low concentrations could have elevated the requirements for fluid so that normal water balance was maintained. Both these factors could explain why the "ethanol/ethanol group" drank more fluid in the home cage than the "ethanol/water group." On the other hand, the "ethanol]water group", with ethanol available only during the test sessions continued to drink in the experimental chamber through 12 per cent to obtain additional calories. At this concentration, a reversal occurred and the caloric drive was ostensibly overridden by the noxious taste of the fluid. These results clearly show that taste and caloric value cannot easily be dismissed in an analysis of psychogenic polydipsia in which ethanol is the test fluid. Surely, the strength of the "drive" for fluids is seriously diminished by taste in the higher percent range, although taste does not appear to be the sole determinant of a rat's selection of a given ethanol solution. Ultimately, the magnitude of ethanol which may be voluntarily ingested under these behavioral conditions will be determined when the factor of taste is circumvented.
REFERENCES
1. Falk, J. Studies on schedule-induced polydipsia. In: Thirst edited by M. Wayner, London: Pergamon Press, pp. 95-116, 1964. 2. Falk, J. Analysis of water and NaCI solution acceptance by schedule-induced polydipsia. J. exp. Analysis. Behav. 9: 111-118, 1966. 3. Holman, R. B. The effect of psychogenic polydipsia on volitional ethanol consumption in the rat. Master of Science Thesis, Purdue University, 1967. 4. I..ester, D. Sclf-maintenance of intoxication in the rat. Q. JI. Stud. Alcohol 22: 223-231, 1961. 5. I.ester, D. and L. Greenberg. Nutrition and the etiology of alcoholism: The effect of sucrose, fat and saccharin on the self-selection of alcohol by rats. Q. JI. Stud. Alcohol. 13: 553-560, 1952. 6. Myers, R. D. Changes in learning, extinction and fluid preferences as a function of chronic alcohol consumption in rats. J. comp. physiol. Psychoi. $4: 510-516, 1961.
7. Myers, R. D. Voluntary alcohol consumption in animals: Peripheral and intraccrcbral factors. Psychosom. Med. 28: 484-497, 1966. 8. Richter, C. and K. Campbell. Alcohol taste thresholds and concentration of solution preferred by rats. Science 91: 507, 1940. 9. Segovia-Riqu©lme, N., A. Hederra, M. Anex, O. Barnier, I. Figuerola-Camps,I. Campos-Hoppe, N. Jara and J. Mardones. Influencia de factores geneticos y nutrimentales sobre la apetancia de etanol. Paper presented at the International Symposium on Alcohol and Alcoholism, Santiago de Chile, 1966. 10. Westerfeld, W. and J. Lawrow. The effect of caloric restriction and thiamin deficiency on the voluntary consumption of alcohol by rats. Q. Jl. Stud. Alcohol 14: 378-384, 1953.