Effect of low dose ethanol on spontaneous motor activity in alcohol-preferring and -nonpreferring lines of rats

Pharma~o/og~ Bto~hern:~tr~,& Behavior, Vol 24, pp 617-623, 1986 ~ Ankho lnternattonal inc Planted m the U S A

0091-3057/86 $3 00 + 00

Effect of Low Dose Ethanol on Spontaneous Motor Activity in Alcohol-Preferring and-Nonpreferring Lines of R a t s I M

B. W A L L E R ,

J M . M U R P H Y , 2 W J M c B R I D E , '~ L AND T.-K. LI

LUMENG

D e p a r t m e n t s o f Psychtatry, M e d t c m e and Btochemtstry, The lnstttute o f Psy¢htatrt¢ Research and The R e g e n s t r l e f lnstttute, Indiana Umverstty School o f M e d w m e and V A Medtcal Center, Indtanapohs, I N 46223 Received 9 October

1984

WALLER, M B , J M MURPHY, W J McBRIDE, L LUMENG AND T -K LI Effect of low dose ethanol on spontaneous motor a~ttvlty m alcohol-preferring and -nonpreferrmg hnes of rats PHARMACOL BIOCHEM BEHAV 24(3) 617-623, 1986 - - T o determine tf behavioral arousal may be assocmted wtth ethanol preference, the effects of low to moderate doses of ethanol on spontaneous motor acUvlty (SMA) were studied m the selectively bred alcohol-preferring (P) and -nonprefemng (NP) hnes of rats as well as m the Maudsley Reacnve (MR/N) and Nonreact,ve (MNR/N) stratus Alcohol-natve rats had food and water available ad hb, but food was removed 24 hr before and dunng activity testmg After an mtrapentoneal m.lectton of sahne (5 ml) or ethanol (0 12 to 1 5 g/kg), SMA was momtored every three mm for 30 mm m an electronic acUvlty momtor The P and MR/N rats exh.btted increased SMA after doses of 0 12 and 0 25 g/kg Both the NP and MNR/N rats faded to show increased SMA at any ethanol dose Moderate doses of ethanol, 1 0 and 1 5 g/kg, conststently depressed SMA m all hnes/stralns In 24 hr-fasted rats, mcreased SMA occurred within 6--12 mln after mjectlon, but free-fed rats exhlbtted tncreased SMA 12-24 mm after an ethanol dose of 0 25 g/kg Free-choice dnnkmg scores (10% ethanol (v/v) versus water) for the P, MR/N, MNR/N and NP rats were 6 6-+0 5, 4 9"--0 8, 2 2"--0 7 and 1 4"--0 3 g ethanol/kg body wt/day (mean-SEM), respectively The data indicate a pos,tlve relaUonshlp between ethanol preference and ethanol-reduced motor sumulauon and suggest that hyperacttvlty may be an expression of the postt~ve reinforcing effect of ethanol for alcohol-prefernng rats Ethanol

Low-dose effects of ethanol

Alcohol-prefemng and -nonprefemng rats

W E have recently reported that the selectively-bred a l c o h o l - p r e f e r n n g (P) and alcohol-nonpreferrlng (NP) hnes of rats do not differ in initial sensitivity to the depressant action of ethanol, but the P rats acquire acute tolerance to the depressant effects of ethanol m o r e rapidly than do the N P rats [31] Although the m o r e rapid acquisition of tolerance m a y facilitate sustained high ethanol mtake, it cannot adequately account for the ethanol preference of the P rats, because blood alcohol c o n c e n t r a t i o n s (BAC) that induce thts kind of tolerance are considerably higher than those usually attained with voluntary oral c o n s u m p t i o n [15] F u r t h e r m o r e , we h a v e found that w h e n the B A C e x c e e d s 50 mg%, the P animals begin to curtail their voluntary alcohol c o n s u m p t m n [30] T h e s e results h a v e suggested to us that the reinforcing properties of ethanol should be sought at low blood alcohol c o n c e n t r a t i o n s

Spontaneous motor acttv~ty

L o w doses o f ethanol reportedly are excttatory and potenttate b e h a v i o r s such as spontaneous m o t o r activity (SMA) in rodents (for r e v i e w see [22]) H o w e v e r , this action o f ethanol appears to be task-specific and is more consistently seen m mice than m rats [22] Studies with mbred and selectively-bred m o u s e lines h a v e d e m o n s t r a t e d that the sttmulatory effect of ethanol is genetically influenced [5, 10, 23, 24, 27] One plausible hypothesis is that stimulation of S M A mduced by low doses of alcohol is an expression of the positive reinforcing feature of ethanol Such a hypothesis is consistent with the notion that excltatton effects (or euphoria) of drugs are important m their d e p e n d e n c e hablhty and the possibility that this stimulating effect might facthtate alcohol ingestion in man [25] A c c o r d m g l y , studies w e r e p e r f o r m e d with several lines of rats, including the Maudsley R e a c t i v e

~Supported by HHS AA-03243 ZRequests for repnnts should be addressed to Dr J M Murphy, Department of Psychiatry, Institute of Psychiatric Research, Indiana Umverslty School of Medtcme, Indlanapohs, IN 46223 SReclplent of Research Sclenttst Development Award MH 00203

617

618

W A L L E R , MU RPH Y , M c B R I D E , L U M E N G A N D LI 225.

TABLE 1

,-I

P MALES,

>

(I)

UJ

>- ~ I," --

o '~m I-,-

FASTED ~'-+ S E M n,6

SPONTANEOUS LOCOMOTOR ACTIVITY OF THE FOUR ANIMAL L I N E S D U R I N G T H E 30 M I N U T E S I M M E D I A T E L Y F O L L O W I N G A N INTRAPERITONEAL INJECTION OF SALINt

15(?- (3) A. (2) o. • (4)

Actlwty Counts Sex

NP

MR/N

MNR/N

811 _+ 100 1141 + 100*v

955 +_ 122 879 = 94~-

801 + 62 664 _+ 59

735 + 120 538 +_ 74

I

7'5.

Z

Male Female

o 0

P

I

I

!

I

f

I

2

3

4

5

6 MINUTE INTERVALS

FIG 1 Effect of repeated saline injections on SMA of fasted (24 hr) male P rats At least four days elapsed between each lnjectmn Differences across trials at each 6 mm interval were statistically evaluated with ANOVA

strata m which behavioral arousal has been reported [13] The purpose of the studies reported here was to determine whether there is an assoclatmn between ethanol dnnklng preference and the st,mulatory effect of low doses of ethanol METHOD

Antmal~ Adult alcohol-prefernng (P), -nonprefemng (NP), Maudsley Reactive (MR/N) and Maudsley Nonreactive (MNR/N) animals were used The P and NP lines were developed through selecttve breeding from a W~star colony (Wrm WRC(WI)BR) at the Walter Reed Army Inst,tute of Research [17] and malntamed m our facditles The Maudsley rats were obtained from the National Institutes of Health Aicohol-nawe male and female rats from each hne were mdlvtdually housed in a temperature- and humidity-controlled enwronment with a 12 hr day-mght cycle (0700 hr hghts on, 1900 hr hghts off) At the start of the experiments, the weights of the animals were (male/female) P, 335--416/211280 g, NP, 190-285/103--179 g, MR/N, 250-315/159--182 g, MNR/N, 164--253/131-176 g Except where indicated, standard laboratory chow (Wayne Lab-Blox, Allied Mills, Inc , Chicago, IL) and water were freely available m the home cages throughout the experiments An ethanol preference score was determined for each rat upon completion of all acttvlty testing. The preference test procedure has been described previously in detail [17]

Statistical significance across hnes determined w~th ANOVA followed by Newman-Keuls test, within hne gender differences evaluated with the mdependent t-test *Significant difference from P males (p<0 05) +Significant difference from NP MR/N and MNR/N females qJ<0 05) l:Sigmficant difference from MNR/N females Ip¢-0 05~ Mean + SEM n 10

scratching The vahdlty of this gain setting was verified by visual observatmn of several ammals not used m the study For subsequent experiments, a standard plastic cage (43 ×21×20 cm) was placed on the sensor umt and, after the rat was placed m the cage, covered with a nonmetallic hd The sensor and cage were located m a qmet, d~mly ht room All testing m the activity monitor was done between 0900 and 1500 hr Ethanol determma.on In some P and MR/N ammals brain ethanol content and cerebral BAC were measured The brains were freeze-stopped by means of the copper tubing method of Slppel [26] Cerebral blood samples were collected from the blood that f l i e d the cavity made upon w~thdrawal of the copper tubing The gas chromatography procedures for blood and tissue sample preparatmn and ethanol determination were the same as those described prevmusly

[18] Statlstt~al analyse~ Analyses of vanance and post-hoc Newman-Keuls tests were used to evaluate statistical differences between SMA after different ethanol doses and after an injection of sahne In experiments using a single ethanol dose, a paared t-test was employed to compare SMA after ethanol and sahne rejections The results of the act~wty testmg are expressed as the mean (-+SEM) counts per time interval above or below the sahne control (sahne=0) calculated from the individual ethanol-saline d,fference scores or as the mean (-+SEM) actual counts per time interval An Independent t-test was used to evaluate mean BAC values for statistically significant differences In all cases, p < 0 05 was taken to indicate a significant difference between scores

Apparatus Spontaneous motor atttvtty An electromc acUvlty momtor (Model 31404, Stoeltlng Co , Chicago, IL) was used to measure spontaneous motor acttvlty (locomotion) following an lnjectmn of ethanol or saline The gain was adjusted to record slow to moderate gross movement, such as locomotmn, and not rap,d movements such as grooming and

Proc edure Expertment I The effe~ t oJ repeated sahne mje¢ tlon~ on SMA o f fasted rats Fasted (24 hr) male P rats (n=6) and female MR/N rats (n=8) were gwen a senes of four reJections of 5 0 ml of sterile saline (0 9% NaCI m water) The reJections were at least four days apart Immedmtely after an

S P O N T A N E O U S MOT O R A C T I V I T Y A N D E T H A N O L P R E F E R E N C E

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ETHANOl.(g/Itg body wl ) FIG 2 Effect of ethanol on spontaneous motor activity of fasted P, NP, MR/N and MNR/N male rats in the first six minutes postlnjectlon The actlvlt~y shown is relative to the saline control (saline=0) All mjecuons were given intrapentoneally following a counterbalanced design At least four days elapsed between rejections Differences were statistically evaluated with ANOVA followed by a Newman-Keuls test *Slgmficant difference when compared with the sahne value

injection, the SMA was monttored every three mln for a total of 30 min in the acttvlty monitor descnbed above Pnor to the senes of salme tnjectlons, these antmals were habttuated by repeated exposure to the apparatus Erpenment 2 The effe( t o f repeated ( ounterbalan~ ed injecttons o f ethanol on SMA o f fasted rats Smce not all possible sequences of ethanol doses and salme could be tested, an mcomplete counterbalancing techmque was used to control for possible sequencmg effects To the extent posstble, each treatment appeared an equal number of times m each ordmai posttton and preceded and followed every other condmon Before each actlvtty-testing sesston, rats were food-deprived for 24 hr and then recetved an mtrapentoneal rejection of ethanol (0 12, 0 25, 0 50, 1 0 or 1 5 g/kg) or 5 0 ml of stenle sahne Thts volume of sahne was chosen because, wtth few exceptions, tt equalled or exceeded the volume of the ethanol doses to be used (range 0 13 to 5 2 ml/ammal) The ethanol for tnjectlon was a 12 0 g% solution prepared from 95% alcohol and stenle salme Each rat received an injection of each dose of ethanol or salme for a total of stx mjecttons The lnjecttons were at least four days apart Immediately following an tnjectlon, the SMA was momtored every three mm for a total of 30 rain m the actwtty momtor described above BACs and brain alcohol concentraUons were determmed in fasted female P (n=6/dose) and male MR/N (n=5/dose) rats s~x mm after the mjectlon of etther 0 12 or 1 5 g ethanol/kg m order to obtain lnformatton on the levels of ethanol whtch produced the observed behavioral sttmulatton or depression The antmals used for these determmattons had previously completed acttvlty and ethanol preference testing Expertment 3 The effe~ t o f repeated ethanol mje~ ttons on SMA o f free-fed and fasted rats In addition to determining if tolerance develops to repeated mjecttons of ethanol, another objectwe of the present experiment was to ascertam if the A BA design could be used for future studies concerned with resolving neurochemtcal correlates of the low dose sUmula-

I

2 6

3 MIN

4

5

INTERVALS

FIG 3 Effect of ethanol on spontaneous activity of fasted P and NP rats for successive s~x minute intervals postlnjectlon (total time=30 minutes) for two selected doses of ethanol Differences were statistically evaluated with a paired t-test *Significant difference when compared with the saline value

tory effect of ethanol Free-fed ammals were tested since they are more desirable to use than fasted antmals for neurochemical studies Alcohol-natve male P rats were randomly assigned to two treatment groups (n=6/group) Followmg an A B A design, the animals received successive injections four days apart as follows Group 1 recetved saline (five injecttons), 0 25 g/kg ethanol (seven tnjectlons) and saline (three tnjecuons), Group 2 was stmllarly treated except the ethanol dose was 1 5 g/kg The volume of salme given to both groups was equivalent to the volume of ethanol given However, m this ex p en m en t the ttme of the maximal effect of ethanol on SMA m Group 1 rats was delayed with respect to that observed with the counterbalanced destgn m Experiment 1 To assess whether the delay resulted from design features (ABA vs counterbalanced) or the feeding condttton (free-fed vs fasted), a second phase of this experiment used 24 hr fasted ammals m the A BA design After a mlmmum of two weeks w~thout any rejections, Group 1 rats were gtven successive rejections four days apart after a 24 hr fast as follows sahne (two mjections), 0 25 g/kg ethanol (three injections) and sahne (two rejections) Other procedural detatls were s~milar to those described for the first phase The data from each phase of this experiment were analyzed separately with a wlthm-sublect design In separate groups of stock Wlstar ammals, alcohol measurements were made as described above to determine whether the brain alcohol concentrations differed in free-fed and fasted rats after an mtrapentoneal mjecuon of 0 25 g/kg of ethanol RESULTS Expertment I The Effe~ t o f Repeated Sahne lnje~ turns on SMA o f Fasted Rats Ftgure 1 shows the effect of lndwidual successtve injections of saline, given at least four days apart, in fasted habituated male P rats The data shown are for the entire 30 mln test penod An analysis of variance across tnals for each 6 rain interval failed to disclose any statlsttcally stgnificant

WALLER, MURPHY, McBRIDE, LUMENG AND IJ

620

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I°-e SALINE l o - - o ETHANOL

%

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0 25 g/kg

INTERVALS

FIG 4 Effect of ethanol on spontaneous activity of fasted MR/N and MNR/N rats for successive six minute intervals postlnjectlon (total time=30 minutes) for two selected doses of ethanol Differences were statistically evaluated with a paired t-test *Significant difference when compared with the sahne value

lntertrlal differences in l o c o m o t o r actwIty by these ammais T h e s e results d e m o n s t r a t e the reproduclbihty o f the momtored b e h a v i o r Slmdar results w e r e obtained with a group of fasted M R / N female animals (data not shown)

Experiment 2 The Effe( t oJ Repeated Counterbalan( ed lnle~ttons of Ethanol on SMA of Fasted Rats The total activity during the 30 rain p e n o d following an mjectton of sahne in male and female ammals from each line used m the study is presented in Table 1 The total S M A for the 30 rain period for the male P, NP, M R / N and M N R / N groups were not s~gnlficantly different from one another H o w e v e r , within the P line, females exhibited significantly more activity than did the males An analys~s of variance across lines r e v e a l e d the P females to be more active than females from the o t h e r lines and the N P females m o r e active than M N R / N females The effect o f ethanol admtmstered intraperltoneally on the S M A of fasted male P, NP, M R / N and M N R / N rats is s h o w n m Fig 2 In the first six rain after rejection, low doses of ethanol (0 12 and 0 25 g/kg) significantly increased S M A in the P and M R / N rats, while doses of 0 5 , 1 0 and 1 5 g ethanol/kg had no effect By contrast, activity of the N P and M N R / N rats was unaffected or depressed by ethanol (Fig 2) Similar results were o b s e r v e d in females of these four lines of rats (data not shown) The S M A of the fasted P and N P male rats at ethanol doses of 0 25 and 1 5 g/kg o v e r 6 rain Intervals of the entire 30 mm test period is presented In Fig 3 The increase ,n a c t w l t y exhibited by P rats after 0 25 g ethanol/kg o c c u r r e d wzthln the first six mm and continued for 12 rain postmjectlon Thereafter, the activity was similar to that seen followmg a saline injection The rejection of l 5 g ethanol/kg slgnlfi-

FASTED 0

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2

3

4

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6 MINUTE INTERVALS FIG 5 Effect of feeding condition on time of onset of ethanolinduced spontaneous motor act~wty of male P rats FREE-FED animals had access to food up to the time of testing FASTED animals were denied access to food for 24 hr before testing Differences were statistically evaluated with a paired t-test *S~gmficant difference when compared with the sahne value

cantly d e c r e a s e d S M A of the P rats by the second 6 mm interval this reduced activity lasted for the remainder of the 30 rain test period The activity profile for N P rats was not slgmficantly altered by a dose of 0 25 g ethanol/kg H o w e v e r . an early onset of depression of S M A of the N P group was induced by 1 5 g ethanol/kg whmh lasted throughout most of the 30 mm test period (Fig 3) A slmdar analysis of successive Ume blocks for the fasted male MPUN and M N R / N animals is shown in Fig 4 The M R / N rats were sumulated only In the first s~x mm p e n o d by the 0 25 g/kg dose and were not significantly affected thereafter except for the last interval The dose of 1 5 g ethanol/kg had a generally depressant action on S M A by the M R / N male rats Both 0 25 and I 5 g ethanol/kg tended to lower S M A m the M N R / N male ammais (Fig 4) The free-chome d n n k m g scores, determined at the conclus~on of activity testing, of the rats used m these experiments were 6 6_+0 5. 4 9_+0 8. 2 2_+0 7 and 1 4_+0 3 g ethanol/kg/day for P. M R / N . M N R / N and NP. r e s p e c t w e l y The n u m b e r of animals tested for ethanol preference was 20/hne or strain Since no sex differences were apparent in ethanol preference, the scores reported represent both male and female animals In P female rats. the cerebral BAC and brain alcohol concentratlon during the p e n o d of m a x i m u m sumulatlon of m o t o r activity were 15_+0 8 mg% and 21___1 5 mg/100 g tissue. r e s p e c t w e l y , after the injection of 0 12 g ethanol/kg Similar values. 12_+0 3 mg% and 16-+1 1 rag/100 g tissue. were o b s e r v e d m M R / N males The depression of S M A ,nduced by 1 5 g ethanol/kg at six mm postlnjectlon was associated with blood and brain alcohol levels of 223_+4 0 mg% and 286_+ 14 4 mg/100 g t~ssue, respectively, m P females and 214_+11 0 mg% and 269_+11 3 mg/100 g tmsue, respectively. In the M R / N males All animals were m the fasted state

SPONTANEOUS

MOTOR ACTIVITY AND ETHANOL PREFERENCE

621

TABLE 2 BRAIN ETHANOL CONCENTRATION IN FREE-FED AND FASTED (24 HR) MALE W1STAR RATS AT DIFFERENT TIMES FOLLOWING AN INTRAPERITONEAL INJECTION OF 0 25 g ETHANOL/kg

~1" 4 0 0 04 i

>- E 3 0 0

mg ethanol/100 g assue

0 U

Feeding Condition

6

12

18

24 min

Free-fed Fasted

282-+ 1 3 289_+07

209_+ 0 9 229_+07

168-+ 07 180_+04

156- 1 0 155_+04

Differences were statlst~cally evaluated at each time point w~th an independent t-test Mean _+ SEM, n=6/condltlon/tlme point

O

SUCCESSIVE INJECTIONS FIG 6 Effect of successive rejections of saline and ethanol on spontaneous motor activity using an ABA design At least four days elapsed between each rejection The stippled band indicates the mean ± SEM for each phase of the design The actual achvlty counts for minutes 12-24 are shown

Experiment 3 The EJJe~ t o f Repeated Ethanol lnje¢ tton~ on SMA o f Free-Fed and Fasted Rats In this study, six P ammals r e c e i v e d multiple injections of saline and ethanol (0 25 g/kg) following an A B A design The excitatory effect of 0 25 g ethanol/kg was consistently apparent m the first 12 mm postmjectlon when the animals were fasted 24 hr prior to testing (Fig 5) The data shown are the mean of three ethanol injections administered at least four days apart T h e r e was no significant difference m S M A between the pre- and post-ethanol series of saline injections H o w e v e r , w h e n these same animals had free access to food up to the time of activity testing, they exhibited a similar degree o f excitation, but the maximal effect occurred during the middle thwd (minutes 12 to 24) of the test period (Fig 5) N o difference b e t w e e n free-fed and fasted P rats in the onset of depression of S M A induced by 1 5 g ethanol/kg was observed (data not shown) Figure 6 shows the results of individual s u c c e s s i v e injections of saline and ethanol (0 25 g/kg) using the A B A design These data further d e m o n s t r a t e that the monitored b e h a v i o r was stable o v e r three weeks There was no e v i d e n c e of habltuahon to saline injections (after the first trial) or the d e v e l o p m e n t of tolerance to the excitatory effects of low dose ethanol, w h e n given successively at least 4 days apart S u c c e s s i v e rejections of 1 5 g ethanol/kg, when given at least 4 days apart, also p r o d u c e d no indication of the d e v e l o p m e n t of tolerance to the depressive effects of high dose ethanol on S M A of free-fed animals (data not shown) In male Wlstar animals, brain ethanol c o n c e n t r a t i o n s w e r e determined m both free-fed and fasted rats (n=6/group/mterval) e v e r y six rain up to 24 rain after an injection of 0 25 g ethanol/kg T h e s e results are presented in Table 2 There were no slgmficanI differences b e t w e e n freefed and fasted animals at any time point DISCUSSION

Behavioral arousal o c c u m n g with low to m o d e r a t e doses of ethanol, as e v i d e n c e d by increased S M A , is a wellestablished p h e n o m e n o n in mice [22] The intensity of stimu-

latlon differs in different inbred strains, indicating the existence of a genetic influence on this m e a s u r e [4, 5, 6, 10, 23, 24, 27] Stimulation of S M A by ethanol has not been consistently o b s e r v e d in rats Whereas s o m e investigators [1, 2, 14, 19] have seen an increase in S M A with low to m o d e r a t e doses of ethanol, others [3, 8, 10, 12, 16] have not It is known that stimulation of S M A by ethanol can be affected by a n u m b e r of variables including the concentration, dose, route and timing of ethanol administration, the sex and age of the rats, and the testing instrument itself [22] The studies reported here indicate in addition that, as with m~ce, the S M A response of rats to low-dose ethanol IS strain or hne specific (Fig 2) In rats, h o w e v e r , stimulation occurs within a n a r r o w e r dose range and with lower doses than in mice T h e s e variables are likely also to contribute to s o m e o f the previous discrepancies In reported data with rats M o r e o v e r , depending upon whether rats are fasted or free-fed, the onset of stimulation may be immediate or delayed (Fig 5) Since the brain alcohol concentrations in free-fed and fasted rats do not differ within the first one-half hour of ethanol injection (Table 2), this difference is due to factors other than a change in ethanol pharmacoklnetlcs Stimulation of S M A was o b s e r v e d m the P and M R / N rats, animals which have high to m o d e r a t e degrees of ethanol p r e f e r e n c e By contrast, the low preference N P and M N R / N rats were unaffected or depressed by ethanol in the low dose range It is unlikely that a p h a r m a c o k l n e t l c difference can account for the different responses to ethanol We have previously reported that. within 2-3 mln o f an lntraperltoneal mjecUon of ethanol, the brain ethanol content is similar in P and N P rats [31] The blood and brain ethanol concentrations at which S M A stimulation occurs m the P and M R / N rats are in the range that P rats consistently attain on free-choice c o n s u m p t i o n of 10 percent ethanol and which do not negatively affect or curtad voluntary c o n s u m p t i o n [30] This posItive relationship b e t w e e n S M A stimulation and alcohol preference in the rat suggests that the former may be an important measure in the study of reinforcing m e c h a m s m s of alcohol-seeking b e h a v i o r As e x p e c t e d , all ammals began to exhibit depression of S M A with 1 0 and 1 5 g ethanol/kg (Figs 2-4) There is, therefore, a d o s e - d e p e n d e n t , blphaslc effect of ethanol on S M A A relationship b e t w e e n ethanol preference and behavioral stimulation has been sought also in mice S o m e Investigators [10, 23, 27] in the past were unable to d e m o n s t r a t e ethanol stimulation of S M A m the alcohol-preferring C57BL/6J strain of mice H o w e v e r , recent studies by Crabbe et a! [6]

622

WALLER.

i n d i c a t e that they do s h o w a l c o h o l - m d u c e d , d o s e - d e p e n d e n t i n c r e a s e s in S M A , followed by d e p r e s s i o n I m p o r t a n t l y , as wtth the P and M a u d s l e y R e a c t i v e rats (Figs 2-3), sttmulatlon in t h e C 5 7 B L / 6 J mice o c c u r r e d early after alcohol injection ( < 4 m m In the mice) a n d lasted for only a b r t e f d u r a t i o n ( < 8 m m ) T h u s , l o w - d o s e s t i m u l a t t o n of S M A by e t h a n o l is s e e n in b o t h a l c o h o l - p r e f e r r i n g rats and m i c e If l o w - d o s e alcohol s t t m u l a t l o n o f S M A ts a reflection of the r e i n f o r c i n g p r o p e r t t e s o f e t h a n o l , o n e should e x p e c t n o s t i m u l a t i o n o f S M A b y alcohol in a n i m a l s with low e t h a n o l p r e f e r e n c e , s u c h as the N P a n d M a u d s l e y N o n r e a c t i v e rats a n d D B A mice I n d e e d , we f o u n d a c o m p l e t e a b s e n c e of alcohol s t t m u l a t l o n of S M A m the N P a n d M a u d s l e y N o n r e a c t i v e rats (Figs 2-4) Only d e p r e s s i o n o f S M A o c c u r r e d wtth e t h a n o l d o s e s of 0 5 g/kg or h t g h e r O n the o t h e r h a n d , the D B A mtce h a v e b e e n s h o w n to e x h i b i t strtklng stlmulatton o f S M A with e t h a n o l [10,27] This r e a c t i o n , h o w e v e r , o c c u r s at all d o s e s of e t h a n o l that d o n o t m d u c e " s l e e p , " e , t h e y do not s h o w a n y d e p r e s s t o n of S M A , only stlmulatton, until the righting reflex is lost Thts u n u s u a l r e s p o n s e to e t h a n o l m the D B A m~ce m a y r e p r e s e n t a u n i q u e l y different p h e n o m e n o n in this strain t h a t will requtre f u r t h e r investigation In the e x p e r i m e n t s r e p o r t e d h e r e , t o l e r a n c e was not obs e r v e d e i t h e r to the d e p r e s s a n t or to t h e s t t m u l a t o r y a c t i o n of a d m m t s t e r e d e t h a n o l (Fig 6) This is h k e l y due to the e x p e r Imental d e s i g n o f spacing the test i n j e c t i o n s at least four d a y s a p a r t Thts e t h a n o l - f r e e interval was d e l i b e r a t e l y c h o s e n to m i n i m i z e c a r r y o v e r effects within the c o u n t e r b a l a n c e d design It s h o u l d b e n o t e d , h o w e v e r , w h e t h e r t o l e r a n c e develops to t h e low d o s e s t t m u l a t o r y effects ts still u n r e s o l v e d R e c e n t studies in mice h a v e failed to d e t e c t t o l e r a n c e to e t h a n o l - s t i m u l a t i o n or h a v e o b s e r v e d " r e v e r s e t o l e r a n c e , "

MURPHY. McBRIDE. LUMENG

A N D LI

l e , m c r e a s e d s t i m u l a t i o n [20,27] O n the o t h e r hand an o l d e r s t u d y m rats [11] r e p o r t e d t h a t t o l e r a n c e d e v e l o p s 1o b o t h the e x c t t a t o r y and to the d e p r e s s a n t effects of ethanol T a b a k o f f and K l m n m a a [27] h a v e suggested that d~flerent.e~ In e x p e r i m e n t a l design, wtth e m p h a s t s o n the possibility of l e a r n e d c o m p e n s a t o r y r e s p o n s e s , could a c c o u n t for confltctmg results Clearly, addttional studies are n e e d e d both in m~ce and in rats to a d d r e s s this tssue If o n e a s s u m e s that the l o w - d o s e s t i m u l a t o r y effect o f e t h a n o l ts a part or a n e x p r e s s i o n of the postttve reinforcing m e c h a n t s m of e t h a n o l and t h a t the s e d a t l v e - h y p n o t t c effect o f e t h a n o l is a v e r s l v e , an a t t r a c t t v e h y p o t h e s i s for e t h a n o l s e e k i n g b e h a v t o r can be f o r m u l a t e d , since t o l e r a n c e to the s e d a t t v e - h y p n o t t c effects does d e v e l o p with c h r o n i c e t h a n o l i n t a k e [28] Thts c o m b i n a t i o n of r e s p o n s e s to e t h a n o l c a n be e n v i s i o n e d to sustain and e n h a n c e d r m k m g o v e r ttme, until p h y s i c a l d e p e n d e n c e b e c o m e s e s t a b h s h e d It has been s h o w n in rats that e t h a n o l - d e p e n d e n c e can i n d u c e the selfa d m i n i s t r a t i o n o f large a m o u n t s o f e t h a n o l in a n i m a l s that do not e x h i b i t this b e h a v t o r in the e t h a n o l - n a i v e state [7] Howe v e r , as we h a v e r e p o r t e d r e c e n t l y , the P rats wdl selfa d m i n i s t e r large a m o u n t s of e t h a n o l , e v e n by the m t r a g a s t n c route, w i t h o u t first h a v m g b e e n forctbly m a d e e t h a n o l d e p e n d e n t [29] T h u s , the r e i n f o r c i n g actions of e t h a n o l m n o n d e p e n d e n t a n i m a l s will be clearly e v i d e n t only w h e n a n t m a l s t h a t h a v e b e e n selected for e t h a n o l p r e f e r e n c e are e m p l o y e d for study

ACKNOWLEDGEMENTS The skdlful techmcal assistance of Gregory Gatto and Mary Beth Welsh IS gratefully apprecmted

REFERENCES 1 Bnck. J . J Y Sun. L Daws and L A Pohorecky Ethanol and the response to electric shock m rats LtJe Sit 18 1293-1298 1976 2 Carlsson. A . J Engel and T H Svensson lnhJbltmn of ethanol-induced exc~tatmn m m~ce and rats by amethyl-p-tyroslne P~whopharma(ologta 26" 307-312. 1972 3 Chesher. G B Faclhtatlon of avoidance acqmsltlon m the rat by ethanol and its abolmon by a-methyl-p-tyrosme P ~ w h , pharmat ologta 39: 87-95. 1974 4 Crabbe. J C Sensltlwty to ethanol m inbred mice Genotyplc correlatmns among several behaworal responses Beha~ Neurone i 97" 280-289. 1983 5 Crabbe. J C . J S Janowsky. E R Young and H Rlgter Strata-specific effects of ethanol on open field achvffy m inbred mice Subvt Ah ohol Ac tton~ Mt~uae l' 537-543. 1980 6 Crabbe. J C . J r . N A Johnson. D K Gray. A Kosobudand E R Young BIphasm effects of ethanol on open-field actlvffy Sensltlwty and tolerance m C57BI/6N and DBA/2N m~ce J Comp Phy ~tol Psvc hol 96:440--451. 1982 7 Deutsch. J A and W T Hardy Ethanol lolerance m the rat measured by the untasted retake of alcohol Beha~ Bml 17 37%389. 1976 8 Duncan. P M and A M Baez The effect of ethanol on wheel running m rats Pharmatol Bmchem Beha~ 15" 81%821. 1981 9 Friedman. H J . J A Carpenter. D Lesterand C L Randall Effect of alpha-methyl-p-tyrosme on dose-dependent mouse strain differences in locomotor actwlty after ethanol I $tud Ahohol 41 l-t0, 1980 10 Frye, G D and G R Breese An evaluatmn of the locomotor stimulating actmn of ethanol m rats and m~ce Ps_vchopharma~olog~ (Berlin) 75. 372-379, 1981

I 1 Hunt. G P and D H Overstreet Evidence for parallel development of tolerance to the hyperacttvatmg and d~scoordlnatlng effects of ethanol P~chopharmacologv (Berhn)55 75-81. 1977 12 Holman. R B . G R Elhott. A M Kramer E Seagraves and J Barchas Stereotypy and hyperacttvlty in rats receLvmg ethanol and a monoamme oxldase inhibitor Psi( hopharmat olog~ (Bethn) 54" 237-239. 1977 13 Kochhar. A and C K Enckson Ethanol-induced behavioral arousal m three rat stratus 4hohohwT~ Chit L~p Re~ 6 147 1982 14 Leonard. B E and B D W~seman The effect of ethanol and amphetamine m~xtures on the act~wty of rats m a Y-maze / Pharm Pharma( ol 22" 967-968. 1970 15 Ll. T -K and L Lumeng Alcohol metabohsm of inbred stratus of rats with alcohol preference and non-preference In Ah oh~d and Alch.h~de Metabohzmg Sv~tem~ vol 3. edited by R G Thurman. J R Wllhamson. H Drott and B Chance New York Academm Press. 1977. pp 625-633 16 Lmakls. J G and C L Cunmngham Effects ofconcentratmn of ethanol injected mtrapentoneally on taste averston, body temperature and activity P~v~hopharma(olog~ (Bethn) 64 61-65. 1979 17 Lumeng. L . T D H a w k m s a n d T - K L~ New strams of rats with alcohol preference and nonpreference In Ahohol tlttcl Aldehyde Metabohzulg S~tem~ ~.ol 3 edited b~ R G Thurman. J R Wllhamson. H R Drott and B Chance New York Academic Press. 1977. pp 537-544 18 Lumeng. L . M B Waller. W J McBnde and T - K Ll Different sensmvltles to ethanol in alcohol-preferring and -nonpreferring rats Pharma¢ol Bto~hem Beha~ 16 125-130 1982

SPONTANEOUS MOTOR ACTIVITY AND ETHANOL PREFERENCE

19 Mason, S T , M E Corcoran and H C Flblger Noradrenerglc processes revolved m the locomotor effects of ethanol Eur J Pharrna¢ol 54: 383-387, 1979 20 Masur, J and R Boerngen The excitatory component of ethanol m mzce A chronic study Pharmacol Biochem Behav 13: 777-780, 1980 21 Mtezejesk~, C M , S Lamon, G Colher and L W Hamilton Partltlomng of behavioral arousal Phvs;ol Behav 17: 581-586, 1976 22 Pohorecky, L A Blphaslc action of ethanol Btobehav Rev 1: 231-240, 1977 23 Randall, C L , J A Carpenter, D Lester and H J Friedman Ethanol-reduced mouse strata dtfference m locomotor activity Pharrnac ol BIt~¢hem Behav 3: 533-535, 1975 24 Sanders, B Sensitivity to low doses of ethanol and pentobarbltai m m~ce selected for senslt~vlty to hypnotic doses of ethanol J Cornp Phwtol Psy~hol 90: 394-398, 1976 25 Seevers, M H Psychopharmacologlcal elements of drug dependence JAMA 206: 1263-1266. 1968

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26 Slppel, H W The acetaldehyde content in rat brain dunng ethanol metabohsm J Neuro~hem 23: 451-452, 1974 27 Tabakoff, B and K Kuanmaa Does tolerance develop to the activating, as well as the depressant, effects of ethanol9 Pharmacol Btochem Behav 17: 1073-1076, 1982 28 Tabakoff, B , C L Melchior and P L Hoffman Commentary on ethanol tolerance AIcohohsm Chn Erp Res 6: 252-259, 1982 29 Waller, M B , W J McBride, G J Gatto, L Lumeng and T - K L~ Intragastncself-mfuslonofethanolbyethanol-prefernng and -nonprefernng lines of rats Scwn~e 225: 78-80, 1984 30 Waller, M B , W J McBride, L Lumeng and T -K Ll Effects of intravenous ethanol and of 4-methylpyrazole on alcohol dnnkmg m alcohol-prefemng rats Pharmac ol Blot hem Behav 17" 763-768, 1982 31 Waller, M B , W J McBride, L Lumeng and T - K Li Imtlal sensitivity and acute tolerance to ethanol in the P and NP hnes of rats Pharma~ ol Bu~c hem Behav 19" 683-686, 1983