Allopregnanolone does not influence ethanol-induced conditioned place preference in DBA/2J mice

Rationale The neurosteroid allopregnanolone (ALLOP; 3-hydroxy-5-pregnan-20-one) produces behavioral and discriminative characteristics similar to that of ethanol (EtOH) and can modulate some of the behavioral and electrophysiological effects of EtOH.Objective The present experiments investigated ALLOP modulation of the effects of EtOH in a place conditioning procedure in male DBA/2J mice.Methods In a series of experiments examining different EtOH doses (1, 2 g/kg) and ALLOP administration times, ALLOP (0, 3.2, 10, 17 mg/kg, IP) was administered four times with EtOH prior to placement on a distinctive floor (CS+). On alternate days, vehicle was administered prior to a saline injection paired with the other floor stimulus (CS–). In a separate experiment, finasteride (0, 50, 100 mg/kg, IP), a 5-reductase inhibitor that blocks ALLOP synthesis, was administered prior to both CS+ and CS– trials. In a final experiment, animals were place conditioned to EtOH alone, and ALLOP (0, 3.2, 10, 17 mg/kg, IP) was administered prior to the preference test only.Results During conditioning, ALLOP increased and finasteride decreased EtOH-stimulated activity compared with vehicle pretreatment. Acquisition of 2 g/kg EtOH-induced conditioned place preference was observed in all mice, regardless of treatment with either ALLOP or finasteride. Similarly, ALLOP did not modulate the expression of EtOH-induced place preference. EtOH increased brain ALLOP levels compared with saline; however, ALLOP administration produced dose-dependent elevations in brain ALLOP levels that were not further augmented by EtOH (2 g/kg) administration.Conclusions These findings indicate that ALLOP does not modulate EtOH-induced place conditioning in male DBA/2J mice.     

Effects of dopamine receptor antagonists on the acquisition of ethanol-induced conditioned place preference in mice

Rationale

Studies support differential roles of dopamine receptor subfamilies in the rewarding and reinforcing properties of drugs of abuse, including ethanol. However, the roles these receptor subfamilies play in ethanol reward are not fully delineated.

Objective

To examine the roles of dopamine receptor subfamilies in the acquisition of ethanol-induced conditioned place preference (CPP), we pretreated animals systemically with antagonist drugs selective for dopamine D1-like (SCH-23390) and D2-like (raclopride) receptors prior to ethanol conditioning trials.

Methods

Effects of raclopride (0–1.2 mg/kg) and SCH-23390 (0–0.3 mg/kg) on the acquisition of ethanol-induced CPP were examined in DBA/2J mice (experiments 1 and 2). Based on significant effects of SCH-23390, we then determined if SCH-23390 (0.3 mg/kg) produced a place preference on its own (experiment 3). To evaluate whether SCH-23390 impaired learning, we used a conditioned place aversion (CPA) paradigm and pretreated animals with SCH-23390 (0–0.3 mg/kg) before conditioning sessions with LiCl (experiment 4).

Results

Whereas raclopride (0–1.2 mg/kg) did not affect acquisition, SCH-23390 (0.1–0.3 mg/kg) impaired the development of ethanol-induced CPP. SCH-23390 (0.3 mg/kg) did not produce place preference when tested alone and SCH-23390 (0.1–0.3 mg/kg) did not perturb the acquisition of LiCl-induced CPA.

Conclusions

Our results support a role for dopamine D1-like but not D2-like receptors in ethanol’s unconditioned rewarding effect as indexed by CPP. Blockade of D1-like receptors did not affect aversive learning in this procedure.     

Mianserin enhancement of ethanol-induced conditioned place preference

This experiment examined the influence of mianserin, a 5-HT(2) receptor antagonist, on the rewarding effect of ethanol in a place conditioning paradigm. Swiss-Webster mice received four pairings of a tactile stimulus with drug treatment consisting of two i.p. injections separated by a 30min interval. Drug treatment groups were as follows: saline (10mg/kg) followed by ethanol (2mg/kg); mianserin (10mg/kg) followed by ethanol; mianserin followed by saline. A different stimulus was paired with two saline injections. During conditioning, ethanol produced increases in locomotor activity that were reduced by mianserin. Mianserin alone reduced activity levels. As expected, group saline-ethanol showed a nonsignificant trend towards conditioned place preference. However, mianserin enhanced the acquisition of ethanol preference, whereas mianserin alone did not produce either place preference or aversion. The results are consistent with the notion that serotonergic systems are important in the response to ethanol, and further suggest that 5-HT(2) receptor blockade increases the rewarding effects of ethanol.     

GABAA receptors modulate ethanol-induced conditioned place preference and taste aversion in mice

  Rationale: GABA_A receptor antagonists have been shown to reduce ethanol self-administration and ethanol-induced conditioned taste aversion (CTA) in rats, suggesting a role for the GABA_A receptor in modulating ethanol’s motivational effects. Objectives: The present experiments examined the effects of the GABA_A receptor antagonists, bicuculline and picrotoxin, on the acquisition of ethanol-induced conditioned place preference (CPP) and CTA in male DBA/2J mice. Methods: Mice in the CPP experiments received four pairings of ethanol (2 g/kg) with a distinctive floor stimulus for a 5-min conditioning session (CS+ sessions). During CS+ sessions, mice also received bicuculline (0, 1.0, 3.0, or 5.0 mg/kg) or picrotoxin (2.0 mg/kg) before an injection of ethanol. On intervening days (CS– sessions), the pretreatment injection was always vehicle followed by saline injections that were paired with a different floor type. For the preference test, all mice received saline injections and were placed on a half grid and half hole floor for a 60-min session. For the CTA experiments, mice were adapted to a 2-h per day water restriction regimen followed by five conditioning trials every 48 h. During conditioning trials, subjects received an injection of vehicle, bicuculline (0.5 and 2.0 mg/kg), or picrotoxin (0.75 and 2.5 mg/kg) before injection of 2 g/kg ethanol or saline following 1-h access to a saccharin solution. Results: Both picrotoxin and the lowest dose of bicuculline (1.0 mg/kg) significantly increased the magnitude of CPP relative to vehicle-treated controls. Picrotoxin alone did not produce place conditioning. Ethanol-stimulated locomotor activity was significantly reduced during conditioning trials with picrotoxin and the higher doses of bicuculline (3.0 and 5.0 mg/kg). Bicuculline did not alter ethanol-induced CTA; however, picrotoxin dose-dependently increased the magnitude of ethanol-induced CTA. Bicuculline and picrotoxin did not produce CTA when administered alone. Conclusions: Overall, these results suggest that blockade of GABA_A receptors with bicuculline and picrotoxin enhances ethanol’s motivational effects in the CPP paradigm; however, only picrotoxin enhances ethanol’s motivational effects in the CTA paradigm. Received: 12 September 1998 / Final version: 21 December 1998     

Extinction of ethanol-induced conditioned place preference and conditioned place aversion: effects of naloxone

 Four experiments examined the effect of naloxone pretreatment on the expression and extinction of ethanol-induced conditioned place preference (experiments 1, 2, 4) or conditioned place aversion (experiments 1, 3). DBA/2 J mice received four pairings of a distinctive tactile (floor) stimulus (CS) with injection of ethanol (2 g/kg) given either immediately before or after 5-min exposure to the CS. A different stimulus was paired with injection of saline. Pre-CS injection of ethanol produced conditioned place preference, whereas post-CS injection of ethanol produced conditioned place aversion. Both behaviors extinguished partially during repeated choice testing after vehicle injection. Naloxone (10 mg/kg) had little effect on the initial expression of conditioned place preference, but facilitated its extinction. Moreover, repeated naloxone testing resulted in the expression of a weak conditioned place aversion to the CS that initially elicited a place preference. In contrast, naloxone (1.5 or 10 mg/kg) enhanced expression of conditioned place aversion, thereby increasing its resistance to extinction. A control experiment (experiment 4) indicated that repeated testing with a different aversive drug, lithium chloride, did not affect rate of extinction or produce an aversion to the CS previously paired with ethanol. These findings do not support the suggestion that naloxone facilitates the general processes that underlie extinction of associative learning. Also, these data are not readily explained by the conditioning of place aversion at the time of testing. Rather, naloxone’s effects appear to reflect a selective influence on maintenance of ethanol’s conditioned rewarding effect, an effect that may be mediated by release of endogenous opioids. Overall, these findings encourage further consideration of the use of opiate antagonists in the treatment of alcoholism. Received: 4 December 1997 / Final version: 16 February 1998     

DBA/2J mice develop stronger lithium chloride-induced conditioned taste and place aversions than C57BL/6J mice

Genetic differences in lithium-induced conditioned aversion were examined using both place- and taste-conditioning procedures. In the place-conditioning procedure, adult male C57BL/6J (B6) and DBA/2J (D2) mice were exposed to a differential conditioning procedure in which each mouse received four 30-min pairings of a distinctive floor cue immediately after IP injections of either 0.75, 1.5, or 3. 0 mEq/kg LiCl. A different floor cue was paired with saline injections. A separate group of control mice received saline injections paired with both floor types. Subsequent floor preference testing revealed greater conditioned aversion in D2 mice compared to B6 mice in groups receiving 3.0 mEq/kg LiCl. Lower LiCl doses did not produce conditioning in either strain. In a conditioned taste-aversion procedure, fluid-restricted mice received four trials in which access to 0.2 M NaCl solution was followed by IP injection of either 0.75, 1.5, 3.0, or 6.0 mEq/kg LiCl. D2 mice showed stronger conditioned taste aversion than B6 mice at all doses, suggesting that taste conditioning may be a more sensitive index of aversive drug sensitivity than place conditioning. These findings are not well explained by strain differences in general learning ability or by strain differences in stimulus salience or innate preference. Rather, these data appear more consistent with previous studies showing strain differences in lithium pharmacokinetics and in general sensitivity to aversive events.     

Acquisition and expression of ethanol-induced conditioned place preference in mice is inhibited by naloxone

The effects of opioid antagonists on conditioned reward produced by ethanol provide variable and sometimes conflicting results, especially in mice. In the present set of experiments, male C57BL/6 mice received 4 vehicle and 4 ethanol conditionings, and the rewarding effects of ethanol were assessed in an unbiased version of the conditioned place preference (CPP) apparatus and an unbiased stimulus assignment procedure. Intraperitoneal (ip) administration of ethanol (2 g/kg, but not 1 g/kg) resulted in the conditioned reward when conditionings lasted for 6 min but not when conditioning lasted for 20 min. Administration of the non-selective opioid receptor antagonist naloxone (1 and 5 mg/kg) before the conditionings attenuated the acquisition of ethanol-induced place preference. Naloxone (1 mg/kg) also inhibited expression of the CPP response, but it did not alter the preference of vehicle-conditioned mice, suggesting the lack of its own motivational effects in this experimental setting. Taken together, the present results suggest that an unbiased version of ethanol-induced CPP in C57BL/6 mice could be a valid model for the study of the motivational effects of ethanol, confirming and expanding previous findings that have demonstrated inhibitory effects of opioid receptor antagonist on alcohol conditioned reward.     

Magnesium-induced conditioned place preference in mice

A conditioned place preference procedure was used in mice to test the hypothesis that magnesium possesses reinforcing properties. Mice were conditioned to the nonpreferred end of a three-compartment straight shuttle box with MgCl2 injections alternating with saline injections on the preferred end. Dose of MgCl2 was varied (0, 15, 30, 125 mg/kg) as well as number of conditioning trials (8 or 16). On the day after the first postconditioning test, animals were given acute injections of 5 mg/kg cocaine, or other test drug, to determine if the conditioned effect on behavior would be potentiated, maintained or blocked by these test drugs. Results demonstrated that 15 mg/kg MgCl2 induced the greatest amount of conditioning and that increasing the number of MgCl2/place pairings did not enhance the amount of conditioning, but rather, it decreased it. Amphetamine potentiated MgCl2-induced place preference; cocaine and pentobarbital maintained it; and haloperidol blocked it. These data indicate that MgCl2 has some primary reinforcing properties in mice and that MgCl2 shares stimulus properties with other stimulants and reinforcing substances.     

Lack of effect of dopamine receptor blockade on expression of ethanol-induced conditioned place preference in mice

Abstract Rationale. Self-administration studies have suggested that dopamine (DA) is important for the reinforcing effects of ethanol. However, ethanol place conditioning studies have less consistently demonstrated a role for DA in conditioned place preference. Objectives. The purpose of the present study was to determine whether blockade of D₁, D₂ or D₃ DA receptors would impact the expression of the conditioned place preference induced by ethanol in DBA/2J mice. Methods. Mice underwent an unbiased place conditioning procedure with 2 g/kg ethanol. Prior to the preference test, mice were injected i.p. with SCH23390 (0, 0.015 or 0.03 mg/kg), raclopride (0, 0.3 or 0.6 mg/kg) or U99194A (0, 10 or 20 mg/kg). Results. Ethanol produced a significant conditioned place preference that was not affected by any of the dopamine antagonists tested. Each of the antagonists decreased locomotor activity, though U99194A was minimally effective. Conclusions. These findings suggest that the conditioned reinforcing effects of ethanol in DBA/2J mice as assessed by place conditioning are mediated by non-dopaminergic mechanisms. Electronic Publication     

Glycyl-glutamine inhibits nicotine conditioned place preference and withdrawal

Glycyl-glutamine (Gly-Gln) is an inhibitory dipeptide synthesized from beta-endorphin(1-31). Previously, we showed that Gly-Gln inhibits morphine conditioned place preference, tolerance, dependence and withdrawal. In this study, we tested whether Gly-Gln's inhibitory activity extends to other rewarding drugs, specifically nicotine. Rats were conditioned with nicotine (0.6 mg/kg, s.c.) for four days and tested on day five. Glycyl-glutamine (100 nmol i.c.v.) inhibited acquisition and expression of a nicotine place preference significantly. Cyclo(Gly-Gln) (100 nmol i.c.v. or 25 mg/kg i.p.), a cyclic Gly-Gln derivative, blocked expression of nicotine place preference but Gly-d-Gln (100 nmol i.c.v.) was ineffective. To study nicotine withdrawal, rats were treated with nicotine (9 mg/kg/day) for seven days and conditioned place aversion was induced with mecamylamine (1 mg/kg, s.c.). Glycyl-glutamine blocked acquisition of place aversion to mecamylamine but not U50,488, a kappa opioid receptor agonist. Glycyl-glutamine thus inhibits the rewarding effects of nicotine and attenuates withdrawal in nicotine dependent rats.     

Effects of withdrawal from chronic escalating-dose binge cocaine on conditioned place preference to cocaine and striatal preproenkephalin mRNA in C57BL/6J mice

Relapse is a serious problem for the effective treatment of cocaine addiction.RationaleExamining cocaine re-exposure-induced behavioral and neurobiological alterations following chronic escalating-dose binge cocaine administration and withdrawal may provide insight into the neurobiological basis of cocaine relapse.ObjectivesOur goal was to determine how exposure to chronic escalating-dose cocaine affects development of subsequent cocaine-induced conditioned place preference (CPP) and changes in endogenous opioid systems.MethodsMice were injected with either escalating-dose binge cocaine (15–30 mg/kg/injection × 3/day) or saline for 14-days and conditioned with 15 mg/kg of cocaine or saline (once per day for 10-days), starting either 1 or 14-days after the last day of binge injections.ResultsMice exposed to chronic escalating cocaine did not develop CPP to cocaine when conditioning commenced on the first day of withdrawal (CPP test on day 10 of withdrawal). By contrast, mice did develop CPP to cocaine when conditioning started on the 14th day of withdrawal (CPP test on day 24 of withdrawal). Furthermore, preproenkephalin (Penk) mRNA levels in caudate putamen were significantly higher in mice that received 14-day withdrawal from escalating-dose binge cocaine before the CPP procedure (tested 24 days post-binge) than those that received 1-day withdrawal (tested 10 days post-binge).ConclusionsThe rewarding effect of cocaine was blunted in early withdrawal from chronic escalating exposure, but recovered in more prolonged withdrawal. Time-dependent elevations in Penk mRNA levels may be part of the underlying mechanisms of this effect.     

Effect of Ro 15-4513 on ethanol-induced conditioned place preference.

The benzodiazepine receptor inverse agonist Ro 15-4513 reverses a number of ethanol's effects, including its reinforcing properties as measured through self-administration. The present study examined the effect of this putative ethanol antagonist in a place conditioning design that has been shown to be sensitive to ethanol's rewarding properties in mice. Using an unbiased differential conditioning procedure, DBA/2J mice received, on alternate days, pairings of a distinctive floor stimulus (CS+) with either ethanol (2 g/kg), Ro 15-4513 (3 mg/kg), or a combination of ethanol and Ro 15-4513. On alternate days, a different distinctive floor stimulus (CS-) was paired with vehicle. Under these conditions, ethanol produced a conditioned place preference that was unaffected by Ro 15-4513. Ro 15-4513 alone did not produce either a place preference or aversion. Ro 15-4513 did produce reductions in locomotor activity during conditioning, indicating it was behaviorally active. These results indicate that a dose of Ro 15-4513 that alters general activity does not affect ethanol reward.     

Localization of genes influencing ethanol-induced conditioned place preference and locomotor activity in BXD recombinant inbred mice

Genetic differences in ethanol's ability to induce conditioned place preference were studied in 20 BXD Recombinant Inbred (RI) mouse strains and in the C57BL/6J and DBA/2J progenitor strains. Male mice from each strain were exposed to a Pavlovian conditioning procedure in which a distinctive floor stimulus (CS+) was paired four times with ethanol (2 g/kg). A different floor stimulus (CS-) was paired with saline. Control mice were injected only with saline. Floor preference testing without ethanol revealed significant genetic differences in conditioned place preference, with some strains spending nearly 80% time on the ethanolpaired floor while others spent only 50% (i.e., no preference). Control mice showed genetic differences in unconditioned preference for the floor cues, but unconditioned preference was not genetically correlated with conditioned preference. There were also substantial genetic differences in ethanol-stimulated activity, but contrary to psychomotor stimulant theory, ethanol-induced activity on conditioning trials was not positively correlated with strength of conditioned place preference. However, there was a significant negative genetic correlation (r=–0.42) between test session activity and preference. Quantitative trait loci (QTL) analyses showed strong associations (P<0.01) between conditioned place preference and marker loci on chromosomes 4, 8, 9, 18 and 19. Weaker associations (0.01<P<0.05) were identified on several other chromosomes. Analysis also yielded several significant QTL for unconditioned preference, ethanol-stimulated activity, and sensitization. Overall, these data support the conclusion that genotype influences ethanol-induced conditioned place preference, presumably via genetic differences in sensitivity to ethanol's rewarding effects. Moreover, several chromosomal regions containing candidate genes of potential relevance to ethanol-induced conditioned place preference have been identified.     

Chronic psychosocial stress causes delayed extinction and exacerbates reinstatement of ethanol-induced conditioned place preference in mice

Rationale

We have shown previously, using an animal model of voluntary ethanol intake and ethanol-conditioned place preference (EtOH-CPP), that exposure to chronic psychosocial stress induces increased ethanol intake and EtOH-CPP acquisition in mice.

Objective

Here, we examined the impact of chronic subordinate colony (CSC) exposure on EtOH-CPP extinction, as well as ethanol-induced reinstatement of CPP.

Methods

Mice were conditioned with saline or 1.5 g/kg ethanol and were tested in the EtOH-CPP model. In the first experiment, the mice were subjected to 19 days of chronic stress, and EtOH-CPP extinction was assessed during seven daily trials without ethanol injection. In the second experiment and after the EtOH-CPP test, the mice were subjected to 7 days of extinction trials before the 19 days of chronic stress. Drug-induced EtOH-CPP reinstatement was induced by a priming injection of 0.5 g/kg ethanol.

Results

Compared to the single-housed colony mice, CSC mice exhibited increased anxiety-like behavior in the elevated plus maze (EPM) and the open field tests. Interestingly, the CSC mice showed delayed EtOH-CPP extinction. More importantly, CSC mice showed increased alcohol-induced reinstatement of the EtOH-CPP behavior.

Conclusion

Taken together, this study indicates that chronic psychosocial stress can have long-term effects on EtOH-CPP extinction as well as drug-induced reinstatement behavior and may provide a suitable model to study the latent effects of chronic psychosocial stress on extinction and relapse to drug abuse.     

Proximal ethanol pretreatment interferes with acquisition of ethanol-induced conditioned place preference

Neurobiological mechanisms underlying rewarding and aversive effects of drugs are often studied by examining effects of various pretreatments on acquisition of conditioned place preference (CPP) or conditioned place aversion (CPA). However, few studies have looked at effects of pretreatment with the same drug used during conditioning. Such studies might offer insight into agonist actions on conditioning while also mimicking real world contingencies experienced by drug users. Previous work from our laboratory, which showed that same drug pre-exposure interfered with acquisition of ethanol CPA but not CPP, was limited by the use of only one pre-treatment time interval (65 min). Thus, the present studies were designed to study other intervals (-5, -15, -30). Pretreatment of DBA/2J mice with ethanol (2 g/kg) reduced the activity response normally evoked by the conditioning dose (2 g/kg) at all pretreatment times, but acquisition of CPP was disrupted only by pretreatment at -5 min. The overall pattern of findings suggests that ethanol's early pharmacological effects interfered with learning the association between the conditioned stimulus (CS) and ethanol 5 min later. Thus, one would expect ethanol agonists, when administered in close proximity to CS-ethanol pairings, to interfere with control of ethanol seeking by that CS.     

Haloperidol reduces ethanol-induced motor activity stimulation but not conditioned place preference

This experiment examined the impact of a dopamine receptor blocker on ethanol's rewarding effect in a place conditioning paradigm. DBA/2J mice received four pairings of a tactile stimulus with ethanol (2 g/kg, IP), haloperidol (0.1 mg/kg, IP) + ethanol, or haloperidol alone. A different stimulus was paired with saline. Ethanol produced increases in locomotor activity that were reduced by haloperidol. However, conditioned preference for the ethanol-paired stimulus was not affected by haloperidol. Haloperidol alone decreased locomotor activity during conditioning and produced a place aversion. These results indicate a dissociation of ethanol's activating and rewarding effects. Moreover, they suggest that ethanol's ability to induce conditioned place preference is mediated by nondopaminergic mechanisms.     

Morphine and ethanol pretreatment effects on expression and extinction of ethanol-induced conditioned place preference and aversion in mice

Psychopharmacology - Opioid receptor antagonists reliably alter the expression or extinction of ethanol’s conditioned motivational effects as indexed by the place conditioning procedure,...     

Susceptibility to conditioned place preference induced by addictive drugs in mice of the C57BL/6 and DBA/2 inbred strains

Rationale In previous studies, we have demonstrated that mice of the inbred strain C57BL/6J (C57) are more susceptible to amphetamine-induced conditioned place preference (CPP) than DBA/2J (DBA) mice. Moreover, we also observed parallel strain differences for the locomotor-stimulant effects of the drug. However, other studies have reported either no difference or opposite strain differences for cocaine- and morphine-induced CPP as well as for the locomotor effects of these drugs, suggesting that amphetamine-related behavioral phenotypes might depend on a specific pharmacological action of the psychostimulant. Objectives This study was aimed at testing strain differences for cocaine- and morphine-related behavioral phenotypes in the same experimental protocol and conditions previously used for amphetamine. Methods C57 and DBA mice were tested for CPP induced by cocaine (0, 5, 10, and 20 mg/kg) and morphine (0, 5, 7.5, and 10 mg/kg). Locomotor activity data were simultaneously obtained by measuring distance moved during all different CPP phases and unconditioned locomotor activity, behavioral sensitization and conditioned hyperactivity were measured together with CPP. Results (a) Either cocaine or morphine promoted significant CPP at lower doses in C57 than in DBA mice; (b) only drug-trained C57 mice showed a significant CPP compared with the control group; and (c) only C57 mice showed dose-dependent effects of cocaine on CPP. Moreover, there was no relationship between drug-induced CPP and locomotion. Conclusions The results demonstrate that C57 and DBA mice differ in their sensitivity to cocaine- and morphine-induced CPP and suggest that the two strains differ in sensitivity to the positive incentive properties of drugs of abuse.     

Effects of oxazepam on methamphetamine-induced conditioned place preference

Our laboratory has been investigating the role for the hypothalamo-pituitary-adrenal (HPA) axis and benzodiazepines in the behavioral effects of cocaine for several years now. The following represents our initial investigation of the influence of benzodiazepines on methamphetamine reward using conditioned place preference. In these experiments, methamphetamine (0.5 mg/kg ip) resulted in a robust conditioned place preference that was attenuated when the rats were pretreated with oxazepam (10 mg/kg ip) on the day of preference testing. These data suggest a potential role for benzodiazepines in the behavioral effects of methamphetamine. Additional research will be necessary to determine if the nature of these effects is similar with what has been observed with cocaine.