Effects of the kappa opioid receptor antagonist MR-2266-BS on the acquisition of ethanol preference

Pergamon Press

Life Sciences, Vol. 46, pp. 1119-1129 Printed in the U.S.A.

RPPECTS

OF

TRR RAPPA

OPIOID ACQUISITION

Carmen Cajal

Sandi*,

RRCRPTOR

AETAWNIST MB-2266-BS OF ETHANOL PREPERENCE

Jose

Borrell

and Carmen

ON THE

Guaza

Institute, Department of Psychobiology, Dr. Arce 37, 28002 Madrid, Spain.

C.S.I.C.,

(Received in final form February 9, 1990)

Using a paradigm by which rats forced to drink a weak ethanol solution (2.51 w/v) (conditiong session) develop ethanol preference in consecutive retention testing days, the effects of the administration of the kappa opioid prior to or after the forced antagonist MB-2266-BS, Pre-conditioning ethanol session, were studied. subcutaneous (s.c.) administration of 1 mg/kg of m-2266BS induced a decrease in subsequent ethanol consumption acquisition of without significantly modifying the Post-conditioning administration of ethanol preference. MB-2266-BS (0.1, 1, 5 or 10 mg/kg) induced both a doseethanol consumption and in dependent reduction in The the three following days. preference throughout results of the present study provide further support of involvement of drinking the opioids on kappa-type behavior, and suggest that receptors may be kappa involved in the consumption and development of preference to ethanol. In recent years, the hypothesis of a functional relationship between ethanol and opiates has received considerable support (1,2,3). However, while endorphins and enkephalins have been extensively studied, the investigation of the possible role of dynorphins on ethanol-induced effects is scarce. Considerably more attention has been focused on the effects of opiates on ingestive responses: in particular, evidence has grown that indicates a role of dynorphins and their corresponding kappa receptors in the modulation of drinking behavior. Some reports indicate that CNS distribution of both kappa opiate receptors (4) and pro-dynorphin-derived peptides show a certain (5,6) correspondence with CNS taste areas. In general, the antidipsogenic effects induced by administration of kappa receptor antagonists are consistent throughout a variety of experimental procedures (7,8,9). However, a more controversial picture exists regarding the kappa agonists' effects on fluid consumption. While some reports indicate drinking reductions following central (10,ll) or systemic (12,13) administration of kappa agonists, other studies show either no changes (14) or increases (15,16). * Supported

by a PFPI fellowship. 0024-3205/90$3.00 +.oo Copyright (c) 1990 Pergamon Press plc

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Evidence also exists for the involvement of kappa opioid peptides in reward or aversion processes. It has been suggested that systemic stimulation of kappa receptors produces aversion of dynorphin induces place(17), while central administration preference conditioning in rats (18). Voluntary ethanol drinking consumption involves both mechanisms and motivational factors (i.e., taste, aversive/rewarding ethanol properties), in which kappa related opioids could play an important role. Naive rats normally consume little alcohol in a spontaneous choice situation (19). However, we have designed a procedure by which rats forced to drink a 2.5% ethanol solution as their only source of fluid prior to having a free choice, develop ethanol preference (20). We are interested in the study of opioid peptlde modulation in the development of preference for ethanol (9,21,22), particularly in the acquisition and initial maintenance of ethanol preference. With regard to kappa opioid peptides, we have shown previously (9) that pretesting B.C. administration of dynorphin Impaired the maintenance of ethanol preference. The aim of the present study was, on the whether or not MB-2266-BS can one hand, to further investigate influence the acquisition of preference for ethanol and, on the other hand, to assess whether or not this antagonist could induce ethanol when conditioned taste preference/aversion to administered after the rats' first ethanol exposure.

Method8 87 Male Wistar rats (C.I.B., Madrid), weighing Subjects: between 200 and 250 g at the beginning of the experiment, were were kept under controlled temperature and used. The animals light conditions (23°C and 12-hr light-dark schedule). They were housed in group cages (4-5 animals per cage) with food and water available ad libitum. After 1 week of adaptation to the Experimental procedure: individually housed and drinking bottles, rats were weighed, during the 5 72 hr.- Subsequently, deprived of water for the animals were procedure, consecutive days of experimental maintained on a 23 hr 45 min water deprivation schedule with fluids available during the 15-min period of the drinking A two-bottle choice procedure was used in order to sessions. evaluate ethanol preference over water. Our previous experiments (20) have shown that rats forced to drink a weak ethanol solution (2.5% w/v) develop a stable baseline of alcohol preference in the of 4% or 7% fail to develop following days, while concentrations forced alcohol Thus, the preference in subsequent testing. session (2.5%) is termed "conditioning session", since rats alcohol. The for without it do not develop a preference experiments started with one day of habituation when the animals The access to tap water in the two bottles. were allowed following day (conditioning day), the two bottles were filled with a 2.5% ethanol solution. On the 3 subsequent days (retention days) the animals were presented with a two-bottle choice between 2.5% ethanol solution and tap water. In one experiment, carried the experimental out using sucrose as the solution studied, procedure followed the same schedule: one habituation day (wate_r in the two bottles), followed by a forced drinking session day

Vol. 46, No. 16, 1990

(4% sucrose testing days water).

K

1121

Opjoid Receptors and Ethanol Preference

solution In (a two-bottle

and 3 subsequent the two bottles), choice between 4% sucrose solution and

[((-)-(3-furylmethyl)-5-9MR-2266-BS Treatment schedule: (gift from H. Merz, C.H. diethyl-2-hydroxy-6,7-benzomorphan) the Boeringer Sohn, Fed. Rep. Germany)] was used throughout experiments. The drug (at the designated doses) was dissolved in saline with the aid of a single drop of HCl (0.01 N). All Control injections were made S.C. in a volume of 1 ml/rat. animals received 1 ml of the the same vehicle as placebo. Animals were treated with two following procedures: 1. Pre-conditioning: rats were ethanol exposure. 2.

Post-conditioning: forced ethanol

MR-2266-BS

injected

rats were exposure.

according

to one of the

15 min before

injected

immediately

the

forced

after

the

Different doses of MR-2266-BS were selected for each experiment. We performed a preliminary set of experiments in order to assess the locomotor activity after subcutaneously administering different doses of the antagonist: the results indicated that doses above 1 mg/kg Induced a significant decrease in locomotor activity (data not shown). From these results, a dose of 1 mg/kg was used In the pre-conditioning treatment in order to avoid a possible interference of motor impairment on the effects of MR-2266-BS in the acquisition of ethanol preference. A wider range of doses (0.1, 1, 5 and 10 mg/kg) were selected for post-conditioning administration to study both the possible influence on the development of ethanol preference and the possible establishment of conditioned taste preference/aversion to ethanol by MR-2266-BS. Statistics: Fluid intake measures were corrected for body weight (ml/100 g body weight). Ethanol preference is expressed by the index: EP = [Ethanol intake / (Ethanol + Water Intake)] x 100. Data were statistically analyzed using one or two-way analyses of variance (ANOVA). For statistical analysis, the preference scores for each animal were subjected to arcsin transformation in order to satisfy the assumptions of the analysis of variance carrying out the ANOVA. This before transformation is used to adjust for the lack of normality of percentage or proportional data (23). Posterior-i Tukey's multiple comparison tests were out when ANOVAs carried revealed significant effects.

Results Table 1 shows that MR-2266-BS (1 mg/kg) administration prior to the first forced ethanol exposure (pre-conditioning treatment) induced a decrease in ethanol consumption (F(1,16)= 9.45: ~~0.01) at the conditioning session. Moreover, MR-2266-BS-treated rats drank less total fluid compared to controls during the three days following treatment (F(1,48)= 32.78; ptO.OO1). This effect is due to a reduction in ethanol intake (F(1,48)= 20.97; p
1122

K Opioid

Receptors and Ethanol Preference

Vol. 46, No. 16, 1990

Total

forced

consueutm drxnkxnq

0.59

3.56

0.56

2.73

f 0.54

0.30

5.2511

t

0.23

(12)

subjected

D A

to rallne

v s

or RR-2266-E

treattent

0.57

2.17

a.29 0.31

t 0.35

?

0.45

0.19

t

2.14 t

Intake _______

Mater

b.51

Total Intake -_-----

2

0.47

0.16

t

6.75

1.10

f

0.17

7.21 t

Total Intake -______

0.46

f

4.41

Sucrose Intake ____---

____________________--_--_

5

0.46

t

3.55

0.58

3.31 t

Hater Intake ____---

Lb0

i

4.19

0.61

5.31 f

Sucrose Intake ___-__

___________________________

0.31

0.31 i

0.23

t

0.68

Intake _______

Total

15 rin

fkueber of anirals coeparism test.

in

parentheses.

Results

are

the

eeans

! SEH.

11

p(O.005

vs.

correspeodinq

salme

group

frm

Tukey’s

eultiple

~~_______~______------~~~~~~~~~~-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(141

?

3.98 ?

Sucrose Intake _------

2.53 t

’ rgh

i _______________________----

6.41 ?

NRR-2266-K

TESTING

TABLE 2 9 body1 on rats

session.

(d/100

~-------_-------------------------------~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~___~

at the

fluld

Saline

Intake

dailv

exposure

FORCED SESSION f.--------------q

sucrose

total

Yatef Intake _______

forced

before

and

fSucrose1 --_____

sucrose

Water,

1124

K Opioid Receptors and Ethanol Preference

Vol. 46, No. 16, 1990

water intake was not modified by the treatment (F(1,48)= 2.11; n.6.). Ethanol preference values for this experiment are shown in to the three Figure 1; neither ANOVA of the data corresponding retention days (F(1,48)1.20; n.s.), or AROVA of the first retention day, (F(1,16)= 0.10; n.s.) reached a significant level. the observed effect on later In order to study whether ethanol consumption induced by pre-conditioning administration of RR-2266-BS was specific for ethanol or a more general effect over taste preferences, we evaluated the effects of the administration of RR-2266-BS (1 g/kg), prior to a forced sucrose drinking session, on later sucrose preference and consumption. The results obtained indicated that this treatment did not modify later sucrose preference (F(1,72)= 0.05; n.s.; data not shown). As is rats drank MR-2266-BS-treated while Table 2, shown in controls than solution) liquid (sucrose significantly less (F(l,24)- 9.87: p
0

SALINE

)-

q

MR-2266

j-

T

T

Img/Kg

::::: 33: ::::: v.

I-

$1:: ::::: .:.:.

lA:.:.: +:.

,-

i$$ $$ ::::: v.-

I-

i. ::::: I

3

-

RETENTION

DAYS

Fig. 1 Lack of effect of MR-2266-BS administration 15 min before the session (pre-conditioning administration) on conditioning ethanol preference throughout the three consecutive testing days. Results show ethanol preference scores: mean f SEM.

ethanol

and

total

daily

fluid

conruqtion

fr11100

TdDLE 3 g bow) MI rats

subjected

to

saline

or

IUf-2266~DS

4.60 i

R-2266-B

2.50 f

t 0.37

4.33

f 0.46

ND-2266-q 5 rglkg

t 0.29

10 q/kg

DAVS

0.26

!

2.01

0.7ottt ? 0.18

2.71111 i 0.30

3.51::: t 0.46

4.66ttt i 0.44

2.27111 i 0.42 1.0111: t 0.22

0.29

4.98ttt 1:

0.33

t

1.85

Total Intake _ _ _ ___ _

0.50

2.791 1

0.69

?

5.34

Intake ----___

Ethanol

2

2.22 f 0.39

0.60

t

3.25

0.38

_,

3.09

0.64

t

2.24

0.53

t

2.24

Intake

Hater

1.64111 i 0.47

1.64111 i 0.58

1.99::: i 0.33

3.06: ? 0.50

4.31 ? 0.69

Intake -------

Ethanol

__________________________

0.38

3.29 t

4.21 ? 0.69

4.e9ttt t0.63 3.87111 i 0.30

0.62

3.33 f

0.61

f

2.41

0.68

5.08111 f 0.39

5.301:: t 0.30

3.33

6.55 2 0.33 1

Intake __ _ _ _ __

Yater

Intake _______

Total

i 0.29

1.38111

1.29::: t 0.26

2.57ttt f 0.55

4.14: t 1.02

1.05

t

5.40

Intake -------

Ethanol

treatrent

0.30

t

4.67111

5.501:: t0.69

5.9011: f 0.48

6.55111 i 0.67

0.46

?

8.81

Intake _______

Total

coqrrison

NUN

test

of anirtls

of

the

in

three

parentheses. retention

Results days.

are

the

means

t SEI.

1 p(O.05

and

111

p(O.001

vs.

saline

free

Tukey’s

rultiple

___~~~______________~~~~~~~~~~~~~~~~~_~~~~~_~______~~~~~________~~________________________~~__________~_~_____________

(8)

4.11

11%2266-K

0.52

* 0.42

2.39

4.50

i q/kg (9)

0.63

?

2.19

0.49

t

2.51

Intake -______

hater

R-2266-B

(81

1 ____________________--_-_-_

0.21

I

RETENTION r___________________________________________________________________________________________~

(8)

q/kg

0.40

(101

0.1

i

Saline

4.93

Intake (Ethanol

rota1

CONDITIDNINS DAY ,______________~

imediately after the drinking session at the conditioning day. ___~__________--~___~~~~~~~_~~~~~_~_______~~~~~~~~_______~~~~~~~_~_____~~~___________~_____________~_~_________________________

Hater,

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ICOpioid Receptore and Ethanol Preference

Vol. 46, No. 16, 1990

Table 3 shows that administration of RR-2266-BS (0.1, 1, 5 or 10 mg/kg) after the first ethanol exposure induced significant reductions of total fluid intake (F(4,114)- 36.54: ptO.OO1) during the three consecutive days. This effect is the consequence of a clear dose-response reduction of ethanol intake (F(4,114)21.41; ptO.OO1) induced by the antagonist, without reliable alterations in water intake (F(4,114)- 1.54; n.8.). Ethanol preference values for this experiment are shown in Figure 2; ANOVA of the data corresponding to the three retention days (F(4,114)= 9.51; ptO.OOl), as well as ANOVA of the first retention day (F(4,38)- 4.67; pt0.005), reached a significant level, due to a persistent reduction on ethanol preference with the doses of 1, 5 and 10 mg/kg. Regression Analyses, carried out to evaluate the possible contribution of animals' body weight on the preference scores for experiments, showed no ethanol sucrose in the different (data not significant correlations between these variables shown).

0

SALINE

IID

MR-2266

0.1 mg/Kg

m

MR-2266

Img/Kg

a

MR-2266

a

MR-2266

RETENTION

Fig.

bmg/Kg lOmg/Kg

DAYS

2

Effects of RR-2266-B8 administration immediately after the conditioning session (post-conditioning administration) on later ethanol preference. Results show ethanol preference scores: mean f SER. Statistical differences: * ~~0.05 and ** ptO.OO1 vs. saline.

Vol. 46, No. 16, 1990

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Opioid Receptors and Ethanol Preference

1127

Di8cu88ion The results of the present study indicate that administration MR-2266-DS prior to or after the first opportunity to drink ethanol was effective in influencing the rats' later propensity to drink the drug. However, the acquisition of ethanol preference was only impaired by post-conditioning treatment. of

Regarding pre-conditioning administration of MR-2266-BS, a reduction of ethanol intake in the conditioning session was first observed. The phenomenon of reduced fluid consumption by rats following treatments with opioid antagonists appears to be well established (24,25). In particular, MR-2266-ES has been reported to decrease fluid consumption motivated by different paradigms (7,8,26). In fact, we have shown previously (9) that, in a forced situation schedule (in which the animals are presented with only one source of fluid), administration of RR-2266~DS diminished both water and ethanol intake, with the effect on ethanol consumption being clearly greater than on water intake. In this study, a similar picture is also observed: the administration of the antagonist prior to the first exposure to sucrose attenuated sucrose intake on the day of treatment (18%), although to a lesser degree than it reduced ethanol intake (27%) In the preconditioning experiment. These data indicate the possibility that, depending on the gustatory cue, different mechanisms (i.e., gustatory mechanisms, postingestional reinforcing/aversive effects, etc) could be Involved in the different degree of fluid reduction induced by the opioid antagonist. In addition to the reduction in ethanol intake at the day of treatment, pre-conditioning administration of MR-2266-BS also induced a slight decrease in ethanol consumption in the following days, suggesting that kappa receptors may play a role in the degree of the ethanol incentive value acquired by the rats on the conditioning day. In fact, although tha swxose intake was also reduced in the day of treatment (forced sucrose-drinking session), the rats' avidity toward sucrose was not modified by administration of the antagonist prior to the first exposure to this substance. Since rats' preference for the used 4% sucrose solution does not depend on learning processes (pilot studies showed that rats with or whithout a previous forced sucrosedrinking session display similar sucrose preference levels) and, under our experimental conditions, rats develop ethanol preference by means of a conditioning session, the results of these experiments indicate that MR-2266-BS slightly reduces the acquired propensity to take ethanol. Considering that rats develop ethanol preference by means of the conditioning session (20), and that treatments administered shortly before this session may influence both the acquisition and consolidation of newly acquired information (27), the possibility of an action of the antagonist during the period subsequent to the forced ethanol-drinking session cannot be disregarded. Moreover, poet-conditioning administration of MR-2266-BS induced a dose-dependent reduction In both ethanol consumption and in preference throughout the three following retentiontesting days. On the basis of the hypothesis that treatments given shortly after training may influence consolidation processes the antagonist interfere with the (27), may

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consolidation of the reinforcing properties of ethanol developed at the forced-consumption session. However, the fact that MR2266-BS-treated rats not only drank less ethanol than controls, but also markedly reduced their total fluid consumption, suggests that a conditioned taste aversion (CTA) to ethanol Is induced by the antagonist. Development of CTA is typically measured in terms of reduced preference in a choice procedure for the test substance (28). Reduction in the intake of the test substance is assumed to be due to an association between the taste of the substance and some aversive action '-not necessarily sickness the rewarding properties of the (29)- of the drug. Studying opioid peptide p-endorphin, existence of a possible the interdependence between increased motor activity and positlvereinforcement at the neural level has been suggested (30). In fact, administration of MR-2266-BS in doses higher than 1 mg/kg Induces a decrease in the rats' locomotor activity (data not shown); ethanol suggesting that the observed effects on preference and consumption by post-conditioning administration of the antagonist -at least with the doses of 5 and 10 mg/kg- may be due to a conditioned taste aversion to the drug. Recently, it has mediate been suggested that peripheral receptors the kappa aversive effects of opiates, whereas central opiate receptors mediate the positive reinforcing effects (31). Thus, the doseresponse curve of ethanol aversion induced by MR-2266-BS in our study could be due to opposite motivational effects mediated by separate neural substrates (i.e., peripheral vs. central). antagonists Although highly some selective kappa (binaltorphimine or nor-binaltorphimine) have recently been developed (32), the preference for kappa receptors of MR-2266-BS has been consistently reported (33,34). Therefore, the results of the present work provide further support for the motivational kappa-relating opioids in modulating the properties of of ethanol acquisition of new responses and, in particular, preference.

Aknowledgsments The authors wish to express their appreciation This work has been for her technical assltance. CAICYT grants.

to C. Bail6n supported by

References 1. 2. 3. 4. 5.

J.D. SINCLAIR, M. RUSI, M.M. AIRAKSINEN and H.L. ALTSHULER, Beta-carbolines and Tetrahydroisoquinolines, pp. 365-376, Alan R. Lisa Inc., New York (1982). C.L. HUBBELL, S.A. CZIRR, G.A. HUNTER, C.M. BEAMAN, N.C. LECANN and L.D. REID, Alcohol 3 39-54 (1986). R.D. MYERS, S. BORG and R. MOSSBERG, Alcohol 3 383-388 (1986). W.C. LYNCH, J. WATT. S. KRALL and C.M. PADEN, Pharmac. Biochem. Behav. 22 699-705 (1985). S.J. WATSON, H. KHACHATURIAN, T. TAYLOR, W. FISCHLI, A. GOLDSTEIN and H. AKIL, Proc. Nat. Acad. Sci. USA 80 891-894 (1983).

Vol. 46, No. 16, 1990

6. 7. 8. 9. 10. 11.

12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

24. 25.

26. 27. 1:: 30. 31. 32. 33.

34.

Opioid Receptors and Ethanol Preference

1129

H. KACHATURIAN, M.E. LEWIS, M.K.H. SHAFER and S.J. WATSON, TINS March 111-119. J.D. LEANDER and M.D. HYNES III, Eur. J. Pharmacol. 87 481484 (1983). W.C. LYNCH, Sot. Neurosci. Abstr. 9 (1983). C. SANDI, J. BORRELL and C. GUAZA, Life Sci. 42 1067-1075 (1988). H. IMURA, K. NAKAO, N. YANAIHARA, G. KATSUURA and M. NAKAMURA, Neuroendccrinology 44 142-148 (1986). R.L. SPENCER, D. DEUPREE, S. HSIAO, H.I. MUSBERG, V. HRUBY, T.F. BURKS and F. PGRRECA, Phannacol. Biochem. Behav. 25 7782 (1986). J.Y. SUMMY-LONG, L.M. ROSELLA and L.C. KEIL, Brain Res. 221 343-357 (1981). J.D. LEANDER, Appetite 5 7-14 (1984). B. HOSKINS and I.K. HO, Life Sci. 39 589-593 (1986). K.W. LOCKE, D.R. BROWN and S.G. HOLTZMAN, Pharmacol. Biochem. Behav. 17 1275-1279 (1982). B.A. WSNELL, A.S. LEVINE and J.E. MORLEY, Life Sci. 38 10811088 (1986). R.F. MUCRA and A. HERZ, Psychopharmacology 86 281-285 (1985). E.T. IWAMOTO, Life Sci. 43 503-508 (1988). K. ERIKSSON, Ann. Zool. Fennie. 6 227-265 (1969). C. GUAZA, S. BORRELL and J. BGRRELL, Psychopharmacology 90 336-340 (1986). C. SANDI, J. BORRELL and C. GUAZA, Pharmacol. Biochem. Behav. 29 39-44 (1988). C. SANDI, J. BORRELL and C. GUAZA, Physiol. Behav. 45 87-92 (1989). R.R. SOKAL and F.J. ROHLF, Biometry (R.R. Sokal and F.J. Rohlf, Eds.), W.H. Freeman and Company, San Francisco (1969). L.D. REID, Am. J. Clin. Nutr. 42 1099-1132 (1985). S.J. COOPER, Endorphins, Opiates and Behavioral Processes (R.J. Rodgers and S.J. Cooper, Eds.), pp. 187-216, John Wiley and Sons Ltd. (1988). K.W. LOCKE, D.R. BROWN and S.G. HOLTZMAN, Pharmacol. Biochem. Behav. 17 1275-1279 (1982). G.A. HEISE, TIPS 2 158-160 (1981). A.J. GGUDIE, Neuropharmacology 18 971-979 (1978). B.D. BERGER, 3. Comp. Physiol. Psychol. 21 26 (1972). M. AMALRIC, E.J. CLINE, J.L. MARTINEZ, F.E. BLOOM and G.F. KOOB, Psychopharmacology 91 14-19 (1987). A. BECHARA and D. VAN DER KGOY, Pharmacol. Bicchem. Behav. 28 227-233 (1987). A.E. TAKEMORI, B.Y. HO, J.S. NAESETH and P.S. PORTOGHESE, J. Pharmacol. Exp. Ther. 246 255-258 (1988). D. ROMER, H. BUSCHER, R.C. HILL, R. MAURER, T.J. PETCHER, H.B.A. WELLE, H.C.C.K. BAKEL and A.M. AKKERMAN, Life Sci. 27 971-978. G.T. SHEARMAN and A. HERZ, Neurophannacol. 20 1209-1213 (1981).