Serotonin mechanisms in alcohol drinking behavior

Association Study of Serotonin 1A Receptor Gene, Personality, and Anxiety in Women with Alcohol Use Disorder

Alcohol use disorder is considered a chronic and relapsing disorder affecting the central nervous system. The serotonergic system, mainly through its influence on the mesolimbic dopaminergic reward system, has been postulated to play a pivotal role in the underlying mechanism of alcohol dependence. The study aims to analyse the association of the rs6295 polymorphism of the 5HTR1A gene in women with alcohol use disorder and the association of personality traits with the development of alcohol dependence, as well as the interaction of the rs6295, personality traits, and anxiety with alcohol dependence in women. The study group consisted of 213 female volunteers: 101 with alcohol use disorder and 112 controls. NEO Five-Factor and State-Trait Anxiety Inventories were applied for psychometric testing. Genotyping of rs6295 was performed by real-time PCR. We did not observe significant differences in 5HTR1A rs6295 genotypes (p = 0.2709) or allele distribution (p = 0.4513). The AUD subjects scored higher on the anxiety trait (p < 0.0001) and anxiety state (p < 0.0001) scales, as well as on the neuroticism (p < 0.0001) and openness (p = 0134) scales. Significantly lower scores were obtained by the AUD subjects on the extraversion (p < 0.0001), agreeability (p < 0.0001), and conscientiousness (p < 0.0001) scales. Additionally, we observed a significant effect of 5HTR1A rs6295 genotype interaction and alcohol dependency, or lack thereof, on the openness scale (p = 0.0016). In summary, this study offers a comprehensive overview of alcohol dependence among women. It offers valuable insights into this complex topic, contributing to a more nuanced understanding of substance use among this specific demographic. Additionally, these findings may have implications for developing prevention and intervention strategies tailored to individual genetic and, most importantly, personality and anxiety differences.

Attenuation of ethanol withdrawal syndrome by extract of Hypericum perforatum in Wistar rats

The effects of Hypericum perforatum (St John's wort) on ethanol withdrawal syndrome have been investigated in ethanol-dependent rats. Adult male Wistar rats were subjects. Ethanol (7.2% v/v) was given to rats by a liquid diet for 15 days. Hypericum perforatum extract (HPE) (25-200 mg/kg) and saline were injected to rats intraperitoneally just before ethanol withdrawal. After second, fourth and sixth hour of ethanol withdrawal, rats were observed for 5 min, and withdrawal signs that included locomotor hyperactivity, stereotyped behavior and tremors were recorded or rated. A second series of injections was given at 6 h after the first one, and subjects were then tested for audiogenic seizures. HPE (25-200 mg/kg) produced some dose-dependent and significant inhibitory effects on locomotor hyperactivity at second and sixth hour of ethanol withdrawal. In addition, it significantly reduced the number of stereotyped behaviors at the same dose range. HPE (50 and 100 mg/kg) produced some significant inhibitory effects on tremor and audiogenic seizures during withdrawal period. These results suggest that HPE has some beneficial effects on ethanol withdrawal syndrome in rats.

Manipulations of serotonin function in the nucleus accumbens core produce differential effects on ethanol and sucrose seeking and intake

OBJECTIVE

Behaviorally relevant stimuli, including alcohol, are processed through the nucleus accumbens/ventral tegmental area (VTA)/prefrontal cortex circuit. It is hypothesized that serotonin affects ethanol-directed behaviors by interacting with this system via projections from the dorsal raphe to the nucleus accumbens and VTA. The current studies utilized two different operant paradigms, one focusing on reinforcer seeking and one focusing on reinforcer self-administration (both with an ethanol and a sucrose solution as the reinforcer) to elucidate serotonin-specific regulation of these behaviors.

METHODS

The present experiments assessed the effects of microinjections of a serotonin1B agonist (CGS12066B) and a serotonin1A agonist (8-OH-DPAT) in the nucleus accumbens core on ethanol- and sucrose-reinforced seeking and intake. In four separate experiments, male Long-Evans rats were trained to complete a single response requirement that resulted in access to 10% ethanol or 2% sucrose for a 20-min drinking period.

RESULTS

Before microinjections, ethanol-reinforced subjects were consuming an average of 0.5-0.95 g/kg ethanol and making 50-100 responses during intermittent nonreinforced sham (no drug) sessions (sucrose groups had similar baseline response levels). In summary, findings from the four experiments showed the following: (1) manipulations of serotonin function that had effects on ethanol-reinforced responding had either no effect or less pronounced effects on sucrose-reinforced responding; (2) administration of the serotonin1B agonist decreased seeking behaviors to a greater degree than drinking behaviors; and (3) administration of the serotonin1A agonist decreased ethanol intake but not seeking with no impact at all on sucrose-reinforced behaviors.

CONCLUSIONS

Manipulations of serotonin activity in the nucleus accumbens core had little effect on sucrose-reinforced behaviors and differential effects on ethanol seeking versus intake, suggesting that this area may play a complex but selective role in the stimulus processing of external and internal alcohol-associated cues.

Effects of venlafaxine on ethanol withdrawal syndrome in rats

The present study was designed to investigate the effects of venlafaxine, a serotonin and noradrenaline reuptake inhibitor (SNRI), on ethanol withdrawal syndrome in rats. Adult male Wistar rats (187-319 g) were used for the study. Ethanol (7.2%, v/v) was given to rats by a liquid diet for 21 days. Control rats were pair-fed an isocaloric liquid diet containing sucrose as a caloric substitute to ethanol. Venlafaxine (5, 10, 20 and 40 mg/kg) and saline were injected to rats intraperitoneally just before ethanol withdrawal. After the 2nd, 4th and 6th hour of ethanol withdrawal, rats were observed for 5 min, and withdrawal signs that included locomotor hyperactivity, agitation, stereotyped behaviour and wet dog shakes were recorded or rated. A second series of injections was given at the 6th hour after the first one, and rats were then tested for audiogenic seizures. Venlafaxine produced some inhibitory effects on locomotor hyperactivity, stereotypic behaviours and wet dog shakes. However, a two-way anova of the data did not indicate any significant effect. It reduced the incidence of the audiogenic seizures at the 6th hour of ethanol withdrawal. Venlafaxine (20 mg/kg) also prolonged the latency of the seizures significantly. Our results suggest that acute venlafaxine treatment has limited beneficial effects on ethanol withdrawal syndrome in rats.

Effects of fluoxetine on ethanol withdrawal syndrome in rats

The present study was designed to investigate the effects of fluoxetine, a selective serotonin reuptake inhibitor, on ethanol withdrawal syndrome in rats. Adult male Wistar rats (218-255 g) were subjects. Ethanol (7.2%, v/v) was given to rats by a liquid diet for 21 days. Control rats were pair fed an isocaloric liquid diet containing sucrose as a caloric substitute to ethanol. Fluoxetine (2.5, 5 and 10 mg/kg) and saline were injected to rats intraperitoneally just before ethanol withdrawal. After 2nd, 4th and 6th hour of ethanol withdrawal, rats were observed for 5 min, and withdrawal signs that included locomotor hyperactivity, agitation, stereotyped behavior, wet dog shakes and tremor were recorded or rated. A second series of injections was given at 6 h after the first one, and subjects were then tested for audiogenic seizures. Fluoxetine produced some dose-dependent and significant inhibitory effects on all the signs of ethanol withdrawal during ethanol withdrawal period. Our results suggest that acute fluoxetine treatment has some beneficial effects on ethanol withdrawal in rats. Thus, this drug may be useful for treatment of ethanol withdrawal syndrome.

Plant derivatives in the treatment of alcohol dependency

The present review summarizes the findings of the effects of extracts of purified compounds from several plants on alcohol intake in alcohol-preferring rats. These include St. John's wort (Hypericum perforatum, HPE), kudzu (Pueraria lobata) and ibogaine (Tabernanthe iboga). Alcohol-preferring (P), Marchigian Sardinian (msP), high-alcohol-drinking (HAD), Fawn-Hooded (FH) rats were allowed to drink alcohol or water voluntarily to establish baseline levels. Pure compounds (puerarin, daidzin, daidzein or analogs) isolated from kudzu, extracts from HPE or ibogaine and its analog were given by either intraperitoneal or oral administration. After acute administration, all agents dose-dependently reduced alcohol intake with minimal effects on food intake. Puerarin and HPE were also effective following chronic treatment. Overall, it is clear that pure compounds (daidzin, puerarin), extracts from St. John's wort, ibogaine and an ibogaine analog suppress alcohol intake in animal models of excessive drinking with minimal effects on other appetitive behaviors. Although the true mechanisms of action of these compounds on alcohol intake are not fully understood, with the current information, it appears that these compounds exert their effects by modulating several neuronal systems implicated in drinking behavior. However, their role in the future of pharmacotherapy for alcoholism will depend upon the outcome of carefully conducted clinical trials.

Alcohol and withdrawal: from animal research to clinical issues

The withdrawal syndrome in alcohol-dependent patients appears to be a major stressful event whose intensity increases with repetition of detoxifications according to a kindling process. Disturbances in the balance between excitatory and inhibitory neural processes are reflected in a perturbed physical state while disturbances in the balance between positive and negative reinforcements are reflected in a perturbed mood state. Our purpose is to link the different behavioral outcomes occurring during withdrawal with specific biological brain mechanisms from the animal to the human being. Better understanding of the various biological mechanisms underlying withdrawal from alcohol will be the key to design and to apply appropriate pharmaceutical management, together with appropriate therapy aimed at inducing protracted abstinence.

Electrical stimulation of nucleus raphe dorsalis changes morphine self-administration and withdrawal symptoms in rats

The involvement of antero-dorsal part of the nucleus raphe dorsalis (NRD) in motivational aspects of drug-taking behaviour during initiation of drug self-administration was investigated using a recently developed behavioural paradigm. In separate experiments animals were allowed to self-administer morphine (1 mg/kg per inf) ten consecutive daily 3-h sessions. During all morphine self-administration sessions lever-press behaviour was measured in absence of electrical stimulation of NRD, as an index of the motivational aspects involved in drug-taking behaviour. The electrical stimulation (pulse 0.5 ms, 150 &mgr;A, 20 Hz) of NRD 30 min before morphine self-administration produced a significant decrease in the initiation of morphine self-administration during all sessions (reduced number of lever-press behaviour). After the last test session, morphine withdrawal syndrome signs (wet dog shakes, jumping, writhing and diarrhoea) in the naloxone-induced behaviour were measured. Our results showed that these withdrawal syndrome signs decreased by application of electrical stimulation in NRD, in comparison with morphine groups. It is concluded that serotonergic system in the NRD might be involved in the motivational processes underlying morphine self-administration.

An investigation of the role of 5-HT(2C) receptors in modifying ethanol self-administration behaviour

We have previously reported that the 5-HT uptake blocker and releaser, dexfenfluramine, attenuates ethanol intake, and that this may be mediated via a 5-HT(2C) receptor mechanism. Our goals were to further determine the contribution made by this receptor subtype in mediating the reduction in ethanol self-administration induced by dexfenfluramine using the selective 5-HT(2C) antagonist, SB242,084. Additionally, we wanted to compare dexfenfluramine's effects on ethanol motivated responding with those elicited by the 5-HT(2C) receptor agonist Ro60-0175. In male Wistar rats trained to self-administer a 12% w/v ethanol solution on an FR-4 schedule, both dexfenfluramine (0.05--2.5 mg/kg ip) and Ro60-0175 (0.1--1 mg/kg sc) produced a significant dose-dependent reduction in ethanol self-administration, which was reversed by SB242,084 (0.5 mg/kg ip). Interestingly, SB242,084 alone (0.1--1 mg/kg ip) significantly increased ethanol motivated responding in both high and low ethanol drinking animals. While dexfenfluramine had no effect on ethanol's kinetic profile, the selective 5-HT(2C) agents used had opposing effects, with the agonist Ro60-0175 decreasing and the antagonist SB242,084 increasing blood ethanol levels. Since there were incongruent drug effects on ethanol self-administration and blood ethanol levels, these data support a role for 5-HT(2C) receptors in modifying ethanol intake independent of their effects on blood ethanol kinetics. Furthermore, 5-HT(2C) receptors may exert a tonic control over ethanol self-administration behaviour, since agonist and antagonist administration had opposing effects on this behaviour.

Effects of ethanol on the dorsal raphe nucleus and its projections to the caudate putamen

The objective of this study was to examine the effects of intraperitoneal injection of ethanol on the activity of the dorsal raphe nucleus (DRN) serotonin (5-hydroxytryptamine [5-HT]) system and its projections to the rostral caudate putamen (CPu) and determine whether rapid tolerance to the effects of ethanol develops in this system. Adult, male, Wistar rats were used in these experiments. In experiment 1, a microdialysis procedure was used to determine (a) the effects of acute intraperitoneal administration of ethanol (1.75 and 2.5 g/kg) on the extracellular levels of 5-HT in the rostral CPu and (b) whether rapid tolerance develops to these effects. In experiment 2, firing rates of 5-HT neurons were determined in the DRN after intraperitoneal administration of 2.5 g/kg of ethanol. The results of the microdialysis experiments indicated that the 2.5-g/kg dose significantly (P < .005) increased the extracellular levels of 5-HT to 150%-160% of baseline. Compared with findings for rats pretreated with saline 24 h earlier, prior treatment 24 h earlier with 2.5 g/kg of ethanol had no effect on the extracellular levels of 5-HT produced by a challenge dose of 2.5 g/kg of ethanol. Contrary to the effects in the CPu, intraperitoneal administration of 2.5 g/kg of ethanol significantly (P<.005) decreased the firing rates of 5-HT neurons in the DRN to approximately 50% of control. Overall, the results suggest to us that there is a dissociation between the effects of acute administration of ethanol on 5-HT cell body neuronal activity and 5-HT synaptic activity. The higher extracellular levels of 5-HT in the CPu may be due to increased release of 5-HT from a direct or an indirect action of ethanol, a result of inhibiting 5-HT reuptake, or related to both of these mechanisms. In addition, the findings suggest to us that rapid tolerance did not develop to the effects of ethanol on the 5-HT system within the CPu.

The psychopharmacology of tachykinin NK-3 receptors in laboratory animals

The present article reviews the studies so far published on the psychopharmacological effects mediated by tachykinin NK-3 receptors in laboratory animals. Central administration of NK-3 receptor agonists has been reported to attenuate alcohol intake in alcohol-preferring rats and to evoke conditioned place preference. These findings suggest that NK-3 receptors may affect reward processes to drugs of abuse. Anxiolytic-like and antidepressant-like effects have been previously reported for NK-1 receptor antagonists, and anxiolytic-like effects for NK-2 receptor antagonists. More recently, it has been shown that NK-3 receptor agonists have anxiolytic-like and antidepressant-like effects in mice and rats, while an NK-3 receptor antagonist was reported to be anxiogenic in mice. These findings indicate that different TK receptor subtypes may be involved in anxiolytic-like and antidepressant-like effects in laboratory animals and raise interest for the possible role of NK-3 receptors in the control of anxiety and depression in man.

Serotonin transporter gene polymorphisms, alcoholism, and suicidal behavior

BACKGROUND

Dysfunction of serotoninergic transmission could predispose to excessive alcohol consumption and dependence. The functional polymorphism of the serotonin transporter gene (5-HTTLPR) has been associated with different disorders, including alcoholism. Considering the likelihood of heterogeneity in the "alcohol dependence" phenotype, 5-HTTLPR may be more specifically implicated in subsamples of patients or in related traits of alcoholism, such as impulsivity.

METHODS

We analyzed the role of this functional polymorphism in the risk for suicide attempt in a population of male alcohol-dependent subjects. One hundred ten male alcohol-dependent patients (DSM-III-R criteria), French for at least two generations, were personally interviewed with the Diagnostic Interview for Genetic Studies and compared with 61 unaffected blood donors.

RESULTS

The "short" (S) allele of the 5-HTTLPR appeared to be unrelated to alcohol dependence and comorbid depression in our sample, but was found associated with an increased risk for suicide attempts. This association was predominantly observed in severe and repetitive suicide attempts, with a significant dose effect of the S allele (0, 1, or 2) on the number and the severity of suicide attempts.

CONCLUSIONS

Mood disorders and alcohol dependence may interact with a genetic (relative) deficiency in serotonin reuptake, thereby increasing the risk for aggressive/impulsive behaviors such as suicide attempts.

Effects of Hypericum perforatum extract on ethanol intake, and on behavioral despair: a search for the neurochemical systems involved

The present study investigated the possible involvement of sigma receptors and of serotonergic mechanisms in the effects of Hypericum perforatum extract (HPE) on immobility time in the forced swimming test (FST) and on ethanol intake in Marchigian Sardinian alcohol-preferring rats. The HPE employed was a dry extract containing 0.3% hypericin and 3.8% hyperforin. Intraperitoneal pretreatment with 20 mg/kg of the sigma receptor antagonist rimcazole (RIM), 30 min prior to HPE, completely suppressed the antiimmobility effect of HPE (3 intragastric injections of 250 mg/kg). Intracerebroventricular pretreatment with 5, 7-dihydroxytryptamine (5,7-DHT), which produced a marked depletion of brain serotonin, reduced the antiimmobility effect, although this reduction was not as pronounced as that of RIM. On the other hand, the inhibitory effect of HPE on 10% ethanol intake was modified neither by 5,7-DHT nor by RIM pretreatment. These results suggest that the antidepressant-like effect of HPE in the FST may be mediated by interaction with sigma receptors and to some extent by increased serotonergic neurotransmission. On the other hand, these mechanisms appear to be unimportant for the effect of HPE on ethanol intake.

Effect of 5-HT(1B) receptor ligands on self-administration of ethanol in an operant procedure in rats

Recent evidence suggests that 5-HT(1B) receptor activation modifies ethanol's reinforcing, intoxicating and discriminative stimulus effects. The present study further explored the role played by 5-HT(1A/1B) receptors by examining their influence on oral ethanol self-administration. Male Wistar rats were trained on an FR 4 schedule to obtain a reinforcer of 0.1 12% w/v ethanol solution. Once responding was stable, the effect of the 5-HT(1A/1B) agonist RU24969 alone and in combination with the 5-HT(1B) antagonist GR127935 or the 5-HT(1A) antagonists (+) WAY100135 and (+) WAY100635 was assessed. The effect of RU24969 on ethanol's pharmacokinetic profile and on operant oral saline self-administration was also examined to assess if alterations in oral ethanol self-administration were due to nonspecific effects on level pressing. For comparison, we examined the effect of another 5-HT(1A/1B) agonist, CGS12066B, on oral ethanol self-administration. Both RU24969 (0.1 to 1 mg/kg) and CGS12066B (0.1 to 1 mg/kg) significantly suppressed oral ethanol self-administration. Administration of GR127935 (1 mg/kg), significantly reversed the effects elicited by RU24969, whereas neither WAY100635 (1 mg/kg) nor (+)WAY100135 (1 mg/kg) had any effect. The effects of lower doses of RU24969 on oral ethanol self-administration were selective as oral saline self-administration and blood ethanol levels were not altered by these doses. These data demonstrate that 5-HT(1B) receptor activation suppresses oral ethanol self-administration. These studies provide further evidence that 5-HT(1B) receptors play a modulatory role in ethanol's behavioral effects.

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

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

Autoradiographic analysis of 5-HT2A binding sites in the brain of Sardinian alcohol-preferring and nonpreferring rats

The density of 5-HT2A binding sites in the brain of Sardinian alcohol-preferring (sP) and nonpreferring (sNP) rats was evaluated, using [3H]ketanserin for quantitative autoradiography. The highest [3H]ketanserin binding levels were found in the anterior olfactory nucleus, prefrontal cortex, medial prefrontal cortex, post-genual anterior cingulate cortex, insular cortex and claustrum. Statistically significant differences between sP and sNP rats were found in prefrontal cortex, medial prefrontal cortex and post-genual anterior cingulate cortex, where sP rats showed about 20% lower [3H]ketanserin binding levels. No significant difference was found in other areas, although some of them showed slightly lower [3H]ketanserin binding density in sP rats. The 5-HT2A receptor agonist, (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane hydrochloride (DOI), microinjected into the medial prefrontal cortex, induced a lower number of wet dog shakes in sP than in sNP rats. These results indicate a different density of 5-HT2A binding sites, and a different functional regulation of 5-HT2A receptor mechanisms in discrete brain areas of sP, in comparison to sNP rats. These findings, and those showing lower levels of 5-HT in the frontal cortex of sP rats, suggest that altered 5-HT function in fronto-cortical areas could be linked to the genetic predisposition to high voluntary ethanol intake in these rats.

Effects of morphine on metabolism of dopamine and serotonin in brains of alcohol-preferring AA and alcohol-avoiding ANA rats

Morphine induces a larger locomotor stimulation in the alcohol-preferring AA rats than in the alcohol-avoiding ANA rats. We have now studied the acute effects of morphine (1 and 3 mg/kg) on metabolism of dopamine and serotonin (5-HT) in the dorsal and ventral striatum of the AA and ANA rats. The basal level of dopamine release, as reflected by the concentration of dopamine metabolite 3-methoxytyramine (3-MT), was lower in the caudate-putamen and nucleus accumbens of the AA rats than in the ANA rats. In the caudate-putamen, morphine increased dopamine metabolism and release more in the AA than in the ANA rats. In the nucleus accumbens and olfactory tubercle, the effects of morphine on dopamine metabolism and release did not differ between the rat lines. Morphine elevated the metabolism of 5-HT in the caudate-putamen and nucleus accumbens of the AA but not in those of the ANA rats. The results suggest that the larger morphine-induced psychomotor stimulation of the AA rats in comparison with the ANA rats is associated with the larger effect of morphine on dopamine metabolism in the caudate-putamen and 5-HT metabolism in the caudate-putamen and nucleus accumbens. Furthermore, low basal dopamine release may play a role in the high alcohol-preference of AA rats.

Mechanism of action for reduction of ethanol intake in rats by the tachykinin NK-3 receptor agonist aminosenktide

Intracerebroventricular (i.c.v.) injection of tachykinin (TK) NK-3 receptor agonists inhibits alcohol intake in genetically selected alcohol-preferring rats. The present study investigated the mechanism of action by which the selective TK NK-3 receptor agonist aminosenktide (NH2-SENK) attenuates ethanol intake in Marchigian Sardinian alcohol-preferring (msP) rats. The effect of NH2-SENK was studied by i.c.v. injection in the conditioned taste aversion (CTA) and in the conditioned place preference (CPP) paradigms; moreover, the effect of NH2-SENK on blood alcohol levels (BAL) following intragastric ethanol administration was investigated. The i.c.v. dose of 125 ng/rat of NH2-SENK, that markedly reduces ethanol intake, did not modify BAL, nor did it increase the CTA induced by intraperitoneal injection of ethanol, 1 g/kg body weight. These findings suggest that the effect of NH2-SENK on alcohol consumption is not related to modification of the pharmacokinetics of ethanol, nor to increase of the aversive properties of ethanol. On the other hand, the same i.c.v. dose of NH2-SENK evoked a pronounced and statistically significant CPP. This finding indicates that the TK NK-3 receptor agonist NH2-SENK possesses rewarding properties in msP rats and suggests that its inhibitory effect on ethanol consumption may be due to substitution of the rewarding properties of ethanol, thus making its consumption redundant.

Quantitative autoradiography of mu-opioid receptors in the CNS of alcohol-naive alcohol-preferring P and -nonpreferring NP rats

The densities of mu-opioid binding sites in the CNS of alcohol-naive adult male P and NP rats (N = 9 each line) were examined using quantitative autoradiography. Coronal sections (20 microm) were prepared from frozen brains and incubated in 5 nM [3H]DAMGO to label mu-opioid receptor sites. Nonspecific binding was determined in the presence of 1 microM DAMGO. The amount of [3H]DAMGO binding was (a) 20-25% higher in the olfactory tubercle, nucleus accumbens shell and core, and basolateral and lateral amygdaloid nuclei; (b) 15% higher in the lateral septal intermediate nucleus and caudate-putamen patches; and (c) 10-30% lower in the pyramidal and radiatum layers in the CA1 region of the anterior dorsal hippocampus, ventral dentate gyrus and CA1 pyramidal layer of the posterior hippocampus, and posterior medial cortical amygdaloid nucleus of the P compared to the NP rat. No line differences were found in any of the other regions examined (e.g., the cerebral cortical subregions and layers, thalamic nuclei, ventral tegmental area, ventral pallidum, lateral hypothalamus, other regions of the hippocampus, and several subcortical structures). The innate differences in the amount of binding to mu-opioid recognition sites in certain limbic structures, such as the nucleus accumbens, amygdala, and olfactory tubercle, of the P and NP lines may be factors contributing to their disparate alcohol drinking characteristics.

Modulation of agonist and antagonist interactions in serotonin 1A receptors by alcohols

The serotonin type IA (5-HT1A) receptors are members of a superfamily of seven transmembrane domain receptors that couple to GTP binding regulatory proteins (G-proteins). Serotonergic signalling has been shown to play an important role in alcohol tolerance and dependence. We have studied the effects of alcohols on ligand (agonist and antagonist) binding to bovine hippocampal 5-HT1A receptor in native as well as solubilized membranes. Our results show that alcohols inhibit the specific binding of the agonist OH-DPAT and the antagonist p-MPPF to 5-HT1A receptors in a concentration-dependent manner.

Central 5-HT3 receptors in P and in AA alcohol-preferring rats: An autoradiographic study

Considerable evidence exists for an involvement of serotonergic mechanisms in the control of alcohol consumption. In the present study, an extensive 5-hydroxytryptamine (5-HT3) receptor autoradiographical investigation was performed using two genetically selected rat strains, alcohol preferring (P) and Alko alcohol (AA) alcohol-preferring rats, as well as the corresponding alcohol nonpreferring (NP) and Alko nonalcohol (ANA) alcohol-nonpreferring rats. The aim was to determine if there are any differences in 5-HT3 binding levels that may illuminate mechanisms of alcohol preference in these animals. For quantitating 5-HT3 binding sites, [3H]S(-)zacopride (0.5 nM) was used. Non-specific binding was measured in the presence of granisetron 10(-6) M. The [3H]S(-)zacopride binding density was measured in two subregions of the amygdaloid nucleus, frontal cortex, piriform cortex, cingulate laminae, parietal anterior cortex, parietal medial cortex, hippocampus CA1, hippocampus CA3, and entorhinal cortex. In all the brain areas investigated, the results showed no differences between AA and ANA rats. In P rats, compared to NP controls, there was a 30% lower 5-HT3 binding level in the lateral nucleus and the posteromedial cortical nucleus of the amygdala. These findings suggest that the expression of high alcohol preference in genetically selected P and AA rats is not associated with a general alteration of central 5-HT3 receptors, although a lower 5-HT3 receptor level in the amygdala of P rats may contribute to the phenotype of this strain of animals.

Sensitivity of brain sites to the inhibitory effect on alcohol intake of the tachykinin aminosenktide

The present study evaluated the sensitivity of several brain sites to the inhibitory effect of the tachykinin (TK) NK-3 receptor agonist aminosenktide (NH2-SENK) on 10% ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring rats. Attention was focused on limbic structures involved in alcohol-seeking behavior and endowed with TK NK-3 receptors. NH2-SENK was bilaterally injected into the shell of the nucleus accumbens (NACC), the medial amygdala (AMY), the dorsal hippocampus (HIPP), the ventral tegmental area (VTA), the bed nucleus of the stria terminalis (BNST), the lateral hypothalamus (LH), and the nucleus basalis magnocellularis (NBM). NH2-SENK (injected up to 25-75 ng/site) into the NACC, AMY, HIPP, and VTA did not significantly modify ethanol intake. Injection of NH2-SENK into the BNST reduced ethanol intake at doses of 25 ng/site or higher, but the same doses also reduced water intake in water-deprived rats and food intake in food-deprived rats. Injection of NH2-SENK into the LH or the NBM at doses of 0.5, 5, or 25 ng/site inhibited 10% ethanol intake even at the lowest dose tested without affecting either food or water consumption in deprived animals. Present results indicate that the LH and the NBM are highly sensitive to the inhibitory effect of the TK NK-3 receptor agonist NH2-SENK on ethanol intake. TK peptides have been shown to evoke conditioned place preference following injection in the LH or the NBM, suggesting that in these brain sites the effect of TK agonists on ethanol intake might be due to interference with reward processes.

Regional CNS densities of serotonin and dopamine receptors in high alcohol-drinking (HAD) and low alcohol-drinking (LAD) rats

The densities of subtypes of serotonin (5-HT) and dopamine (DA) receptors were determined in the CNS of male alcohol-naive HAD and LAD lines of rats. Autoradiographic studies were undertaken to measure the densities of (a) 5-HT1A sites labelled with 2 nM [3H]8-OH DPAT, (b) 5-HT2A sites labelled with 2 nM [3H] ketanserin, (c) D1 sites labelled with 1 nM [3H]SCH23390, and (d) D2 sites labelled with 20 nM [3H]sulpiride. Membrane binding, using tissue combined from the olfactory bulb, olfactory tubercle, and nucleus accumbens, was carried out to determine Kd and Bmax values for the binding of 0.25-8.0 nM [3H]7-OH DPAT to D3 sites. Among the 14 regions measured for densities of 5-HT1A sites, no interline differences were found in the cerebral cortical regions or in the septal nuclei; however, within the hippocampus, 15-20% lower binding of [3H]8-OH DPAT was observed in the posterior dorsal CA3 and dentate gyrus of the HAD line. There were no interline differences in any of the 10 regions examined for [3H]ketanserin binding to 5-HT2A sites, or in the densities of D1 and D2 sites in the mesolimbic and nigrostriatal DA systems, except for a 35% higher density of D2 sites in the substantia nigra pars compacta of the HAD line. There were no interline differences in the Kd or Bmax values for [3H]7-OH DPAT binding to D3 sites. Overall, these results indicate that no marked interline differences are evident in the densities of 5-HT1A, 5-HT2A, D1, D2, and D3 receptors within the mesolimbic system that could be associated with the disparate alcohol drinking behaviors of the HAD and LAD rats.

5,7-dihydroxytryptamine lesion does not affect ethanol-induced conditioned taste and place aversion in rats

The effect of the lesion of central serotonergic neurons by 5,7-dihydroxytryptamine (5,7-DHT), on ethanol-induced taste and place aversion conditioning was studied in male Wistar rats. Control biochemical analysis revealed that 5,7-DHT (250 micrograms per rat, free base, i.c.v.) produced marked and selective depletion of serotonin (5-HT) in the hippocampal formation and the limbic forebrain complex. Ethanol-induced (1.5 g/kg, i.p.) conditioned taste aversion (CTA) to saccharin solution was unaffected by the lesion of central serotonergic neurons. The 5,7-DHT-lesioned and sham-lesioned rats showed comparable ethanol-induced CTA even 30 days after the last ethanol injection. Similarly, ethanol-induced (1.5 g/kg, i.p.) conditioned place aversion (CPA) was unaffected by 5,7-DHT administration. These results suggest that central serotonergic pathways are not primarily involved in the aversive effects of high ethanol doses in rats.

Regional CNS densities of monoamine receptors in alcohol-naive alcohol-preferring P and -nonpreferring NP rats

The densities of subtypes of serotonin (5-HT) and dopamine (DA) receptors were determined in the CNS of alcohol-naive alcohol-preferring P and -nonpreferring NP lines of rats. Autoradiography studies were undertaken to measure the densities of 5-HT1B sites labelled with 100 pM [125I](-)-iodocyanopindolol, 5-HT3 sites labelled with 2 nM [3H]LY 278584, and D1 sites labelled with 1 nM[3H]SCH 23390. Membrane binding, using tissue combined from the olfactory bulb, olfactory tubercle, and nucleus accumbens, was carried out to determine Kd and B max values for the binding of 0.25-8.0 nM[3H]7-OH DPAT to D3 sites. Among the 48 regions measured for differences in 5-HT1B recognition sites, statistically significant differences (p < 0.05) were found only in the cingulate and retrosplenial cortices, in the lateral and medial septum, and in the lateral nucleus of the amygdala, with lower values being found in the P than the NP line. There were no significant differences in the regional CNS densities of D1 or 5-HT3 sites between the P and NP lines. There were also no differences between the rat lines in the Kd or Bmax values for [3H]7-OH DPAT binding to D3 sites. The lower densities of 5-HT1B sites in the CNS of the P compared to the NP rats may be a result of reduced numbers of 5-HT1B presynaptic autoreceptors as well as postsynaptic receptors in the P line. The observation that there are no differences in the amount of radioligand binding to D1, 5-HT3, and D3 sites between the P and NP lines suggests that the disparate alcohol drinking behaviors of these two lines is not associated with an innate alteration in the densities of these receptor subtypes.

Amphetamine and fenfluramine suppress ethanol intake in ethanol-dependent rats

Alcohol intake or preference for alcohol has been attributed to concomitant dopamine and serotonin dysfunction in rats. Amphetamine and fenfluramine, administered alone, have been shown to reduce food and fluid intake as well as alcohol consumption while acute coadministration of these agents has been shown to suppress audiogenic seizure in rats withdrawn from alcohol. The present study was designed to assess the effectiveness of chronic amphetamine and fenfluramine coadministration on reducing alcohol intake. Chronic coadministration of amphetamine (2 mg/kg) and fenfluramine (8 mg/kg) reduced alcohol consumption during choice trials in both alcohol-dependent and alcohol-nondependent rats while not affecting water intake. The findings indicate that coadministration of amphetamine and fenfluramine, a treatment effective in reducing alcohol withdrawal seizures, also selectively attenuates alcohol consumption.

Stimulation of tachykinin NK-3 receptors in the nucleus basalis magnocellularis reduces alcohol intake in rats

Injections in the nucleus basalis magnocellularis (NBM) of the tachykinin (TK) NK-3 receptor agonist [Asp5,6,MePhe8]substance P(5-11), also referred to as amino-senktide (NH2-SENK), markedly reduced alcohol intake in genetically selected alcohol-preferring rats, offered 10% ethanol 2 h/day. The threshold dose in the NBM was 0.5 ng/site, while neither 1 nor 10 ng/rat of NH2-SENK inhibited alcohol intake following administration into the lateral ventricle. Injection of NH2-SENK, 25 ng/site, in the NBM did not modify water or food intake in water deprived rats, providing evidence for the behavioral selectivity of the effect on ethanol intake. The selective TK NK-3 receptor antagonist, R-820, injected in the NBM at the dose of 1000 ng/site 5 min before NH2-SENK 5 ng/site, significantly reduced the effect of NH2-SENK. The selective TK NK-1 receptor agonist [Sar9,Met(O2)11]substance P inhibited alcohol intake following injection in the NBM only at 25 ng/site; but the same dose induced marked grooming and inhibited also water intake in water deprived rats. The present results confirm that TK NK-3, but not NK-1, receptor agonists selectively inhibit ethanol intake in alcohol-preferring rats and suggest that the NBM is a site of action for their effect.

Autoradiographic mapping of brain 5-HT2A binding sites in P and in AA alcohol-preferring rats

There is considerable evidence for an involvement of serotonergic mechanisms in the control of alcohol consumption. In the present study, an extensive 5-HT2A receptor autoradiographic investigation was carried out in two genetically selected rat strains, P and AA alcohol-preferring rats, respectively, as well as in the corresponding NP and ANA alcohol-nonpreferring rats. The aim was to determine if there is any common pattern in 5-HT2A binding site densities that may illuminate mechanisms of alcohol preference in these animals. For quantitating 5-HT2A binding sites, [3H]ketanserin (2 nM) was used. Nonspecific binding was measured in the presence of methysergide 10(-6) M. Results demonstrated a lower level (from 50 to 70%) of 5-HT2A binding sites in the layer IV of prefrontal cortex, frontal cortex, parietal cortex of P rats compared to NP controls. Similarly, in the claustrum, 5-HT2A binding density of P rats was 50% lower than that of NP rats, although this failed to achieve statistical significance. No difference was detected in the other areas investigated, including the olfactory tubercles, nucleus accumbens, caudate putamen, pyriform cortex, ventral tegmental area, temporal cortex, and entorhinal cortex. In AA rats, [3H]ketanserin binding density measured in these brain areas was very similar to that observed in ANA nonpreferring controls, and statistical analysis did not reveal any significant difference between the two rat lines. The present study confirms previous reports demonstrating lower densities of 5-HT2A binding sites in the P rats and provides the first autoradiographic evidence showing that such an alteration does not occur in AA rats. These findings suggest that the expression of high alcohol preference in genetically selected P and AA rats is not associated with a shared neurochemical alteration of the 5-HT2A receptor system.

Serotonin2C receptors and serotonin2C receptor-mediated phosphoinositide hydrolysis in the brain of alcohol-preferring and alcohol-nonpreferring rats

To examine the role of serotonin2C (5HT2C) receptors in alcohol drinking behavior, the binding indices of 5HT2C receptors were determined in various brain regions of alcohol-preferring (P) and alcohol-nonpreferring (NP) rats. 5HT2C receptor-mediated phosphoinositide hydrolysis in the choroid plexus of P and NP rats was also determined. It was observed that the densities of 5HT2C receptors are significantly higher in the hippocampus, the amygdala, and the choroid plexus, but not in the cortex of P rats compared with NP rats. The Kd values of [3H]mesulergine binding to 5HT2C receptors were not different in these brain regions of P rats compared with NP rats. It was also observed that 5HT-stimulated [3H]inositol 1-phosphate formation was significantly higher in the choroid plexus of P rats compared with NP rats. The results of this study indicate that the numbers of 5HT2C receptors are higher in the hippocampus, the amygdala, and the choroid plexus, and that 5HT2C receptor-mediated phosphoinositide hydrolysis is more elevated in the choroid plexus of P rats compared with NP rats. Thus, it seems from these results that increased 5HT2C receptors may be involved in the genetic vulnerability to alcohol drinking behavior.

Pharmacology of serotonin as related to anesthesia

Serotonin (5-hydroxytryptamine) is an important biogenic amine that fulfills the role of neurotransmitter and neuromodulator. It has been a focus of interest during the last decade. Its diversity of pharmacologic actions is related to a wide variety of receptors and effector mechanisms. Seven serotonin receptor families have been identified thus far. They are genetically different transmembrane proteins composed of several hundred amino acids. The majority of these are G-protein-coupled, except the 5-HT3 receptors, which are directly ligand gated to fast ion channels. Serotonin is widely distributed in the body within the central and peripheral nervous systems, smooth muscles, and platelets, in particular. Consequently, its effects manifest mainly in these organs and influence a wide variety of neural, vascular, smooth muscle, and platelet functions. (Melatonin, a physiologically active metabolite of serotonin, is also instrumental in affecting many neural and hormonal functions.) Several selective agonists and particularly many selective antagonists have been developed for serotonin, which helped the serotonin receptor subtype classification. Some of these drugs are also used therapeutically in the treatment of migraine (eg, sumatriptan, which is a 5-HT1 receptor agonist), vascular disorders (5-HT2 antagonists), and nausea and vomiting (5-HT3 antagonists, eg, dolasetron, granisetron, ondansetron, and tropisetron), and have been investigated in gastrointestinal motility disorders (5-HT4 antagonists) and behavioral psychopathologies (5-HT1 agonists and 5-HT2-4 antagonists). Serotonin reuptake inhibitors are of particular clinical importance in the treatment of psychological illness. Future use of these drugs is also envisioned in the treatment of certain types of pain syndromes. Awareness of the serotonergic drugs and the recognition of possible drug interactions among drugs that influence serotonergic mechanisms in humans are becoming increasingly important in the practice of anesthesiology.

Alterations in serotonin1B (5HT1B) receptor subtypes in the brain of ethanol-treated rats

The effects of acute or chronic ethanol treatment and of withdrawal (24 h) after chronic ethanol treatment on 5HT1B receptor subtypes in different regions of the rat brain were investigated. Male Sprague-Dawley rats were fed the ethanol (9% v/v)-containing Lieber-DeCarli liquid diet or the control liquid diet for 1 day in the acute study and for 15 days in the chronic study. The ethanol-withdrawn group received the Lieber-DeCarli control liquid diet instead of the ethanol diet on the 15th night. Ethanol-withdrawn rats after 15 days of ethanol treatment were rated for withdrawal symptoms (e.g. hyperactivity, piloerection, squealing, and enhanced startle reflex) and were found to exhibit such symptoms after 24 h of ethanol withdrawal. The rats were decapitated, and cortices, cerebelli, striata, and hippocampi were separated for measurement of 5HT1B receptors by receptor binding techniques using 125I-cyanopindolol (CYP) as the ligand. It was observed that acute ethanol treatment had no significant effect on the maximum number of binding sites (Bmax) or the apparent dissociation constant (KD) of 5HT1B receptor binding sites in the various brain regions. On the other hand, chronic ethanol treatment produced a significant increase in Bmax of 125I-CYP binding to 5HT1B receptors in the rat cortex and hippocampus, which remained increased after 24 h of ethanol withdrawal. In contrast, in the striatum and the cerebellum of chronic ethanol-treated and withdrawn rats, the 5HT1B binding parameters (Bmax and KD) were unchanged. These results suggest the possible involvement of cortical and hippocampal 5HT1B receptors in ethanol dependence.

Suppression of alcohol intake after administration of the Chinese herbal medicine, NPI-028, and its derivatives

The Chinese herbal medicine, NPI-028, has been used for centuries in China to counteract alcohol intoxication. The present study used a number of different experimental conditions to determine whether NPI-028 and its derivatives might selectively influence alcohol intake in rodents that naturally exhibit high alcohol intakes. It was determined that intraperitoneal (i.p.) injections of NPI-028 (0.5, 0.75, and 1.0 g/kg) suppressed alcohol intake by up to 30% in both alcohol-preferring P and Fawn-Hooded (FH) rats during a continuous access schedule. These injections did not significantly affect food or water intakes, nor did the highest dose of NPI-028 (1 g/kg) alter blood ethanol levels after an i.p. injection of 2.5 g/kg of ethanol. In P rats, it was found that NPI-028 was orally active with the dose of 1.5 g/kg having a greater effect on ethanol intake than the 1.0 g/kg dose; once again, food and water intakes were not significantly altered. In FH rats maintained on a limited access schedule (1 hr/day), alcohol intake was completely abolished by 1.5 g/kg of NPI-028. Chronic i.p. administration of NPI-028 (0.75 g/kg) for four consecutive days in FH rats maintained on a continuous access schedule did not lead to any diminution of its alcohol-suppressant effects. Thus, NPI-028 has significant effects on alcohol intake without much effect on water and food intake, and tolerance does not readily develop to these effects. The i.p. administration of a partially purified extract (NPI-031) of NPI-028, obtained by countercurrent chromatography, also dose-dependently suppressed ethanol intake in FH rats, but the highest dose 200 mg/kg) also significantly decreased food intake. Finally, the i.p. administration of puerarin (NPI-31G), an isoflavone isolated from NPI-031 by countercurrent chromatography, significantly reduced ethanol intake in FH rats without affecting food or water intake. Therefore, NPI-028 and one of its pure components, NPI-031G, selectively reduced ethanol intake in alcohol-preferring rats.

Modulation of serotonin2A/2C receptors and these receptor-linked phosphoinositide system by ethanol

Studies related to 5-HT2A/2C receptors and these receptor-linked phosphoinositide (PI) system in the rat brain during chronic ethanol treatment and withdrawal are discussed. Chronic ethanol treatment (60 days) has no effect on 5-HT2A/2C receptors in the cortex and the hippocampus but significantly decreased 5-HT-stimulated PI hydrolysis in the rat cortex. On the other hand, chronic ethanol treatment (60 days) significantly increased 5-HT2C receptors and 5-HT-stimulated PI hydrolysis in the rat choroid plexus. Ethanol withdrawal (24 h) after chronic ethanol consumption (15 days) results in the down-regulation of 5-HT2A receptors and in a decrease in 5-HT-stimulated PI hydrolysis in the rat cortex. Taken together, these results, along with other reports in the literature, suggest that 5-HT2A/2C receptors or their function are altered during chronic ethanol consumption and withdrawal. Further studies are needed to explore the role of 5-HT2A/2C receptors and the PI signal transduction system in the development of ethanol withdrawal symptoms after chronic ethanol consumption.

The 5-HT4 receptor antagonist, GR113808, reduces ethanol intake in alcohol-preferring rats

The present study evaluated the effect of the selective 5-HT4 receptor antagonist, GR113808, on ethanol intake in alcohol-preferring rats. Rats were offered 10% ethanol 2 h/day. In the first experiment, rats had food and water ad lib and 10% ethanol was offered from 1800 to 2000 h. In the second experiment, food was freely available, 10% ethanol was offered 2 h/day, from 1800 to 2000 h, and water was offered for 4 h, from 1800 to 2200 h. In both experiments GR113808 was subcutaneously injected at doses of 1, 3, or 10 mg/kg for 4 consecutive days, 5 min before access to ethanol. From the first day of administration, GR113808 significantly reduced the volitional ethanol intake in water sated rats at the three doses tested. In water-deprived rats, it reduced ethanol intake at 3 and 10 mg/kg, without modifying total fluid and food intake. In both experiments the effect of GR113808 remained rather stable during the 4 days of administration. The present findings, showing that the 5-HT4 receptor antagonist, GR113808, selectively reduces ethanol intake in alcohol-preferring rats, suggest that 5-HT4 receptors may play a role in alcohol intake control.

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

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