Effect of lacosamide on ethanol induced conditioned place preference and withdrawal associated behavior in mice: Possible contribution of hippocampal CRMP-2

BackgroundExcessive consumption of ethanol is known to activate the mTORC1 pathway and to enhance the Collapsin Response Mediator Protein-2 (CRMP-2) levels in the limbic region of brain. The latter helps in forming microtubule assembly that is linked to drug taking or addiction-like behavior in rodents. Therefore, in this study, we investigated the effect of lacosamide, an antiepileptic drug and a known CRMP-2 inhibitor, which binds to CRMP-2 and inhibits the formation of microtubule assembly, on ethanol-induced conditioned place preference (CPP) in mice.MethodsThe behavior of mice following ethanol addiction and withdrawal was assessed by performing different behavioral paradigms. Mice underwent ethanol-induced CPP training with alternate dose of ethanol (2 g/kg, po) and saline (10 ml/kg, po). The effect of lacosamide on the expression of ethanol-induced CPP and on ethanol withdrawal associated anxiety and depression-like behavior was evaluated. The effect of drug on locomotor activity was also assessed and hippocampal CRMP-2 levels were measured.ResultsEthanol-induced CPP was associated with enhanced CRMP-2 levels in the hippocampus. Lacosamide significantly reduced the expression of ethanol-induced CPP and alleviated the levels of hippocampal CRMP-2 but aggravated withdrawal-associated anxiety and depression in mice.ConclusionThe present study demonstrated the beneficial effect of lacosamide in attenuation of expression of ethanol induced conditioned place preference via reduction of hippocampal CRMP-2 level. These findings suggest that lacosamide may be investigated further for ethanol addiction but not for managing withdrawal.     

Effects of catecholamine synthesis inhibition on ethanol-induced withdrawal symptoms in mice

alpha-Methyl-p-tyrosine, a catecholamine synthesis inhibitor, was studied to determine its effects against ethanol-induced withdrawal symptoms in mice. Signifilcant (P < 0.001) potentiation of the withdrawal convulsion score induced by ethanol vapour exposure for three days was observed in mice. The synergistic effect was not due to alteration of ethanol metabolism. These results indicate that reductions in catecholamines (dopamine and noradrenaline) augment seizure activity induced by subchronic exposure to ethanol.     

Fluoxetine, Desipramine, and the Dual Antidepressant Milnacipran Reduce Alcohol Self-Administration and/or Relapse in Dependent Rats

A few clinical studies have shown that dual antidepressants (serotonergic (5-HT) and noradrenergic (NE) transporter inhibitors, SNRIs) may be effective in alcoholism treatment. We studied the effect of the dual antidepressant milnacipran on ethanol operant self-administration in acutely withdrawn ethanol-dependent and in -non-dependent Wistar rats, and used fluoxetine and desipramine to dissect both 5-HT and NE components, respectively, in the effect of milnacipran. Milnacipran was also tested for relapse after protracted abstinence and on ethanol-induced (1.0 g/kg) conditioned place preference in control rats and ethanol-induced locomotor sensitization in DBA/2J female mice. Milnacipran dose dependently (5–40 mg/kg) attenuated the increased ethanol self-administration observed during early withdrawal and was more potent in preventing reinstatement in dependent rats after protracted abstinence as compared with non-dependent rats. Desipramine and fluoxetine (10 mg/kg) blocked ethanol self-administration during early withdrawal, and recovery was delayed in dependent animals, indicating a potent effect. Ethanol self-administration was also reduced 1 day after treatment with desipramine and fluoxetine but not with milnacipran. Finally, milnacipran prevented ethanol-induced place preference in ethanol-naive rats and reduced the magnitude of ethanol-induced sensitization associated with a delayed induction in mice. Desipramine (20 mg/kg) countered sensitization development and reduced its expression at 1 week after treatment; fluoxetine (10 mg/kg) reduced sensitization expression. Thus, 5-HT and NE transmissions during sensitization expression may mediate the effect of milnacipran on sensitization induction. These results support that SNRIs may have a potential use in alcoholism treatment.     

Elevated anxiety-like behavior following ethanol exposure in mutant mice lacking neuropeptide Y (NPY)

BACKGROUND: Neuropeptide Y (NPY) is a neuromodulator with anxiolytic properties. Recent evidence suggests that NPY modulates neurobiological responses to ethanol. Because withdrawal from ethanol is associated with elevated anxiety-like behavior, and because central NPY modulates anxiety, we assessed anxiety-like behavior in mutant mice lacking normal production of NPY (NPY-/-) and in normal wild-type mice (NPY+/+) 6h after removal of a liquid diet containing 4.5% ethanol. METHODS: NPY-/- and NPY+/+ mice on a pure 129/SvEv genetic background were given 6 days of access to a liquid ethanol diet (ED) or control diet (CD). Six hours before elevated plus maze (EPM) testing, ED was replaced with CD in the ethanol-withdrawn group. RESULTS: Ethanol-withdrawn NPY-/- mice showed significantly less open arm time and total proportion of time spent in the open arm of the EPM relative to ethanol-withdrawn NPY+/+ mice and when compared to NPY-/- and NPY+/+ mice that had access to the CD. On the other hand, ethanol-withdrawn NPY+/+ mice did not show altered EPM behavior relative to controls. CONCLUSIONS: Central NPY is protective against anxiety-like behavior stemming from exposure to and/or withdrawal from ethanol. Targets aimed at NPY receptors may be useful compounds for treating anxiety associated with ethanol dependence.     

Role of test activity in ethanol-induced disruption of place preference expression in mice

Rationale Reduced expression of a drug-induced conditioned place preference (CPP) may reflect a decrease in the drug’s conditioned rewarding effects. However, CPP is also open to disruption by processes unrelated to the underlying motivation. In unpublished studies, we previously observed that ethanol pretreatment before testing disrupted expression of ethanol-induced CPP in DBA/2J mice. We hypothesized that this interference effect was due to large ethanol-induced increases in activity. Objective The present studies were designed to examine the relationship between test activity and expression of ethanol-induced CPP both in the presence and absence of ethanol. To assess the generality of this relationship, we examined these effects both in DBA/2J (which are highly activated by ethanol) and in NZB/B1NJ mice (which show similar CPP, but less ethanol-induced activation). Materials and methods In separate experiments, inbred mice from each strain underwent ethanol (2 g/kg) place conditioning. Saline or ethanol was then administered immediately before the test. Results Ethanol, given immediately before the test, blocked the expression of ethanol CPP in DBA/2J, but not in NZB/B1NJ mice. Moreover, ethanol significantly increased test activity levels in DBA/2J and to a much lesser degree in NZB/B1NJ mice. Correlation analyses showed an inverse phenotypic relationship between preference and test activity, reflecting stronger preferences in less active mice. Conclusions Disruption of ethanol-CPP observed in DBA/2J mice may be a consequence of high ethanol-induced activity levels. More generally, these studies suggest that competing behaviors can affect expression of a drug-induced CPP independent of affecting the conditioned rewarding effects of the drug.     

Modulation of multiple ethanol withdrawal-induced anxiety-like behavior by CRF and CRF1 receptors

Previous work demonstrated that rats subjected to multiple withdrawals from chronic ethanol exhibit a sensitization of anxiety-like behavior compared to animals withdrawn from treatment with an equal but continuous amount of ethanol. This study sought to examine whether corticotropin-releasing factor (CRF) could modulate this ethanol-withdrawal-induced anxiety-like behavior. Initially, rats were administered with CRF (1 microg) or vehicle intraventricularly on two occasions 5 days apart while on control diet (CD) followed by exposure to 7% ethanol diet (ED) for 5 days, with social interaction assessed 5 h into withdrawal. Social interaction was significantly reduced in the CRF-treated animals compared to vehicle-treated rats and vehicle- and CRF-treated rats maintained on CD, indicative that CRF given before ethanol exposure was capable of inducing an adaptive change that sensitized withdrawal-induced anxiety-like behavior. Next, the CRF(1) receptor antagonist CRA1000 (3 mg/kg, systemically), the CRF(2) receptor antagonist antisauvagine-30 (20 microg intraventricularly), or vehicle was injected 4 h after the ethanol was removed following the first and second cycles of chronic ethanol exposure and the effect on the multiple-withdrawal-induced anxiety-like behavior determined after the third withdrawal cycle. The CRF(1) receptor antagonist blocked the reduced social interaction behavior, whereas the CRF(2) receptor antagonist was without effect. Similar pretreatment with another CRF(1) receptor antagonist CP-154,526 (10 mg/kg systemically) during the first and second withdrawals also counteracted anxiety-like behavior. These findings indicate that the CRF system and CRF(1) receptors play key roles in the adaptive change responsible for the anxiety-like behavior induced by repeated withdrawals from chronic ethanol.     

Role of endocannabinoids in alcohol consumption and intoxication: studies of mice lacking fatty acid amide hydrolase.

Endocannabinoid signaling plays the important role in regulation of ethanol intake. Fatty acid amide hydrolase (FAAH) is a key membrane protein for metabolism of endocannabinoids, including anandamide, and blockade of FAAH increases the level of anandamide in the brain. To determine if FAAH regulates ethanol consumption, we studied mutant mice with deletion of the FAAH gene. Null mutant mice showed higher preference for alcohol and voluntarily consumed more alcohol than wild-type littermates. There was no significant difference in consumption of sweet or bitter solutions. To determine the specificity of FAAH for ethanol intake, we studied additional ethanol-related behaviors. There were no differences between null mutant and wild-type mice in severity of ethanol-induced acute withdrawal, conditioned taste aversion to alcohol, conditioned place preference, or sensitivity to hypnotic effect of ethanol. However, null mutant mice showed shorter duration of loss of righting reflex induced by low doses of ethanol (3.2 and 3.4 g/kg) and faster recovery from motor incoordination induced by ethanol. All three behavioral phenotypes (increased preference for ethanol, decreased sensitivity to ethanol-induced sedation, and faster recovery from ethanol-induced motor incoordination) seen in mutant mice were reproduced in wild-type mice by injection of a specific inhibitor of FAAH activity--URB597. These data suggest that increased endocannabinoid signaling increased ethanol consumption owing to decreased acute ethanol intoxication.     

Lack of stimulant and anxiolytic-like effects of ethanol and accelerated development of ethanol dependence in mu-opioid receptor knockout mice

The opioid system is implicated in various aspects of alcoholism. Acute ethanol administration produces anxiolytic-like effects in rodents while alcohol withdrawal induces anxiogenic-like effects. Mice lacking the mu-opioid receptor (MOR) do not self-administer ethanol and display decreased anxiety-like behavior. We hypothesized that MOR might be involved in the development and expression of alcoholism, particularly in relation to anxiety states. In mice lacking MOR (MOR-/- mice), we examined the acute anxiolytic-like and locomotor stimulant effects of ethanol (0, 0.75, 1.25, 1.75 g/kg, i.p.). In a separate experiment, mice were submitted to chronic ethanol-containing liquid diet and we assessed somatic and affective ethanol withdrawal on three consecutive withdrawal episodes by scoring handling-induced convulsions and anxiety-like behavior. Deletion of MOR blocked the acute anxiolytic-like and stimulant effects of ethanol. Furthermore, MOR-/- mice displayed affective and physical signs of ethanol withdrawal in earlier withdrawal tests than wild-type mice. The present results implicate MOR in affective and somatic aspects of ethanol exposure and withdrawal. In addition, our findings support the hypothesis that the clinical efficacy of the opioid receptor antagonist naltrexone against relapse to alcoholism might be related to an action on the acute positive effects of alcohol rather than the negative affect of abstinence.     

The role of group I mGlu receptors in the expression of ethanol-induced conditioned place preference and ethanol withdrawal seizures in rats

In animal models, N-methyl-d-aspartate (NMDA) receptors antagonists inhibit physical dependence and the reinforcing effects of ethanol. The group I metabotropic glutamate (mGlu) receptors antagonists (mGlu1 and mGlu5) attenuate excitatory effect of glutamate by functional modulation of the glutamate/NMDA receptors. The objective of the present study was to evaluate the effects of a selective mGlu5 receptors antagonist—MTEP, and mGlu1 receptors antagonist—EMQMCM, on two processes relevant to alcohol addiction: the expression of ethanol-induced conditioned place preference (CPP) paradigm, and ethanol withdrawal audiogenic seizures in rats. Our experiments indicated that EMQMCM at the doses of 5 and 10 mg/kg, and MTEP at the doses of 2.5 and 5 mg/kg, significantly attenuated the expression of ethanol CPP. Furthermore, both group I mGlu receptor antagonists, i.e. EMQMCM at the dose of 10 mg/kg and MTEP at the dose of 5 mg/kg, attenuated audiogenic seizures induced by the sound stimulus 12 h after withdrawal of ethanol in dependent rats. Our study shows the importance of mGlu5 and mGlu1 receptors for the expression of ethanol-induced CPP and withdrawal seizures, although mGlu5 receptors antagonist (MTEP) was more potent than the antagonist of mGlu1 receptors (EMQMCM).     

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.     

Activation of adenosine A1 receptors reduces anxiety-like behavior during acute ethanol withdrawal (hangover) in mice.

Elevated signs of anxiety are observed in both humans and rodents during withdrawal from chronic as well as acute ethanol exposure, and it represents an important motivational factor for ethanol relapse. Several reports have suggested the involvement of brain adenosine receptors in different actions produced by ethanol such as motor incoordination and hypnotic effects. In addition, we have recently demonstrated that adenosine A1 receptors modulate the anxiolytic-like effect induced by ethanol in mice. In the present study, we evaluated the potential of adenosine A1 and A2A receptor agonists in reducing the anxiety-like behavior during acute ethanol withdrawal (hangover) in mice. Animals received a single intraperitoneal administration of saline or ethanol (4 g/kg) and were tested in the elevated plus maze after an interval of 0.5-24 h. The results indicated that hangover-induced anxiety was most pronounced between 12 and 18 h after ethanol administration, as indicated by a significant reduction in the exploration of the open arms of the maze. At this time interval, ethanol was completely cleared. The acute administration of 'nonanxiolytic' doses of adenosine and the selective adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA), but not the adenosine A2A receptor agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl]adenosine (DPMA), at the onset of peak withdrawal (18 h), reduced this anxiogenic-like response. In addition, the effect of CCPA on the anxiety-like behavior of ethanol hangover was reversed by pretreatment with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). These results reinforce the notion of the involvement of adenosine receptors in the anxiety-like responses and indicate the potential of adenosine A1 receptor agonists to reduce the anxiogenic effects during ethanol withdrawal.     

Stress sensitization of ethanol withdrawal-induced reduction in social interaction: inhibition by CRF-1 and benzodiazepine receptor antagonists and a 5-HT1A-receptor agonist.

Repeated withdrawals from chronic ethanol sensitize the withdrawal-induced reduction in social interaction behaviors. This study determined whether stress might substitute for repeated withdrawals to facilitate withdrawal-induced anxiety-like behavior. When two 1-h periods of restraint stress were applied at 1-week intervals to rats fed control diet, social interaction was reduced upon withdrawal from a subsequent 5-day exposure to ethanol diet. Neither this ethanol exposure alone nor exposure to three restraint stresses alone altered this measure of anxiety. Further, the repeatedly stressed singly withdrawn rats continued to exhibit a reduction in social interaction 16 days later, upon withdrawal from re-exposure to 5 days of chronic ethanol, consistent with a persistent adaptation by the multiple-stress/withdrawal protocol. Weekly administration of corticosterone in place of stress induced no significant change in social interaction upon withdrawal from the single chronic ethanol exposure, indicative that corticoid release is not responsible for the stress-induced reduction in anxiety-like behavior during withdrawal. In the multiple-withdrawal protocol, stress applied during withdrawal from voluntary ethanol drinking by P-rats facilitated ethanol drinking sufficiently, to induce a withdrawal-induced reduction in social interaction. Administration of a CRF-1 receptor antagonist, a benzodiazepine receptor antagonist, or a 5-HT(1A) receptor agonist prior to each stress minimized sensitization of the withdrawal-induced reduction in anxiety-like behavior. Since these pharmacological consequences on the induction of anxiety-like behavior following the stress/withdrawal protocol are like those previously seen when these drug treatments were given prior to multiple withdrawals, evidence is provided that repeated stresses and multiple withdrawals sensitize the withdrawal reduction in social interaction by similar central adaptive mechanisms.     

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.     

Motivational properties of ethanol in mice selectively bred for ethanol-induced locomotor differences

Ethanol-induced locomotor stimulation has been proposed to be positively correlated with the rewarding effects of ethanol (Wise and Bozarth 1987). The present experiments provided a test of this hypothesis using a genetic model. Three behavioral indices of the motivational effects of ethanol (drinking, taste conditioning, place conditioning) were examined in mice from two independent FAST lines, selectively bred for sensitivity to ethanol-induced locomotor stimulation, and mice from two independent SLOW lines, selectively bred for insensitivity to ethanol-induced locomotor stimulation. In a single-bottle procedure, mice were allowed access to drinking tubes containing ethanol in a concentration (1–12% v/v) that increased over 24 consecutive days. FAST mice consumed greater amounts of ethanol solution. In a two-bottle procedure, mice were allowed access to tubes containing water or various concentrations of ethanol (2–8% v/v) over 6 days. FAST mice generally showed greater preference for ethanol solutions than SLOW mice. In a conditioned taste aversion procedure, mice received access to saccharin solution followed by injection of 2.5 g/kg ethanol (IP). SLOW mice developed aversion to the saccharin flavor more readily than FAST mice. In a series of place conditioning experiments, tactile stimuli were paired with various doses of ethanol (0.8–2.0 g/kg). During conditioning, FAST mice showed locomotor stimulation after 1.0, 1.2 and 2.0 g/kg ethanol while SLOW mice did not. During testing, mice conditioned with 1.2 g/kg and 2.0 g/kg ethanol showed conditioned place preference, but there were no line differences in magnitude of preference. These results indicate that genetic selection for sensitivity to ethanol-stimulated activity has resulted in genetic differences in ethanol drinking and ethanol-induced conditioned taste aversion but not ethanol-induced conditioned place preference. Overall, these data provide mixed support for the psychomotor stimulant theory of addiction.     

Acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in mice: effects of exposure to stress and modulation by mecamylamine

Nicotinic acetylcholine receptors mediate some of the rewarding and motivational effects of ethanol, including relapses. Relapses are common in drug addicts during abstinence when exposure to any stressor ensues. However, the role of nicotinic acetylcholine receptors in the ethanol- and stress-induced reinstatement of ethanol-induced conditioned place preference has not yet been explored. Therefore, the present study investigated the influence of mecamylamine, a nicotinic acetylcholine receptors antagonist on acquisition, expression, and reinstatement of ethanol-induced conditioned place preference in adult male Swiss mice. The results revealed that mecamylamine (0.1-10 μg/mouse, intracerebroventricularly) dose dependently prevented the development, expression, and reinstatement of ethanol-induced conditioned place preference. Further, acute treatment with mecamylamine blocked the restraint stress and forced swim stress-induced reinstatement of ethanol-induced conditioned place preference. All of these treatments had no influence on the locomotor activity. Therefore, it is concluded that mecamylamine blocks the acquisition, expression and reinstatement of conditioned reinforcing effects of ethanol without per se reinforcing or aversive influence. This ability of mecamylamine might be a potential advantage in the treatment of alcoholism.     

FOS expression induced by an ethanol-paired conditioned stimulus

To identify brain areas involved in ethanol-induced Pavlovian conditioning, brains of male DBA/2J mice were immunohistochemically analyzed for FOS expression after exposure to a conditioned stimulus (CS) previously paired with ethanol (2 g/kg) in two experiments. Mice were trained with a procedure that normally produces place preference (Before: ethanol before the CS) or one that normally produces place aversion (After: ethanol after the CS). Control groups received unpaired ethanol injections in the home cage (Delay) or saline only (Na?ve). On the test day, mice were exposed to the 5-min CS 90 min before sacrifice. Before groups showed a conditioned increase in activity, whereas the After group showed a conditioned decrease in activity. FOS expression after a drug-free CS exposure was significantly higher in Before-group mice than in control mice in the bed nucleus of the stria terminalis (Experiment 1) and anterior ventral tegmental area (Experiments 1-2). Conditioned FOS responses were also seen in areas of the extended amygdala and hippocampus (Experiment 2). However, no conditioned FOS changes were seen in any brain area examined in After-group mice. Overall, these data suggest an important role for the mesolimbic dopamine pathway, extended amygdala and hippocampus in ethanol-induced conditioning.     

Selective blockade of the orexin-2 receptor attenuates ethanol self-administration, place preference, and reinstatement

Rationale

Orexin-1 receptor antagonists have been shown to block the reinforcing effects of drugs of abuse and food. However, whether blockade of orexin-2 receptor has similar effects has not been determined. We have recently described the in vitro and in vivo effects of JNJ-10397049, a selective and brain penetrant orexin-2 receptor antagonist.

Objective

The goal of these studies was to evaluate whether systemic administration of JNJ-10397049 blocks the rewarding effects of ethanol and reverses ethanol withdrawal in rodents. As a comparison, SB-408124, a selective orexin-1 receptor antagonist, was also evaluated.

Methods

Rats were trained to orally self-administer ethanol (8% v/v) or saccharin (0.1% v/v) under a fixed-ratio 3 schedule of reinforcement. A separate group of rats received a liquid diet of ethanol (8% v/v) and withdrawal signs were evaluated 4?h after ethanol discontinuation. In addition, ethanol-induced increases in extracellular dopamine levels in the nucleus accumbens were tested. In separate experiments, the acquisition, expression, and reinstatement of conditioned place preference (CPP) were evaluated in mice.

Results

Our results indicate that JNJ-10397049 (1, 3, and 10?mg/kg, sc) dose-dependently reduced ethanol self-administration without changing saccharin self-administration, dopamine levels, or withdrawal signs in rats. Treatment with JNJ-10397049 (10?mg/kg, sc) attenuated the acquisition, expression, and reinstatement of ethanol CPP and ethanol-induced hyperactivity in mice. Surprisingly, SB-408124 (3, 10 and 30?mg/kg, sc) did not have any effect in these procedures.

Conclusions

Collectively, these results indicate, for the first time, that blockade of orexin-2 receptors is effective in reducing the reinforcing effects of ethanol.     

Effects of Aripiprazole,an Atypical Antipsychotic,on the Motor Alterations Induced by Acute Ethanol Administration in Mice

Aripiprazole is an antipsychotic that acts as a partial agonist at dopamine receptors. As the effects of most drugs of abuse converge to enhance dopamine‐mediated neurotransmission, the present study was designed to test the hypothesis that aripiprazole would inhibit the acute effects of ethanol, a widely abused substance. Male Swiss mice received acute injections and were evaluated for motor activity in three distinct tests. In the open field, ethanol (1.5, 2.5 and 3.5 g/kg) induced an increase in locomotion in a U‐shaped dose‐related fashion, whereas aripiprazole (0.1, 1 and 10 mg/kg) did not affect this parameter. All the doses of the antipsychotic were able to prevent the stimulant effects of 2.5 g/kg of ethanol. In the rotarod test, ethanol (2.5 and 3.5 g/kg) reduced the latency to fall from the apparatus, an effect also observed with the higher dose of aripiprazole. Contrary to what was observed in the open field, this antipsychotic did not interfere with the effects of ethanol in motor balance. Finally, we tested animals in the wire hang test, in which ethanol, but not aripiprazole, reduced latency to fall at all doses. In this test, aripiprazole did not change ethanol effects. The present data lead to the conclusion that aripiprazole prevents the stimulant effects of ethanol on locomotion, without interfering with the motor impairment induced by this drug.     

Withdrawal from repeated treatment with ethanol induces a protracted decrease in novelty-seeking behavior and enhancement of environmental habituation in mice

Ethanol withdrawal syndrome is characterized by somatic and behavioral symptoms, including increased anxiety and anhedonia. In animal models, however, there are many studies on the anxiogenic effects occurring during the first 24 h after ethanol withdrawal, while anhedonia has been overlooked. Recently, we have found that amphetamine withdrawal reduced novelty seeking and enhanced environmental habituation in mice, two motivation-related behaviors. We now investigate the effects of withdrawal from ethanol, a drug of abuse with a different pharmacological profile, on these two motivation-related behaviors. Swiss male mice (3 months old) were treated with 1.8 g/kg ethanol for 21 consecutive days in their home cages. Seven days after ethanol withdrawal, mice were tested in a free-choice novelty apparatus containing one familiar and one novel compartment. Novelty-seeking behavior was assessed by comparing time spent in the novel compartment versus the familiar compartment, whereas environmental habituation was concomitantly evaluated by the time-response curve of total locomotion (novel + familiar). Novelty seeking was decreased and environmental habituation was enhanced during ethanol withdrawal. These anhedonic responses were not associated with concurrent changes in the anxiety-like behavior of mice (as confirmed in the elevated plus-maze test). We propose that the concomitant evaluation of novelty-seeking behavior and environmental habituation can be useful to study the behavioral consequences not only of amphetamine withdrawal but also of ethanol withdrawal. Furthermore, the present data support recent clinical findings that suggest the occurrence of protracted anhedonia well beyond the limited period immediately following the abrupt cessation of ethanol intake.     

Suppression of dopamine-related side effects of morphine by aripiprazole, a dopamine system stabilizer

Dopamine receptor antagonists are commonly used to counter the adverse effects of opioids such as hallucinations, delusions and emesis. However, most of these agents themselves have side effects, including extrapyramidal symptoms. Here, we investigated the effect of the dopamine system stabilizer aripiprazole on morphine-induced dopamine-related actions in mice. Morphine-induced hyperlocomotion and reward were significantly suppressed by either the dopamine receptor antagonist prochlorperazine or aripiprazole. Catalepsy was observed with a high dose of prochlorperazine, but not with an even higher dose of aripiprazole. The increased level of dialysate dopamine in the nucleus accumbens stimulated by morphine was significantly decreased by pretreatment with aripiprazole. These results suggest that the co-administration of aripiprazole may be useful for reducing the severity of morphine-induced dopamine-related side effects.