Selective reduction by the 5-HT antagonist amperozide of alcohol preference induced in rats by systemic cyanamide

Involvement of local serotonin-2A but not serotonin-1B receptors in the reinforcing effects of ethanol within the posterior ventral tegmental area of female Wistar rats

RATIONALE

Previous studies indicated that ethanol could be self-infused into the posterior ventral tegmental area (p-VTA) and that activation of local serotonin-3 (5-HT(3)) receptors was involved. 5-HT(1B) and 5-HT(2A) receptors are involved in the effects of 5-HT and ethanol on VTA dopamine neurons.

OBJECTIVE

The current study used the intracranial self-administration (ICSA) procedure to determine the involvement of local 5-HT(1B) and 5-HT(2A) receptors in the self-infusion of ethanol into the p-VTA.

MATERIALS AND METHODS

Female Wistar rats were implanted unilaterally with a guide cannula aimed at the p-VTA. Seven days after surgery, rats were placed into the two-lever operant conditioning chambers for ICSA tests. The tests consisted of four acquisition sessions with self-infusion of 200 mg% ethanol alone, two or three sessions with co-infusion of the 5-HT(1B) antagonist GR 55562 (10, 100, or 200 microM) or the 5-HT(2A) antagonist R-96544 (10, 100, or 200 microM) with 200 mg% ethanol, and one final session with 200 mg% ethanol alone.

RESULTS

During the acquisition sessions, all rats readily self-infused ethanol and discriminated the active from inactive lever. Co-infusion of GR 55562, at all three doses, had no effect on the self-infusion of ethanol. In contrast, co-infusion of R-96544, at the two higher doses, attenuated responding on the active lever for ethanol infusion (p < 0.05).

CONCLUSION

The results suggest that the reinforcing effects of ethanol within the p-VTA are modulated, at least in part, by activation of local 5-HT(2A), but not 5-HT(1B), receptors.

Update on neuropharmacological treatments for alcoholism: scientific basis and clinical findings

The past decade has seen an expansion of research and knowledge on pharmacotherapy for the treatment of alcohol dependence. The Food and Drug Administration (FDA)-approved medications naltrexone and acamprosate have shown mixed results in clinical trials. Oral naltrexone and naltrexone depot formulations have generally demonstrated efficacy at treating alcohol dependence, but their treatment effect size is small, and more research is needed to compare the effects of different doses on drinking outcome. Acamprosate has demonstrated efficacy for treating alcohol dependence in European trials, but with a small effect size. In U.S. trials, acamprosate has not proved to be efficacious. Research continues to explore which types of alcohol-dependent individual would benefit the most from treatment with naltrexone or acamprosate. The combination of the two medications demonstrated efficacy for treating alcohol dependence in one European study but not in a multi-site U.S. study. Another FDA-approved medication, disulfiram, is an aversive agent that does not diminish craving for alcohol. Disulfiram is most effective when given to those who are highly compliant or who are receiving their medication under supervision. Of the non-approved medications, topiramate is among the most promising, with a medium effect size in clinical trials. Another promising medication, baclofen, has shown efficacy in small trials. Serotonergic agents such as selective serotonin reuptake inhibitors and the serotonin-3 receptor antagonist, ondansetron, appear to be efficacious only among certain genetic subtypes of alcoholic. As neuroscientific research progresses, other promising medications, as well as medication combinations, for treating alcohol dependence continue to be explored.

Role of the serotonergic system in the neurobiology of alcoholism: implications for treatment

Preclinical studies have contributed greatly to our understanding of the neurochemical pathways associated with the development and maintenance of alcohol-seeking behaviour. These studies have demonstrated the important role of serotonin pathways, particularly as they relate to dopaminergic function, which mediates alcohol-induced reward associated with its abuse liability. Naturally, this has led to the study of serotonergic agents as treatments for alcoholism.SSRIs do not appear to be effective treatment for a heterogeneous alcoholic group. However, they may be useful as treatment for late-onset alcoholics, or alcoholism complicated by comorbid major depression. Buspirone, a serotonin 5-HT1A partial agonist, does not appear to be an effective treatment for alcoholics without comorbid disease. Buspirone may, however, have some utility for treating alcoholics with comorbid anxiety disorder. The 5-HT2 antagonist ritanserin, at pharmacologically relevant clinical doses, does not appear to be an effective treatment for alcoholism. Ondansetron, a 5-HT3 antagonist, is an efficacious and promising medication for the treatment of early-onset alcoholism. Preliminary evidence suggests that combining the mu antagonist naltrexone with the 5-HT3 antagonist ondansetron promises to be more effective for treating alcoholism than either alone. The differential treatment effect of SSRIs and ondansetron among various subtypes of alcoholic is intriguing. Future research is needed to understand more clearly the molecular genetic differences and the interactions of such differences with the environment that typify a particular alcoholic subtype. Such an understanding could enable us to make comfortable predictions as to which alcoholic subtype might respond best to a particular serotonergic agent, which could then be provided.

Effects of cocaine and putative atypical antipsychotics on rat social behavior: an ethopharmacological study

The effects of cocaine, amperozide, clozapine, olanzapine and cocaine/atypical antipsychotic combinations on aggression, affiliation and defensive behaviors was examined. Acute cocaine (30.0 mg/kg) decreased basal aggression and affiliation yet increased basal defense. Amperozide (1.0, 3.0 and 5.0 mg/kg) decreased basal aggression, affiliation and defense had no effect on the cocaine-induced decrease in affiliation, and accentuated the cocaine-induced decrease in aggression. Near basal levels of defense were observed for animals treated with either amperozide, clozapine (3.0 and 10.0 mg/kg but not 30.0 mg/kg) or olanzapine followed by cocaine. Clozapine (3.0, 10.0 and 30.0 mg/kg) decreased basal aggression and affiliation. Clozapine (30.0 mg/kg but not 3.0 or 10.0 mg/kg) decreased basal defense. Clozapine attenuated the cocaine-induced decrease in aggression. Although 3.0 and 10.0 mg/kg clozapine attenuated the cocaine-induced decrease in affiliation, 30.0 mg/kg clozapine accentuated this cocaine-induced effect. Olanzapine (1.0, 3.0 and 10.0 mg/kg) decreased basal aggression, affiliation and defense. Olanzapine had no effect on the cocaine-induced decrease in aggression. Olanzapine (3.0 mg/kg but not 1.0 or 10.0 mg/kg) attenuated the cocaine-induced decrease in affiliation. Thus, acute cocaine administration had an antiaggressive effect, suppressed affiliative behavior and enhanced defensive behavior. Amperozide, clozapine and olanzapine have anticonflict and anxiolytic effects, as well as potent and specific antiaggressive effects.

Amperozide influences feeding independently of 5-HT2A receptor antagonism

Amperozide has been biochemically classified as a selective 5-HT2A (serotonin type 2A) receptor antagonist. However, research on the behavioral effects of amperozide suggests the possibility of other mechanisms. The present study in the male rat is an investigation of the effect of amperozide on feeding, a behavior which can be inhibited by 5-HT2A agonists such as 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Experiments revealed that amperozide acted to inhibit feeding behavior both when administered alone and when administered in combination with DOI. These results are inconsistent with 5-HT2A receptor antagonism by amperozide. Further experiments suggested that amperozide may be acting via alpha 2-adrenergic or 5-HT1A receptors to inhibit feeding. These studies imply that amperozide's selective 5-HT2A antagonistic activity is behaviorally specific.

The effects of amperozide on cocaine-induced social withdrawal in rats

Cocaine decreases social interactions in both humans and animals, but it is not known whether the drugged animal withdraws from an undrugged conspecific, the undrugged conspecific avoids the drugged animal, or a combination of these two factors occurs. In the first experiment, the source of cocaine-induced social withdrawal was determined using a tether paradigm, in which the movement of one of the rats was restricted to one half of the observation chamber, such that the freely moving rat had the option of escaping social interactions. There were decreases in social interactions in the condition in which both rats were freely moving, and in the condition in which the undrugged rat was tethered, but not when the drugged rat was tethered and could not escape social contact. A second experiment was conducted to test the efficacy of the potent serotonin receptor antagonist, amperozide, in attenuating cocaine-induced social withdrawal using the condition in which the drugged rat was freely moving. Either amperozide (1.0, 3.0, and 5.0 mg/kg) or saline vehicle was injected into rats 1 h before receiving a 30.0 mg/kg cocaine dose. Cocaine decreased social interactions. Amperozide restored social interactions to near control levels and elevated social interactions in the animals treated with saline vehicle.

The cardiovascular effects of amperozide: interactions with cocaine

Amperozide is a 5-HT2A receptor antagonist that significantly reduces the acquisition and expression, by rats, of a cocaine conditioned place preference. In order to rule out the possibility that amperozide affects a cocaine conditioned place preference due to effects on blood pressure or heart rate, the cardiovascular effects of amperozide were investigated. Alternating cumulative doses of amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) or saline and phenylephrine (8 microg kg(-1)) were administered through the femoral vein of awake freely-moving Sprague-Dawley rats and blood pressure and heart rate were recorded from the femoral artery. A single dose of cocaine (5.0 mg kg(-1)) was administered after all the amperozide or saline doses were given. Amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) did not have any significant effect on blood pressure compared to the saline control treatment to the same animals. However, 0.5 mg kg(-1) amperozide significantly decreased heart rate at 5 and 10 min. after administration. but higher doses did not further depress heart rate. Amperozide did not affect the increased blood pressure and decreased heart rate caused by phenylephrine. an alpha1-adrenoceptor agonist. In addition, amperozide did not affect the cardiovascular response to an intravenous dose of 5.0 mg kg(-1) cocaine. These results suggest that amperozide does not cause direct cardiovascular effects. The mechanism by which the lowest dose of amperozide caused a decrease in heart rate is unknown. Amperozide affects neither alpha-adrenoceptor mediated vasoconstriction nor the increased sympathetic activity caused by the peripheral and central effects of cocaine. The significance of these results, in terms of locomotor activity and the cocaine conditioned place preference paradigm, is discussed.

Interaction of the novel antipsychotic drug amperozide and its metabolite FG5620 with central nervous system receptors and monoamine uptake sites: relation to behavioral and clinical effects

Behavioral, biochemical, and electrophysiological studies suggest that amperozide affects mesolimbic and mesocortical dopamine neurotransmission. The receptor binding profile of amperozide is discussed and related to behavioral and clinical, i.e., antipsychotic, effects of the drug. As previously reported, amperozide displayed high affinity for serotonin 5-HT2A receptors (Ki = 16 nmol/L), and moderate affinity for striatal dopamine D2 (Ki = 540 nmol/L) and cortical alpha 1-adrenergic receptors (Ki = 172 nmol/L). In the present study amperozide displayed low affinity for several serotonin receptor subtypes as well as for the dopamine D4 receptor transfected in COS7 cells (Ki D4.2 = 769 nmol/L and Ki D4.4 = 384 nmol/L). Amperozide was very weak or did not interact with several other receptor species including adrenergic, histaminergic, muscarinic, benzodiazepine, gamma-aminobutyric acid, amino acid, opiate, and Ca channels; however, amperozide was found to compete for [3H]paroxetine binding for the serotonin transporter in the nanomolar range (Ki = 49 nmol/L). In vitro and in vivo binding potency of amperozide correlates best with behavioral effects, indicating 5-HT2A antagonism, although serotonin uptake inhibition may contribute to the effects of amperozide on dopamine neurotransmission. The metabolite of amperozide, FG5620, displayed 5-10 times lower pharmacologic activity than amperozide. These properties of amperozide may suggest that the antipsychotic effects of amperozide are mediated by 5-HT2A receptors, although 5-HT uptake inhibition and alpha 1-adrenergic receptor-mediated effects may be considered, particularly at higher doses.

Odor of specific alcohol solutions selectively alters locomotor activity of alcohol-drinking P rats

Evidence exists that the olfactory property of alcohol affects cerebral processes to influence the pattern of alcohol drinking in an experimental animal. In this study, the level of activity was quantified in the genetically selected alcohol-preferring P rats during exposure to the odor of 4 concentrations of alcohol. A Mini-Mitter transmitter was implanted intraperitoneally in each animal to record individual locomotor activity continuously, in terms of counts per unit time. In the first experiment, each rat was exposed between 1730 and 1930 h to the odor of 5%, 15%, 30%, or 60% alcohol placed in 2 petri dishes flanking both sides of each cage. The control condition was identical, except that the petri dishes were empty. In the second experiment, each rat was offered water and its individually preferred solution of alcohol in the drinking tubes during 1730 to 1930 h on alternate days of exposure to the odor of alcohol. During the odor condition alone, the 30% concentration of alcohol increased the activity counts significantly from the control level of 228.8 +/- 23.9 to 303.5 +/- 28.1 over the first 30 min of the 2-h test period. Plots of activity every 30 min for each alcohol solution, calculated as percent of control, also showed that the odor of 30% alcohol evoked significantly greater activity during the first and fourth intervals, in contrast to the exposure to 5%, 15%, and 60% alcohol, which failed to shift activity beyond the control level. When the P rats were exposed to 30% alcohol 24 h after 2 h of alcohol drinking, their profile of activity was concordant with that prior to alcohol drinking. These results demonstrate that the odor of a specific concentration of alcohol (i.e., 30%) selectively enhances the activity of the P rat. This could reflect an association of the sensory quality of alcohol with an anticipation of drinking. Finally, these experiments provide the first quantitative evidence that an olfactory cue associated with the unique odor of a specific solution of alcohol may determine the nature of the drinking response.

The mixed 5-HT 1A/2A receptor drug FG5938 suppresses alcohol drinking while enhancing feeding in P rats

The neurotransmitter serotonin (5-HT) has long been implicated in the etiology of aberrant consumption of alcohol. Several compounds thought to possess a potential therapeutic value to counteract drinking have high affinities for 5-HT1A and 5-HT2A receptors in the brain. For example, amperozide and FG5865 significantly reduce the volitional intake of alcohol, without altering food intake, both in rats genetically predisposed or chemically induced to drink alcohol. The present study was undertaken in the alcohol-preferring (P) rat to determine whether an amperozide like drug. FG5938 (1-[4-(p-fluorophenyl)butyl]-4-(6-methyl-2-pyridinyl)-piperazine fumarate). exerts an action on the volitional drinking of alcohol as well as on the intakes of food and water. In 11 male P rats, the pattern of preference for different concentrations of alcohol was determined by an 11-day test for water vs. 3 to 30% alcohol solutions. After maximally preferred alcohol concentrations, i.e., 9 to 15% had stabilized for 4 days, saline or FG5938 was injected subcutaneously at 1600 and 2200 h in a dose of 2.5, 5.0, or 10.0 mg/kg over 4 consecutive days. Following treatment, preference testing for the same concentrations of alcohol was continued for 5 additional days. FG5938 caused a significant suppression in alcohol drinking in terms of both absolute g/kg and proportion to total fluid intake. During its administration, FG5938 also enhanced the ingestion of food and water of the P animals significantly, with the largest intake occurring on the initial day, while body weights increased. After FG5938 injections, food and water intakes returned to predrug levels. The saline control vehicle had no significant effect on the intakes of alcohol, food, or water of the P rats. Overall, these results show that FG5938 acts to attenuate alcohol preference while simultaneously increasing the ingestion of food paradoxically. To our knowledge, this is the first known drug to possess this unique property. Finally, these findings support the view that a compound having affinities to both 5-HT1A and 5-HT2A receptors may be useful as a therapeutic agent in the treatment of alcoholism.

Differential efficacy of serotonergic drugs FG5974, FG5893, and amperozide in reducing alcohol drinking in P rats

Amperozide (FG5606), a 5-HT2 receptor antagonist, is well known to suppress alcohol consumption in different rat models of drinking. The present study compared the efficacy of three drugs, FG5974, FG5893, and amperozide, which have differential affinities for 5-HT1A and 5-HT2A receptors, on alcohol drinking in the genetic alcohol-preferring (P) rat. After preference for alcohol vs. water was determined over 10 days when concentrations of alcohol were increased from 3% to 30%, the maximal concentration of alcohol preferred by each animal was selected for drug testing. A 4-day predrug preference test was followed by SC injection of the saline control vehicle or doses of 1.0 and 2.5 mg/kg FG5974, FG5893, or amperozide given at 1600 and 2200 h for 4 days. Alcohol preference testing concluded with a final 4-day interval. A total daily dose of 5.0 mg/kg FG5974 reduced absolute g/kg intake of alcohol and proportional intakes of the P rats significantly; the lower dose of FG5974 also reduced alcohol drinking significantly following treatment. The mixed 5-HT1A agonist/5-HT2A antagonist, FG5893, which suppresses drinking in cyanamide-treated rats, was without effect on alcohol ingested by the P rats. However, amperozide caused a dose-dependent decline in both absolute intakes and proportion of alcohol that was more intense than that of FG5974. The control vehicle failed to alter alcohol drinking and, like the FG compounds, did not affect food intake or body weight. Although the inhibition of alcohol drinking by amperozide corresponds precisely with previous findings, the effect of FG5974 contrasts to results obtained with a structurally analogous drug FG5893. Thus, the genetic strain of rat as well as the nature of the chemical characteristics of a 5-HT agonist/antagonist will determine the differential efficacy of a drug in influencing the volitional drinking of alcohol.

Opiate and 5-HT2A receptors in alcohol drinking: preference in HAD rats is inhibited by combination treatment with naltrexone and amperozide

Amperozide, a 5-HT2A receptor antagonist, and naltrexone, an opiate receptor antagonist, have been shown to suppress volitional drinking of alcohol in experimental animals. The present study examined the effects of the concurrent administration of both drugs on the volitional intake of alcohol in the selectively bred, high alcohol drinking (HAD) rat. Individual preferences for alcohol were determined by a standard 10-day test in which alcohol concentrations were increased from 3% to 30%. Following a 4-day predrug test during which water together with a maximally preferred concentration of 7% to 20% was offered to each HAD rat, amperozide and naltrexone were injected SC over a second 4-day period as follows: 1) amperozide at 1600 h and naltrexone at 2200 h; 2) the same drugs but in reversed temporal order; and 3) amperozide and naltrexone administered simultaneously at 1600 and 2200 h. Thereafter, alcohol preference testing continued for a third 4-day period. The alternate delivery of both drugs attenuated significantly the absolute g/kg and proportional intakes of alcohol in the HAD rats, whereas the saline vehicle was without effect. Although the simultaneous administration of naltrexone and amperozide produced an even greater decline in alcohol intake, without side effects on food and water intakes or on body weight, some residual drinking of alcohol persisted. Nevertheless, the results corroborate our previous findings on the suppression of alcohol drinking by antagonists of opiate and 5-HT2A receptors. Because amperozide and naltrexone together reduce the apparent reinforcing property of alcohol, the theory is supported that the addictive liability to alcohol is underpined by multiple receptor subtypes within the mesolimbic and other systems in the brain.

Synthesis of dopamine and 5-HT in anatomical regions of the rat's brain is unaffected by sustained infusion of amperozide

The 5-HT2A antagonist, amperozide, is considered to be a potentially useful drug for the treatment of substance abuse. The effects of this drug on the Sprague-Dawley rat were examined on the synthesis of dopamine and serotonin (5-HT) as well as on the intakes of food and water and the level of body weight. Amperozide was delivered subcutaneously by osmotic minipump in doses of 2.5 mg/kg or 5.0 mg/kg per day for 7 days. After injection of 100 mg/kg NSD-1015, each brain was dissected post mortem into midbrain, pons, hypothalamus, septum, nucleus accumbens, striatum, frontal cortex and the hippocampus. Neither concentration of amperozide altered the synthesis of dopamine or 5-HT, as measured in terms of the formation of 1-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP), respectively, in any of the 8 brain regions analyzed. Both doses of amperozide reduced food intake by 20% within 24 hr after implantation of the pumps, but feeding resumed postoperatively at the control level within 48 hr. Amperozide affected neither the intake of water nor the level of body weight. The lack of effect on the synthesis of dopamine and 5-HT and the absence of side effects on the intakes of food and water suggest that amperozide may be a specific agent for suppressing alcohol drinking.

Tomato juice, chocolate drink, and other fluids suppress volitional drinking of alcohol in the female Syrian golden hamster

Although the hamster generally prefers alcohol at a level similar to that of the rat or mouse selectively bred to consume alcohol, the drinking hamster demonstrates neither physical dependence on alcohol nor elevated blood levels of alcohol, which are two typical criteria characterizing an animal model of alcoholism. The present investigation was designed to determine whether a third criterion of an animal model (i.e., consumption of high levels of alcohol in the presence of a palatable fluid, fulfilled by the P rat) would be met by the female Syrian golden hamster (Mesocricetus auratus). A standard 3-bottle preference test was undertaken in 6 female hamsters over an 11 day period, in which water was presented in one tube and, in a second tube, a v/v solution of alcohol which was increased in concentration from 3% to 50% on each day as follows: 3%, 5%, 7%, 9%, 12%, 15%, 20%, 25%, 30%, 40%, and 50%. Then each hamster was offered its individually determined, maximally preferred concentration of alcohol for 4-8 days, which was 20%, 25%, or 30% alcohol. The mean absolute intake of alcohol during this period was 17.9 +/- 1.1 g/kg per day, whereas the mean proportion of alcohol to total fluid was 0.68 +/- 0.05. Then over a 4-day interval, a solution of tomato juice, peach juice, mango juice, dextrose and a chocolate beverage (Ensure Plus), all made isocaloric to the alcohol solutions with dextrose, was placed in the third tube simultaneously with water and the individually preferred concentration of alcohol.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective serotonin reuptake inhibitors: effects of chronic treatment on ethanol-reinforced behavior in mice

Several lines of evidence suggest that aspects of ethanol drinking are mediated, at least in part, by serotonergic (5-HT) neurotransmitter systems. Ethanol-preferring animals show decreases in serotonin function and receptor densities. In addition, serotonin uptake inhibitors have been shown to decrease ethanol consumption in animal models and in humans. However, the time course of these effects and their duration remain undetermined. In the present studies, C57BL/6J male mice were treated with one of three selective 5-HT reuptake inhibitors (SSRIs): fluoxetine, sertraline, or paroxetine. All three drugs produced initial decreases in operant lever pressing behavior for ethanol followed by a return to baseline on subsequent days. Immediately following 14 days of this initial treatment, subsequent treatment with higher SSRI doses was ineffective in decreasing ethanol-reinforced behavior. However, after a several week "washout period," SSRI pretreatment again produced an initial decrease in responding for ethanol, again followed by a return to baseline. Thus, suppression of ethanol drinking may be related to immediate changes in 5-HT function following treatment with SSRIs, and tolerance to this effect appears to develop rapidly.

Female Syrian golden hamster: drinking of high concentrations of ethanol aversive to other mammals

The present experiments were designed to determine: 1) the pattern of preference for different concentrations of ethanol in the female Syrian golden hamster (Mesocricetus auratus), and 2) the influence of drinking ethanol on their intakes of food and total calories. A standard three-bottle preference test was undertaken in six female hamsters over an 11-day period in which water was offered together with ethanol, which was increased in concentration over 11 days from 3% to 50% as follows: 3%, 5%, 7%, 9%, 12%, 15%, 20%, 25%, 30%, 40%, 50%. Then, each hamster was offered its individually preferred concentration for a period of 8 days until the intake of ethanol had stabilized. During the preference testing for 3-25% solutions, the proportional intakes ranged between 0.6 and 0.8 whereas the mean absolute amount consumed per day increased from 2.3 to 16.1 g/kg at the 25% concentration. However, at the 50% concentration, ethanol drinking declined substantially to 8.7 g/kg per day. The overall mean percent concentration of ethanol preferred by the hamsters was 24.2 +/- 1.5%. During the following 8-day period when the maximally preferred concentration of ethanol of each hamster was offered with water, the mean intake of ethanol was 17.9 +/- 1.1 g/kg per day. Throughout the test sequence, the caloric intake of the animals was maintained in that calories obtained from food declined at the same rate as the calories obtained from ethanol in rising concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

The abilities of 5-HT3 receptor antagonist ICS 205-930 to inhibit alcohol preference and withdrawal seizures in rats

Recent evidence suggests that central 5-HT3 are intimately involved in the ethanol (ETOH) dependence mechanism. In the present study we observed the effects of the 5-HT3 receptor antagonist ICS 205-930 on audiogenic seizure response (ASR) in ETOH-withdrawn rats and on ETOH intake and preference. Low doses of ICS 205-930 (0.001 mg/kg), but not higher doses (0.1 mg/kg), markedly reduced both ASR and ETOH intake in a high preference group of animals. The possible mechanism of different effects of low and high drug doses is discussed.

Amperozide, a 5-HT2 antagonist, attenuates craving for cocaine by rats

Amperozide, a novel 5-HT2 receptor antagonist with little affinity for the dopamine receptor, suppresses the intake of alcohol in rats without affecting food intake or inducing other side effects. Because of these actions, amperozide was examined for its efficacy on the oral preference by the rat for a solution of cocaine. In this study, rats were selected for their voluntary consumption of at least 10 mg/kg of cocaine per day in a two-choice paradigm. A solution of 0.02% to 0.06% cocaine plus 0.03% saccharin in water was offered to each animal simultaneously with a solution of only 0.03% saccharin in water. The consumption of food and both fluids, as well as body weight, was recorded daily for three successive periods: 4 days of pretreatment baseline; 3 days during injections of either amperozide or the saline vehicle solution; and 4 days postinjections. Amperozide was administered SC twice daily in a dose of 0.5, 1.0, or 2.5 mg/kg. The volitional intake of cocaine was significantly reduced not only during the 3-day period of injections of amperozide but also during the 4-day posttreatment period. Amperozide exerted little or no effect on the intake of food or on body weight. Radioligand binding experiments confirmed that amperozide has at least a twentyfold greater affinity for 5-HT2 receptors in the frontal cortex of the rat, as compared to striatal DA1 and DA2 receptors, with the proportion value similar to that of the 5-HT2 receptor antagonist, ritanserin.(ABSTRACT TRUNCATED AT 250 WORDS)

5-HT1A autoreceptor-mediated effects of the amperozide congeners, FG5865 and FG5893, on rat brain 5-hydroxytryptamine neurochemistry in vivo

The two diphenylbutylpiperazinepyridinyl derivatives, FG5865 and FG5893, have a unique receptor binding profile in that they show very high and essentially equipotent affinities for both 5-HT1A and 5-HT2 receptors. The present report describes the acute effects of FG5865 and FG5893 on presynaptic 5-hydroxytryptamine (5-HT) neuronal function in the rat CNS, using established ex vivo and in vivo neurochemical techniques. Post-mortem measurements of tissue levels of 5-HT, its metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and of the formation of 5-hydroxytryptophan (5-HTP; after inhibition of aromatic amino acid decarboxylase by NSD 1015) showed that FG5865 (0.1-20 mg/kg, s.c.) and FG5893 (0.1-20 mg/kg, s.c.) dose dependently decreased the synthesis and the metabolism/turnover of 5-HT--this to an extent comparable to the reference 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin. Reserpine (5 mg/kg, s.c.) pretreatment did not prevent the FG5893-induced decrease of 5-HT synthesis rate. In contrast, about 25-50 times higher doses of FG5865 were required to produce a comparable decrease in brain 5-HT synthesis in reserpinized vs. non-pretreated rats. In in vivo microdialysis experiments, both FG5865 (0.1-3.0 mg/kg, s.c.) and FG5893 (0.03-1.0 mg/kg, s.c.) caused a marked and dose-dependent decrease of 5-HT release in the ventral hippocampus. Pretreatment with the 5-HT1A receptor antagonist, (+/-)-pindolol (8 mg/kg, s.c.), abolished the FG5865 (0.3 mg/kg, s.c.)-induced reduction of 5-HT release, and (-)-pindolol (8 mg/kg, s.c.) similarly reversed the FG5893 (0.3 mg/kg, s.c.)-induced decrease. Local infusion of FG5865 into the ventral hippocampus (10 microM, 20-min pulse) resulted in a rapid and transient elevation of the 5-HT output, an effect that was independent of extracellular Ca2+. FG5893, on the other hand, did not affect the 5-HT release upon local administration. The results demonstrate that FG5865 and FG5893 potently affect a range of neurochemical indices of rat brain 5-HT neuronal activity in vivo, in a way consistent with indirect (FG5865) and direct (FG5865 and FG5893) stimulation of the 5-HT1A autoreceptors in the raphe nuclei.

5-HT2 receptor blockade by amperozide suppresses ethanol drinking in genetically preferring rats

Previously, it was shown that the unique diphenylbutylpiperazinecarboxamide derivative, amperozide (FG 5606), inhibits the volitional drinking of ethanol induced in the rat by the inhibitor of aldehyde dehydrogenase, cyanamide. In this study, the efficacy of this long-acting psychotropic agent and potent 5-hydroxytryptamine2 (5-HT2) receptor antagonist was examined in the genetic line of ethanol-preferring (P) and -nonpreferring (NP) rats. In both lines, the pattern of drinking of ethyl alcohol was determined by a standard preference test for 3-30% ethanol vs. water. Then, the maximally preferred concentration of ethanol was determined for each individual, which ranged from 9-15% for P rats and 9-13% for NP animals. After a 4-day predrug test, either the saline control vehicle or amperozide was administered SC b.i.d. at 1600 and 2200 h. The drug was given over a 3-day period in one of three doses: 0.5, 1.0, or 2.5 mg/kg. The intake of ethanol of P rats was reduced significantly in a dose-dependent manner in terms of both absolute g/kg and proportion of ethanol to water during injections of amperozide. The same doses of amperozide had no effect on the low intake of ethanol in NP rats. The saline control vehicle also did not alter the consumption of ethanol of P or NP rats. Further, neither the consumption of food nor level of body weight was affected by amperozide either during or after its administration. These results demonstrate that in the individual predisposed genetically to drink ethanol amperozide exerts a palliative effect on the aberrant preference for ethanol consumed in a pharmacologically significant amount. Presently, dopaminergic and serotonergic synapses in the brain are implicated in the genetic differences in the patterns of ethanol consumption that distinguish the P from the NP line of rats. Because amperozide influences the functional activity of both dopaminergic and serotonergic neurons in the mesolimbic system, it is envisaged that the drug attenuates ethanol drinking by way of its direct action on these neurons.

Sensitization to 5-HT1C receptor agonist in rats observed following withdrawal from chronic ethanol

Anxiogenic action of m-chlorophenylpiperazine (mCPP), a 5-HT1C receptor agonist, was studied in naive rats and in ethanol-tolerant rats following withdrawal from chronic ethanol administration. The purpose of this investigation was to determine whether a sensitization to mCPP develops during withdrawal from chronic ethanol. Male Long-Evans hooded rats were fed a liquid diet containing 4.5% ethanol or dextrin (as control) for four days. Twelve hours (acute withdrawal) or 4 days (protracted withdrawal) after the last dose of ethanol, rats were injected with saline or mCPP (0.08-5.0 mg/kg) and were tested in the elevated plus-maze 15 min postinjection. A reduction in percent open-arm activity, indicative of anxiogenic behavior, was observed in ethanol-treated rats injected with saline. Administration of mCPP further reduced the percent open-arm entries and time in ethanol-withdrawn rats. An eightfold reduction in maximum effective dose of mCPP was observed during acute ethanol withdrawal as compared to that in naive rats. During protracted ethanol withdrawal the maximum effective dose of mCPP was reduced by 75%. A shift of the mCPP dose-response curve to the left following withdrawal from chronic ethanol may indicate that 5-HT1C receptor sites are more sensitive to the activation by an agonist. This effect may be exploited in developing specific 5-HT1C receptor antagonists for the treatment of ethanol withdrawal symptoms.

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)

Alcohol drinking in rats is attenuated by the mixed 5-HT1 agonist/5-HT2 antagonist FG 5893

Over the last three decades, the neurotransmitter serotonin (5-HT) has been implicated in the etiological mechanisms underlying the excessive drinking of ethyl alcohol. Recently, the 5-HT2 antagonist amperozide was found to reduce selectively the high intake of alcohol in the cyanamide-induced drinking rat without any adverse side effects. The purpose of the present study was to determine the action on alcohol drinking of the novel second-generation amperozide-like drug, which is a mixed 5-HT1 agonist/5-HT2 antagonist, FG 5893 (2-[4-[4,4-bis(4-fluorophenyl)butyl]-1-piperazinyl]-3-pyridinecarb oxylic acid methyl ester). To induce preference for alcohol in Sprague-Dawley rats, the enzyme aldehyde dehydrogenase was inhibited by cyanamide administered in the absence of alcohol in a dose of 10 mg/kg twice a day over three days. A standard three-bottle preference test was used in which water and a maximally preferred concentration of alcohol were offered to each animal. Following control tests of alcohol preference for 3 days, either a saline control vehicle or FG 5893 in a dose of 0.5, 1.0, or 2.5 mg/kg was administered subcutaneously at 1600 and 2200 for 3 consecutive days. Whereas control injections of saline were without effect on alcohol consumption, all doses of FG 5893 significantly reduced the 24-h intake of alcohol in terms of both absolute g/kg and proportion of alcohol to total fluid intake. Further, the 1.0 and 2.5 mg/kg doses of FG 5893 continued to suppress alcohol consumption over two 4-day tests immediately following the injection sequence and after a 40-day interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Irreversible suppression of alcohol drinking in cyanamide-treated rats after sustained delivery of the 5-HT2 antagonist amperozide

The purpose of this study was to evaluate the long-term effect of sustained treatment with amperozide, which has been shown to attenuate the volitional drinking of ethyl alcohol in the rat without side effects. Preference for alcohol first was induced pharmacologically in Sprague-Dawley rats by the inhibitor of aldehyde dehydrogenase, cyanamide, administered in a dose of 10 mg/kg twice daily for 3 days. Then following a standard preference test, each rat was offered water and its maximally preferred concentration of alcohol which ranged from 7% to 15%. Following a 4-day pre-drug test, saline control vehicle or amperozide was administered for 7 days by an osmotic minipump implanted in the intrascapular space. A single dose of 208 micrograms/kg/h (i.e., 5.0 mg/kg/day) was selected on the basis of a prior dose response study of amperozide. During the interval of sustained release of amperozide, the consumption of alcohol declined significantly in terms of both absolute g/kg intake and proportion of alcohol to water. When the preference of the rats was retested at 4, 30, 70, 110, and 140 day intervals after the pump had exhausted amperozide, the absolute g/kg consumption of alcohol continued to decline significantly. Unlike other drugs, amperozide did not produce any side effects, particularly on the intake of food or water or on body weight, which suggests a pharmacological specificity of its action.(ABSTRACT TRUNCATED AT 250 WORDS)