Differential effects of a 5-HT2 receptor blocker on alcohol intake in rats selectively bred for high and low catecholamine responses to stress

Ritanserin in relapse prevention in abstinent alcoholics: results from a placebo-controlled double-blind international multicenter trial. Ritanserin in Alcoholism Work Group

Ritanserin, a long-acting specific 5-HT2 receptor antagonist, revealed promising effects on alcohol intake behavior in both animal and preliminary human studies. To test its effectiveness in alcohol dependence this phase III clinical trial was initiated. In a placebo-controlled, randomized, double-blind international multicenter study 493 patients with moderate or severe alcohol dependence (DSM-III-R) were treated with three doses of ritanserin 2.5 mg/day (n = 122), 5 mg/day (n = 123), 10 mg/day (n = 126), or placebo (n = 122) over a period of 6 months. Ritanserin was well tolerated. The most frequent adverse experiences were headache and insomnia. A small increase in weight in the ritanserin-treated patients was observed. There were no significant differences between any dose of ritanserin and placebo in the relapse-rate, the time to relapse, craving for alcohol, or quantity and frequency of drinking after relapse. So far, neither ritanserin nor any other serotonergic medication has shown its specific effectiveness in relapse prevention in alcohol dependence.

Research strategies to assess pharmacotherapies for alcoholism

1. The development and implementation of standardized basic and clinical research strategies is necessary for the discovery and testing of new and effective pharmacotherapies for alcohol dependence. While many animal studies have indicated the involvement of central serotonin, endogenous opioids and dopamine, their exact mechanisms of action have not been fully discerned. One problem is the use of various animal models, making it difficult to compare or replicate results from different laboratories. 2. Once a drug appears to decrease alcohol intake in animals, assessing its effects in humans can be even more challenging. 3. Most drugs were developed and may be even registered for another indication, so Phase I trials must be repeated in heavy alcohol users in case the drug has behavioural, pharmacokinetic or pharmacodynamic interactions with alcohol. 4. Phase II trials, assessing the effects of the drug on alcohol intake, are usually radically different from the animal models: most are long (> 6 months), use varied designs, and accept only abstinence as successful outcome. Moderately dependent alcoholics, who comprise the majority of patients, prefer a goal of nonhazardous drinking. 5. In Phase III multicentre trials, especially international ones, it is almost impossible to control for potentially confounding variables, such as patient characteristics and concomitant psychosocial treatment. 6. Also, research in pharmacotherapies for alcoholism is influenced by external factors such as sources of funding and other resources. Thus, this methodical progression from Phase I to Phase III clinical trials is often abbreviated. 7. The authors developed a brief early Phase II clinical paradigm to assess pharmacotherapies for moderately dependent alcoholics, and conducted 3 studies with the serotonin uptake inhibitors, citalopram and fluoxetine, and a serotonin antagonist, ritanserin. This paradigm, which includes a short (1 to 2 weeks) outpatient phase and two experimental drinking sessions, measures alcohol intake, desire to drink, alcohol's subjective effects, and intoxication. While it may have limited relevance to a goal of abstinence, it is efficient and economical to screen drug effects on alcohol intake and suggest mechanisms (desire to drink, subjective effects). It is also the only human model concordant with results in animals. 8. Development of new pharmacotherapies for alcoholism may benefit from acceptance of both abstinence and moderation of drinking as acceptable treatment goals.

Single-dose ritanserin and alcohol in healthy volunteers: a placebo-controlled trial

A double blind cross-over design trial was carried out to investigate the effect of simultaneous administration of alcohol (0.5 g/kg) and ritanserin (10 mg) on biological and behavioral functioning. Twenty healthy volunteers were selected to participate in the study. To assess the effect of treatments the following evaluations were performed: psychomotor tests, vital signs, intoxication, euphoria, and mood. In addition, ritanserin and alcohol plasma concentration were measured. Psychomotor performance and vital signs during the ritanserin session did not differ significantly from the placebo session. Similar results were obtained in regard to alcohol intoxication, euphoria, and mood, except for tiredness and alertness, which were significantly different compared to placebo. Differences in blood alcohol concentration between the ritanserin and the placebo sessions did not attain significance. Plasma ritanserin concentration was 143 ng/ml 1 h after alcohol administration and decayed to 53 ng/ml 6 h after alcohol consumption in the active treatment session. Our findings tend to indicate that ritanserin neither enhances the central nervous system depressant effect of alcohol nor produces a pharmacokinetic interaction during acute alcohol ingestion.

New drugs for the treatment of experimental alcoholism

This article presents a current overview of the efforts to suppress pharmacologically the craving, dependence, or other factors associated with the self-selection of alcohol in an experimental animal. The contemporary status of the pharmacotherapy of experimental alcoholism similarly is described for different animal models of alcohol drinking. An evaluation is presented of several classes of drug for their efficacy in ameliorating the volitional ingestion of alcohol in the presence of an alternative fluid. Currently, two main experimental animal models of alcoholism are being used in this endeavor: (a) genetic lines or substrains of high alcohol preferring or high drinking rats; and (b) strains of nondrinking or low alcohol preferring rats which are induced chemically to prefer alcohol. Because of technical, methodological, and other issues surrounding the procedures used to assess the efficacy of a drug in reducing alcohol intake, several of the newer findings remain controversial. For example, serious side effects on the intake of food, caloric regulation, motor activity, or other functions would preclude the clinical utility of the drug. However, several drugs which affect monoaminergic neurons as well as opioid systems in the brain now seem to offer promise as agents which do possess clinical benefits. Two of these drugs, FG5606 (amperozide) and FG 5893 are essentially "antialcoholic" or anticraving and are without any significant side effects on cerebral mechanisms responsible for hunger, caloric intake, motor activity, or other physiological process. Amperozide, a 5-HT2 receptor antagonist with dopamine releasing properties, is particularly notable because of its irreversible nature in attenuating alcohol preference for months after its administration. It is concluded that future pharmacological research on presently available and newly developed compounds will provide exciting opportunities to the clinician who can utilize a particular drug as an adjunctive tool in the therapeutic treatment of the alcoholic individual.

Ritanserin and voluntary alcohol intake in rats

In a previous study (Rammsayer & Vogel, 1991), rats selectively bred for high and low catecholamine responses to stress showed a selective response to the 5-HT2 receptor blocker ritanserin. However, it remained unclear whether selective breeding resulted in a decrease in 5-HT responsivity, as suggested by the lack of an effect in high stress responding rats, or in an increase in 5-HT responsivity, as suggested by ritanserin-induced reduction in alcohol intake in low-responding rats. To answer this question, nonselectively bred rats were forced to drink a 5% alcohol solution for 10 days. For the subsequent six days, animals were injected subcutaneously with 2.5 mg/kg/2 ml ritanserin or vehicle only, and both a 5% solution of alcohol and water were presented to the animals. Ritanserin neither affected alcohol nor total fluid intake suggesting that in the general population of N/NIH (Hansen) rats as well as in rats of the same strain selectively bred for high catecholamine responses, mesolimbic dopaminergic activity is not effectively modulated by specific blockade of 5-HT2 receptors. However, a very pronounced ritanserin induced difference in daily water intake between nonbred male and female rats became evident.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Influence of the 5-HT1A receptor agonist ipsapirone on voluntary alcohol intake in rats

The effect of the azapirone derivative ipsapirone on anxiety and the free-choice consumption of alcohol was studied in male rats. Animals were housed three in a cage with a different composition each day to increase anxiety. The animals were offered a two-bottle free choice consumption of tap water or a 5% ethanol solution. Ipsapirone was given in the drinking fluid daily at about 10 mg/kg per day. As expected, social unstable groups exhibited a higher level of anxiety as compared to social stable groups. Ipsapirone reduced significantly the anxiety in the unstable group. Pretreatment with ipsapirone before alcohol exposure resulted in a marked decrease of subsequent ethanol intake by about 45% as compared to drug free control animals. Administration of the drug to rats already drinking alcohol showed a similar decrease of ethanol intake by about 50%. These results indicate that the relatively specific 5-HT1A receptor agonist ipsapirone, given orally, reduces anxiety as well as alcohol initiation or maintenance in rats.

Suppression of alcohol consumption by fenfluramine in Fawn-Hooded rats with serotonin dysfunction

The high preference for alcohol intake observed in Fawn-Hooded rats has been attributed to the central serotonin (5-HT) dysfunction in this strain. To further characterize the involvement of 5-HT in alcohol-seeking behavior in Fawn-Hooded rats, the effect of both acute and subchronic administration of fenfluramine, a 5-HT releaser, on alcohol intake and preference was determined. Rats were individually housed and provided free access to a solution of 10% alcohol, food, and water. After establishing a stable baseline, rats were injected twice daily for 1 day or for 5 consecutive days either with saline or 0.1, 0.25, 0.5, and 1.0 mg/kg of fenfluramine at 0930 h and 1600 h, and their consumption of alcohol, food, and water was measured for 24 h. Another group of rats scheduled with a limited access (1 h/day) to alcohol and free access to food and water were injected with either saline or 0.25, 0.5, 0.75, and 1.0 mg/kg fenfluramine 20 min before exposure to alcohol, and their alcohol consumption was measured at the end of 1 h exposure. Further, to determine the effect of fenfluramine on alcohol metabolism, rats were injected with 1.0 mg/kg fenfluramine or saline and 15 min later with 2.5 g/kg alcohol (16%, v/v). Blood alcohol levels were then measured at 1, 3, and 5 h after alcohol administration. Our results demonstrate that both acute and subchronic administration of fenfluramine dose-dependently attenuate alcohol intake and increased water intake without a significant effect on food intake. Fenfluramine did not affect the pharmacokinetics of alcohol, indicating a central effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the action of the 5-HT2 antagonists amperozide and trazodone on preference for alcohol in rats

Previous studies in the rat demonstrated that the 5-hydroxytryptamine2 (5-HT2) antagonist amperozide attenuates the volitional intake of both alcohol and cocaine solutions in a free-choice situation. However, another 5-HT2 antagonist, ritanserin, has not been found to reduce alcohol drinking consistently in the rat. In this study, trazodone was compared to amperozide for its effect on the volitional consumption of alcohol because, like amperozide, trazodone is a potent 5-HT2 receptor antagonist but a weak inhibitor of 5-HT reuptake. Male Sprague-Dawley rats were induced to drink alcohol by 10 mg/kg cyanamide injected for 3 days b.i.d. One week later the rats were offered a choice of water and increasing concentrations of alcohol solutions ranging from 3% to 30% v/v in a three-bottle two-choice paradigm. After the concentration of alcohol that produced maximal daily intake was determined for each rat, trazodone or amperozide was injected b.i.d. SC in doses of 1.0 mg/kg or 2.5 mg/kg for three days. Whereas the higher dose of amperozide produced a significant, 55.6% decrease from pretreatment baseline of alcohol intake, trazodone did not alter alcohol preference at either the 1.0- or 2.5-mg/kg dose. These results are discussed in terms of whether the antagonism of 5-HT2 receptors by amperozide is critical to its attenuating effect on preference for alcohol solutions.

Addiction and the potential for therapeutic drug development

Therapeutic drug development in alcoholism could be targeted at any of the following: direct antagonism, substitution, treatment of abstinence, enhancement of aversion, modification of biodisposition, or craving. Ritanserin is a potent, centrally acting, highly selective 5-HT1C/2 antagonist which, in addition to having a sleep-regulating and anti-depression/anti-axiety effect, displays a unique pharmacological action in several animal paradigms of substance abuse which assess drug-craving. In fact, the latter pharmacological action was demonstrated after initial clinical observations suggested an effect of ritanserin in the chronic withdrawal phase after detoxification from alcohol in patients. The results of a recent double-blind, placebo-controlled, trial indicated that ritanserin did not induce aversion to drink alcohol in normal volunteers who display social drinking, but are not suffering alcohol dependence. Currently, a full clinical development program of ritanserin in cocaine and alcohol abuse is ongoing. Three major double-blind, placebo-controlled trials in alcohol dependent patients are in progress. Patients of different severity levels, ranging from mild to very severe, are studied. The dosages of ritanserin tested (2.5 mg, 5 mg, and 10 mg o.d.) are known to be well tolerated and safe. Two trials aim for relapse prevention--clinically defined in one, biochemically defined in the other-, and one trial has improved (reduced) drinking behaviour as a therapeutic goal. This program, which involves close to 900 alcohol-dependent patients, is well under way, and is still picking up momentum.

The nucleus accumbens is a site of action for the inhibitory effect of ritanserin on ethanol intake in rats

The present study evaluated the effect of central injections of the 5-HT2/1C receptor antagonist, ritanserin, on ethanol intake in rats with developed preference for 3% ethanol. Intracerebroventricular (ICV) injections of ritanserin (10 micrograms/rat/day for 10 days) decreased ethanol preference, while subcutaneous (SC) treatment with the same dose was ineffective. Ritanserin ICV, 1 microgram/rat/day, did not reduce alcohol preference. Bilateral injections of ritanserin into the nucleus accumbens (NAC; 0.5 microgram/site/day for 10 days) produced a prompt and very pronounced suppression of ethanol preference, without affecting total fluid intake. Bilateral injections of ritanserin (0.5 microgram/site/day for 10 days) into the ventral tegmental area (VTA) or into the medial prefrontal cortex (MPC) evoked only slight and variable reduction of ethanol preference. Injections of ritanserin, 5 micrograms/site/day, into the VTA gave a nonselective suppression of the ingestive behavior. The present results provide evidence for a central site of action for the effect of ritanserin on ethanol intake and suggest that the NAC might be a highly sensitive site for its action. Since the NAC is a major target of the mesolimbic dopaminergic system, they also suggest that the effect of ritanserin might be due to interference with this system.

Failure of the 5-HT2 receptor antagonist, ritanserin, to alter preference for alcohol in drinking rats

The purpose of this study was to determine whether the 5-HT2 receptor antagonist, ritanserin, possesses the same sort of efficacy as another central 5-HT2 antagonist, amperozide, in reducing the pharmacologically induced preference for ethyl alcohol in the rat. Following the repeated administration of the inhibitor of aldehyde dehydrogenase, cyanamide, the preference for alcohol vs. water was determined in each of 20 Sprague-Dawley rats by a standard test using 3-30% concentrations. Then, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 9-15% and was consumed at a mean of 5.02 +/- 0.44 g/kg per day. After a 4-day predrug control test, either the saline control solution or 0.1, 0.3, or 1.0 mg/kg ritanserin was administered SC at 1600 h over 3 days. The daily intakes of alcohol of rats both during and after treatment with ritanserin were unchanged in terms of absolute g/kg and proportion of alcohol to total fluid consumed. Similarly, the control saline also was without any effect on alcohol consumption. Neither the consumption of food and total fluids nor the level of body weight was affected by these doses of ritanserin. Because our findings fail to coincide with previous reports on the effect of ritanserin on alcohol preference, it is envisaged that a methodological difference in earlier experimental procedures, such as the use of a weak 3% concentration of alcohol, could explain the discrepancy. Further, the present results contrast with the prolonged reduction in drinking produced by another 5-HT2 receptor antagonist, amperozide, which also acts centrally on dopaminergic neurons in the limbic system.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of disulfiram administration on brain tryptophan, serotonin and peripheral tryptophan content

The prophylactic deterrent effect of disulfiram (DS) has been attributed to its ability to exacerbate sympathetic function. Though there are reports to indicate that DS administration could as well affect the neurotransmitter metabolism, few reports implicate the possibility of central nervous system (CNS) mediated anticraving effect of the drug. The present study involving the oral administration of DS to rats for 45 days has clearly shown a significant increase in 5-HT (815.4 +/- 74.7 ng/g, P < 0.01) and 5-HIAA (506.1 +/- 86.3 ng/g, P < 0.02) contents in brain when compared to control rats. The observed increase in 5-HT and 5-HIAA content was found to correlate (zeta = 0.89) with the concomitant increase in brain tryptophan content (4.15 +/- 1.05 nmol/g, P < 0.001) following DS administration. Further, the study on peripheral tryptophan content has shown an increase in both total and free fraction (ultrafiltrate) of plasma, which in turn was found to have an inverse relationship (zeta = -0.94, P < 0.05) with the decrease in liver tryptophan content following DS administration. Thus the observed increase in brain 5-HT level is attributed to the ability of DS to mobilise peripheral tryptophan for 5-HT synthesis in CNS. As there are reports to imply the hyposerotonergic function as responsible for craving, the present findings, that DS could enhance the 5-HT metabolism in brain, may partially explain the CNS mediated anticraving effect of DS.