Involvement of the serotonergic system in ethanol intake in the rat

Receptors and Channels Associated with Alcohol Use: Contributions from Drosophila

Alcohol Use Disorder (AUD) is a debilitating disorder that manifests as problematic patterns of alcohol use. At the core of AUD's behavioral manifestations are the profound structural, physiological, cellular, and molecular effects of alcohol on the brain. While the field has made considerable progress in understanding the neuromolecular targets of alcohol we still lack a comprehensive understanding of alcohol's actions and effective treatment strategies. Drosophila melanogaster is a powerful model for investigating the neuromolecular targets of alcohol because flies model many of the core behavioral elements of AUD and offer a rich genetic toolkit to precisely reveal the in vivo molecular actions of alcohol. In this review, we focus on receptors and channels that are often targeted by alcohol within the brain. We discuss the general roles of these proteins, their role in alcohol-associated behaviors across species, and propose ways in which Drosophila models can help advance the field.

Serotonergic Systems in the Pathophysiology of Ethanol Dependence: Relevance to Clinical Alcoholism

Alcoholism is a progressive brain disorder that is marked by increased sensitivity to the positive and negative reinforcing properties of ethanol, compulsive and habitual use despite negative consequences, and chronic relapse to alcohol drinking despite repeated attempts to reduce intake or abstain from alcohol. Emerging evidence from preclinical and clinical studies implicates serotonin (5-hydroxytryptamine; 5-HT) systems in the pathophysiology of alcohol dependence, suggesting that drugs targeting 5-HT systems may have utility in the treatment of alcohol use disorders. In this Review, we discuss the role of 5-HT systems in alcohol dependence with a focus on 5-HT interactions with neural circuits that govern all three stages of the addiction cycle. We attempt to clarify how 5-HT influences circuit function at these different stages with the goal of identifying neural targets for pharmacological treatment of this debilitating disorder.

The role of serotonin in drug use and addiction

The use of psychoactive drugs is a wide spread behaviour in human societies. The systematic use of a drug requires the establishment of different drug use-associated behaviours which need to be learned and controlled. However, controlled drug use may develop into compulsive drug use and addiction, a major psychiatric disorder with severe consequences for the individual and society. Here we review the role of the serotonergic (5-HT) system in the establishment of drug use-associated behaviours on the one hand and the transition and maintenance of addiction on the other hand for the drugs: cocaine, amphetamine, methamphetamine, MDMA (ecstasy), morphine/heroin, cannabis, alcohol, and nicotine. Results show a crucial, but distinct involvement of the 5-HT system in both processes with considerable overlap between psychostimulant and opioidergic drugs and alcohol. A new functional model suggests specific adaptations in the 5-HT system, which coincide with the establishment of controlled drug use-associated behaviours. These serotonergic adaptations render the nervous system susceptible to the transition to compulsive drug use behaviours and often overlap with genetic risk factors for addiction. Altogether we suggest a new trajectory by which serotonergic neuroadaptations induced by first drug exposure pave the way for the establishment of addiction.

Critical thoughts on current rodent models for evaluating potential treatments of alcohol addiction and withdrawal

Despite years of neurobiological research that have helped to identify potential therapeutic targets, we do not have a reliable pharmacological treatment for alcoholism. There are a range of possible explanations for this failure, including arguments that alcoholism is a spectrum disorder and that different population subtypes may respond to different treatments. This view is supported by categorisations such as early- and late-onset alcoholism, whilst multifactorial genetic factors may also alter responsivity to pharmacological agents. Furthermore, experience of alcohol withdrawal may play a role in future drinking in a way that may distinguish alcoholism from other forms of addiction. Additionally, our neurobiological models, based largely upon results from rodent studies, may not mimic specific aspects of the human condition and may reflect different underlying phenomena and biological processes from the clinical pattern. As a result, potential treatments may be targeting inappropriate aspects of alcohol-related behaviours. Instead, we suggest a more profitable approach is (a) to identify well-defined intermediate behavioural phenotypes in human experimental models that reflect defined aspects of the human clinical disorder and (b) to develop animal models that are homologous with those phenotypes in terms of psychological processes and underlying neurobiological mechanisms. This review describes an array of animal models currently used in the addiction field and what they tell us about alcoholism. We will then examine how established pharmacological agents have been developed using only a limited number of these models, before describing some alternative novel approaches to achieving homology between animal and human experimental measures.

Role of the serotonergic system in alcohol dependence: from animal models to clinics

Alcohol dependence remains among the most common substance abuse problems worldwide, and compulsive alcohol consumption is a significant public health concern. Alcohol is an addictive drug that alters brain function through interactions with multiple neurotransmitter systems. These neurotransmitter systems mediate the reinforcing effects of alcohol. Specifically, the serotonergic system is important in mediating alcohol reward, preference, dependence, and craving. In this review chapter, we first discuss the serotonin system as it relates to alcoholism, and then outline interactions between this system and other neurotransmitter systems. We emphasize the serotonin transporter and its possible role in alcoholism, then present several serotonergic receptors and discuss their contribution to alcoholism, and finally assess the serotonin system as a target for pharmacotherapy, with an emphasis on current and potential treatments.

Serotonin-3 receptors in the posterior ventral tegmental area regulate ethanol self-administration of alcohol-preferring (P) rats

Several studies indicated the involvement of serotonin-3 ([5-hydroxy tryptamine] 5-HT(3)) receptors in regulating alcohol-drinking behavior. The objective of this study was to determine the involvement of 5-HT(3) receptors within the ventral tegmental area (VTA) in regulating ethanol self-administration by alcohol-preferring (P) rats. Standard two-lever operant chambers (Coulbourn Instruments, Allentown, PA) were used to examine the effects of seven consecutive bilateral microinfusions of ICS 205-930 (ICS), a 5-HT(3) receptor antagonist, directly into the posterior VTA on the acquisition and maintenance of 15% (vol/vol) ethanol self-administration. P rats readily acquired ethanol self-administration by the fourth session. The three highest doses (0.125, 0.25, and 1.25 microg) of ICS prevented acquisition of ethanol self-administration. During the acquisition postinjection period, all rats treated with ICS demonstrated higher responding on the ethanol lever, with the highest dose producing the greatest effect. In contrast, during the maintenance phase, the three highest doses (0.75, 1.0, and 1.25 microg) of ICS significantly increased responding on the ethanol lever; after the 7-day dosing regimen, responding on the ethanol lever returned to control levels. Microinfusion of ICS into the posterior VTA did not alter the low responding on the water lever and did not alter saccharin (0.0125% wt/v) self-administration. Microinfusion of ICS into the anterior VTA did not alter ethanol self-administration. Overall, the results of this study suggest that 5-HT(3) receptors in the posterior VTA of the P rat may be involved in regulating ethanol self-administration. In addition, chronic operant ethanol self-administration and/or repeated treatments with a 5-HT(3) receptor antagonist may alter neuronal circuitry within the posterior VTA.

Electrolytic lesions of the medial nucleus accumbens shell selectively decrease ethanol consumption without altering preference in a limited access procedure in C57BL/6J mice

The central extended amygdala (cExtA) is a limbic region proposed to play a key role in drug and alcohol addiction and to contain the medial nucleus accumbens shell (MNAc shell). The aim of this study was to examine the involvement of the MNAc shell in ethanol and sucrose consumption in a limited and free access procedure in the C57BL/6J (B6) mouse. Separate groups of mice received bilateral electrolytic lesions of the MNAc shell or sham surgery, and following recovery from surgery, were allowed to voluntarily consume ethanol (15% v/v) in a 2 h limited access 2-bottle-choice procedure. Following 1 week of limited access ethanol consumption, mice were given 1 week of limited access sucrose consumption. A separate group of lesioned and sham mice were given free access (24 h) to ethanol in a 2-bottle choice procedure and were run in parallel to the mice receiving limited access consumption. Electrolytic lesions of the MNAc shell decreased ethanol (but not sucrose) consumption in a limited access procedure, but did not alter free access ethanol consumption. These results suggest that the MNAc shell is a component of the underlying neural circuitry contributing to limited access alcohol consumption in the B6 mouse.

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.

Morphometry of dorsal raphe nucleus serotonergic neurons in alcoholism

BACKGROUND

Reduced serotonergic function is hypothesized in alcohol abuse and dependence. Serotonergic innervation of the cortex arises predominantly from the dorsal raphe nucleus (DRN). We sought to determine the number and morphometric characteristics of DRN serotonergic neurons postmortem in alcoholic individuals (n=9; age: 16-66 years; 8M:1F) compared with psychiatrically normal, nonalcoholic controls (n=6; age: 17-74 years; 4M:2F).

METHODS

Brainstems were collected at autopsy, fixed and cryoprotected. Alcohol dependence or abuse was determined by psychological autopsy (DSM-IV), the presence of liver fatty changes or cirrhosis and/or high blood alcohol level. Tissue was sectioned at 50 microm (-25 degrees C). A series of 1:10 sections was immunoreacted with antiserum to tryptophan hydroxylase (TPH), the rate-limiting enzyme in the biosynthesis of serotonin. The total number of TPH-immunoreactive (IR) DRN neurons was determined by stereology. Neuron morphometry indices were determined using a video-based imaging system attached to a microscope. We identified TPH-IR neurons every 1,000 microm in each brainstem and measured neuron area, total cross sectional neuron area, and the total area and density of immunolabeled processes.

RESULTS

Dorsal raphe nucleus neuron number (controls: 80,386+/-10,238; alcoholic individuals: 85,884+/-12,478) was not different between groups but TPH-IR was greater in alcoholic individuals throughout the rostrocaudal extent of the DRN. The volume of the DRN was 66+/-9 mm3 in controls and 55+/-5 mm3 in alcoholic individuals (p>0.05). The average size of DRN neurons did not differ between groups (353+/-12 microm2 for controls vs 360+/-15 microm2 for alcoholic subjects). However, the area occupied by neuron processes (area of processes/DRN area) was 2.2-fold greater in alcoholic individuals compared with controls (p<0.05).

CONCLUSIONS

The increased area occupied by neuron processes in alcoholic individuals may represent sprouting and, together with greater TPH-IR, be a compensatory response to impaired serotonergic transmission or cumulative effects of alcohol on the serotonin system.

Monoamine metabolism and behavioral responses to ethanol in mitochondrial aldehyde dehydrogenase knockout mice

BACKGROUND

It is widely accepted that, in addition to removing acetaldehyde produced during the metabolism of ethanol, mitochondrial aldehyde dehydrogenase (ALDH2) functions in the pathway by which aldehyde metabolites of the monoamines dopamine (DA) and serotonin (5-HT) are converted to their acidic metabolites. Moreover, studies of ALDH2 inhibitors used for treating alcoholism suggest that their antidipsotropic effects may be related to inhibition of monoamine metabolism. Therefore, we examined the hypothesis that altered brain monoamine metabolism is related to the influence of ALDH2 on behavioral responses to ethanol.

METHODS

Mice were generated with a gene-trap mutation of the ALDH2 gene. ALDH2 mRNA was absent in ALDH2-/- mice. Western blot analysis of liver mitochondria confirmed the absence of ALDH2 protein in the ALDH2-/- mice. Wild-type and ALDH2-deficient mice were tested for the effects of different doses of ethanol on locomotor activity, ataxia, and a 2-bottle ethanol-water preference test.

RESULTS

Wild-type and ALDH2+/- mice preferred ethanol to water. However, ALDH2-/- mice drank significantly less ethanol than wild-type or ALDH2+/- mice. Locomotor activity and ataxia were significantly more affected by ethanol in ALDH2-/- mice than in wild-type or ALDH2+/- mice. There was no effect of genotype on levels of 5-HT, DA, or their precursors or metabolites in several brain regions, as measured by HPLCec.

CONCLUSIONS

The results indicate that: (1) the effect of the mutant genotype on behavioral responses to ethanol is unrelated to altered brain monoamine metabolism and (2) ALDH2 is not required for the metabolism of brain monoamines in vivo.

Can experimental paradigms and animal models be used to discover clinically effective medications for alcoholism?

Evaluating medications in animal laboratory paradigms can reveal whether the compound is effective in an established alcoholism model, at clinically relevant doses and exposure conditions, when administered orally (or transdermally) and without serious limiting side effects. Positive outcomes constitute a possible discovery for relevance to alcoholism and, under favorable marketing conditions, encourage further development. Medication testing using animal models of alcoholism might also guide clinical testing by discriminating clinically effective from clinically ineffective compounds. This ability rests on whether there are tests or, more reasonably, batteries of tests having this discriminative ability. The present paper examines this possibility. Effects of naltrexone and acamprosate in animal paradigms which model behavioral aspects of alcoholism are reviewed and compared with the effects of compounds which have limited effects in alcoholics. It is not clear at present whether any single paradigm or combination of paradigms differentiates clinically effective from clinically limited compounds. Steps are suggested to improve the use of preclinical laboratory tests to predict which compounds are likely to be effective medications for reducing drinking and sustaining abstinence in human alcoholics.

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.

The status of serotonin-selective pharmacotherapy in the treatment of alcohol dependence

Research performed during the past 20 years has shown that serotonin (5-hydroxytryptamine; 5-HT) neurotransmission is related to alcohol dependence. Both theoretical and empirical research have supported the idea that alcohol dependence is a chronic disease and that, in addition, biological vulnerabilities contribute to the pathogenesis of alcohol dependence. Preclinical studies have consistently demonstrated that there is a relationship between 5-HT function and alcohol consumption. Furthermore, there is evidence building that lends support for the existence of distinct alcoholic subtypes that may be differentiated by the type or complexity of their 5-HT dysfunction. Beyond excessive drinking, behaviors that are indicators of 5-HT dysregulation are depression, anxiety, impulsiveness, and early-onset problem drinking. This chapter will discuss the usefulness of 5-HT-selective pharmacotherapy in treating alcohol dependence and will provide both historical and current perspectives on its use.

A double-blind, placebo-controlled trial of sertraline in depressed adolescent alcoholics: a pilot study

In order to preliminarily evaluate the efficacy, safety and tolerability of the serotonin reuptake inhibitor, sertraline, in the treatment of adolescents with a primary depressive disorder and a comorbid alcohol use disorder, a 12-week double-blind, placebo-controlled trial of sertraline plus cognitive behavior group therapy was conducted. Subjects were 10 outpatient treatment-seeking adolescents. Baseline assessment included the K-SADS, HAM-D, SCID, and the Time-Line Follow-Back. The HAM-D and the Time-Line Follow-Back were performed weekly thereafter. Both groups showed a significant reduction in depression scores with an average reduction between baseline and endpoint HAM-D score of -9.8 (F(1,8)=26.14, p</=0.001), although there were no significant group differences. There was an overall reduction in Percent Days Drinking (PDD); (F(1,8)=8.90, p<0.02) and in Drinks Per Drinking Day (DDD); (F(1,8)=20.48, p<0.002), however, there were no group differences. Depression responders tended to have higher baseline PDD than non-responders (F(1,8)=3.9, p=0.08) and change in HAM-D scores tended to correlate with change in PDD (r=0.57, p=0.09). Our data support that sertraline is safe and well tolerated in the treatment of adolescents with depression and alcohol dependence. Small sample size and cognitive behavior group therapy given to all subjects may limit the lack of group differences. Copyright 2000 John Wiley & Sons, Ltd.

Effects of 5-HT(3) receptor antagonists on daily alcohol intake under acquisition, maintenance, and relapse conditions in alcohol-preferring (P) rats

Previous research indicated that 5-HT(3) antagonists can reduce ethanol drinking in rats, but drinking conditions and other environmental manipulations influenced the efficacy of these antagonists. The current experiments were conducted to examine the effects of the 5-HT(3) antagonists MDL 72222 (MDL) or ICS 205-930 (ICS) on 24-h ethanol (10% v/v) consumption during acquisition, maintenance, and following a period of deprivation in selectively bred high alcohol-preferring (P) male rats. In an analysis of the acquisition of ethanol consumption, daily injections of MDL (1 mg/kg; s.c.) or ICS (1 or 5 mg/kg) were administered to separate groups of P rats during the initial 10 days of ethanol exposure. To examine the maintenance of ethanol drinking, these same groups of rats were allowed access to ethanol for 21 days with no pharmacological manipulations, and were then administered either saline or the 5-HT(3) antagonist. To examine the effects of a 5-HT(3) antagonist on relapse of ethanol drinking, another group of P rats was allowed access to ethanol for 6 weeks and was then deprived of ethanol for 3 weeks. Prior to ethanol reinstatement, rats were treated chronically (seven daily injections) or acutely with MDL (1 mg/kg), saline, or received no injections. MDL (1 mg/kg) and ICS (1 or 5 mg/kg) reduced ethanol intake during acquisition (60-80%) and during maintenance drinking (35-70%) in P rats pretreated with saline during acquisition. However, in rats pretreated with MDL or ICS during acquisition, there was a significant reduction in the effectiveness of either MDL or ICS to reduce ongoing ethanol drinking. Neither acute nor chronic treatment with 1 mg/kg MDL altered the 80% increase in ethanol consumption observed on the first day of reinstatement following a 3-week deprivation period. However, in a follow-up study, acute treatment with MDL (3 mg/kg) or ICS (5 mg/kg) did prevent the 80% increase in ethanol consumption observed on the first day of reinstatement. Overall, the results suggest that 5-HT(3) receptors are involved in the acquisition and maintenance of 24-h ethanol drinking, and that neuroadaptations may occur as a result of chronic treatment with 5-HT(3) antagonists, or during prolonged alcohol deprivation, which alter the involvement of these receptors in regulating alcohol drinking in the P rat.

A tryptophan-free diet markedly reduces frontocortical 5-HT release, but fails to modify ethanol preference in alcohol-preferring (sP) and non-preferring (sNP) rats

It has been hypothesised that rat lines genetically selected for their alcohol preference consume large amounts of ethanol because they have a low 5-HT content. Since brain tryptophan (TRP) availability controls the rate at which neurons synthesise and release serotonin (5-HT), we assessed whether the administration of a TRP-supplemented or TRP-free diet for 3 consecutive days influenced alcohol intake in alcohol-preferring and non-preferring sP and sNP rats, respectively. In the same animals extracellular 5-HT concentration was monitored by microdialysis in the frontal cortex. A TRP-free diet progressively and markedly decreased cortical extracellular 5-HT in sP and sNP rats during the treatment period with respect to a balanced diet. However, the TRP-free diet failed to modify alcohol consumption and preference in sP and sNP rats. The TRP-supplemented diet also failed to alter the intake of alcohol in either group of rats. Therefore, these results do not support a specific role of 5-HT transmission in ethanol intake and preference in sP and sNP rats.

Delta-opioid and 5-HT3 receptor antagonist effects on ethanol reward and discrimination in C57BL/6 mice

The effects of the receptor antagonists MDL 72222 (MDL, 5-HT3) and naltrindole (delta-opioid) on ethanol reward and its discrimination were examined in ethanol-preferring C57BL/6 (C57) mice. MDL attenuated lever responding for 12% ethanol delivered on a fixed-ratio 8 reinforcement schedule at a dose that did not influence responding for water reward, thus confirming a previous report that ICS 205-930 reduced ethanol reward for Long-Evans rats. Our study in combination with the reduced ethanol consumption reported for C57 mice injected with odansetron indicates that 5-HT3 receptor systems are involved in mediating behavior directed toward obtaining ethanol as well as its consumption. By attenuating the rewarding effects of ethanol or of ethanol conditioned cues (e.g., the operant environment), 5-HT3 antagonists may be useful in the treatment of alcohol abuse. The 5-HT3 antagonist effects in this study are comparable with the effects of naltrexone on ethanol reward in C57 mice, although higher doses were required to reduce operant responding for ethanol reward. In contrast to the 5-HT3 antagonist and naltrexone effects, naltrindole, an antagonist with greater specificity for the delta-opioid receptor, was without effect on ethanol reward. This result and recent reports for rats and monkeys suggests that the general antagonists might be more efficacious in attenuating ethanol reward. Both MDL and naltrindole produced only slight reductions in the ethanol discriminative cue, suggesting that the rewarding and discriminative effects of ethanol are not likely mediated by identical neural mechanisms as previously suggested.

5-HT2A and 5-HT2C/5-HT1B receptors are differentially involved in alcohol preference and consummatory behavior in cAA rats

The present study aimed to investigate the role of serotonin 5-HT2A and 5-HT2C receptors in the control of alcohol preference and consummatory behavior in alcohol-preferring cAA rats. Effects of the 5-HT(2A/2C) receptor agonist, DOI, the 5-HT(2C/1B) receptor agonist, mCPP, the 5-HT(2A/2C) receptor antagonist, ritanserin, and the 5-HT2A receptor antagonist, MDL 100,907, on ethanol (EtOH, 10% v/v) preference and intake, as well as total fluid and food intake were evaluated in a 12-h limited-access two-bottle paradigm. DOI (0.3-3 mg/kg, i.p.) reduced EtOH intake and preference, but not total fluid or food intake; whereas mCPP (1-10 mg/kg, s.c.) reduced EtOH, total fluid, and food intake. Therefore, it is concluded that DOI induces a specific and selective antialcohol effect, whereas mCPP rather induces a general suppressive effect on consummatory behavior. Ritanserin (1-10 mg/kg, i.p.) did not affect EtOH intake and preference, nor total fluid and food consumption. MDL 100,907 (0.1-1 mg/kg, i.p.) induced only a small reduction of food intake at the highest dose tested. Pretreatment with ritanserin (3 mg/kg, i.p.) and MDL 100,907 (0.3 mg/kg, i.p.) blocked the effects of DOI (3 mg/kg, i.p.), but not those of mCPP (10 mg/kg, i.p.). It is suggested that activation of 5-HT2C and/or 5-HT1B receptors results in a general decrease of consummatory behavior, whereas activation of 5-HT2A receptors selectively decreases EtOH intake and preference, as assessed in the cAA rat model of alcoholism.

A Low Protein, High Carbohydrate Diet Attenuates Alcohol Intake in Rats

To test whether a tryptophan-enhancing diet will reduce alcohol intake as serotonergic drugs do, two studies were conducted. In Experiment 1, 32 male, alcohol-drinking rats were randomly assigned to one of four isocaloric diets containing 25%-protein/65%-carbohydrate, 25%-protein/4%-carbohydrate, 4%-protein/65%-carbohydrate, or 4%-protein/4%-carbohydrate. Following a baseline week during which they ate standard lab chow, rats were offered their assigned experimental diet, water, and 5%-alcohol solution ad lib for three weeks. Alcohol and diet intakes were measured daily. In Experiment 2, 32 naive male, alcohol-drinking rats were assigned to one of the experimental diets used in Experiment 1. Following a one-week baseline, rats were offered their assigned diet, water, and 5%-alcohol/1%-sucrose solution ad lib for two weeks and then were switched back to standard lab chow for one week, with alcohol intake measured daily. Rats consuming the low protein, high carbohydrate diet drank 60-80% less alcohol than did rats offered other diets. This reduction in alcohol intake is most likely due to increased brain serotonin levels produced by the dietary manipulation.

Comparison of effects of a range of 5-HT receptor modulators on consumption and preference for a sweetened ethanol solution in rats

This study assessed the effects of a range of serotonergic agents on preference for a slightly sweetened ethanol solution (10% ethanol, 3% glucose) in rats. A two-bottle, free-choice paradigm was used following induction of ethanol consumption. The model used provides a robust and reliable level of ethanol self-administration in normal laboratory rats. Ethanol consumption was significantly and selectively reduced by the 5-hydroxytryptamine-1A (5-HT1A) full agonist 8-OH-DPAT (0.3-1.0 mg/kg) and the 5-HT3 antagonist granisetron (0.1-1.0 mg/kg). Non-specific reductions in fluid consumption were induced by the 5-HT1B agonist RU 24969 (0.1-1.0mg/kg) and the 5-HT2 antagonist ritanserin (1.0-6.0 mg/kg). These studies thus confirm the potential for decreasing ethanol consumption and ethanol preference of 5-HT1A agonists and 5-HT3 antagonists, but failed to find any selective effects for agents acting at 5-HT1B or 5-HT2 receptors.

Pharmacological treatment of alcoholism

1. Pharmacological treatments are effective as part of a treatment plan that includes substantial education, psychological therapy and social support. This paper reviews recent literature on animal models of and treatment for alcohol abuse under seven categories: agents to block craving or reduce alcohol intake, agents to induce aversion to alcohol, agents to treat acute alcohol withdrawal, agents to treat protracted alcohol withdrawal, agents to diminish drinking by treating associated psychiatric pathology, agents to decrease drinking by treating associated drug abuse, and agents to induce sobriety in intoxicated individuals. 2. The benzodiazepines provide safe and effective treatment for detoxification, although current research focuses on finding drugs with a smaller likelihood of dependence. As yet, there are no drugs that effectively reverse the intoxicating effects of alcohol. 3. Currently, only two major groups of drugs that are relatively safe have shown any effect at reducing alcohol consumption: aversives such as disulfiram, and opioid antagonists such as naltrexone. 4. Finally, it is important to customize therapy for each patient rather than putting everyone through a standard treatment plan, especially in regards to the use of antidepressant or antipsychotic medications. Tailoring the program to the patient's needs dramatically improves the outcome of therapy and reduces the risk of adverse effects.

Serotonin3 receptor antagonism of alcohol intake: effects of drinking conditions

The effects of 5-HT3 receptor antagonists on ethanol intake were examined in the selectively bred alcohol-preferring P line of rats under continuous and limited access to 10% (v/v) ethanol with food and water ad lib. Single daily injections of either MDL 72222 (MDL) or ICS 205-930 (ICS) (0.01-3.0 mg/kg, SC) given 60 min before a 4-h scheduled access period for 4 consecutive days failed at all doses to alter the intake of a 10% (v/v) ethanol solution by P rats. However, multiple daily injections of either MDL (1-3 mg/kg, SC) or ICS (3.0 and 5.0 mg/kg, SC), given three times daily at 4-h intervals, significantly reduced ethanol intake under 24-h free-choice conditions on the first treatment day. Additionally, a single administration of 1.0 mg/kg MDL reduced 24-h free-choice ethanol intake by approximately 50% of control values and had no effect on 24-h saccharin intake. The effects of MDL were further examined in a 2-h schedule access paradigm in which rats received the access period at the same time every day (Fixed) or randomly during the dark cycle (Variable). Although 1.0 mg/kg MDL had little effect on ethanol drinking in the Fixed group, ethanol intake was reduced by 55% of control levels in the Variable group. Overall, the data indicate that drinking conditions influence the effectiveness of 5-HT3 antagonists to reduce ethanol consumption. Furthermore, the results suggest that conditions, associated with limited access ethanol drinking, markedly reduce the actions of 5-HT3 antagonists on ethanol intake.

Nefazodone attenuates the behavioral and neurochemical effects of ethanol

This study evaluated the influence of nefazodone, a combined 5-HT2A receptor antagonist and 5-HT reuptake inhibitor, on the behavioral and neurochemical effects of ethanol in nonselected male Wistar rats. In microdialysis experiments, ethanol (2.5 g/kg, i.p.) increased extracellular accumbal dopamine levels by 36% (p = 0.0073) compared to baseline levels, and elevated the maximal DOPAC and HVA levels by 26% (p = 0.0093) and 52% (p = 0.0010), respectively, Nefazodone (50 mg/kg, s.c.) per se increased accumbal dopamine levels by 28% (p = 0.0199) but, when injected 40 min before ethanol, reduced the ethanol-induced elevation of accumbal dopamine overflow (p = 0.0132) and decreased the ethanol-induced HVA levels (p = 0.0159). In an ethanol(6% v/v)/water free-choice paradigm, nefazodone (50 mg/kg, s.c.) decreased ethanol intake by 51% (p = 0.0251) and preference by 22% (p = 0.0251) in high- but not low-preferring rats from a nonselected Wistar strain. These results show that nefazodone modulates the mesolimbic dopamine system in a dopamine activity-dependent manner, and influences the neurochemical and behavioral effects of ethanol in the rat.

Experimental findings in the study of the reduction of alcohol intake

Alcohol dependence represents a major problem in public health and different animal models of dependence have been developed in rodents with the aim of studying the mechanisms of alcohol abuse. Different ways of animal alcoholisation have been established. They permit a better understanding of which neurotransmitter system is involved in the regulation of alcohol dependence. Considerable attention has been given to the role of serotonin in the control of both alcohol craving and alcohol related pathologies, i.e. anxiety, aggression or memory loss. In conclusion, the use of animal models of alcohol abuse facilitates the understanding of alcohol behavior and permits the development of new therapeutic agents.

Prevalence of high serotonin uptake in lymphocytes of abstinent alcoholics

An impairment in serotonergic neurotransmission may be associated with alcoholism. We recently identified a high-affinity serotonin transporter (5-HTT) in human peripheral blood lymphocytes (PBLs). Moreover, molecular analysis of RNA samples of human lymphocytes using reverse transcription, coupled with polymerase chain reaction, enabled us to confirm the expression of a 5-HTT identical to the one reported in neuronal tissues, as evidenced by hybridization and sequence analysis. In this investigation, we measured the serotonin (5-HT) uptake in PBLs of recovering alcoholics (N = 10) with long-term abstinence (2-10 years) and non-alcoholic controls (N = 10). 5-HT uptake was measured by incubating 1 x 10(7) cells of PBLs with [3H]5-HT (3-1000 nM; sp. act. 23 Ci/mmol) for 10 min at 37 degrees. The results of this preliminary study revealed that abstinent alcoholics had significantly (P < 0.01) increased uptake of 5-HT (43.6 +/- 5.70 pmol/10(7) cells) as compared with controls (23.33 +/- 2.50 pmol/10(7) cells). An enhanced uptake of 5-HT in PBLs of abstinent alcoholics agrees with previously reported observations of increased 5-HT uptake in brain and platelets of former alcoholics and their descendants. This suggested that a serotonergic mechanism may be linked to the heredity of alcoholism.

Effects of a range of dopamine receptor agonists and antagonists on ethanol intake in the rat

The aim of this study was to assess the effects of a range of dopaminergic agents on consumption of an ethanol solution (10% ethanol, 3% glucose) in rats. A two-bottle, free-choice paradigm was used following induction of ethanol consumption and preference in standard laboratory rats. The model used provides a robust and reliable level of ethanol oral administration in normal laboratory rats. Both ethanol intake and preference were reduced by a dopamine D1 receptor partial agonist, SFK 38393 ((+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride), in a dose-dependent manner. The dopamine D2/D3 receptor agonist 7-OH-DPAT ((+/-)-7-hydroxy-N,N-(di-n-propyl-2-aminotetralin)) at the lowest dose of 0.01 mg/kg increased both ethanol intake and preference. At higher doses (0.03-0.1 mg/kg) no significant effects were found. The dopamine D1 receptor antagonist SCH 23390 (R-(+)-7-chloro-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzazepine-8- ol), dopamine D2/D3 receptor antagonist raclopride and 5-HT2/D2 receptor antagonist risperidone did not affect ethanol consumption, although all at high doses induced a significant decrease in water intake, indicating a non-specific decrease in consummatory behavior with these compounds. These results suggest the involvement of the dopaminergic system in ethanol intake and ethanol reinforcement with dopamine D1 and D2/D3 receptors playing opposing roles. Blockade of dopamine D2 receptors had no selective effect on ethanol consumption and ethanol preference.

Central serotonergic lesions increase voluntary alcohol consumption in Sprague Dawley rats: moderation by long-term ethanol administration

The relationship between central serotonergic activities and voluntary alcohol consumption was studied in Sprague-Dawley rats, which normally have low alcohol preference. After initial screening for an evenly matched baseline alcohol preference, selective central serotonergic lesioning was induced by intracisternal injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). Control rats received injections of vehicle only. Both 5,7-DHT and vehicle-treated rats were further divided into two subgroups, which either had continued free access to ethanol (alcohol-drinking) or were deprived of it (alcohol-free). All rats were then tested again for alcohol preference. All rats were then killed, and the levels of monoamines in the brains were determined by high performance liquid chromatography with electrochemical detection. Behavioral results indicated that all 5,7-DHT-treated rats had significantly higher alcohol preference and consumption than the corresponding sham controls. Except in the cerebellum, the 5,7-DHT-treated rats had significantly lower levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in most brain regions compared with those in the corresponding sham controls. Treatment with 5,7-DHT also resulted in a decrease in serotonin turnover in all brain regions in the alcohol-free rats, except in the cerebellum. In alcohol-drinking rats, however, 5,7-DHT treatment only reduced serotonin turnover in the pons. The levels of norepinephrine and dopamine in several brain regions were not significantly different. Thus, it appeared that in the Sprague Dawley rats, 5,7-DHT treatment depleted 5-HT and 5-HIAA levels in most brain regions while increasing alcohol consumption. Chronic alcohol-drinking attenuated the increase in alcohol consumption associated with serotonergic lesions. Voluntary alcohol consumption seemed more associated with 5-HT turnover than with tissue 5-HT levels. Our data also suggested that tolerance to alcohol-induced hypothermia was primarily attributable to long-term alcohol drinking rather than serotonergic lesioning.

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.

Ipsapirone enhances the dopamine outflow via 5-HT1A receptors in the rat prefrontal cortex

In the present study, we investigated both the effect of ipsapirone on the dopamine outflow and its selectivity towards 5-HT1A receptors in the rat prefrontal cortex. Using a brain microdialysis method in freely moving animals, it was found that ipsapirone, 5 and 10 mg/kg dose-dependently enhanced the outflow of dopamine, while 2.5 mg/kg was ineffective. The above effects of ipsapirone were mimicked by buspirone (2.5 and 5 mg/kg), another 5-HT1A receptor agonist, but not 1-PP (1-pyrimidinylpiperazine, 5 mg/kg)-a centrally active metabolite of ipsapirone. The effect of ipsapirone (10 mg/kg) on the dopamine outflow in the rat prefrontal cortex was antagonized by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN-190, 1 mg/kg) and (N-tert-butyl-3-(4-(2-methoxyphenylpiperazin-1-yl)-2- phenylpropionamide (WAY 100135, 10 mg/k.g.), i.e. substances with agonistic/antagonistic and antagonistic properties in relation to 5-HT1A receptors, respectively. NAN-190 (1 mg/kg) enhanced the outflow of dopamine, while WAY 100135 (10 mg/kg) failed to alter it. It is concluded that 5-HT1A receptor agonists may be involved in the regulation of dopaminergic neurotransmission in the rat prefrontal cortex and may have therapeutic potential in the treatment of disorders associated with dysfunction of the mesocortical dopaminergic system.

Effect of ethanol on extracellular 5-HT and glutamate in the nucleus accumbens and prefrontal cortex: comparison between the Lewis and Fischer 344 rat strains

The present study investigated the impact of systemic (i.p.) ethanol administration on extracellular levels of serotonin and glutamate in the prefrontal cortex and the nucleus accumbens in Lewis and Fischer 344 rat strains using in vivo microdialysis. At 1.0 g/kg, ethanol elicited a significant increase in nucleus accumbens-dialysate levels of both 5-HT (44% +/- 16, P = 0.002) and glutmate (90% +/- 43, P = 0.009) in Lewis rats. In Fischer rats, there was no increase in 5-HT (6% +/- 7: P = 0.5), and a trend toward an increase in glutamate (88% +/- 46: P = 0.1). The 0.5 and 2.0 g/kg doses did not result in any significant change in extracellular 5-HT or glutamate in the nucleus accumbens or prefrontal cortex of either strain. The basal levels of glutamate, in both brain regions, were significantly lower in Lewis than in Fischer 344 rats. The basal levels of 5-HT were also lower in the nucleus accumbens of Lewis rats. These findings suggest that enhanced sensitivity of the mesoaccumbens 5-HT or glutamate systems to ethanol and/or inherent low basal levels of 5-HT or glutamate activity may be associated with the predisposition to alcohol-drinking behavior seen in Lewis rats.

Prefrontal levels of 5-HIAA, but not dopamine, predict alcohol consumption in male Wistar rats following 6-OHDA lesions

To examine the effects of dopamine (DA) on alcohol consumption, male Wistar rats were subjected either to 6-OHDA lesions of the frontal cortex (MPFC) or to a sham lesion/no lesion. Following surgery, rats were trained to drink alcohol on a sucrose-fading paradigm over the course of 6 weeks, at the completion of which they consumed a solution of 3% sucrose/10% alcohol. Daily consumption of alcohol was computed for each rat. Animals were sacrificed and the MPFC, nucleus accumbens (NA), and ventral tegmentum (VTA) were removed. Levels of DA and its metabolites (i.e., HVA and DOPAC), norepinephrine (NE), and serotonin (5-HT) and its metabolite (i.e., 5-HIAA) were measured for each brain region using HPLC with electrochemical detection. Post hoc analyses were run examining the relationship of DA and its metabolites, 5-HT and its metabolite (5-HIAA), and norepinephrine (NE) in the MPFC, NA, and VTA with alcohol consumption. The 6-OHDA lesions depleted DA to 74.5% of control levels in the MPFC, but did not significantly affect alcohol consumption. Post hoc analyses found that the "high" alcohol consumption group had significantly reduced levels of MPFC 5-HIAA in comparison to the "low" consumption group, but that there was no relationship of 5-HIAA levels in the VTA or NA to alcohol consumption. These findings suggest that MPFC DA is not critically involved in the regulation of alcohol consumption. They further suggest that MPFC serotonergic systems may play an important role in the regulation of alcohol consumption, although future experimentation directly manipulating 5-HT systems in the MPFC will be required to fully assess these findings.

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.

5-HT1A receptor agonists: recent developments and controversial issues

During the last decade, serotonin (5-HT)1A receptors have been a major target for neurobiological research and drug development. 5-HT1A receptors have been cloned and a variety of selective agonists, such as the aminotetraline 8-OH-DPAT and the pyrimidinylpiperazine ipsapirone, have become available. Demonstrations of apparent intrinsic activity of these ligands at 5-HT1A receptors, however, depend highly on the particular assay system. This may be due to the possible existence of receptor subtypes and to assay (or brain region)-dependent differences in receptor reserve and the nature of receptor-effector coupling. Nevertheless, the apparent intrinsic activity of 8-OH-DPAT seems to be higher (although possibly not yet maximal) than that of the pyrimidinylpiperazines. In the brain, 5-HT1A receptors are located presynaptically as somatodendritic receptors on 5-HT neurons and postsynaptically in particular limbic and cortical regions. Although it is generally accepted that presynaptic 5-HT1A receptors control 5-HT neuronal activity, recent evidence suggests an additional role of postsynaptic 5-HT1A receptors in cortex as part of a negative feedback loop. Anxiolytic and antidepressive properties of selective 5-HT1A receptor agonists have now been confirmed by clinical studies. Although it is well established that the latter properties depend on the agonistic activity of these compounds, the optimal level of intrinsic activity is still a matter of debate and may be dependent on the clinical indication. Such compounds may also have antiaggressive effects, and possibly anticraving effects (manifested by their alcohol intake-reducing effects in dependent animals), but the specificity of these so-called anti-impulsivity effects is still controversial and not yet tested clinically. Anticataleptic, antiemetic and neuroprotective properties have been demonstrated in different species. Behavioral studies on the mechanisms underlying the anxiolytic and antidepressive effects have examined the relative contribution of pre- and postsynaptic 5-HT1A receptors by means of local cerebral application and lesion techniques. Most evidence points towards a critical involvement of presynaptic receptors in the anxiolytic effects of 5-HT1A receptor agonists (although a possible contribution of postsynaptic receptors cannot be excluded). With regard to the antidepressive properties, a case can be made for the reverse; i.e., a strong involvement of postsynaptic receptors and a questionable contribution of presynaptic receptors. However, as the therapeutic effects of those 5-HT1A receptor (partial) agonists which have been tested clinically require repeated administration, attention has been directed increasingly towards chronic studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Modification of behavioral effects of 8-hydroxy-2-(di-n-propylamino)tetralin following chronic ethanol consumption in the rat: evidence for the involvement of 5-HT1A receptors in ethanol dependence

Behavioral effects induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; i.e., lower lip retraction, flat body posture, and forepaw treading) were examined in rats during ethanol withdrawal following a 2-week period of access to a liquid diet containing 9% (v/v) ethanol. After an 18 h withdrawal period, tolerance to 8-OH-DPAT-induced flat body posture and, conversely, sensitization to the effects of 8-OH-DPAT on lower lip retraction were observed in the 9% ethanol group as compared to control rats fed an isocaloric diet. In contrast, 8-OH-DPAT-induced forepaw treading in the 9% ethanol group was not significantly different in comparison to control rats. Plasma corticosterone levels were significantly higher in the ethanol-exposed group than in control animals, an effect which was not additive with the increase in corticosterone levels normally observed after the administration of low doses of 8-OH-DPAT. Altered flat body posture and lower lip retraction responses to a submaximal dose of 8-OH-DPAT (2.5 mg/kg i.p.) were still observed as late as 3 days after withdrawal of the 9% ethanol liquid diet, but were no longer apparent at 7 days. Interestingly, prominent ethanol withdrawal signs such as tremor and rigidity, while occurring on the first day, were completely absent on the third day. Taken together, these results indicate that chronic ethanol exposure differentially alters sensitivity to several pharmacological effects of the 5-HT1A receptor ligand 8-OH-DPAT. They further support the involvement of 5-HT (5-hydroxytryptamine, serotonin) systems in alcohol abuse and therapeutic interventions using 5-HT1A ligands.

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)

Effect of the 5-HT3 antagonist ondansetron on voluntary ethanol intake in rats and mice maintained on a limited access procedure

The effect of the 5-HT3 antagonist ondansetron on ethanol self-administration was examined in a limited access paradigm. Acute administration of ondansetron (0.01 and 0.1 mg/kg) reduced ethanol intake in male Wistar rats by 35%, whilst water intake was unaffected. Both a lower (0.001 mg/kg) and higher dose (1 mg/kg) of ondansetron failed to modify ethanol consumption. Ondansetron did not, however, alter the pharmacokinetic profile of an orally administered dose of ethanol (1 g/kg) over the same dose range. To examine the generality of these findings and to determine if tolerance would develop to the suppressant effects of ondansetron on ethanol intake, male C57BL/6 mice were treated with ondansetron (0.001, 0.01 and 0.1 mg/kg) over 22 days, 30 min prior to scheduled access to ethanol. Both 0.01 and 0.1 mg/kg doses reduced ethanol intake; however, water intake was not altered by either dose. This finding confirms and extends the generality of the effects of 5-HT3 receptor antagonists on ethanol intake across different species and different paradigms of ethanol consumption. More importantly, the present study shows that the reduction in ethanol intake induced by ondansetron was maintained even after a prolonged period of treatment and is not due to an alteration in the absorption or metabolism of ethanol.

Consequence of long-term exposure to corticosterone or dexamethasone on ethanol consumption in the adrenalectomized rat, and the effect of type I and type II corticosteroid receptor antagonists

The daily fluid intake of male Wistar rats with simultaneous access to 6% ethanol and water was determined during a baseline period (1 week), following adrenalectomy (1 week) and for 3 weeks following SC implantation of hormone pellets containing corticosterone (CORT) or dexamethasone (DEX). Ethanol consumption dropped during the first week of adrenalectomy (ADX) but increased again in the absence of hormone replacement to reach preoperative levels during the ensuing weeks. The CORT treatment, which produced plasma hormone levels similar to the 24-h mean concentration of adrenally intact rats, not only reversed the effect of ADX on alcohol consumption but also enhanced it to levels above those observed in intact rats. Water intake was not affected by the CORT treatment. DEX implants stimulated water intake, but did not enhance the drinking of ethanol. SC injections of RU 28318 (type I corticosterone receptor antagonist; 10 mg/kg) or mifepristone (RU 38486; type II receptor antagonist; 25 mg/kg) at the beginning and halfway through three daily, 6-h tests failed to affect ethanol drinking in adrenally intact rats or in ADX rats bearing CORT implants. Similarly, there was no effect of giving the two antagonists in combination. These results suggest that exogenous CORT can induce excessive alcohol intake in genetically unselected rats and that this facilitatory effect may be mediated by non-genomic cellular mechanisms.

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.

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.

Serotonin 5-HT3 antagonists fail to affect ethanol self-administration of rats

Five Long-Evans hooded rats were trained to lever press according to fixed-ratio 5 reinforcement schedules for 0.06 ml dipper deliveries of 8% w/v ethanol during daily (M-F) 0.5-h experimental sessions. After ethanol self-administration was established, doses of the serotonin 5-HT3 antagonists, ondansetron (0.03-3.0 mg/kg), granisetron (0.01-1.0 mg/kg), and SC-51296 (0.1-10.0 mg/kg) were administered prior to ethanol sessions to determine their effects on ethanol self-administration. None of the doses of the antagonists had significant effects on numbers of obtained ethanol deliveries. Subsequently, each antagonist (ondansetron, 0.1 mg/kg; granisetron, 0.3 mg/kg; SC-51296, 0.1 mg/kg) was administered b.i.d. for five consecutive daily sessions. During none of these chronic tests with the 5-HT3 antagonists were there significant main effects of drug administration. Overall, these results do not support the hypothesis that the serotonin 5-HT3 antagonists would have robust therapeutic efficacy in the treatment of alcoholism.