Relationship between central serotonergic neurotransmission and reduction in alcohol intake by citalopram

Effects of stress and dietary tryptophan enhancement on craving for alcohol in binge and non-binge heavy drinkers

Stress is known to play an important role in alcohol abuse, whereas binge drinking may increase individuals' susceptibility to the development of alcohol dependence. We set out to investigate whether binge drinkers (BDs) or non-BDs (NBDs) are at a greater risk of an increase in their desire for alcohol following experimental stress induction (modified Trier Social Stress Test; Experiment 1) and to explore the biological mechanisms underlying such an effect (Experiment 2). Preclinical evidence suggests that serotonin may mediate stress-induced reinstatement of alcohol intake. We therefore tested whether dietary tryptophan (TRP) enhancement would modulate stress-induced desire for alcohol and whether it would affect the two populations (BD/NBD) differently. In Experiment 1 (14 NBDs, 10 BDs; mean weekly alcohol intake 50.64 U), stress induction selectively increased strong desire for alcohol compared with the nonstressful condition in BDs. Throughout the experiment, BDs reported greater negative reinforcement type of craving than NBDs, but also a higher expectancy of alcohol-induced negative effects. In Experiment 2, 41 participants (22 NBDs, 19 BDs; mean alcohol intake 38.81 U) were given either the TRP-rich (TRP+; 9 BDs, 11 NBD) or the control (CTR; 10 BD, 11 NBD) diet before undergoing stress induction. In BDs, the TRP+ diet prevented the stress-induced increase in strong desire that was observed in individuals receiving the CTR diet. In NBDs, the TRP+ diet appeared to facilitate an increase in strong desire. These findings suggest that BDs may indeed be at a greater risk than NBDs of an increase in their craving for alcohol when stressed. Furthermore, whereas enhancement of 5-hydroxytryptamine function may moderate the impact of stress on craving in BDs, it seems to facilitate stress-induced craving in NBDs, suggesting that the serotonergic system may be differentially involved depending on individual binge drinking status.

Prolactin response to fenfluramine in abstinent, alcohol-dependent patients

It has been suggested that serotonin (5HT) function is abnormal in alcoholics even during abstinence. The prolactin response to fenfluramine (PRF) is generally believed to reflect the activity of the 5HT system and has been previously used to investigate 5HT activity in a variety of conditions, including alcoholism. The origin of the cortisol (CORT) response to fenfluramine is less clear. The objectives of this paper are to examine the prolactin (PRL) and CORT response to dl-fenfluramine in a large cohort of males with alcohol dependence who had been abstinent for 3 weeks, and to compare this with an age-matched control group. Ninety-four subjects with a DSM-III-R diagnosis of moderate to severe alcohol dependence who had been abstinent for 3 weeks, and 23 control subjects underwent neuroendocrine challenge with dl-fenfluramine (10 mg per 10 kg body weight). PRL and CORT responses were measured. No significant difference was found in PRF between abstinent, alcoholic patients and controls (F = 2.7, d.f. = 1.115, P = 0.10). CORT response was significantly lower in abstinent alcoholics than in controls (F = 10.0, d.f. = 1.116, P = 0.002). The results suggest no clear difference in 5HT function between abstinent alcoholics and healthy controls. The reduced CORT response in abstinent alcoholics further supports evidence of hypofunction of the adrenocortical system in this group.

Personality profile in type I alcoholism: long duration of alcohol intake and low serotonergic activity are predictive factors of anxiety proneness

The aim of the present study was to further investigate personality profiles in male type I alcohol-dependent subjects (n = 33), in relation to central serotonergic neurotransmission, history of excessive alcohol consumption and present use of tobacco. Central serotonergic neurotransmission was assessed by the prolactin (PRL) response to D-fenfluramine. By using the Temperament and Character Inventory and the Karolinska Scales of Personality, all subjects self-rated their personality profile. The results showed that individuals with low PRL response and long duration of excessive alcohol consumption had significantly higher anxiety proneness, and that years of excessive alcohol consumption was the strongest predictor. Long duration of excessive alcohol consumption thus appears to have an influence on personality traits in male type I alcohol-dependent individuals and these personality traits may therefore be a consequence of, rather than preceding, alcoholism in these individuals.

Maternal ethanol administration inhibits 5-hydroxytryptamine synthesis and tryptophan hydroxylase expression in the dorsal raphe of rat offspring

Maternal ethanol consumption during pregnancy has a detrimental effect on the central nervous system (CNS) development of fetus. 5-Hydroxytryptamine (5-HT) is an important neurotransmitter and/or neuromodulator in the mammalian CNS. Tryptophan hydroxylase (TPH) is the rate limiting enzyme of 5-HT synthesis. Ethanol is known to induce neuropsychiatric disorders by alteration of the central serotonergic system. In the present study, the effects of maternal ethanol intake on the 5-HT synthesis and the TPH expression in the dorsal raphe of rat offspring were investigated. The present results show that the synthesis of 5-HT and the expression of TPH in the dorsal raphe of rat offspring were suppressed by maternal ethanol intake and that the suppressive effect of alcohol was more potent in the 5 weeks old rat pups compared to the 3 weeks old rat pups. Based on the present study, it can be suggested that the pathogenesis of ethanol-induced neuropsychological disorders involves ethanol-induced suppression on the 5-HT synthesis and the TPH expression in the dorsal raphe of offspring.

Polymorphism in the serotonin transporter gene and response to treatment in African American cocaine and alcohol-abusing individuals

The serotonin transporter (5-HTT) regulates serotonin transmission and modulates behavioral effects of drug of abuse. A polymorphism in the promoter region of the serotonin transporter gene (5-HTTLPR) yielding a short (S) and long (L) allele has been associated with severity of substance abuse. The aims of the study were to investigate whether 5-HTTLPR genotypes differed in their response to treatment in cocaine- and alcohol-abusing patients. Polymerase chain reaction-based genotyping of a 44 base pair insertion/deletion polymorphism was performed in 141 African American cocaine-dependent patients with concurrent alcohol use who were entering a 12-week behaviorally oriented outpatient treatment program. In treatment, end of treatment and 6-month follow-up outcome measures included changes in Addiction Severity Index (ASI) scores, urine drug screens, days in treatment, individual/group sessions, dropout and completion rates. As expected, there was a reduction in substance abuse by the end of treatment and follow-up (F = 5.15, p = 0.000). However, there were no differences in the reduction in cocaine use across the LL, LS and SS genotypes. Interestingly, individuals with the S allele showed greater severity of alcohol use at admission (F = 4.84, p = 0.03), and the SS genotype showed less improvement in alcohol measures than the LL at follow-up (F = 3.68, p = 0.03), after controlling for baseline variables. While we found no association of the 5-HTTLPR variants with severity of cocaine abuse or any cocaine-related outcome measures, the data suggested that the 5-HTTLPR polymorphism may distinguish responders from non-responders to behavioral treatment in terms of alcohol use. Further investigations are required to determine the role of the 5-HTTLPR polymorphism in influencing treatment - outcome among substance abusers.

Efficacy of fluvoxamine in preventing relapse in alcohol dependence: a one-year, double-blind, placebo-controlled multicentre study with analysis by typology

Patients with a diagnosis of alcohol dependence, detoxified and abstinent for 10-30 days, were randomly allocated to placebo or the serotonin reuptake inhibitor, fluvoxamine (up to 300 mg per day), plus counselling and support. In the intention to treat sample of 493, there was a trend for the fluvoxamine group to do worse than the placebo group on the primary outcome criteria: abstinence; and relapse defined as drinking > or =5 units on an occasion and > or =4 such occasions in a week, or > or =12 units on an occasion (1 unit = 9g ethanol). When typology of alcoholism was assigned by scores on the Tridimensional Personality Questionnaire, Types I and II had similar rates of survival without relapse on placebo (PLC I: 19.3%, n = 135; PLC II: 18.2%, n = 110), but on fluvoxamine Type II did worse than Type I (FLU I: 13.7%, n = 131; FLU II: 6.14%, n = 114) (P < 0.01). When typology was assigned on the basis of age of onset of alcohol problems (< or = age 25, or > age 25), early-onset patients in the fluvoxamine group relapsed more frequently than late-onset patients in that group (no longer significant after adjustment for gender), as did those who commenced regular drinking before age 25 (both with and without adjustment for gender). One explanation for our finding could be that impulsivity in early-onset or Type II patients may be accentuated by serotonin enhancement.

Biological markers of cocaine addiction: implications for medications development

The search for effective medications for cocaine addiction has been elusive. The failure to find such medications so far could be due to poor understanding of the underlying biology both in the premorbid condition and following the disease state of chronic cocaine use. Population heterogeneity could be a major factor in response to medications. In an attempt to highlight the issue of biomarkers we reviewed physiological, neuroendocrine and neuroimaging studies to identify specific biological changes/markers that could be used to characterize subgroups among chronic cocaine users. Merging the biology within medications studies of cocaine abusers could prove useful for targeting specific pharmacological agents to subgroups of patients, prediction of response to medication and relapse to use.

Alcohol and nicotine administration inhibits serotonin synthesis and tryptophan hydroxylase expression in dorsal and median raphe of young rats

Serotonin (5-hydroxytryptamine, 5-HT) has been implicated in the pathophysiology of various neuropsychiatric disorders. In the present study, the effects of alcohol and nicotine on the synthesis of 5-HT and the expression of tryptophan hydroxylase (TPH), the rate-limiting enzyme of 5-HT synthesis, in the dorsal and median raphe of young rats were investigated via immunohistochemistry. The numbers of the 5-HT-positive and TPH-positive cells were reduced by alcohol and nicotine treatment in a dose-dependent manner. Based on the results, it can be suggested that the pathogenesis of alcohol- and nicotine-induced neuropsychological disorders involves alcohol- and nicotine-induced suppression of 5-HT synthesis and TPH expression in raphe, and that this may be of particular relevance in the consumption of alcohol and nicotine during adolescence.

Neurodevelopmental liabilities in alcohol dependence: central serotonin and dopamine dysfunction

Alcoholism is a complex disorder with symptoms ranging from abuse to dependence, often comorbid with depression, antisocial personality, or anxiety. Neurodevelopmental causes of the disorder are unknown but inferences are possible from current knowledge. Neurobiological studies implicate multiple brain changes, which may be characterized as premorbid or morbid. These studies have also examined specific aspects of the alcohol dependence syndrome, including alcohol reinforcement and craving. Here, we review the evidence for vulnerability factors in alcohol dependence, with an emphasis on central serotonin (5-HT) and dopamine (DA). Serotonin dysfunction likely contributes to the development of alcoholism since studies of alcohol-preferring rodents show decreased 5-HT function on many measures. We have shown that serotonin-enhancing drugs reduce consumption and craving in mild to moderate alcoholics, yet similar studies in severely dependent individuals remain inconclusive. Studies indicate that serotonin dysfunction may contribute to the development of dependence via impaired impulse control and/or mood regulation. The mesocorticolimbic dopamine pathway represents another important pathophysiological target in alcoholism. Differences in D(2) receptor density, dopamine sensitivity, and gene expression have been linked to consumption, reinforcement, craving, and relapse. However, while DA agonists reduce self-administration in animals, we found no effect in humans with long-acting bromocriptine, a D(2) agonist. Dopamine may contribute differentially to the development of dependence via its effects on alcohol wanting, reinforcement, and reward memory. Although animal experiments show consistent roles for serotonin and dopamine in alcohol dependence, human studies are not always concordant. Such discrepancies highlight the complexity of dependence-related behaviors in humans and of identifying vulnerabilities to alcoholism.