Giancarlo Colombo

APPETITE SUPPRESSION AND WEIGHT LOSS AFTER THE CANNABINOID ANTAGONIST SR 141716

The effect of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight was assessed in adult, non-obese Wistar rats. The daily administration of SR 141716 (2.5 and 10 mg/kg; i.p.) reduced dose-dependently both food intake and body weight. Tolerance to the anorectic effect developed within 5 days; in contrast, body weight in SR 141716-treated rats remained markedly below that of vehicle-treated rats throughout the entire treatment period (14 days). The results suggest that brain cannabinoid receptors are involved in the regulation of appetite and body weight.

Sardinian alcohol-preferring rats: A genetic animal model of anxiety

The present study was designed to assess the anxiety profile of the selectively bred alcohol-preferring sP and alcohol-nonpreferring sNP rats. Rats were offered either water (ethanol-naive rats) or a free choice of 10% (v/v) ethanol and water (ethanol-experienced rats) for 14 consecutive days prior to the test. Spontaneous exploration of an elevated plus maze was used as a behavioral measure of anxiety. Ethanol-naive sP rats spent less time in and made fewer entries into the open arms of the maze than ethanol-naive sNP rats. These results suggest a higher innate degree of anxiety in sP than in sNP rats. Moreover, time spent in and number of entries into the open arms of the maze were higher in ethanol-experienced than in ethanol-naive sP rats. This finding suggests that ethanol consumed voluntarily produces anxiolytic effects in sP rats. The results of the present study are discussed in terms of (a) anxiety as a genetic trait related to ethanol-preference in sP rats and (b) self-medication of anxiety as a possible factor promoting voluntary ethanol consumption in sP rats.

Ethanol markedly increases “GABAergic” neurosteroids in alcohol-preferring rats

Alcohol administration (1 g/kg, i.p.) increased the levels of the neurosteroids 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) and 3alpha,21-dihydroxy-5alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, THDOC) in the cerebral cortex and hippocampus both in alcohol-naive Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats (two rat lines selectively bred for alcohol preference and non-preference, respectively). However, the increase reached several fold higher levels in sP than in sNP rats (6-24 vs. 2-11 fold the basal levels, respectively). Since the two neurosteroids are the most potent endogenous positive modulators of GABA(A) receptors and elicit anxiolytic and rewarding effects, while voluntary alcohol consumption produces anxiolytic and rewarding effects in sP but not in sNP rats, the results suggest that the neurosteroids may play a role in the anxiolytic and rewarding effects of alcohol in sP rats.

Effect of spontaneous ingestion of ethanol on brain dopamine metabolism

The effect of ethanol, either administered by gavage or voluntarily ingested, on brain dopamine (DA) metabolism was studied in alcohol-preferring and alcohol non-preferring rats. In alcohol non-preferring rats ethanol administration (2 g/kg) increased 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) and reduced DA levels in the caudate nucleus and olfactory tubercle but was ineffective in the medial prefrontal cortex. In alcohol-preferring rats ethanol effect was greater than in non-preferring animals and ethanol influenced DA metabolism also in the medial prefrontal cortex. The effect of voluntary ethanol ingestion was studied in alcohol-preferring rats trained to consume their daily fluid intake within 2 hrs. Voluntary ingestion of ethanol (3.1 +/- 0.7 g/kg in 1 hr) increased DA metabolites and reduced DA levels in the caudate nucleus, olfactory tubercle and medial prefrontal cortex. The results suggest that voluntary ethanol ingestion increases the release of DA from nigro-striatal and meso-limbic DA neurons.

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.

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.

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.

Rapid suppression of alcohol withdrawal syndrome by baclofen

Alcohol withdrawal syndrome is a distressing and at times life-threatening condition in alcohol-dependent patients (1). Usually, symptoms develop within 6 –24 hours after the last drink (2). Early symptoms include raised blood pressure and pulse rate, tremor, hyperreflexia, and anxiety with increased irritability. Clinical management is aimed at symptom relief, prevention of seizures and delirium, and a smooth transition to a treatment program to maintain long-term abstinence from alcohol (3). Benzodiazepines are presently the drug of choice (4). We recently found that baclofen, a -aminobutyric acid (GABA)B receptor agonist used to control spasticity (5), reduced voluntary alcohol intake in alcohol-preferring rats (6), as well as alcohol craving and intake, up to complete alcohol abstinence, in alcohol-dependent patients (7). Furthermore, baclofen suppressed the intensity of alcohol withdrawal syndrome in rats who were physically dependent on alcohol (6). We therefore studied the effects of oral administration of baclofen in patients with severe alcohol withdrawal syndrome.

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.