Salvatore Serra

Role of GABAB receptors in the sedative/hypnotic effect of γ-hydroxybutyric acid

Abstract The present study was aimed at identifying the receptor systems involved in the mediation of the sedative/hypnotic effect of γ-hydroxybutyric acid (GHB) in DBA mice. Administration of the putative antagonist of the GHB binding site, 6,7,8,9-tetrahydro-5-hydroxy-5 H -benzocyclohept-6-ylideneacetic acid (NCS-382; 50–500 mg/kg, i.p.), significantly increased the duration of loss of righting reflex induced by GHB (1000 mg/kg, i.p.). In contrast, the GABA B receptor antagonists, (2 S )(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 25–100 mg/kg, i.p.) and (3-aminopropyl)(cyclohexylmethyl)phosphinic acid (CGP 46381; 12.5–150 mg/kg, i.p.), completely prevented the sedative/hypnotic effect of GHB. SCH 50911 (100 and 300 mg/kg, i.p.) was also capable to readily reverse the sedative/hypnotic effect of GHB (1000 mg/kg, i.p.) in mice that had lost the righting reflex. SCH 50911 (100 mg/kg, i.p.) also completely abolished the sedative/hypnotic effect of the GABA B receptor agonist, baclofen. These results indicate that the sedative/hypnotic effect of GHB is mediated by the stimulation of GABA B receptors and add further support to the hypothesis that the GABA B receptor constitutes a central site of action of GHB.

Role of GABAB receptor in alcohol dependence: Reducing effect of baclofen on alcohol intake and alcohol motivational properties in rats and amelioration of alcohol withdrawal syndrome and alcohol craving in human alcoholics

The present paper describes the results of recent preclinical and clinical studies conducted in this laboratory in order to characterize the anti-alcohol properties of the GABAB receptor agonist, baclofen. At a preclinical level, the repeated administration of non-sedative doses of baclofen dose-dependently suppressed the acquisition and maintenance of alcohol drinking behavior in selectively bred Sardinian alcohol-preferring (sP) rats tested under the homecage, 2-bottle “alcohol vs water” choice regimen. Acute injection of baclofen completely blocked the temporary increase in voluntary alcohol intake occurring after a period of alcohol abstinence (the so-called alcohol deprivation effect, which models alcohol relapses in human alcoholics). Acute treatment with baclofen also dose-dependently suppressed extinction responding for alcohol (an index of motivation to consume alcohol) in sP rats trained to lever-press for oral alcohol self-administration. Taken together, these results suggest the involvement of the GABAB receptor in the neural substrate mediating alcohol intake and alcohol motivational properties in an animal model of excessive alcohol consumption. Further, acutely administered baclofen dose-dependently reduced the severity of alcohol withdrawal signs in Wistar rats made physically dependent upon alcohol.Preliminary clinical surveys suggest that the antialcohol properties of baclofen observed in rats may generalize to human alcoholics. Indeed, a doubleblind survey demonstrated that repeated daily treatment with baclofen was associated, when compared to placebo, with a higher percentage of subjects totally abstinent from alcohol and a higher number of days of total abstinence. Treatment with baclofen also suppressed the number of daily drinks and decreased the obsessive and compulsive components of alcohol craving. Finally, a single non-sedative dose of baclofen resulted in the rapid disappearance of alcohol withdrawal symptomatology, including delirium tremens, in alcohol-dependent patients. In both clinical studies, baclofen was well tolerated with minimal side effects. These results suggest that baclofen may represent a potentially effective medication in the treatment of alcohol-dependent patients.

Suppression by baclofen of alcohol deprivation effect in Sardinian alcohol-preferring (sP) rats

Alcohol deprivation effect (ADE), i.e. the transient increase in alcohol intake that takes place in laboratory animals after a period of alcohol deprivation, has been proposed to model alcohol relapses in alcoholics. The present study investigated the effect of the GABA(B) receptor agonist, baclofen, on the development of ADE in selectively bred Sardinian alcohol-preferring (sP) rats. Acute administration of non-sedative doses of baclofen (0, 1, 1.7 and 3 mg/kg, i.p.) resulted in the complete suppression of the extra-amount of alcohol consumed during the first hour of re-access to alcohol after 7 days of deprivation. These results implicate the GABA(B) receptor in the neural substrate mediating ADE and suggest that baclofen may possess anti-relapse properties.

Endocannabinoid system and alcohol addiction: Pharmacological studies

The present paper describes the results of recent pharmacological studies implicating the cannabinoid CB1 receptor in the neural circuitry regulating alcohol consumption and motivation to consume alcohol. Cannabinoid CB1 receptor agonists have been found to specifically stimulate alcohol intake and alcohols motivational properties in rats. Conversely, the cannabinoid CB1 receptor antagonist, SR 141716, has been reported to specifically suppress acquisition and maintenance of alcohol drinking behavior, relapse-like drinking and alcohols motivational properties in rats. More recent data indicate that opioid receptor antagonists a) blocked the stimulatory effect of cannabinoids on alcohol intake, and b) synergistically potentiated the suppressing effect of SR 141716 on alcohol intake and alcohols motivational properties. Consistently, SR 141716 blocked the stimulatory effect of morphine on alcohol intake. These results suggest a) the existence of a functional link between the cannabinoid and opioid receptor systems in the control of alcohol intake and motivation to consume alcohol, and b) that novel and potentially effective therapeutic strategies for alcoholism may come from the combination of cannabinoid and opioid receptor antagonists.

Blockade by the cannabinoid CB1 receptor antagonist, SR 141716, of alcohol deprivation effect in alcohol-preferring rats

Abstract The present study investigated the effect of the cannabinoid CB 1 receptor antagonist, SR 141716 ( N -piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide), on alcohol deprivation effect (i.e. the temporary increase in alcohol intake after a period of alcohol withdrawal) in Sardinian alcohol-preferring (sP) rats. As expected, alcohol-deprived rats virtually doubled voluntary alcohol intake during the first hour of re-access. Acute administration of SR 141716 (0, 0.3, 1 and 3 mg/kg, i.p.) completely abolished the alcohol deprivation effect. These results suggest that the cannabinoid CB 1 receptor is part of the neural substrate mediating the alcohol deprivation effect and that SR 141716 may possess anti-relapse properties.

The cannabinoid receptor antagonist SR 141716 prevents acquisition of drinking behavior in alcohol-preferring rats

The cannabinoid CB(1) receptor antagonist, N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide) (SR 141716); 0.3-3 mg/kg, i.p., twice daily for 10 days), prevented the acquisition of alcohol drinking behavior in rats genetically selected for alcohol preference (Sardinian alcohol-preferring (sP) rats), having the free choice between alcohol (10%, v/v) and water. The results suggest that activation of cannabinoid CB(1) receptors is essential for the acquisition of alcohol drinking behavior in animals with a genetically determined alcohol preference.

Central effects of 1,4-butanediol are mediated by GABAB receptors via its conversion into γ-hydroxybutyric acid

Abstract The aliphatic alcohol 1,4-butanediol in converted into γ-hydroxybutyric acid (GHB) via two enzymatic steps: first, it is oxidised by alcohol dehydrogenase in γ-hydroxybutyraldehyde; second, the latter is transformed, likely by aldehyde dehydrogenase, into GHB. Initially, the present study compared the sedative/hypnotic effect of GHB and 1,4-butanediol, measured as loss of righting reflex. 1,4-Butanediol was more potent than GHB, presumably because of a more rapid penetration of the blood brain barrier. Further alcohol dehydrogenase inhibitors, 4-methylpyrazole and ethanol, totally prevented the sedative/hypnotic effect of 1,4-butanediol; the aldehyde dehydrogenase inhibitor disulfiram partially blocked the sedative/hypnotic effect of 1,4-butanediol. Finally, the sedative/hypnotic effect of 1,4-butanediol was antagonised by the GABA B receptor antagonists, SCH 50911 [(2 S )(+)-5,5-dimethyl-2-morpholineacetic acid] and CGP 46381 [(3-aminopropyl)(cyclohexylmethyl)phosphinic acid], but not by the putative GHB receptor antagonist NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5 H -benzocyclohept-6-ylideneacetic acid), indicating that it is mediated by GABA B but not GHB receptors. Taken together, these results suggest that the sedative/hypnotic effect of 1,4-butanediol is mediated by its conversion in vivo into GHB which, in turn, binds to GABA B receptors. Accordingly 1,4-butanediol, unlike GHB, failed to displace [ 3 H]GHB and [ 3 H]baclofen in brain membranes.

Boosting effect of morphine on alcohol drinking is suppressed not only by naloxone but also by the cannabinoid CB1 receptor antagonist, SR 141716

The present study investigated the effect of the cannabinoid CB(1) receptor antagonist, SR 141716 (N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide), on the ability of low and high doses of morphine to, respectively, augment and suppress voluntary alcohol intake in selectively bred Sardinian alcohol-preferring rats. Acute administration of a low dose of morphine (1 mg/kg, s.c.) produced a specific and marked increase in alcohol intake, which correlated with an increase in blood alcohol levels and was prevented by either SR 141716 (0.3 mg/kg, i.p.) or naloxone (0.1 mg/kg, i.p.). A higher dose (10 mg/kg, s.c.) of morphine reduced both alcohol and food intakes and produced sedation and hypomotility. The suppressant effect of morphine on alcohol intake was blocked by naloxone (0.1 mg/kg, i.p.) but not by SR 141716 (0.3 mg/kg, i.p.). These results are in agreement with those showing the ability of SR 141716 to antagonize the appetitive and positive reinforcing properties of morphine and add further support to the hypothesis of the existence of a functional link between the action of opioids and of cannabinoids.

Stable preference for high ethanol concentrations after ethanol deprivation in Sardinian alcohol-preferring (sP) rats

Results of a recent study have demonstrated that exposure to multiple ethanol concentrations and repeated ethanol deprivation periods in Indiana ethanol-preferring (P) rats resulted in the development of an alcohol deprivation effect (ADE; the temporary increase in voluntary ethanol intake after a period of deprivation from ethanol) characterized by consumption of intoxicating amounts of ethanol. The current study was designed to possibly extend these results to Sardinian alcohol-preferring (sP) rats, generated with the same selective program previously used for P rats. To this aim, ethanol-naive sP rats were exposed initially to the home cage four-bottle choice [10%, 20%, and 30% (vol./vol.) ethanol solutions and water] for eight consecutive weeks. Subsequently, rats were divided into two groups: The first group had continuous access to the four-bottle regimen (nondeprived rats), and the second group was exposed to five cycles of 14-day periods of deprivation from ethanol and 14-day periods of reexposure to the four-bottle regimen. An ADE developed after each deprivation period. However, the extra intake of ethanol was limited to the first hour of each reaccess period. Magnitude of ADE did not change with repeated periods of deprivation. However, a shift in preference toward the two highest concentrations of ethanol solutions was evident from the first reexposure to ethanol and was maintained throughout the study. These results provide further evidence on the heterogeneity of ethanol-drinking behavior among rat lines selectively bred for high ethanol preference and consumption.

Differences in ethanol-induced conditioned taste aversion in Sardinian alcohol-preferring and Sardinian alcohol-nonpreferring rats.

In the present study, we investigated whether aversion to the pharmacological effects of ethanol developed to a differential extent in selectively bred Sardinian alcohol-preferring (sP) and Sardinian alcohol-nonpreferring (sNP) rats, and whether this different response was consistent with their genetically determined differences in ethanol preference and consumption. To this purpose, a conditioned taste aversion paradigm was used. Male sP and sNP rats were exposed to five sessions in which a 20-min availability of a saccharin solution (1 g/l) was paired to the injection of ethanol (0, 0.5, or 1 g/kg, i.p.), delivered immediately after removal of the saccharin bottle (conditioning phase). Subsequently, the choice between saccharin solution and water was offered for 18 consecutive daily 20-min sessions (postconditioning phase). Ethanol at 1g/kg produced a marked aversion to saccharin in sNP rats: The reduction in saccharin intake was already evident on the second day of the conditioning phase and lasted for 15 days of the postconditioning phase. In contrast, this dose of ethanol elicited a modest, if any, conditioned taste aversion in sP rats, although blood ethanol levels were comparable to those assessed in sNP rats. These results indicate the existence of a differential degree of aversion to the postingestional effects of ethanol between sP and sNP rats, and support the suggestion that it may contribute, at least in part, to the opposite preference for and consumption of ethanol monitored in these rat lines.