Reduction of alcohol intake by the positive allosteric modulator of the GABA(B) receptor, rac-BHFF, in alcohol-preferring rats

Previous research has demonstrated that treatment with the positive allosteric modulator (PAM) of the GABA(B) receptor (GABA(B) PAM), rac-BHFF, suppressed lever-responding for alcohol and amount of self-administered alcohol in Sardinian alcohol-preferring (sP) rats. The present study was designed to extend the investigation on the anti-alcohol effects of rac-BHFF to alcohol drinking behavior. To this end, sP rats were exposed to the homecage, 2-bottle "alcohol (10%, v/v) vs water" choice regimen, with unlimited access for 24 h/day. rac-BHFF was administered once daily and for 7 consecutive days at the doses of 0, 50, 100, and 200 mg/kg (i.g.). Treatment with rac-BHFF resulted in an immediate, stable, and dose-related reduction in daily alcohol intake; the overall magnitude of reduction in alcohol intake averaged approximately 25%, 40%, and 65% in 50, 100, and 200 mg/kg rac-BHFF-treated rat groups, respectively. An increase in daily water intake fully compensated the reduction in alcohol intake, so that daily total fluid intake was unaffected by treatment with rac-BHFF. Daily food intake tended to be reduced only by the highest dose of rac-BHFF. These results complement closely with previous data indicating that (a) rac-BHFF suppressed operant, oral alcohol self-administration in sP rats and (b) the prototypic GABA(B) PAMs, CGP7930 and GS39783, reduced alcohol drinking in sP rats. However, while the reducing effect of CGP7930 and GS39783 on the daily alcohol intake tended to vanish after the first 2-3 days of treatment, the reducing effect of rac-BHFF on daily alcohol intake remained unchanged over the entire 7-day treatment period. These data strengthen the hypothesis that GABA(B) PAMs may represent a step forward in the search for GABA(B) receptor ligands with therapeutic potential for alcoholism.

Comparison of the effect of the GABAΒ receptor agonist, baclofen, and the positive allosteric modulator of the GABAB receptor, GS39783, on alcohol self-administration in 3 different lines of alcohol-preferring rats

BACKGROUND

Administration of the GABA(B) receptor agonist, baclofen, and positive allosteric modulator, GS39783, has been repeatedly reported to suppress multiple alcohol-related behaviors, including operant oral alcohol self-administration, in rats. This study was designed to compare the effect of baclofen and GS39783 on alcohol self-administration in 3 lines of selectively bred, alcohol-preferring rats: Indiana alcohol-preferring (P), Sardinian alcohol-preferring (sP), and Alko Alcohol (AA).

METHODS

Rats of each line were initially trained to respond on a lever, on a fixed ratio (FR) 4 (FR4) schedule of reinforcement, to orally self-administer alcohol (15%, v/v) in daily 30-minute sessions. Once responding reached stable levels, rats were exposed to a sequence of experiments testing baclofen (0, 1, 1.7, and 3 mg/kg; i.p.) and GS39783 (0, 25, 50, and 100 mg/kg; i.g.) on FR4 and progressive ratio (PR) schedules of reinforcement. Finally, to assess the specificity of baclofen and GS39783 action, rats were slightly food-deprived and trained to lever-respond for food pellets.

RESULTS

The rank of order of the reinforcing and motivational properties of alcohol was P>sP>AA rats. Under both FR and PR schedules of reinforcement, the rank of order of potency and efficacy of baclofen and GS39783 in suppressing alcohol self-administration was P>sP>AA rats. Only the highest dose of baclofen reduced lever-responding for food pellets; this effect was common to all 3 rat lines. Conversely, no dose of GS39783 altered lever-responding for food in any rat line.

CONCLUSIONS

These results suggest that: (i) the strength of the reinforcing and motivational properties of alcohol differ among P, sP, and AA rats; (ii) the reinforcing and motivational properties of alcohol in P, sP, and AA rats are differentially sensitive to treatment with baclofen and GS39783; (iii) the heterogeneity in sensitivity to baclofen and GS39783 of alcohol self-administration in P, sP, and AA rats may resemble the differential effectiveness of pharmacotherapies among the different typologies of human alcoholics; and (iv) the GABA(B) receptor is part of the neural substrate mediating the reinforcing and motivational properties of alcohol.

Anti-Alcohol and Anxiolytic Properties of a New Chemical Entity, GET73

N-[(4-trifluoromethyl)benzyl]4-methoxybutyramide (GET73) is a newly synthesized compound structurally related to the clinically used, alcohol-substituting agent, gamma-hydroxybutyric acid (GHB). The present study was designed to assess whether GET73 may share with GHB the capacity to reduce alcohol intake in rats. Additionally, the effect of treatment with GET73 on anxiety-related behaviors and cognitive tasks in rats was investigated. A series of in vitro binding assays investigated the capacity of GET73 to bind to the GHB binding site and multiple other receptors. GET73 (10(-9)-10(-3) M) failed to inhibit [(3)H]GHB binding at both high- and low-affinity GHB recognition sites in rat cortical membranes. GET73 displayed minimal, if any, binding at dopamine, serotonin, GABA, and glutamate receptors in membranes from different rat brain areas. Acute treatment with low-to-moderate, non-sedative doses of GET73 (5-50 mg/kg, i.g. or i.p.) (a) reduced alcohol intake and suppressed "alcohol deprivation effect" (a model of alcohol relapse) in selectively bred, Sardinian alcohol-preferring (sP) rats, (b) exerted anxiolytic effects in Sprague-Dawley (SD) and sP rats exposed to the Elevated Plus Maze test, and (c) tended to induce promnestic effects in SD rats exposed to a modified water version of the Hebb-Williams maze test. Although the mechanism of GET73 action is currently unknown, the results of the present study suggest that GET73 has a multifaceted pharmacological profile, including the capacity to reduce alcohol drinking and anxiety-related behaviors in rats.

Characterization of COR627 and COR628, two novel positive allosteric modulators of the GABA(B) receptor

The potential efficacy of GABA(B) receptor agonists in the treatment of pain, drug addiction, epilepsy, cognitive dysfunctions, and anxiety disorders is supported by extensive preclinical and clinical evidence. However, the numerous side effects produced by the GABA(B) receptor agonist baclofen considerably limit the therapeutic use of this compound. The identification of positive allosteric modulators (PAMs) of the GABA(B) receptor may constitute a novel approach in the pharmacological manipulation of the GABA(B) receptor, leading to fewer side effects. The present study reports the identification of two novel compounds, methyl 2-(1-adamantanecarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate (COR627) and methyl 2-(cyclohexanecarboxamido)-4-ethyl-5-methylthiophene-3-carboxylate (COR628), which act as GABA(B) PAMs in 1) rat cortical membranes and 2) in vivo assay. Both compounds potentiated GABA- and baclofen-stimulated guanosine 5'-O-(3-[(35)S]thio)-triphosphate binding to native GABA(B) receptors, while producing no effect when given alone. GABA concentration-response curves in the presence of fixed concentrations of COR627 and COR628 revealed an increase of potency of GABA rather than its maximal efficacy. In radioligand binding experiments [displacement of the GABA(B) receptor antagonist, 3-N-[1-((S)-3,4dichlorophenyl)-ethylaminol]-2-(S)hydroxypropyl cyclo-hexylmethyl phosphinic acid ([(3)H]CGP54626)], both COR627 and COR628 increased the affinity of high- and low-affinity binding sites for GABA, producing no effect when administered alone up to a concentration of 1 mM. In vivo experiments indicated that pretreatment with per se ineffective doses of COR627 and COR628 potentiated the sedative/hypnotic effect of baclofen. In conclusion, COR627 and COR628 may represent two additional tools for use in investigating the roles and functions of positive allosteric modulatory binding sites of the GABA(B) receptor.

Activation of the GABA(B) Receptor Prevents Nicotine-Induced Locomotor Stimulation in Mice

Recent studies demonstrated that activation of the GABA(B) receptor, either by means of orthosteric agonists or positive allosteric modulators (PAMs), inhibited different nicotine-related behaviors, including intravenous self-administration and conditioned place preference, in rodents. The present study investigated whether the anti-nicotine effects of the GABA(B) receptor agonist, baclofen, and GABA(B) PAMs, CGP7930, and GS39783, extend to nicotine stimulant effects. To this end, CD1 mice were initially treated with baclofen (0, 1.25, and 2.5 mg/kg, i.p.), CGP7930 (0, 25, and 50 mg/kg, i.g.), or GS39783 (0, 25, and 50 mg/kg, i.g.), then treated with nicotine (0 and 0.05 mg/kg, s.c.), and finally exposed to an automated apparatus for recording of locomotor activity. Pretreatment with doses of baclofen, CGP7930, or GS39783 that did not alter locomotor activity when given with nicotine vehicle fully prevented hyperlocomotion induced by 0.05 mg/kg nicotine. These data extend to nicotine stimulant effects the capacity of baclofen and GABA(B) PAMs to block the reinforcing, motivational, and rewarding properties of nicotine. These data strengthen the hypothesis that activation of the GABA(B) receptor may represent a potentially useful, anti-smoking therapeutic strategy.

Increase in alcohol intake, reduced flexibility of alcohol drinking, and evidence of signs of alcohol intoxication in Sardinian alcohol-preferring rats exposed to intermittent access to 20% alcohol

BACKGROUND

This study assessed in Sardinian alcohol-preferring (sP) rats a procedure known to promote alcohol drinking and based on the intermittent (once every other day) access to 2 bottles containing alcohol (20%, v/v) and water, respectively (Wise, 1973).

METHODS

To this end, sP rats were exposed - under the 2-bottle choice regimen - to: (i) 10% (v/v) alcohol with continuous access (CA10%; i.e., the procedure under which sP rats had been selectively bred); (ii) 10% (v/v) alcohol with intermittent access (IA10%); (iii) 20% (v/v) alcohol with continuous access (CA20%); (iv) 20% (v/v) alcohol with intermittent access (IA20%; the "Wise" condition) (Experiment 1). Additional experiments assessed the influence of (i) adulteration with quinine of the alcohol solution (Experiment 2) and (ii) concurrent presentation of a saccharin solution (Experiment 3) on alcohol drinking under the CA10% and IA20% conditions. Finally, it was assessed whether alcohol drinking under the CA10% and IA20% conditions resulted in motor incoordination at the Rota-Rod task, as a possible sign of alcohol intoxication (Experiment 4).

RESULTS

Daily alcohol intake markedly escalated in rats exposed to the IA20% condition, averaging 9.0 g/kg (in comparison with the average intake of 6.5 g/kg in the CA10% rat group). CA20% and IA10% rats displayed intermediate values of daily alcohol intake between those of CA10% and IA20% rats. Alcohol intake was virtually abolished by addition of quinine or by concurrent presentation of the saccharin solution in CA10% rats; conversely, alcohol intake in IA20% rats was only partially affected by gustatory aversion or concurrent presentation of an alternative reinforcer. Finally, alcohol intake in IA20%, but not in CA10%, rats resulted in clear motor-incoordinating effects.

CONCLUSIONS

These data suggest that the "Wise" procedure is effective in inducing marked increases in alcohol intake in sP rats. These increases are associated with a reduced flexibility of alcohol drinking (suggesting the development of "behavioral" dependence) and produce signs of alcohol intoxication that are not detected when sP rats are exposed to the more conventional CA10% condition.

Reducing effect of a Phaseolus vulgaris dry extract on food intake, body weight, and glycemia in rats

Extracts of kidney beans ( Phaseolus vulgaris ) are known to reduce food intake and glycemia in rodents and humans. This study evaluated the effect of a novel extract of P. vulgaris on food (regular food pellets, starch-enriched diet, and chocolate-flavored beverage) intake, body weight, and glycemia in rats. The effect of the combination of the colecistokinin (CCK) receptor antagonist, lorglumide, and P. vulgaris dry extract on food intake was also investigated. Administration of doses of P. vulgaris dry extract devoid of any behavioral toxicity dose-dependently decreased food intake (irrespective of the diet), body weight gain, and glycemia. Pretreatment with lorglumide blocked the reducing effect of P. vulgaris dry extract on food intake. The capacity of this P. vulgaris dry extract to reduce food intake, body weight, and glycemia in rats may be due to (a) inhibition of alpha-amylase, (b) stimulation of CCK release from the intestinal brush border cells, and/or (c) interference with the central mechanism(s) regulating appetite, food intake, and food palatability.

Repeated exposure to alcoholic beer does not induce long-lasting changes in alcohol self-administration and intake in sardinian alcohol-preferring and sardinian non-preferring rats

AIMS

Rats avidly consume non-alcoholic beer, and addition of alcohol to non-alcoholic beer may function as a medium to induce intake of large amounts of alcohol in rats. The present study investigated whether Sardinian alcohol-preferring (sP) and Sardinian non-preferring (sNP) rats, initially exposed to non-alcoholic beer, and subsequently to non-alcoholic beer containing increasing concentrations of alcohol, would develop unusually high alcohol self-administration and drinking behaviours: (i) when alcohol was added to non-alcoholic beer, and (2) once beer was withdrawn and a plain alcohol solution was made available.

METHODS

In Experiment 1, rats were exposed to operant, 30-min/day self-administration sessions of non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] for a total of 45 days. After a brief 'beer-fading' phase, the rats were exposed to self-administration sessions of a plain 10% (v/v) alcohol solution. In Experiment 2, the rats were exposed to non-alcoholic beer with increasing concentrations of alcohol [0, 2.5, 5, 7.5, and 10% (v/v)] and water under the 2-bottle choice regimen with unlimited access (24 h/day) for a total of 35 days. After a brief 'beer-fading' phase, the rats were exposed to the choice between a plain 10% (v/v) alcohol solution and water.

RESULTS

sP and sNP rats did not differ in self-administration (Experiment 1) and intake (Experiment 2) of non-alcoholic beer. In Experiment 1, as alcohol content increased, the amount of self-administered alcohol increased progressively in sP rats (up to 1-1.2 g/kg) and remained stable in sNP rats (approximately 0.65 g/kg). When the plain 10% alcohol solution was available, the amount of self-administered alcohol in sP rats initially dropped, and tended to increase-up to approximately 0.6 g/kg-on continuing exposure. In sNP rats, their lever-pressing behaviour was rapidly extinguished after beer withdrawal. In Experiment 2, as alcohol content was increased, daily alcohol intake increased progressively in sP rats (up to 8-9 g/kg) and averaged approximately 2.4 g/kg in sNP rats. When the plain alcohol solution was available, daily alcohol intake in sP rats was initially low, reaching control values on continuing exposure; conversely, daily alcohol intake was completely suppressed in sNP rats.

CONCLUSIONS

These results suggest that exposure to alcoholic beer resulted in unusually high intakes of alcohol in both sP and sNP rats for as long as non-alcoholic beer was added to alcohol; however, these high levels of alcohol self-administration and intake were not maintained once non-alcoholic beer was withdrawn.

Evaluation for the withdrawal syndrome from gamma-hydroxybutyric acid (GHB), gamma-butyrolactone (GBL), and 1,4-butanediol (1,4-BD) in different rat lines

A severe and life-threatening gamma-hydroxybutyric acid (GHB) withdrawal syndrome, clinically similar to the alcohol withdrawal syndrome, is increasingly being reported in GHB addicts. We investigated for the occurrence of withdrawal in Wistar and Sprague-Dawley rats, and in the selectively bred lines of GHB-sensitive (GHB-S) and Sardinian alcohol-preferring (sP) rats, following chronic administration of GHB, gamma-butyrolactone (GBL), and/or 1,4-butanediol (1,4-BD). Using validated rodent alcohol withdrawal scoring scales, little to no spontaneous or pharmacologically precipitated withdrawal effects were observed in Wistar, Sprague-Dawley, or GHB-S rats. Conversely, sP rats displayed both spontaneous and precipitated audiogenic seizures following abrupt cessation of chronic GHB or 1,4-BD administration and following pharmacological challenge with the GABA(B) receptor-selective antagonist, SCH 50911, respectively.

Phenotypic characterization of genetically selected Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats

Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats are one of the pairs of rat lines selectively bred for high and low alcohol preference and consumption, respectively, under the homecage, continuous two-bottle choice regimen. sP rats meet most of the fundamental criteria for an animal model of alcoholism, in that they voluntarily consume sufficient amounts of alcohol to achieve significant blood alcohol levels and produce psychopharmacological effects, including anxiolysis and motor stimulation. sP rats are also willing to 'work' (such as lever-pressing) for alcohol. Chronic alcohol drinking in sP rats results in the development of tolerance to a given effect of alcohol (specifically, motor incoordination) and relapse-like drinking (the alcohol deprivation effect). Conversely, sNP rats avoid alcohol virtually completely; their avoidance for alcohol being resistant even to an environmental manipulation such as long-term exposure to alcohol plus sucrose. sP and sNP rats have been characterized for different phenotypes, possibly associated to their different alcohol preference and consumption. In comparison with sNP rats, alcohol-naive sP rats displayed (1) more anxiety-related behaviors; (2) higher initial sensitivity to the locomotor stimulating and sedative/hypnotic effects of alcohol; and (3) lower sensitivity to the aversive effects of alcohol. The present paper reviews the data collected to date on alcohol drinking behavior and other alcohol-related behaviors in sP and sNP rats. The behavioral profile of sP rats is also compared with that of other lines of selectively bred alcohol-preferring rats and the heterogeneity resulting from this comparison is discussed in terms of different animal models for the different forms of alcoholism.

Lack of tolerance to the suppressing effect of rimonabant on chocolate intake in rats

RATIONALE AND OBJECTIVES

Previous work indicated that tolerance to the anorectic effect of the cannabinoid CB1 receptor antagonist/inverse agonist, rimonabant, developed rather rapidly in rats and mice given access to a standard rodent chow. The present study was designed to investigate whether the reducing effect of rimonabant on intake of a highly palatable food such as a chocolate-flavoured beverage underwent a development of tolerance as rapid as that manifested on intake of a standard rodent chow.

MATERIALS AND METHODS

To this aim, Wistar rats were concurrently exposed, with unlimited access for 24 h/day, to the chocolate-flavoured beverage, regular food pellets and water. Rimonabant (0, 1.25, 2.5 and 5 mg/kg; i.p.) was administered once a day for 21 consecutive days.

RESULTS

Rimonabant administration resulted in a dose-dependent suppression of the high, daily intake of the chocolate-flavoured beverage; this effect lasted for the entire 21-day treatment period, without any apparent development of tolerance. Conversely, rimonabant-induced reduction in daily intake of regular food pellets was of a smaller magnitude and was limited to the first 3-4 days of treatment.

CONCLUSIONS

Together, these results indicate that chronically administered rimonabant was more effective and longer-lasting in reducing the intake of a highly palatable food than that of regular food pellets in rats. These results also suggest that rimonabant may be more active on the hedonic rather than nutritive properties of diets.

Reducing effect of the positive allosteric modulators of the GABA(B) receptor, CGP7930 and GS39783, on alcohol intake in alcohol-preferring rats

The gamma-aminobutyric acidB (GABA(B)) receptor full agonists, baclofen and CGP44532, have been found to suppress different aspects of alcohol drinking behavior, including acquisition and maintenance, in selectively bred Sardinian alcohol-preferring (sP) rats. The present study was designed to assess whether this capability extends to the recently synthesized, positive allosteric modulators of the GABA(B) receptor, 2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) and N,N'-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783). In the "acquisition" experiments, CGP7930 (0, 25, 50 and 100 mg/kg; i.g.) and GS39783 (0, 6.25, 12.5 and 25 mg/kg; i.g.) were administered for 5 consecutive days to alcohol-naive sP rats. In the "maintenance" experiments, (0, 50 and 100 mg/kg; i.g.) and GS39783 (0, 50 and 100 mg/kg; i.g.) were administered for 5 consecutive days to alcohol-experienced sP rats. Alcohol intake was evaluated under the standard, homecage 2-bottle "alcohol (10%, v/v) vs water" regimen with unlimited access for 24 h/day. Both CGP7930 and GS39783 dose-dependently suppressed the acquisition of alcohol drinking behavior. In the "maintenance" experiments, CGP7930 and GS39783 reduced daily alcohol intake by 30-40% only at the highest dose when compared to vehicle-treated rats; this effect tended to vanish on continuing treatment. The results of the present study suggest that positive allosteric modulation of the GABA(B) receptor produced an effect on alcohol drinking behavior similar to that produced by GABA(B) receptor full agonists. These data also suggest that positive allosteric modulation of the GABA(B) receptor may constitute a potential strategy for developing new drugs for treating alcohol dependence.

Withdrawal syndrome from γ-hydroxybutyric acid (GHB) and 1,4-butanediol (1,4-BD) in Sardinian alcohol-preferring rats

Gamma-hydroxybutyric acid (GHB) and its precursors, 1,4-butanediol (1,4-BD) and gamma-butyrolactone (GBL), are recreational drugs widely abused in the US, Europe and Australasia. A severe withdrawal syndrome from GHB, 1,4-BD and GBL has been increasingly documented over the last years, necessitating the development of a reliable animal model for investigations of potential therapeutic approaches. The present study describes the induction and occurrence of audiogenic seizures as a sign of withdrawal from GHB and 1,4-BD in selectively bred Sardinian alcohol-preferring (sP) rats, treated with escalating doses of GHB (1.5-3.5 g/kg, twice daily; i.g.) or 1,4-BD (500-1000 mg/kg, twice daily; i.g.) for 9 consecutive days. Acute administration of the selective GABA(B) receptor antagonist, SCH 50911, dramatically increased seizure occurrence. We propose that the inherent sensitivity of sP rats to different GHB-associated responses may have contributed to the unraveling of a phenomenon which was otherwise not recognizable in other rat strains.

GHB-C rats: The control line of GHB-sensitive (GHB-S) and GHB-resistant (GHB-R) rats

Gamma-hydroxybutyric acid (GHB)-sensitive (GHB-S) and GHB-resistant (GHB-R) rats have been selectively bred for their opposite sensitivity to the sedative/hypnotic effect of GHB. This opposite sensitivity has been found to generalize to the GABA(B) receptor agonist, baclofen. A control line [named GHB-control (GHB-C)] has been derived from the foundation stock of GHB-S and GHB-R rats. GHB-C rats have been bred without any evaluation of their sensitivity to GHB. The experiments described here were designed to evaluate the sensitivity of GHB-C rats, from the 13th generation, to the sedative/hypnotic effect of GHB (1 g/kg, i.p.) and baclofen (20 mg/kg, i.p.). All measures (onset, sleep time and r = sleep time/onset) of sensitivity to GHB- and baclofen-induced sedation/hypnosis in GHB-C rats were significantly different from and intermediate to those recorded in GHB-S and GHB-R rats. Furthermore, these values were similar to those recorded in the foundation stock. These results suggest that GHB-C rats may constitute a valid control line for GHB-S and GHB-R rats, representing the "general population" from which GHB-S and GHB-R rats were derived. Furthermore, the relative equidistance of sensitivity to GHB- and baclofen-induced sedation/hypnosis of GHB-C rats from those of GHB-S and GHB-R rats suggests that genetic factors contributes to the development of both sensitivity in GHB-S rats and resistance in GHB-R rats.

Endogenous gamma-aminobutyric acid (GABA)(A) receptor active neurosteroids and the sedative/hypnotic action of gamma-hydroxybutyric acid (GHB): a study in GHB-S (sensitive) and GHB-R (resistant) rat lines

In the rat brain, gamma-hydroxybutyric-acid (GHB) increases the concentrations of 3alpha-hydroxy,5alpha-pregnan-20-one (allopregnanolone, 3alpha,5alpha-THP) and 3alpha,21-dihydroxy,5alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone/3alpha,5alphaTHDOC), two neurosteroids acting as positive allosteric modulators of gamma-aminobutyric acid (GABA)(A) receptors. This study was aimed at assessing whether neurosteroids play a role in GHB-induced loss of righting reflex (LORR). Basal and GHB-stimulated brain concentrations of endogenous 3alpha,5alpha-THP and 3alpha,5alpha-THDOC were analyzed in two rat lines, GHB-sensitive (GHB-S) and GHB-resistant (GHB-R), selectively bred for opposite sensitivity to GHB-induced sedation/hypnosis. Basal neurosteroid concentrations were similar in brain cortex of the two rat lines. However, in male GHB-S rats, administration of GHB (1000 mg/kg, i.p., 30 min) increased brain cortical concentrations of 3alpha,5alpha-THP and 3alpha,5alpha-THDOC 7- and 2.5-fold, respectively, whilst male GHB-R animals displayed only a 4- and 2-fold increase, respectively. In GHB-S rats this increase lasted up to 90 min and declined 180 min following GHB administration, a time course that matches LORR onset and duration. In contrast, in GHB-R rats, which failed to show GHB-induced LORR, brain cortical 3alpha,5alpha-THP and 3alpha,5alpha-THDOC had returned to control values within 90 min. At onset of LORR, a similar increase in brain cortical levels of 3alpha,5alpha-THP and 3alpha,5alpha-THDOC (2-3-fold) was observed in GHB-S female rats and in the few female GHB-R rats that lost the righting reflex after GHB administration, but not in female GHB-R rats failing to show LORR. Sub-hypnotic doses (7.5 and 12.5 mg/kg, i.p.) of pregnanolone, administered 10 min before GHB, dose-dependently facilitated the expression of GHB-induced LORR in GHB-R male rats. These results suggest that the GHB-induced increases of brain 3alpha,5alpha-THP and 3alpha,5alpha-THDOC concentrations are implicated in the eliciting of the sedative/hypnotic action of GHB.

Different sensitivity to the motor incoordinating effects of γ-hydroxybutyric acid (GHB) and baclofen in GHB-sensitive and GHB-resistant rats

The present study investigated whether the differential sensitivity of selectively bred gamma-hydroxybutyric acid (GHB)-sensitive (GHB-S) and GHB-resistant (GHB-R) rats to GHB- and baclofen-induced sedation/hypnosis generalized to the motor incoordinating effect of the two drugs. To this aim, GHB-S and GHB-R rats were tested on a Rota-Rod after the acute administration of GHB (100-500 mg/kg, i.p.) and baclofen (1.25-5 mg/kg, i.p.). Significant line differences were observed in the dose-response curves for both GHB and baclofen, with GHB-S rats displaying a greater sensitivity to the motor incoordinating effects of both drugs than GHB-R rats. No line difference was observed in diazepam (1.25-5 mg/kg, i.p.), pentobarbital (5-15 mg/kg, i.p.), and ethanol (1-1.5 g/kg, i.p.) dose-response curves. These results suggest that the differential sensitivity of GHB-S and GHB-R rats to GHB and baclofen extends to the effects produced by doses of the two drugs which are 5-10 times lower than those for which rats have been selectively bred. These results are discussed in terms of the GABA(B) receptor being the likely neural substrate on which the differential sensitivity of GHB-S and GHB-R rats resides.

Suppression of maintenance of alcohol-drinking behavior by the concurrent availability of saccharin in Sardinian alcohol-preferring (sP) rats

In the current study, we investigated the effect of the concurrent presentation of saccharin on the maintenance of alcohol-drinking behavior in selectively bred Sardinian alcohol-preferring (sP) rats. Rats were initially given access to alcohol [10% (volume/volume) in water] and water under the home cage, two-bottle, free-choice regimen, with unlimited access for 24 h/day for eight consecutive weeks. Next, a third bottle, containing saccharin [0%, 0.01%, 0.1%, 1%, or 3% (weight/volume) in water], was concomitantly offered for an additional 10 consecutive days. Intake of saccharin solution resulted as an inverted-U function of saccharin concentration, with the 0.1% saccharin solution being the highest accepted. Alcohol intake was a U function of saccharin concentration, being reduced by 65%-95% in the group of rats exposed to the 0.1% saccharin solution. These results indicate that (1) the concurrent presentation of highly palatable solutions of saccharin markedly reduced alcohol intake in alcohol-experienced sP rats and (2) the reducing effect of saccharin solutions on the alcohol intake in sP rats was positively related to their degree of acceptability. We hypothesized that saccharin solutions may have functioned as a reinforcer, partially substituting for alcohol reinforcement and rendering alcohol drinking less urgent.

Suppression of acquisition of alcohol-drinking behavior by the concurrent availability of saccharin in Sardinian alcohol-preferring (sP) rats

In the current study, we investigated the effect of the concurrent presentation of saccharin on the acquisition of alcohol-drinking behavior in selectively bred Sardinian alcohol-preferring (sP) rats. Alcohol-naive rats were given access to saccharin [0%, 0.01%, 0.1%, 1%, or 3% (weight/volume) in water], alcohol [10% (volume/volume) in water], and water under the home cage, three-bottle, free-choice regimen, with unlimited access for 24 h/day for 10 consecutive days. Intake of saccharin solution resulted as an inverted-U function of saccharin concentration, reaching polydipsic-like values at the 0.1% concentration. In contrast, alcohol intake was a U function of saccharin concentration, being virtually suppressed in the groups of rats exposed to the highly accepted 0.1% and 1% concentrations of saccharin. These results indicate that (1) the concurrent presentation of highly palatable solutions of saccharin suppresses acquisition of alcohol-drinking behavior in sP rats and (2) the suppressive effect of saccharin solutions on the acquisition of alcohol-drinking behavior in sP rats was positively related to their degree of acceptability. We hypothesize that an immediate and continuous access to the highly palatable saccharin solution may have distracted the rat, preventing it from consuming the amounts of alcohol solution needed to disclose and experience the psychopharmacologic effects of alcohol on which alcohol-drinking behavior in sP rats is based.

Completion by the 10th generation of the bidirectional selective breeding of GHB-sensitive and GHB-resistant rats

The present paper describes the completion of the bidirectional selective breeding of gamma-hydroxybutyric acid (GHB)-sensitive (GHB-S) and GHB-resistant (GHB-R) rats, which display opposite sensitivity to the sedative/hypnotic effect of 1 g/kg GHB. Completion of the selective breeding process was achieved by the F10, when 100% of rats of each line fulfilled the selection criterion. GHB-S and GHB-R rats may constitute a valuable tool for investigations on GHB physiology and pharmacology.

Immunocytochemical study of the forebrain serotonergic innervation in Sardinian alcohol-preferring rats

RATIONALE

The anxiolytic effect of ethanol is generally considered to be causally related to the development of alcohol dependence, and serotonin (5-HT) has been involved in both alcohol abuse and anxiety disorders. Several lines of evidence suggest an inverse relationship between alcohol abuse and central serotonergic neurotransmission.

OBJECTIVES

When tested in the elevated plus-maze, selectively bred Sardinian alcohol-preferring (sP) rats display a higher degree of anxiety than Sardinian alcohol-non-preferring rats (sNP); this behavior is reversed by voluntary ethanol intake. The present study examined whether sP rats differed with respect to the 5-HT innervation in different forebrain areas.

METHODS

We performed an immunohistochemistry study using an antibody raised against serotonin transporter (SERT), a marker for 5-HT fibers, coupled with an unbiased stereology, the method used to count the number of 5-HT neurons in the raphe nuclei.

RESULTS

The SERT-positive innervation density was found to be significantly lower in the medial-prefrontal cortex and in the shell of the nucleus accumbens of the ethanol-naive sP rats (sP-N) when compared with the sNP and unselected Wistar rats. No differences were found in the caudate putamen and hippocampus. The stereological analysis showed a significant difference in the number of 5-HT neurons in the dorsal but not in the median raphe of sP-N rats, compared with sNP and Wistar rats. Analysis of the cell body cross-sectional area revealed no differences among the three lines of rats either in the dorsal or in the median raphe. In sP rats that had voluntarily drunk ethanol for 14 consecutive days (sP-exp), no differences were found in the 5-HT innervation relative to sP-N animals.

CONCLUSIONS

These results indicate a selective reduction of innervation in the medial portion of the mesocorticolimbic 5-HT system in sP rats, suggesting that this genetically determined difference may be involved in the contrasting alcohol preference and consumption of sP and sNP animals.

Long-term exposure to a sweetened alcoholic solution does not alter genetic aversion to ethanol in Sardinian alcohol-nonpreferring (sNP) rats

Results of a recent investigation revealed that selectively bred Indiana ethanol-nonpreferring (NP) rats could be "environmentally" conditioned to consume high amounts of ethanol. Specifically, a long-term exposure to a sucrose-plus-ethanol solution resulted, when sucrose was faded out, in an ethanol intake that was equivalent to that recorded in the counterpart ethanol-preferring (P) rats. The current study was designed to extend the above investigation to the selectively bred Sardinian alcohol-nonpreferring (sNP) rats. To this aim, rats of the sNP and Sardinian alcohol-preferring (sP) lines were exposed to a 108-day sucrose-fading procedure, which was virtually identical to that previously used with NP and P rats. Results indicated that intake of the sucrose-plus-ethanol solution in sNP rats was maintained predominantly by sucrose, as negligible intakes of ethanol were observed when sucrose was faded out. In contrast, sP rats maintained high levels of ethanol intake both during and after the induction procedure. These results support the suggestion that an environmental manipulation such as a long-term exposure to a sucrose-fading procedure did not overcome the genetically determined predisposition to avoid ethanol in sNP rats.

Characterization of wild-type (R100R) and mutated (Q100Q) GABAA alpha 6 subunit in Sardinian alcohol non-preferring rats (sNP)

Sardinian alcohol non-preferring (sNP) rats, selected for their low ethanol preference and consumption, carry a point mutation (R100Q) in the gene coding for GABA(A) receptor alpha(6) subunit, which becomes more sensitive to diazepam-evoked GABA currents. We performed binding studies in the cerebellum of normal (RR) and mutated (QQ) sNP rats using [3H]Ro 15-4513, an inverse agonist for the benzodiazepine site which binds both diazepam insensitive and diazepam sensitive sites. Saturation curves performed on cerebellar membrane from genotyped rats indicated an higher affinity of [3H]Ro 15-4513 for GABA(A) receptors in QQ with respect to RR rats (K(d) values 4.0+/-0.67 and 6.24+/-0.95 nM, respectively), with similar B(max) values (3.5+/-0.25 and 3.9+/-0.39 pmol/mg protein, respectively). Diazepam displacement curves showed a two component model for both genotypes, with similar K(i1) values for QQ and RR (3.6+/-0.62 and 4.9+/-0.33 nM, respectively). In QQ rats diazepam is able to completely displace [3H]Ro 15-4513 (K(i2)=1.48+/-0.27 microM), while in RR rats the diazepam sensitive sites are still present (K(i2)>10 microM). The basal mRNA and protein expression level of the alpha(6) subunit were similar in RR and QQ rats. The electrophysiological profile of oocytes of Xenopus laevis injected with cerebellar synaptosomes showed that ethanol positively modulated GABA-evoked currents significantly more in QQ than in RR rats. These data contribute to the characterization of the function of GABA(A) alpha(6) subunit and its involvement in determining alcohol related behavior.