Alcohol drinking attenuated by sertraline in rats with 6-OHDA or 5,7-DHT lesions of N. accumbens: a caloric response?

Ayahuasca blocks ethanol preference in an animal model of dependence and shows no acute toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Ayahuasca, a psychoactive beverage prepared from Banisteriopsis caapi and Psychotria viridis, is originally used by Amazon-based indigenous and mestizo groups for medicinal and ritualistic purposes. Nowadays, ayahuasca is used in religious and shamanic contexts worldwide, and preliminary evidence from preclinical and observational studies suggests therapeutic effects of ayahuasca for the treatment of substance (including alcohol) use disorders.

AIM OF THE STUDY

To investigate the initial pharmacological profile of ayahuasca and its effects on ethanol rewarding effect using the conditioned place preference (CPP) paradigm in mice.

MATERIALS AND METHODS

Ayahuasca beverage was prepared using extracts of B. caapi and P. viridis, and the concentration of active compounds was assessed through high performance liquid chromatography (HPLC). The following behavioral tests were performed after ayahuasca administration: general pharmacological screening (13, 130, or 1300 mg/kg - intraperitoneally - i.p., and 65, 130, 1300, or 2600 mg/kg - via oral - v.o.); acute toxicity test with elevated doses (2600 mg/kg - i.p., and 5000 mg/kg - v.o.); motor activity, motor coordination, and hexobarbital-induced sleeping time potentiation (250, 500, or 750 mg/kg ayahuasca or vehicle - v.o.). For the CPP test, the animals received ayahuasca (500 mg/kg - v.o.) prior to ethanol (1.8 g/kg - i.p.) or vehicle (control group - i.p.) during conditioning sessions.

RESULTS

Ayahuasca treatment presented no significant effect on motor activity, motor coordination, hexobarbital-induced sleeping latency or total sleeping time, and did not evoke signs of severe acute toxicity at elevated oral doses. Ayahuasca pre-treatment successfully inhibited the ethanol-induced CPP and induced CPP when administered alone.

CONCLUSIONS

Our results indicate that ayahuasca presents a low-risk acute toxicological profile when administered orally, and presents potential pharmacological properties that could contribute to the treatment of alcohol use disorders.

Behavioral consequences of the downstream products of ethanol metabolism involved in alcohol use disorder

Research concerning Alcohol Use Disorder (AUD) has previously focused primarily on either the behavioral or chemical consequences experienced following ethanol intake, but these areas of research have rarely been considered in tandem. Compared with other drugs of abuse, ethanol has been shown to have a unique metabolic pathway once it enters the body, which leads to the formation of downstream metabolites which can go on to form biologically active products. These metabolites can mediate a variety of behavioral responses that are commonly observed with AUD, such as ethanol intake, reinforcement, and vulnerability to relapse. The following review considers the preclinical and chemical research implicating these downstream products in AUD and proposes a chemobehavioral model of AUD.

Optogenetic investigation of neural mechanisms for alcohol-use disorder

Optogenetic techniques have been widely used in the study of neuropsychiatric diseases such as anxiety, depression, and drug addiction. Cell-type specific targeting of optogenetic tools to neurons has contributed to a tremendous understanding of the function of neural circuits for future treatment of neuropsychiatric disorders. Though optogenetics has been widely used in many research areas, the use of optogenetic tools to uncover and elucidate neural circuit mechanisms of alcohol's actions in the brain are still developing. Here in this review article, we will provide a basic introduction to optogenetics and discuss how these optogenetic experimental approaches can be used in alcohol studies to reveal neural circuit mechanisms of alcohol's actions in regions implicated in the development of alcohol addiction.

Ethanol consumption in the Sprague-Dawley rat increases sensitivity of the dorsal raphe nucleus to 5,7-dihydroxytryptamine

Alcoholism afflicts 1 in 13 US adults, and comorbidity with depression is common. Levels of serotonin (5-HT) metabolites in alcoholic or depressed humans and rat strains are lower compared to healthy counterparts. Rats bred for ethanol (EtOH) preference are common in EtOH studies, however out-bred strains better model the range of EtOH consumption in humans. We examined voluntary EtOH consumption in out-bred Sprague-Dawley (SD) rats placed in the 20% EtOH intermittent access drinking paradigm (IA). Acquisition of 20% EtOH consumption (g EtOH/kg/24h) was assessed during the first 6-8 weeks of IA. Rats naturally separated into two groups (Drinkers or Non-drinkers) based on EtOH intake above or below 0.5 g/kg/24h prior to treatment intervention. We examined the effect of central 5-HT depletion on EtOH consumption by infusing 5,7-dihyroxytryptamine (5,7-DHT; i.c.v., 200-300 μg) or vehicle and measured EtOH consumption for 4 weeks post-operatively in IA. Compared to baseline, there was no effect of vehicle or 5,7-DHT on EtOH consumption during the post-operative period. Quantification of 5-HT depletion in the dorsal raphe nucleus (DRN) using tryptophan hydroxylase-2 (TPH2) immunohistochemistry resulted in a 76% decrease in staining with 5,7-DHT treatment. Interestingly, preservation of the ventromedial (VM) sub-regions was evident in all animals treated with 5,7-DHT, regardless of drinking behavior. In addition, Drinkers treated with 5,7-DHT had significantly more TPH2 depletion in the DRN compared to Non-drinkers. Our findings indicate that out-bred SD rats exhibit a natural EtOH consumption behavior (Drinker or Non-drinker) that is stable across time and independent of 5-HT depletion in the CNS. In addition, rats that regularly consumed >0.5 g EtOH/kg had greater sensitivity to 5,7-DHT in the DRN, indicating an interaction between EtOH and sensitivity of DRN 5-HT cells to neurotoxic substances. This may contribute to the dysfunctionality of the 5-HT system in alcoholic humans and lead to a better understanding of current pharmacological treatments for this addiction.

Contingent and non-contingent effects of low-dose ethanol on GABA neuron activity in the ventral tegmental area

Ventral tegmental area (VTA) GABA neurons appear to be critical regulators of mesocorticolimbic dopamine (DA) neurotransmission, which has been implicated in alcohol reward. The aim of this study was to evaluate the effects of low-dose "non-contingent" intravenous (IV) ethanol (0.01-0.1 g/kg) on VTA GABA neuron firing rate and synaptic responses, as well as VTA GABA neuron firing rate during low-dose "contingent" IV ethanol self-administration. Intravenous administration of 0.01-0.03 g/kg ethanol significantly increased VTA GABA neuron firing rate and afferent-evoked synaptic responses. In the runway self-administration paradigm, presentation of an olfactory cue (S+; almond extract) or no-cue (S-; no odor) in the Start box was paired with IV administration of low-dose ethanol (0.01 g/kg) or saline in the Target box. Runway excursion times decreased significantly in association during S+, and increased significantly during S- conditions. The firing rate of VTA GABA neurons markedly increased when rats received 0.01 g/kg IV ethanol in the Target box. VTA GABA neuron firing increased in the Start box of the runway in association with S+, but not S-. These findings demonstrate that VTA GABA neurons are activated by low-dose IV ethanol and that their firing rate increases in anticipation of ethanol reward.

Roles of the nucleus accumbens and amygdala in the acquisition and expression of ethanol-conditioned behavior in mice

Although progress has been made identifying the neural areas underlying the primary reinforcing effects of ethanol, few studies have examined the neural areas mediating ethanol-induced conditioned effects. Previous work using the conditioned place preference (CPP) procedure implicates the ventral tegmental area (VTA) (Bechtholt and Cunningham, 2005), but the downstream neural areas modulating the conditioned rewarding effects of ethanol have not been identified. Although the nucleus accumbens (Acb) and the amygdala (Amy), which both receive dopamine innervation from the VTA, have been implicated in the primary reinforcing effects of ethanol, the roles these areas play in ethanol-conditioned behaviors are unknown. In the present set of experiments, we use the CPP procedure along with selective electrolytic lesions to examine the neural areas underlying the acquisition and expression of ethanol conditioned behavior. In the acquisition experiment, male DBA/2J mice received bilateral lesions of the Acb or Amy before CPP training. In the expression experiments, mice received bilateral lesions of the Acb, Acb shell, Acb core, and Amy, or unilateral lesions of the Amy after training but before testing. Lesions of the Acb and Amy before training disrupted acquisition and expression of ethanol CPP. However, when given after training, only lesions of the Amy disrupted expression, whereas lesions of the Acb core facilitated loss of responding, of ethanol CPP. For the first time, these results demonstrate the role of the Acb and Amy in the acquisition and expression of ethanol-induced conditioned reward.

Effect of DOV 102,677 on the volitional consumption of ethanol by Myers' high ethanol-preferring rat

BACKGROUND

Inhibitors of monoamine neurotransmitter transporters are well established as antidepressants. However, the evidence that single (serotonin) or dual (serotonin-norepinephrine) neurotransmitter uptake inhibitors can treat ethanol abuse, either as a comorbidity with depression or as a separate entity, is inconsistent. Drugs that have, in addition, the ability to inhibit dopamine uptake may have an advantage in the treatment of alcohol abuse. Therefore, the inhibitor of norepinephrine, serotonin and dopamine uptake, DOV 102,677, was tested for its effects on the volitional consumption of ethanol by an ethanol-preferring rat strain.

METHODS

Myers' high ethanol-preferring rats were screened by a 10-day, 3 to 30% step-up test and then given free access to the preferred concentration of ethanol in a 3-bottle choice task. Consumption of ethanol (g/kg), water, food, and body weight were measured daily during a 3-day predrug treatment period, a 3-day treatment period, and a 3-day posttreatment period. Additional Sprague-Dawley rats were observed for 24 hours for the behavioral effects of 2.0 mg/kg s.c. reserpine after a 30-minute pretreatment with different doses of DOV 102,677.

RESULTS

The triple monoamine uptake inhibitor DOV 102,677 dose-dependently decreased the volitional consumption of ethanol by as much as 71.2% (20 mg/kg i.p., b.i.d.) over 3 days of administration. This effect carried over into the posttreatment period. Similarly, the proportion of ethanol to total fluids consumed declined by 66.2% (20 mg/kg s.c., b.i.d.), while food consumption and body weight were unaltered. In contrast, amperozide (2 mg/kg i.p., b.i.d.) suppressed the amount of ethanol consumed by 56%, while naltrexone (5 mg/kg i.p., b.i.d.) was without effect. DOV 102,677 (40 mg/kg s.c.) inhibited reserpine-induced akinesia and ptosis, but not hypothermia in Sprague-Dawley rats, consistent with its transient inhibition of serotonin transport, and more long-lived inhibition of norepinephrine and dopamine uptake.

CONCLUSIONS

DOV 102,677 significantly decreased the volitional consumption of ethanol with minimal alterations in the intake of food or on body weight in an ethanol-preferring rat strain, suggesting that triple reuptake inhibitors may find utility in treating alcohol abuse.

The role of mesolimbic dopamine in the development and maintenance of ethanol reinforcement

The neurobiological processes by which ethanol seeking and consumption are established and maintained are thought to involve areas of the brain that mediate motivated behavior, such as the mesolimbic dopamine system. The mesolimbic dopamine system is comprised of cells that originate in the ventral tegmental area (VTA) and project to several forebrain regions, including a prominent terminal area, the nucleus accumbens (NAcc). The NAcc has been subdivided into core and shell subregions. Both areas receive converging excitatory input from the cortex and amygdala and dopamine input from the VTA, with the accumbal medium spiny neuron situated to integrate the signals. Although forced ethanol administration enhances dopamine activity in the NAcc, conclusions regarding the role of mesolimbic dopamine in ethanol reinforcement cannot be made from these experiments. Behavioral experiments consistently show that pharmacological manipulations of the dopamine transmission in the NAcc alter responding for ethanol, although ethanol reinforcement is maintained after lesions of the accumbal dopamine system. Additionally, extracellular dopamine increases in the NAcc during operant self-administration of ethanol, which is consistent with a role of dopamine in ethanol reinforcement. Behavioral studies that distinguish appetitive responding from ethanol consumption show that dopamine is important in ethanol-seeking behavior, whereas neurochemical studies suggest that accumbal dopamine is also important during ethanol consumption before pharmacological effects occur. Cellular studies suggest that ethanol alters synaptic plasticity in the mesolimbic system, possibly through dopaminergic mechanisms, and this may underlie the development of ethanol reinforcement. Thus, anatomical, pharmacological, neurochemical, cellular, and behavioral studies are more clearly defining the role of mesolimbic dopamine in ethanol reinforcement.

Rats on the grog: novel pharmacotherapies for alcohol craving

Current pharmacotherapies for alcohol dependence in humans (e.g., naltrexone, acamprosate) are meeting with only limited therapeutic success. The development of novel pharmacotherapies is urgently needed but is reliant upon the screening of large numbers of candidate "anticraving" drugs using appropriate animal models. The development of animal models is complex because (1) laboratory animals are often reluctant to consume large quantities of alcohol, (2) inducing a state of alcohol dependence, analogous to the human condition, may require many months of alcohol exposure, (3) concluding that a given drug selectively reduces alcohol craving requires very carefully controlled experiments, and (4) false positives and false negatives may result from the sometimes distinct physiology and psychology of the alcohol-addicted human and rat. To address some of these problems, our laboratory has recently developed the "beer model" of alcohol dependence and craving. Rats, like humans, have a prodigious appetite for beer and will drink much more beer than equivalent ethanol solutions in water. Beer consumption in rats leads to clear signs of intoxication, anxiety reduction, and signs of withdrawal when beer access is suddenly denied. We have found that beer craving in rats is selectively reduced by the cannabinoid receptor antagonist SR 141716 and the opioid receptor antagonist naltrexone. Combining these two drugs appears to have a synergistic anticraving effect. Other promising pharmacotherapies for the future are discussed.

The effects of antidepressant treatment on serotonergic and dopaminergic systems in Fawn-Hooded rats: a quantitative autoradiography study

Fawn-Hooded (FH) rats exhibit a phenotype including depressive behaviour and high alcohol preference, and as such tricyclic antidepressants and selective serotonin reuptake inhibitors (SSRIs) reduce alcohol consumption in this rat strain [Psychiatr. Genet. 12 (2002) 1-16]. However, the neurochemical effects of these antidepressants on monoamine systems in the brain, especially in mesolimbic areas have not been studied in FH rats. Therefore, the present study investigated neurochemical effects of subchronic treatment (10 days) with desipramine (DMI) and sertraline on several neurochemical markers of serotonin and dopamine systems. Binding to these markers including dopamine transporters (DATs), 5-HT transporters (SERTs), 5-HT(1A)- and 5-HT(2A)-receptors in rat brain sections was performed by quantitative autoradiography. The findings from the present study revealed that DMI and sertraline exhibited differential effects on SERTs and DATs in FH rat brain. For example, DMI caused a dramatic up-regulation of DATs whereas sertraline had no effect on DAT binding. In addition, both antidepressants showed some common and some differential effects on the binding to 5-HT(1A)- and 5-HT(2A)-receptors dependent upon region. These data demonstrate that DMI and sertraline differentially effect serotonergic and dopaminergic systems in mesolimbic regions in FH rats, suggesting that there may be different neurochemical mechanisms underlying their efficacy to reduce ethanol consumption in this animal model.

Double-blind clinical trial of sertraline treatment for alcohol dependence

Clinical studies that have evaluated serotonergic medications to reduce alcohol consumption have yielded conflicting results. These studies primarily treated patients with alcohol dependence, excluding those with a current depressive disorder, in an effort to differentiate any medication effects directly on drinking from those on mood. Yet despite the exclusion of current depression, a group of alcohol-dependent patients who are not depressed can be highly heterogeneous. For example, this subgroup can include those with a lifetime depressive disorder. If these patients were more sensitive to serotonergic medications than patients without a lifetime depressive disorder, medication effects in a subgroup of patients who were not depressed could be obscured. Thus, the purpose of this study was to examine the efficacy of sertraline for treating alcohol dependence in patient groups that were differentiated by the presence or absence of lifetime depression. This study examined the effectiveness of sertraline (200 mg/day) or placebo for 14 weeks in 100 alcohol-dependent subjects with (N = 53) or without (N = 47) a lifetime diagnosis of comorbid depression. Sertraline treatment seemed to provide an advantage in reducing drinking in alcohol-dependent patients without lifetime depression, illustrated best with a measure of drinking frequency during treatment. However, sertraline was no better than placebo in patients with a diagnosis of lifetime comorbid depression, and current depression did not change the results. Treatment with selective serotonin reuptake inhibitors may be useful in alcohol-dependent patients who are not depressed. Subtyping those with alcohol dependence on the basis of the absence versus the presence of a lifetime depressive disorder may help to resolve conflicting findings in the literature on the treatment of alcohol dependence with serotonergic medications.

Role of serotonin and serotonin-selective pharmacotherapy in alcohol dependence

The majority of studies that have examined the usefulness of pharmacotherapies selective for serotonin (5-hydroxytryptamine; 5-HT) as a treatment for alcohol dependence have been standard, double-blind clinical trials that include patients with a variety of clinical presentations. Almost all of the early studies evaluated heavy social drinkers and found only a modest advantage for 5-HT pharmacotherapies in reducing the number of drinks per day. Also, the advantage of these pharmacotherapies was observed primarily when these agents were given at higher daily dosages than suggested prescribing practices for use as an antidepressant. The few studies that evaluated treatment-seeking patients found that 5-HT pharmacotherapies were not instrumental in reducing drinking rates compared with placebo. These results led to a dampening of enthusiasm for use of these agents in treating alcohol dependence. However, more recent investigations have begun to target subgroups with potential abnormalities in 5-HT neurotransmission. The thinking is that these medications should be most useful in alcohol-dependent individuals who have more clearly delineated suggestive signs of 5-HT dysfunction, such as concomitant depression or anxiety. Although few results are available to date, there is growing evidence to suggest that alcohol-dependent subgroups are differentially responsive to 5-HT pharmacotherapies with respect to drinking-related outcomes. This may explain the modest and variable 5-HT pharmacotherapeutic effects that were reported in the earlier studies, which included large heterogeneous patient groups. Further investigations are needed to confirm these initial optimistic results.

Effects of chronic ethanol administration on serotonin metabolism in the various regions of the rat brain

Changes in serotonin (5-HT) and 5-hydroxy indole acetic acid (5-HIAA), its major metabolite, in cerebral cortex, corpus striatum and hippocampus were investigated at 10th and 21st days of chronic ethanol ingestion in Wistar rats. Ethanol (7.2% v/v) was given to rats in a modified liquid diet. Biochemical analysis was performed in two groups of ethanol-treated and control rats (n = 6 for each group). Rats in each group were decapitated at the 10th and 21st days of ethanol consumption. Brains were removed and cerebral cortex, corpus striatum and hippocampus were dissected. 5-HT and 5-HIAA levels were measured in respective brain regions by using high performance liquid chromatography. In cerebral cortex and corpus striatum, 5-HT levels were significantly lower than control at the 10th day of ethanol consumption. At the 21st day, the levels tended to remain low, but not significantly different statistically. In hippocampus, 5-HIAA levels were significantly higher than control at 10th day of ethanol consumption. Increased 5-HIAA level returned to control values at the 21 st day of ethanol consumption. Our results suggest that, 5-HT clearly seems to play a critical role in the brain at the 10th day of chronic ethanol consumption.

Comparison of the effects of the selective serotonin-reuptake inhibitors fluoxetine, paroxetine, citalopram and fluvoxamine in alcohol-preferring cAA rats

Clinical studies indicate that selective serotonin-reuptake inhibitors (SSRIs) may decrease alcohol intake and craving in particular subgroups of alcoholics. The aim of the present study was to compare the behavioral profile of various SSRIs in alcohol-preferring cAA rats, a genetic model of alcoholism. The effects of acute IP administration of fluoxetine (doses in mg/kg 1-10), citalopram (3-30), fluvoxamine (3-30) and paroxetine (1-10) on ethanol (EtOH) intake and preference, as well as food and total fluid intake, were determined in a 12-h access, water vs. 10% v/v EtOH two-bottle choice paradigm. Each compound reduced EtOH intake [Minimal Effective Doses (MEDs) 5, 10, 30 and 1 mg/kg for fluoxetine, citalopram, fluvoxamine, and paroxetine, respectively]. The degree of selectivity, that is, the extent to which reductions in EtOH intake could be separated from reductions in food and/or total fluid intake varied across the compounds. Thus, whereas EtOH intake was more markedly affected than food intake by fluoxetine, both parameters were equally affected by citalopram, and food intake was more markedly affected than EtOH intake by fluvoxamine and paroxetine. The anti-alcohol effect also differed with respect to specificity, that is, the degree to which effects on EtOH intake coincided with effects on EtOH preference. Whereas fluoxetine showed the highest level of specificity, followed by citalopram and fluvoxamine, the effect of paroxetine was nonspecific. The observed variation in the degree of selectivity and specificity of the anti-alcohol effect of SSRIs suggests that reductions in EtOH intake are not merely a consequence of a general suppressive effect on consummatory behavior. It is hypothesized that differences between the behavioral profiles of these compounds reflect a differential involvement of 5-HT receptor subtypes.

Genetics of alcoholism: rapid development of a new high-ethanol-preferring (HEP) strain of female and male rats

A genetically based animal model of alcoholism has been developed in a relatively short period of 3 years. The new strain is characterized by an intense preference for ethanol over water as well as unique behavioral, neurochemical and other attributes. This new strain, termed high-ethanol-preferring (HEP) rats, was derived initially from selective cross-breeding of a variant strain of female Harlan Sprague-Dawley (SD) rats with the outbred Wistar line of male ethanol-preferring (P) rats. In this study, drinking patterns of both genders were obtained over 10 days by presenting water and ethanol in concentrations ranging from 3% to 30%. To expedite the development of the new strain, only three to five female and male rats served as breeders, which were chosen from all litters on the basis of their maximum g/kg intake integrated with proportion of ethanol to total fluid values. Profiles of intake of preferred concentrations of ethanol were obtained over 24 h of unlimited access as well as during 2-h intervals of limited access to ethanol. Levels of blood ethanol were measured in both female and male HEP animals during bouts of ethanol drinking in the limited access paradigm. By the sixth generation of HEP rats, ethanol consumption of the females often exceeded that of any other rat genetically bred to drink ethanol (e.g., at a concentration of 15.7%, 10.3 g/kg per day). Seven additional characteristics are notable: 1) the HEP rats prefer ethanol in the presence of a nutritious chocolate drink or nonnutrient sweetened solution (aspartame); 2) high levels of blood ethanol are associated with their drinking; 3) females drink significantly greater g/kg amounts of ethanol than HEP males and prefer a higher percent concentration of ethanol; 4) the drinking of ethanol by the female HEP animals does not fluctuate during the estrous cycle; 5) neurochemical assays show differential profiles of 5-HT, dopamine, and their metabolites in different regions of the brain; 6) measures of activity using the elevated plus maze, open field, and cork gnawing reveal differences between genders of HEP rats and SD rats; and 7) the HEP animals are without phenotypically expressed abnormalities. Finally, one cardinal principle derived from this study revealed that the breeding strategy to develop high-ethanol-drinking rats centers on the use of multiple solutions of ethanol whereby the intakes of ethanol in concentration of 9% through 20% dictate the ultimate selection of breeding pairs over successive F generations. Further, it is concluded that because of an intense rise in ethanol drinking of the F1 generation of female HEP rats well above that of the parental SD female breeders, the complex genotypic characteristic of the male P rat is predominantly responsible for evoking ethanol drinking in female offspring.

Citalopram as an inhibitor of voluntary ethanol intake in the male rat

Psychological dependence was induced in rats by a 1-year intermittent exposure to intoxicating doses of ethanol, and recorded by the rat's ability to later take the same dose of ethanol independent of the offered concentration. Citalopram (10 or 40 mg/kg/day) was given for 3 weeks with ethanol available only the first and the last day; 10 mg/kg had no effect. On the first treatment day 40 mg/kg decreased ethanol intake. On the last treatment day 40 mg/kg had no effect. The following week the ethanol intake was higher than before the treatment in the 40 mg/kg group. During the four posttreatment weeks the ethanol intake of the 40 mg/kg group dropped significantly. Citalopram was retested 18 weeks after the first treatment during 1 week, with continuous access to ethanol; 10 mg/kg had no effect and 40 mg/kg decreased ethanol intake at day 1, reaching a minimum in day 3. A tolerance to this effect was seen at the end of the week. Thus, in this model an acute dose of citalopram can decrease ethanol intake, but tolerance to this effect develops when citalopram is given both with and without access to ethanol.

Putative oxidative metabolites of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline of potential relevance to the addictive and neurodegenerative consequences of ethanol abuse

Ethanol is metabolized in the brain by catalase/H2O2 to yield acetaldehyde and by an ethanol-inducible form of cytochrome P450 (P450 IIE1) in a reaction that yields oxygen radicals. Within the cytoplasm of serotonergic axon terminals these metabolic pathways together provide conditions for the endogenous synthesis of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (1), by reaction of acetaldehyde with unbound 5-hydroxytryptamine (5-HT), and for the oxygen radical-mediated oxidation of this alkaloid. The major initial product of the hydroxyl radical (HO.)-mediated oxidation of 1 in the presence of free glutathione (GSH), a constituent of nerve terminals and axons, is 8-S-glutathionyl-1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (6). When administered into the brains of mice, 6 is a potent toxin (LD50 = 2.9 microg) and evokes episodes of hyperactivity and tremor. Compound 6 binds at the GABA(B) receptor and evokes elevated release and turnover of several neurotransmitters. Furthermore, the GABA(B) receptor antagonist phaclofen attenuates the behavioral response caused by intracerebral administration of 6. These observations suggest that 6 might be an inverse agonist at the GABA(B) receptor site. Accordingly, it is speculated that ethanol drinking might potentiate formation of 6 that contributes to elevated release of several neurotransmitters including dopamine (DA) and endogenous opioids in regions of the brain innervated by serotonergic axon terminals. Subsequent interactions of DA and opioids with their receptors might be related to the initial development of dependence on ethanol. Redox cycling of 6 (and of several putative secondary metabolites) in the presence of intraneuronal antioxidants and molecular oxygen to produce elevated fluxes of cytotoxic reduced oxygen species might contribute to the degeneration of serotonergic pathways. Low levels of 5-HT in certain brain regions of the rat predisposes these animals to drink or augments drinking. Accordingly, 6, formed as a result of ethanol metabolism in the cytoplasm of certain serotonergic axon terminals, might contribute to the initial development of dependence on ethanol, by mediating DA and opioid release, and long-term preference and addiction to the fluid as a result of the progressive degeneration of these neurons.

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

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

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

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

Lesioning of midbrain raphe nuclei with 5,7-DHT fails to alter ethanol intake in the low alcohol drinking (LAD) rat

1. The effect of 10 g 5,7-dihydroxytryptamine (5,7-DHT) micro-injected into both the dorsal (DRN) and the median raphe nuclei (MRN) on the intake of ethanol in the low alcohol drinking (LAD) rat was measured using a standard 3-30% ethanol preference test. 2. The combined lesion of both midbrain structures depleted the levels of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) significantly in each of eight major regions of the brain. The levels of norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) remained unchanged after the lesion. 3. The effects of the neurotoxin lesions on the intakes of ethanol, food, water and total amount of fluid consumed were not significant. 4. The results corroborate our previous findings with the Sprague-Dawley strain of rat and suggest that although brain 5-HT may play a role in the maintenance of basal patterns of ethanol drinking, this monoamine may not be able to modify further the consumption of this fluid after lesioning with 5,7-DHT.

Influence of glutathione on the oxidation of 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline: chemistry of potential relevance to the addictive and neurodegenerative consequences of ethanol use

Recent evidence suggests that intraneuronal metabolism of ethanol by catalase/H2O2 and an ethanol-inducible form of cytochrome P450 together generate acetaldehyde and oxygen radicals including the hydroxyl radical (HO.). Within the cytoplasm of serotonergic neurons, these metabolic processes would thus provide acetaldehyde, which would react with unbound 5-hydroxytryptamine (5-HT) to give 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (1), known to be formed at elevated levels in the brain following ethanol drinking, and HO. necessary to oxidize this alkaloid. In this study, it is demonstrated that the HO.-mediated oxidation of 1 at physiological pH yields 1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (8) that reacts avidly with free glutathione (GSH), a significant constituent of axons and nerve terminals, to give diastereomers of 8-S-glutathionyl-1-methyl-1,2,3,4-tetrahydro-beta-carboline-5,6-dione (9A and 9B). In the presence of free GSH, ascorbic acid, other intraneuronal antioxidants/reductants, and molecular oxygen diastereomers, 9A/9B redox cycle in reactions that generate H2O2 and, via trace transition metal ion catalyzed decomposition of the latter compound, HO.. Further reactions of 9A/9B with GSH and/or HO. generate several additional glutathionyl conjugates that also redox cycle in the presence of intraneuronal reductants and molecular oxygen forming H2O2 and HO.. Thus, intraneuronal formation of 1 and HO. as a consequence of ethanol drinking and resultant endogenous synthesis of 8,9A, and 9B would, based on these in vitro chemical studies, be expected to generate elevated fluxes of H2O2 and HO. leading to oxidative damage to serotonergic axons and nerve terminals and the irreversible loss of GSH, both of which occur in the brain as a consequence of ethanol drinking. Furthermore, deficiencies of 5-HT and loss of certain serotonergic pathways in the brain have been linked to the preference for and addiction to ethanol.

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.

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.

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.

Alcohol drinking in rats injected ICV with 6-OHDA: effect of 8-OHDPAT and tropisetron (ICS 205930)

6-Hydroxydopamine (6-OHDA) was administered ICV to Wistar male rats. Lesioned animals displayed lower preference for ethanol (ETOH) than sham-operated rats. Among 6-OHDA lesioned rats only 9% became high-preferring whereas 20% of sham-operated animals became high-preferring ones. Both tropisetron (the antagonist of 5-HT3 receptors) and 8-OHDPAT (the 5-HT1A receptor agonist) reduced ETOH drinking in high-preferring rats. However, in 6-OHDA lesioned rats the effect of tropisetron was reduced although 8-OHDA retained its effect on ETOH consumption. These results suggest that brain DA neurons are involved in tropisetron action but are not responsible for antipreference effect of 8-OHDPAT.

The effects of sertraline on nicotine self-administration and food-maintained responding in squirrel monkeys

Recent reports suggested the involvement of serotonergic mechanisms in nicotine self-administration. The present study assessed the effects of sertraline, a selective serotonergic uptake inhibitor, on the reinforcing effects of i.v. nicotine (30 microgram/kg per injection) in squirrel monkeys responding under a fixed-ratio schedule. Nicotine (10-100 micrograms/kg per injection) produced a significant inverted U-shaped distribution on FR rate. Vehicle or sertraline (3, 6, 12, 24 mg/kg, p.o.) produced no changes in the response rates maintained by 30 micrograms/kg per injection i.v. nicotine, but sertraline produced non-significant increases response rates maintained by 10 micrograms/kg per injection nicotine and vehicle. In a separate group of monkeys, sertraline given in combination with i.m. doses of nicotine produced a significant dose-dependent decrease in responding maintained by food-pellet delivery. Thus, sertraline produced differential effects on response rates that may be related to (1) route of nicotine administration and (2) whether the behavior was maintained by nicotine or food. In addition, the results of the self-administration study suggest that sertraline would not disrupt well-maintained responding for nicotine.

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.

Genetics of alcoholism: simultaneous presentation of a chocolate drink diminishes alcohol preference in high drinking HAD rats

Through selective crossbreeding of the N/Nih heterogeneous stock of rats, two genetic lines of rats have been developed that are categorized by their preference for ethyl alcohol as high alcohol drinking (HAD) and low alcohol drinking (LAD) animals. Corresponding to other strains of rat bred for alcohol selection or rejection, they were subdivided on the basis of their intake of a solution of 10% alcohol vs. water. The present experiments were designed to determine whether the HAD-1 and LAD-1 lines are similar to the P and NP rats in their profile of alcohol consumption. Five successive three-bottle preference tests for alcohol drinking in the presence of water were undertaken in both HAD (n = 9) and LAD (n = 10) rats as follows: 10% alcohol for 5 days; 3-30% concentrations of alcohol increased over 11 days; the maximally preferred concentration of alcohol for 5 days; this maximally preferred concentration of alcohol plus either chocolate Slender for 5 days, or an aspartame solution for 5 days. The intake of alcohol of the LAD rats during the 10% test was 0.4 g/kg/day, whereas during the 3-30% test, the maximum intake was 1.7 g/kg/day; their maximally preferred concentrations ranged between 7% and 9% alcohol. In contrast, the intake of 10% alcohol of the HAD rats was 6.5 g/kg/day, whereas during the 3-30% test the mean daily intake was 6.6 g/kg/day; the maximally preferred solutions of the HAD rats ranged between 13 to 20%, with the mean maximum intake of 10.57 g/kg/day reached at the 20% concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Alcohol drinking in rats treated with 5,7-dihydroxytryptamine: effect of 8-OH-DPAT and tropisetron (ICS 205-930)

5,7-Dihydroxytryptamine (5,7-DHT) was administered ICV to Wistar male rats. Lesioned rats displayed higher preference for ETOH than sham-lesioned animals. Among 5,7-DHT-pretreated rats 38% became high-preferring, while only 22% of sham-lesioned rats displayed this behavioural pattern (p < 0.05). Both 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; the agonist of serotonin 5-HT1A receptors) and tropisetron (ICS 205-930, the antagonist of 5-HT3 receptors) reduced ETOH consumption in high-preferring, sham-lesioned rats. However, in 5,7-DHT rats the effect of 8-OH-DPAT was completely abolished, while tropisetron retained its antipreference activity. Therefore, it seems that 5-HT1A autoreceptors are critically involved in 8-OH-DPAT action, while 5-HT3 receptor sites responsible for tropisetron action are located beyond the 5-HT system.

Low doses of the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH DPAT) increase ethanol intake

Previous work has reported that the 5-hydroxytryptamine (5-HT)1A agonist, 8-hydroxy 2-(di-n-propylamino)tetralin (8-OH DPAT), reduces ethanol intake by rats. However, as 8-OH DPAT reduces 5-HT neurotransmission, these findings are inconsistent with the proposed inhibitory role of central 5-HT neurons on ethanol intake. We examined the effect of 8-OH DPAT on ethanol, water and food intake in rats maintained on a limited access schedule using a lower dose range (6-250 micrograms/kg) and by assessing concomitant changes in behaviour. Low doses of 8-OH DPAT enhanced ethanol intake even when food and water were offered as alternatives. Suppression in ethanol intake was observed at higher doses where elements of the 5-HT syndrome were apparent. Similar observations were made in both fluid and non-fluid deprived water drinking rats, suggesting the latter effect is non-selective. Therefore 8-OH DPAT may both increase or decrease ethanol consumption in the rat depending on the dose used.

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

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

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

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

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

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

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

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

Involvement of the serotonergic system in ethanol intake in the rat

A two-bottle, free-choice paradigm was used to investigate the influence of the serotonergic (5-HT) system on ethanol intake in genetically heterogeneous Wistar rats. Systemic administration of the 5-HT1A agonist ipsapirone (1.25-5.0 mg/kg) caused a dose-dependent decrease in ethanol preference and intake, while the 5-HT2 antagonist ritanserin (1.25-5.0 mg/kg) and the 5-HT3 antagonists ondansetron (0.01-1.0 mg/kg) and granisetron (0.5-1.0 mg/kg) failed to alter ethanol consumption. The effect of ipsapirone treatment on ethanol intake was more pronounced in high-preferring animals than in low-preferring. A closer look at the microstructure of the rat's drinking behaviour by means of a microcomputer-controlled data acquisition system showed that ipsapirone treatment caused a significant decrease in the number of licks recorded at the ethanol-containing bottle and a decrease in the time spent at this bottle. Furthermore, ipsapirone treatment caused a significant increase in the number of breaks in licking behaviour recorded at this bottle. The drinking behaviour at the water-containing bottle was not affected by the ipsapirone treatment. Neither was the rat's eating behaviour altered by this treatment. These findings support the hypothesis that the 5-HT system is involved in the regulation of ethanol intake, with special emphasis on the involvement of the 5-HT1A receptor subtype, and may indicate that central reward-mediating mechanisms are influenced.

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

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

Ethanol consumption following acute fenfluramine, fluoxetine, and dietary tryptophan

Male Sprague-Dawley rats fed a commercial diet with or without tryptophan supplementation (0.5% L-TRP) were treated with single IP injections of fenfluramine or fluoxetine. Rats had been water deprived prior to injection and food was removed during the period of fluid availability. They were offered, following drug or saline injection, water, a 5% ethanol solution, or an isocaloric sucrose solution (8.75%) for 1 h. Fenfluramine injection significantly reduced intake of all fluids, but its effect on ethanol was significantly greater than for water or sucrose solutions. Fluoxetine suppressed water and ethanol intake but not that of sucrose; the reduction in ethanol intake was significantly greater than for water. Ingestion of the tryptophan-supplemented diet in the absence of any drug treatment had no effect on fluid intake. However, the tryptophan supplementation significantly enhanced the reduction in ethanol intake induced by fenfluramine and fluoxetine. It appears that both fenfluramine and fluoxetine decrease ethanol intake more so than that of water or sucrose and that this effect is exacerbated by tryptophan supplementation.

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

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

Effect of dexfenfluramine on alcohol intake in alcohol-preferring "P" rats

The intake of alcohol, in 2-h daily sessions, by the preferring (P) line of rats was reduced in a dose-related manner by acute subcutaneous (SC) administration of dexfenfluramine (DFEN). Ad lib intake of alcohol was reduced by chronic SC administration of DFEN. The effective doses and magnitude of effects of DFEN on alcohol intake are comparable to those previously reported for DFEN anorexia. Because DFEN anorexia is related to increased brain serotonin (5HT) activity, its effect on alcohol consumption may also be via 5HT.

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

This investigation was undertaken to determine the effect of a unique psychotropic agent on the volitional drinking of alcohol induced pharmacologically in the rat by an inhibitor of aldehyde dehydrogenase. Following administration of cyanamide in a dose of 10 mg/kg twice daily for 3 days, the pattern of drinking of ethyl alcohol was determined in each of 12 Sprague-Dawley rats by means of a standard preference test for 3-30% alcohol vs. water. Then, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 7-15%. After a 4-day predrug test, either the saline control vehicle or the diphenylbutylpiperazinecarboxamide derivative, amperozide, was administered subcutaneously. The injections of amperozide were given b.i.d. at 1600 and 2200 h over 3 days in a dose of 0.5, 1.0, or 2.5 mg/kg. The intake of alcohol during the sequence of amperozide injections was significantly reduced in a dose-dependent manner in terms of both absolute g/kg and proportion of alcohol to water intake, whereas the saline control vehicle was without any effect on alcohol consumption. Although the highest dose of amperozide reduced the total intake of fluid due to the sharp decline in alcohol drinking, neither the consumption of food nor level of body weight was affected by any dose of the drug either during or after its administration. Because amperozide acts centrally on the synaptic activity of dopaminergic and serotonergic neurons in limbic system structures, it is envisaged that the drug ameliorates the aberrant drinking of alcohol by virtue of a direct effect on either one or both of these classes of neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol inhibition of NMDA-stimulated catecholamine efflux in aging brain

The influence of aging on the ability of ethanol to inhibit N-methyl-D-aspartate-stimulated catecholamine overflow in rat brain was examined. Alcohol effects on N-methyl-D-aspartate stimulated [3H]norepinephrine or [3H]dopamine overflow from the cortex, hippocampus, and striatum of aged (24-28 months) middle aged (12-14 months), and young (3-5 months) rats were examined. N-methyl-D-aspartate (500 microM) stimulated catecholamine overflow in all brain regions, with aged rats showing declines in overflow of 33% in the hippocampus and 41% in the striatum. Alcohol (30-200 mM) produced a concentration-dependent inhibition of overflow at all ages and brain regions tested. The IC50 for alcohol inhibition of NMDA-stimulated catecholamine release was not significantly different in aged brain or across brain regions. These results indicate that alcohol's ability to inhibit NMDA-stimulated catecholamine release is not significantly altered with aging.

Effect of drugs influencing 5-HT function on ethanol drinking and feeding behaviour in rats: studies using a drinkometer system

In the present study, we have investigated how various 5-HT agonists (m-chlorophenylpiperazine (mCPP) (0.1-1 mg/kg), 8-hydroxy 2-(di-N-propylamino) tetralin (8-OH DPAT) (0.125-2 mg/kg) and 5-HT (0.5-2 mg/kg)), the 5-HT uptake blocker sertraline (1-10 mg/kg), and the 5-HT uptake blocker and releaser dexfenfluramine (0.5-2.5 mg/kg), affect ethanol intake in a continual access paradigm using Wistar rats. By means of a drinkometer system the effect of each drug on microdrinking parameters (e.g., drink latency, number, and duration of drinking bouts) was assessed. The effect of various 5-HT antagonists (metergoline, ritanserin, ondansetron, and xylamidine) against the dexfenfluramine-induced suppression was studied. Furthermore, threshold doses for the anorectic and the suppressant effects of mCPP, sertraline and dexfenfluramine on ethanol intake were identified. From these studies, it seemed that similar mechanisms may be responsible for the suppressant effects of the various 5-HT agonists studied (direct and indirect) on ethanol and food intake. The 5-HT3 receptor antagonist, ondansetron, also reduced ethanol (but not food) intake. However, the profile of this effect may suggest an alternative means by which 5-HT3 receptors regulate ethanol intake in the rat by comparison to the various 5-HT agonists studied.