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

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.

Family history of alcoholism is associated with lower 5-HT2A receptor binding in the prefrontal cortex

BACKGROUND

5-Hydroxytryptophan (5-HT(2A)) receptor involvement in alcoholism is suggested by less 5-HT(2A) binding in alcohol preferring rats, association of a 5-HT(2A) receptor gene polymorphism with alcohol dependence and reduced alcohol intake with 5-HT(2A) antagonists. We sought to determine postmortem whether 5-HT(2A) receptors are altered in the prefrontal cortex (PFC) of alcoholics.

METHODS

Brain tissue from 25 alcoholics and 19 controls was collected at autopsy. Diagnosis of DSM-IV alcoholism/abuse and other psychiatric disorders and the determination of family history of alcoholism were made by psychological autopsy. Specific binding to 5-HT(2A) ((3)H-ketanserin) receptors in the PFC was measured by quantitative autoradiography.

RESULTS

5-HT(2A) binding decreased with age [Brodmann areas (BA) 9, 46 gyrus; r = -0.381, -0.334, p < 0.05]. No differences in receptor binding between alcoholics and controls were detected in the gyrus or sulcus of any PFC area examined. Cases (controls or alcoholics) with a family history of alcoholism (n = 23) had less 5-HT(2A) binding throughout PFC than subjects without (n = 21) a family history of alcoholism (p < 0.05). 5-HT(2A) receptor binding in alcoholics without a family history of alcoholism (n = 7) did not differ from controls without a family history of alcoholism (n = 14). There was no association between alcoholism or alcohol rating and genotype. There was an association between genotype and the total amount of (3)H-ketanserin binding in BA46 with the TT genotype having more binding (TT>TC approximately CC).

CONCLUSIONS

Lower 5-HT(2A) receptor binding in the PFC of cases with a family history of alcoholism suggests a genetic predisposition to alcoholism. Alcohol abuse by itself did not have a significant effect on PFC 5-HT(2A) binding and as 5-HT(2A) binding in alcoholics is not different from controls and antagonists may be therapeutic, fewer receptors may result in downstream developmental effects on the brain resulting in a predisposition to alcoholism.

A double-blind, placebo-controlled pilot trial of quetiapine for the treatment of Type A and Type B alcoholism

BACKGROUND

Atypical antipsychotics may be useful in the treatment of alcohol dependence. Human trials suggest that atypical antipsychotics may reduce alcohol craving and consumption, especially among patients with comorbid psychopathology. Therefore, these medications may be more useful for treating more severely affected alcoholics, such as patients with Type B alcoholism. Type B alcoholics are characterized by an early age of onset of problem drinking, high severity of alcohol dependence, increased psychopathology, and treatment-resistance. Quetiapine is an atypical antipsychotic with a favorable side effect profile, and may be a promising medication for the treatment of alcohol dependence, particularly Type B alcoholism.

METHODS

Male and female alcoholics (33 Type A and 28 Type B) were included in a 12-week, double-blind, placebo-controlled trial. After detoxification, patients were randomized to receive quetiapine (n = 29), 400 mg/d at bedtime, or placebo (n = 32). The primary outcome measure was the quantity and frequency of alcohol consumption, measured by the timeline follow back.

RESULTS

Forty-seven patients (77%) completed the trial, with no significant between-group differences in treatment retention. Nine quetiapine-treated patients (31%) maintained complete abstinence compared with 2 placebo-treated patients (6%) (chi(2) = 6.3, P = 0.012). There was a significant interaction between quetiapine and alcoholic subtype. As predicted, quetiapine- versus placebo-treated Type B alcoholics had significantly fewer days of drinking and fewer days of heavy drinking. Alcohol craving was also significantly reduced in quetiapine-treated compared with placebo-treated Type B alcoholics. Among Type A alcoholics, quetiapine provided no advantage over placebo in improving drinking outcomes.

CONCLUSIONS

Quetiapine may be effective for the treatment of alcohol dependence, particularly in the more complicated Type B, early-onset alcoholics.

Clozapine reduces alcohol drinking in Syrian golden hamsters

Alcohol abuse contributes substantially to the overall morbidity of schizophrenia. While typical antipsychotic medications do not limit alcohol use in patients with schizophrenia, emerging data suggest that the atypical antipsychotic clozapine does. To further elucidate the effects of these antipsychotics on alcohol use, we initiated a study in alcohol-preferring rodents. Syrian golden hamsters were given free-choice, unlimited access to alcohol. Nine days of treatment (s.c. injection) with clozapine (2-4 mg/kg/day), but not haloperidol (0.2-0.4 mg/kg/day), reduced alcohol drinking. Clozapine reduced alcohol drinking by 88% (from 11.3+/-1.7 to 1.4+/-0.2 g/kg/day) while increasing both water and food intake. Alcohol drinking gradually (during 24 days) returned toward baseline in the clozapine-treated animals when vehicle was substituted for clozapine. Further increasing the doses of haloperidol (0.6-1.0 mg/kg/day) had no effect on alcohol drinking; moreover, very low doses of haloperidol (0.025-0.1 mg/kg/day) tested in separate groups of hamsters also had no effect on alcohol drinking. This study demonstrates that clozapine, but not haloperidol, can effectively and reversibly decrease alcohol consumption in alcohol-preferring hamsters. The results are compatible with the observations that clozapine, but not haloperidol, limits alcohol use in patients with schizophrenia. These data further suggest that clozapine may serve as a prototype for developing novel treatments for alcohol abuse.

Risperidone reduces limited access alcohol drinking in alcohol-preferring rats

An atypical antipsychotic drug risperidone reduced ethanol drinking of ethanol-preferring Alko, Alcohol (AA) rats in a limited access paradigm. Its effect was transient at a dose known to preferentially antagonize the 5-HT(2) receptors (0.1 mg/kg, s.c.), but long-lasting when the dose was increased to 1.0 mg/kg that also blocks dopamine D(2) receptors. Risperidone also reduced dose-dependently locomotor activity and limited access saccharin intake of the AA rats, indicating that its effect on ethanol drinking was not selective. Risperidone at 0.1 mg/kg given before four successive daily ethanol-drinking sessions significantly reduced the ethanol intake. These data from an animal model of high ethanol intake suggest that risperidone should be tested in various populations of alcoholics for reducing ethanol consumption.

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.

Activation of 5-HT2A/2C receptors within the nucleus accumbens increases local dopaminergic transmission

This study was designed to assess the involvement of the 5-hydroxytryptamine (5-HT)2A/2C receptor subtypes in the regulation of in vivo dopamine release in the rat nucleus accumbens (NAC). Extracellular dopamine (DA) in the NAC was measured using intracerebral microdialysis coupled with an HPLC-EC system. 5-HT2A/2C receptor agonist, (+/-)-1-(4-lodo-2,5-dimethoxyphenyl)-2-aminopropane (DOI) and antagonists, LY-53,857 and ketanserin, were all administered via a dialysis probe into the NAC. The results showed that perfusion with DOI at concentrations of 10, 50, 100, and 300 microM elicited a significant and concentration-dependent increase in extracellular DA. DA levels returned to control values within 40-60 min after terminating DOI perfusion. The increased DA induced by perfusion with 100 microM DOI was sensitive to sodium channel blockade with tetrodotoxin, and antagonized by co-perfusion with either LY-53,857 (25 and 50 microM) or ketanserin (50 microM). Perfusion with 50 microM LY-53,857 alone failed to alter basal levels of DA. The results suggest that local application of DOI increases DA release via a receptor-mediated process, and are consistent with the concept that activation of 5-HT2A/2C receptors within the NAC can augment dopaminergic transmission in this region although these receptors are not involved in the regulation of basal accumbal DA release.

Extracellular dopamine and serotonin after ethanol monitored with 5-minute microdialysis

In order to determine potential rapid changes in extracellular dopamine (DA) and 5-hydroxytryptamine (serotonin, 5-HT) during the first 5-10 min after ethanol, intracerebral microdialysis coupled with microbore HPLC was used. Ethanol at the doses of 0.5, 1, and 2 g/kg was administered IP and extracellular DA and 5-HT in 5-min dialysates from the nucleus accumbens (NAC) of freely moving rats were determined. Ethanol at all doses significantly increased extracellular DA and 5-HT. DA and 5-HT peaked at 10, 15, 20 min and 20, 20, 55 min following 0.5, 1, and 2 g/kg, respectively. Based on previous reports showing that brain or blood ethanol levels peaked within 10-20 min after administration, the results indicate that peak increases in extracellular DA and 5-HT in the NAC occurred at approximately the same time, with the DA time course more temporally correlated with the blood or brain alcohol concentration curve reported in the literature. These results support the concept that the reinforcing properties of ethanol derive, at least in part, from its ability to stimulate DA release in the NAC. In addition, the present data are not in opposition with a role of 5-HT in the ethanol reinforcing effect.

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.

Different behavioral patterns related to alcohol use in rodents: a factor analysis

To estimate genetic correlations among behavioral measures from explorative crossmaze, inescapable slip funnel, as well as from drinking tests, the data from five pairs of high/low alcohol drinking rat (AA/ANA, P/NP, HAD1/LAD1, HAD2/LAD2, HIGH-IPH/LOW-IPH) and from three pairs of mouse (B10.AKM/B10.A(4R), HD/LD, Small_Brain/ Large_Brain) lines were evaluated by the use of principal component analysis. The analysis yielded a two-factor solution explaining 71.8% of total variability. Both the factors had high positive loadings on alcohol drinking. The first factor had sufficient positive loadings on latency of crossmaze exploration and total time of slip funnel immobility, whereas, there was a negative loading on slip funnel avoidance. The second factor had positive loadings on efficacy of crossmaze exploration and slip funnel escape attempts, whereas there was a negative loading on slip funnel immobility. The number of defecations in the crossmaze, time in open arms of the elevated plus-maze, time immobile during the forced-swim test, as well as intake of a saccharin solution, additionally available for a lesser number of the lines, were studied for correlations with the factor scores. The first factor of "alcohol drive with timidity and meekness" exhibited positive relation to saccharin intake. Time in the open arms of the elevated plus-maze showed significant negative correlation with a latency of crossmaze exploration. The second factor of "alcohol drive with novelty seeking and persistence" showed a negative link to crossmaze defecations and forced-swim immobility.

An investigation into the effects of 5-HT agonists and receptor antagonists on ethanol self-administration in the rat

Pharmacological manipulation leading to altered 5-HT function has been widely demonstrated to reduce ethanol intake in free choice tests. The aim of the present study was to examine the effects of a range of compounds known to influence 5-HT neurotransmission, including selective 5-HT receptor agonists and antagonists, on ethanol ingestion and maintained behaviour in an operant self-administration paradigm. Female Sprague-Dawley rats were trained to respond for 8% ethanol (v/v) in a 60-min test by a previously described technique. The number of responses and ethanol reinforcers (dipper deliveries), ethanol consumption (g/kg of body weight), and locomotor activity (LMA) were measured following administration of 5-HT agonists (5-HT, d-fenfluramine, fluoxetine, buspirone, TFMPP, and DOI) and antagonists (metergoline, ritanserin, and ondansetron) 30 min prior to testing. d-Fenfluramine, fluoxetine, buspirone, TFMPP, and DOI all produced a reduction in ethanol ingestion and maintained behaviour at doses that failed to reduce LMA. Conversely, metergoline and ritanserin only reduced ethanol self-administration at doses that concomitantly reduced LMA. 5-HT and ondansetron were without effect on any measure. These results demonstrate that, under the present experimental conditions, activation of central 5-HT1A, 5-HT1B, and 5-HT2 receptors reduced ethanol intake and reinforced behaviour in an operant paradigm.

Genetic selection of alcohol preference can be countered by conditioning processes

Twenty-four P rats and 24 NP rats were conditioned to consume 10% w/v alcohol in daily 0.5-h limited access periods using a modified version of Samson's sucrose fading procedure. Both P and NP rats demonstrated a strikingly similar day-to-day pattern of alcohol intakes. For the most part, P rats drank more than NP rats, but by the middle of the fourth month of drinking, P and NP rats were drinking equivalent amounts of alcohol. Both P and NP rats consumed alcohol in amounts similar to two outbred strains of rats (Wistar and Sprague-Dawley) previously conditioned to drink alcohol in this laboratory.

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.

Pharmacotherapies for alcohol problems: a review of research with focus on developments since 1991

Research on medications to treat alcohol problems has flourished in the last 5 years. Whereas before this time most projects focused on withdrawal agents, at least equal interest has now extended to drugs that may directly reduce urge to drink. The most promising medications in this regard are the opiate antagonists and acamprosate. Considerable attention has also been devoted to serotonergic agents. As aids to detoxification, pharmacologic agents that affect the multiple neural systems disrupted by acute alcohol withdrawal remain under active investigation. Significant progress is also being made in identifying medications to assist alcoholics suffering collateral psychopathology, especially depression and anxiety based disorders. Unfortunately, fewer gains have been realized in the development of medications to assist patients simultaneously dependent on both alcohol and illicit drugs. Also, research to develop amethystic agents remains in its very early stages.

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.

Selective destruction of midbrain raphe nuclei by 5,7-DHT: is brain 5-HT involved in alcohol drinking in Sprague-Dawley rats?

Since serotonin (5-HT) reportedly is involved in aberrant drinking of ethyl alcohol, the present study examined a possible role of the concentration of 5-HT in systems originating in the dorsal raphe nucleus (DRN), median raphe nucleus (MRN) or both nuclei. The preference for alcohol offered in concentrations increased over 10 days from 3% to 30% was determined for each Sprague-Dawley rat. After the rats were anesthetized with sodium pentobarbital, either 10 microg 5,7-DHT or artificial cerebrospinal fluid (CSF) was micro-injected stereotaxically into the DRN, MRN or both nuclei. After 10 days, a second alcohol preference test was offered to the animals. Then the rats were decapitated, each brain removed, and the block of tissue containing injection sites was saved for histological analysis. The remaining portion was dissected into separate regions for analysis by HPLC of 5-HT, 5-hydroxyindoleacetic-acid (5-HIAA), norepinephrine (NE), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). The 5,7-DHT lesion of the DRN depleted the levels of 5-HT and 5-HIAA by 50-55% in the midbrain and pons and by 70-80% in the frontal cortex, whereas, the 5,7-DHT lesion of MRN reduced 5-HT in all regions except the corpus striatum. The depletion of 5-HT was lower in MRN-lesioned than in DRN-lesioned rats in the frontal cortex and nucleus accumbens. The combined lesion of both DRN and MRN produced a massive decline of >90% of 5-HT and 5-HIAA in all structures except the pons where 5-HT was reduced by 70%. Whereas the level of NE was reduced mainly in the frontal cortex, the levels of DA and its metabolites were essentially unaffected by the 5,7-DHT lesions. Although single or combined lesions of the DRN and MRN failed to alter the intake of alcohol of the rats, the combined serotonergic lesions increased significantly the ingestion of water but not food. Correlational analyses in the sham groups showed a negative association between the intake of alcohol and cortical dopamine and possible hippocampal 5-HT and NE as well as between the ingestion of food and of 5-HT in the frontal cortex. Taken together, these observations in the Sprague-Dawley rat suggest that lower levels of these monoamines in certain regions of the brain may play a role in the maintenance of the basal intake of alcohol but not in the drinking after the injection of 5,7-DHT. Explanations of our findings include: (1) a compensatory neurochemical change in pre- or postsynaptic 5-HT receptors subsequent to the dysfunction of serotonergic neurons in the forebrain; (2) a unique characteristic of the Sprague-Dawley strain of rat; and (3) residual quanta of 5-HT which sustains the pattern of alcohol drinking.

Chronic alcoholization alters the expression of 5-HT1A and 5-HT1B receptor subtypes in rat brain

The expression of central 5-HT1A and 5-HT1B receptors was studied in several brain areas of rats subjected to a 2-week period of chronic alcoholization, followed by 18 h withdrawal. Quantitative autoradiography indicated that the ethanol treatment provoked an increase (approximately +30%) in the labeling by [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) and [3H]N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide ([3H]WAY-100635) of 5-HT1A autoreceptors in the dorsal raphe nucleus, accompanied by a concomitant decrease in the labeling of postsynaptic 5-HT1A receptors in the hippocampus (approximately -20%), anterior (approximately -30%) and posterior (approximately -32%) cortices. These changes were associated with a tendency toward an increase and decrease in 5-HT1A mRNA levels in the anterior raphe area and hippocampus, respectively, suggesting that the changes observed are due to modifications in 5-HT1A receptor protein synthesis. The autoradiographic labeling of 5-HT1B receptors by serotonin-O-carboxymethylglycyl[125I]iodotyrosinamide ([125I]GTI) was found to increase (+55%) in the globus pallidus of alcoholized rats. Interestingly, a significant increase (+57%) in 5-HT1B receptor mRNA levels was observed in the striatum, which contains cell bodies of neurons projecting into the globus pallidus. These data suggest that altered sensitivity of chronically alcoholized rats to 5-HT1A and 5-HT1B receptor ligands may result from alcohol-induced changes in the transcription of the genes encoding these receptors.

Volitional consumption of ethanol by fawn-hooded rats: effects of alternative solutions and drug treatments

Behavioral and neurochemical measures of brain 5-hydroxytryptamine (5-HT) function in the Fawn-Hooded rat are abnormal relative to outbred strains of rats. Fawn-Hooded rats freely drink large amounts of 10% ethanol in the presence of water and have been proposed to be an animal model for studies related to alcoholism. In this study, Fawn-Hooded rats were given solutions of ethanol increasing in concentration from 3% to 30% (w/v in tap water) over 10 days with tap water in a second drinking tube and a third tube left empty. The solutions of ethanol that produced maximal drinking with a preference (ml ethanol/ml total fluid) near 50% ranged from 5% to 13%, which became the fixed individual concentrations for each rat. After a 5-day baseline period the rats were offered a solution in the third drinking tube of either 0.5% aspartame or chocolate Ultra SlimFast (diluted with water 2:1). The chocolate drink, but not aspartame, significantly reduced the consumption of alcohol by 73%. For the drug experiments, the rats were given successive 4-day periods of: baseline drinking; drug or saline injections b.i.d.; and a posttreatment period. Neither ipsapirone, a 5-HT1a partial agonist, nor naltrexone injected inhibited the intakes of ethanol solutions. Treatment with 2.5 mg/kg of amperozide, a 5-HT2 antagonist, decreased the consumption of ethanol by 38%, but also caused a decrease in consumption of food. These results show a pattern of drinking of increasing concentrations of ethanol different than other strains of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

A relationship between increased voluntary alcohol preference and basal hypercorticosteronemia associated with an attenuated rise in corticosterone output during stress

Some of the multiple biological effects of stress include activation of a variety of neuroendocrine systems, resulting in enhanced secretion of many hormones, including corticosterone, as well as facilitation of drug-seeking behavior. Therefore, we have examined the potential relationship between voluntary alcohol consumption (VAC) and corticosterone output profile using: (1) selectively bred alcohol-preferring (P) and nonpreferring (NP) rats; and (2) outbred male Holtzman Sprague-Dawley rats selected for (a) low basal corticosterone (< 2 micrograms/mg Cr) and high stimulation (> 250%) (L-H rats), and (b) high basal corticosterone (> 4 micrograms/mg Cr) and low stimulation of corticosterone output on 24-hour fasting stress (< 125%) (H-L rats). The results of this study show: (a) the corticosterone output profiles of P and NP rats were similar to those of H-L and L-H rats, respectively; and (b) the H-L rats exhibited significantly higher VAC than the L-H rats. In conclusion, these data suggest that basal hypercorticosteronemia associated with attenuated rise in corticosterone output during stress may be associated with increased VAC.

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.

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.

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)