Serotonergic Dysfunction, Negative Mood States, and Response to Alcohol

An Expanded Evaluation of the Relationship of Four Alleles to the Level of Response to Alcohol and the Alcoholism Risk

BACKGROUND

Alcoholism is a complex, genetically influenced disorder the cause of which may be better understood through the study of genetically influenced phenotypes that mediate the risk. One such intermediate phenotype is the low level of response (LR) to alcohol. This project used a case-control approach to search for genes that may contribute to LR.

METHODS

Data were available from alcohol challenges at approximately age 20 and regarding the development of alcohol use disorders over the subsequent 20 years for 85 men, including 40 reported in a previous genetic analysis. LR was evaluated using oral consumption of 0.75 ml/kg of alcohol, after which changes in subjective feelings of intoxication and body sway were measured. Alcohol abuse and dependence were diagnosed by DSM-III-R criteria through structured interviews administered to both the participant and an informant (usually the spouse) 10, 15, and 20 years after initial testing. Four polymorphisms were evaluated, including the serotonin transporter HTTLPR promoter ins/del, GABAAalpha6 Pro385Ser, NPY Leu7Pro, and catalase 262C>T. Two of these, HTTLPR and GABAAalpha6 Pro385Ser, had been previously associated with LR and alcoholism in a preliminary study.

RESULTS

The HTTLPR L allele was significantly related to both the LR and alcoholism in an allele-dosage (stepwise) manner. Furthermore, the association remained when L alleles were subdivided into recently reported functional subtypes: the lowest LR was associated with genotypes correlated with the highest serotonin transporter expression. The GABAAalpha6 Ser385 allele showed a nonsignificant trend for association to a low LR, as had been previously observed, although the Ser385 allele is uncommon, and only 18 heterozygotes were in the current group. However, the six men with both LL and Pro385/Ser385 genotypes had the lowest LR, and each had developed alcoholism during follow-up. Neither NPY nor catalase was associated with either LR or alcoholic outcomes, although the sample did not have sufficient power for definitive conclusions.

CONCLUSIONS

This report strengthens the support for a relationship between the HTTLPR L and GABAAalpha6 Ser385 alleles to low alcohol LR and to alcoholism in a prospectively studied cohort evaluated for LR in young adulthood and before the onset of alcohol dependence.

Platelet serotonin uptake and paroxetine binding among allelic genotypes of the serotonin transporter in alcoholics

Expression rates of long (L) and short (S) alleles of the serotonin (5-HT) transporter (5-HTT) gene have been shown to differ under various circumstances. We compared 5-HTT uptake (function) level and paroxetine binding (density) in platelets of alcoholics as indices of 5-HTT expression rate among LL, LS, and SS genotypes. Concentration curves of [3H]5-HT and [3H]paroxetine were used to quantify the equilibrium constant (Km) and maximum 5-HT uptake rate (Vmax) for 5-HTT uptake into intact platelets and the dissociation constant (Kd) and maximum specific binding density (Bmax) for paroxetine binding to platelet membranes, respectively. Genotypes were determined using electrophoresis with fluorescent markers. Vmax for 5-HTT uptake did not correlate with Bmax for paroxetine binding (r=-0.095, P=0.415). Means of Vmax and Bmax did not differ in a statistically significant manner among LL, LS, and SS genotypes in these alcoholic subjects. However, Vmax for LL and SS appeared to have a bimodal distribution, so the percentage of subjects with Vmax <200 fmol/min-10(7) platelets was statistically significantly higher in LL than in SS (51.5% vs. 22.7%, respectively), with an odds ratio of 3.6 (P<0.05). The percentage of Vmax <200 fmol/min-10(7) platelets for LS was 39.3% (not significant vs. LL or SS). Previous studies of healthy human controls have shown that 5-HTT density in raphe nuclei and 5-HTT uptake in platelets are higher in the LL genotype than in S carriers. Our findings in currently drinking alcoholics support the hypothesis that those with the LL genotype of the 5'-HTTLPR region of the 5-HTT gene have reduced 5-HTT function.

Acute effect of a brief bout of exercise on alcohol urges

AIM

To examine whether a brief bout of moderate intensity exercise reduces alcohol urges and mood disturbance in those with alcohol dependence.

DESIGN

A counterbalanced cross-over design (within-subjects).

SETTING

A hospital-based alcohol rehabilitation clinic.

PARTICIPANTS

Twenty males and females [mean (SD) age = 40.1 (8.2) years, mean (SD) Severity of Alcohol Dependence Questionnaire score = 34.2 (13.4)] who had recently completed alcohol detoxification [mean (SD) days since completing detoxification = 3.5 (2.3)].

INTERVENTION

On the first day of experimentation all participants (N = 20) were randomized to undergo one of two conditions, either: (i) a single bout of 10 minutes of moderate intensity cycling (experimental), or (ii) a single bout of 10 minutes of very light intensity cycling (control). On the following day they underwent the remaining condition.

MEASUREMENTS

All participants completed the Alcohol Urge Questionnaire and a six-item measure of mood disturbance at the following times: (i) immediately before exercise (baseline), (ii) during exercise (at 5 minutes), (iii) immediately following exercise, (iv) 5 minutes following exercise and (v) 10 minutes after exercise.

FINDINGS

Relative to baseline, there was a significant decline in alcohol urges for the experimental condition versus control during exercise (P = 0.02) but not at any measurement point following exercise. At baseline, by chance, there was a non-significant tendency for there to be higher ratings of alcohol urges for the experimental condition versus the control. For mood, there was no evidence for significant differences between treatment conditions for baseline versus any subsequent measurement point.

CONCLUSIONS

A brief bout of moderate intensity exercise may provide some short-term relief from alcohol urges during exercise. Further studies are required to replicate the present findings and to confirm whether any moderating effect of exercise on alcohol urges is sustained following exercise.

Reduced 5-HT3 receptor binding and lower baseline plus maze anxiety in the alcohol-preferring inbred fawn-hooded rat

The present investigation sought to explore the relationship between the 5-HT(3) receptor and anxiety-like behavior in fawn-hooded (FH/Wjd) rats, an inbred strain that exhibits a high intake and preference for ethanol, and the alcohol-nonpreferring ACI/N strain. Using quantitative autoradiography, we examined whether there were differences in central 5-HT(3) receptor binding in FH/Wjd versus ACI/N rats. Ten to 14 days prior to being used in the autoradiographic studies, rats were first confirmed to be representative of their strains by subjecting them to a two-bottle choice procedure for 2 weeks. The binding of [3H]LY 278584 to 5-HT(3) receptors was significantly reduced in frontal cortex, CA1 region of hippocampus, and in the medial and lateral nuclei of the amygdala of FH/Wjd versus ACI/N rats. In the anterior cingulate cortex and in the dentate gyrus region of the hippocampus the reduction in [3H]LY 278548 binding in the FH/Wjd versus ACI/N strain (40% and 41%, respectively) did not reach statistical significance. In a separate group of animals, the effects of the 5-HT(3) receptor antagonist MDL 72222 (3 mg/kg ip) on anxiety-related behaviors were assessed in the elevated plus maze. In vehicle-treated rats, the FH/Wjd strain exhibited significantly greater percent of time spent on the open arms and percent open arm entries, an indication of less anxiety. Pretreatment with MDL 72222 did not alter these behaviors in the FH/Wjd rats, but had an anxiolytic-like effect in the ACI/N strain, significantly increasing the percent of time spent on the open arms and percent open arm entries. Further research into 5-HT(3) receptor function in the alcohol-preferring FH/Wjd rats is needed to elucidate the relationship among 5-HT(3) receptors, alcohol drinking, and anxiety.

Sexual dichotomy of an interaction between early adversity and the serotonin transporter gene promoter variant in rhesus macaques

A polymorphism in the human serotonin transporter gene promoter (5-HTTLPR) is associated with anxiety and increased risk for developing depression in the face of adversity. Here, we report that among infant rhesus macaques, an orthologous polymorphism (rh5-HTTLPR) interacts with adversity in the form of peer rearing to influence adrenocorticotropic hormone (ACTH) response to stress and, further, that this interaction is sexually dichotomous. ACTH responses to separation are higher in l/s than in l/l males. In females, however, it is only among those with a history of adversity that the s allele is associated with increased ACTH responses to stress. Of interest, peer-reared animals, in particular females carrying the s allele, also exhibit lower cortisol responses to stress, a pattern that has been recognized in association with certain stress-related neuropsychiatric disorders. By extension, our findings suggest the intriguing possibility that human females carrying the 5-HTTLPR s allele could be more vulnerable to the effects of early adversity. This interactive effect may underlie the increased incidence of certain stress-related disorders in women.

Ondansetron reduces mood disturbance among biologically predisposed, alcohol-dependent individuals

BACKGROUND

Early-onset alcoholics (EOA) differ from late-onset alcoholics (LOA) by developing problem drinking during youth, experiencing severe behavioral problems, having a familial disease history, and possessing a tendency toward subsyndromal mood disturbance, including symptoms of depression, anxiety, and hostility. Subsyndromal mood disturbance is, therefore, an important component of the early-onset syndrome and may be mediated by serotonin dysfunction. Therefore, the serotonin-3 antagonist ondansetron, which has been shown to be effective at improving drinking outcomes and promoting abstinence among EOA, presumably by ameliorating serotonin dysfunction, also may exert its beneficial effects by alleviating mood disturbance among EOA.

METHODS

After one lead-in week of single-blind placebo administration, subjects underwent 11 weeks of double-blind outpatient treatment using a 2 x 4 factorial design that examined age of onset (EOA versus LOA) and medication dose (placebo, or ondansetron 1, 4, or 16 microg/kg twice daily) combined with weekly standardized group cognitive-behavioral therapy. The placebo lead-in week was used to adjust for study entrance effects but not for excluding subjects. Assessments of mood were performed by using the overall score and subscales of the Profile of Mood States both at screening and at weekly intervals during the study.

RESULTS

Subsyndromal mood disturbance was shown to be an important component of early-onset alcoholism. Ondansetron (16 microg/kg twice daily) showed greater therapeutic efficacy at alleviating symptoms of overall mood disturbance, fatigue, vigor, confusion/bewilderment, and depression among EOA compared with LOA. EOA-associated improvements in mood disturbance seemed to be independent of drinking behavior.

CONCLUSIONS

Ondansetron has been shown to be an effective treatment for early-onset alcoholism. Ondansetron's ability to improve symptoms of depression, anxiety, and hostility among EOA may make an additional contribution to its therapeutic effect. Mechanistic studies are needed to delineate more clearly the relationship between serotonin dysfunction and pathophysiology among various subtypes of alcohol-dependent individuals.

Violence related injuries in the emergency room: alcohol, depression, and conduct problems

OBJECTIVE

The aim of this study was to obtain epidemiological measures of the association between alcohol consumption and emergency room (ER) attendance due to violence, compared to the general population in the city of Pachuca, Mexico, during October-November, 1996 and June-July, 1997.

METHOD

The study was a population-based case-control design.

INTERVENTION AND MEASUREMENTS

Data consisted of an interviewer-administered questionnaire, collected on a 24-h basis, during the entire week.

SETTING AND PARTICIPANTS

Cases were 127 patients (78% male) admitted to the ER because of an injury that was the result of violence (being in a fight or being attacked by someone). A sample of residents from Pachuca (n = 920) was the comparison group.

RESULTS

Patients reporting drinking within 6h compared to nondrinkers were more likely to suffer a violence-related injury [34.0 (17.5-66.2)] and alcohol dependent patients were more likely to be involved in a violence-related injury [7.4 (3.5-15.6)] compared to noncurrent drinkers. When both alcohol prior and alcohol dependence were considered simultaneously in multiple models among current drinkers, patients with violence-related injuries were more likely to report alcohol prior but not to be positive for alcohol dependence. Depressive symptoms, but not conduct problem behavior, were also associated with violent injury in simultaneous regressions that included alcohol variables.

CONCLUSIONS

In the city of Pachuca, Mexico, a large relationship between drinking prior to the event and violence-related injury, regardless of alcohol dependence, was found. Depression was also related to violence, suggesting the need for more comprehensive intervention with these patients.

Rearing condition and rh5-HTTLPR interact to influence limbic-hypothalamic-pituitary-adrenal axis response to stress in infant macaques

BACKGROUND

In humans and macaques, a promoter polymorphism that decreases transcription of the serotonin transporter gene is associated with anxiety. Serotonin transporter gene disruption in rodents produces anxious animals with exaggerated limbic-hypothalamic-pituitary-adrenal (LHPA) responses to stress. We wanted to determine whether serotonin transporter gene promoter variation (rh-5HTTLPR) and rearing condition would interact to influence endocrine responses to stress in infant rhesus macaques.

METHODS

Animals were reared with their mothers (MR, n = 141) or in peer-only groups (PR, n = 67). At 6 months of age, adrenocorticotropic hormone (ACTH) and cortisol levels were determined at baseline and during separation stress. Serotonin transporter genotype (l/l and l/s) was determined with polymerase chain reaction followed by gel electrophoresis.

RESULTS

Cortisol levels increased during separation, and there was a main effect of rearing condition, with decreased cortisol levels among PR macaques. Animals with l/s rh5-HTTLPR genotypes had higher ACTH levels than did l/l animals. Adrenocorticotropic hormone levels increased during separation, and there was a separation x rearing x rh5-HTTLPR interaction, such that PR-l/s animals had higher ACTH levels during separation than did other animals studied.

CONCLUSIONS

These data demonstrate that serotonin transporter gene variation affects LHPA axis activity and that the influence of rh5-HTTLPR on hormonal responses during stress is modulated by early experience.

Stress sensitization of ethanol withdrawal-induced reduction in social interaction: inhibition by CRF-1 and benzodiazepine receptor antagonists and a 5-HT1A-receptor agonist

Repeated withdrawals from chronic ethanol sensitize the withdrawal-induced reduction in social interaction behaviors. This study determined whether stress might substitute for repeated withdrawals to facilitate withdrawal-induced anxiety-like behavior. When two 1-h periods of restraint stress were applied at 1-week intervals to rats fed control diet, social interaction was reduced upon withdrawal from a subsequent 5-day exposure to ethanol diet. Neither this ethanol exposure alone nor exposure to three restraint stresses alone altered this measure of anxiety. Further, the repeatedly stressed singly withdrawn rats continued to exhibit a reduction in social interaction 16 days later, upon withdrawal from re-exposure to 5 days of chronic ethanol, consistent with a persistent adaptation by the multiple-stress/withdrawal protocol. Weekly administration of corticosterone in place of stress induced no significant change in social interaction upon withdrawal from the single chronic ethanol exposure, indicative that corticoid release is not responsible for the stress-induced reduction in anxiety-like behavior during withdrawal. In the multiple-withdrawal protocol, stress applied during withdrawal from voluntary ethanol drinking by P-rats facilitated ethanol drinking sufficiently, to induce a withdrawal-induced reduction in social interaction. Administration of a CRF-1 receptor antagonist, a benzodiazepine receptor antagonist, or a 5-HT(1A) receptor agonist prior to each stress minimized sensitization of the withdrawal-induced reduction in anxiety-like behavior. Since these pharmacological consequences on the induction of anxiety-like behavior following the stress/withdrawal protocol are like those previously seen when these drug treatments were given prior to multiple withdrawals, evidence is provided that repeated stresses and multiple withdrawals sensitize the withdrawal reduction in social interaction by similar central adaptive mechanisms.

Serotonin transporter and GABAA alpha 6 receptor variants are associated with neuroticism

BACKGROUND

A tendency to experience negative affect, as measured by the neuroticism component of the Neuroticism, Extraversion, and Openness Personality Inventory (NEO-PI), is a trait marker for major depression. Epidemiologic studies indicate a strong genetic component, but to date few specific genetic variants have been definitively implicated. A serotonin transporter promoter polymorphism (5-HTTLPR) has been extensively studied in neuroticism and several psychiatric disorders, with inconclusive results. A GABA(A) receptor alpha6 subunit variant (Pro385Ser) has been associated with alcohol-related traits but has not been studied in neuroticism or depression.

METHODS

A total of 384 subjects who completed the NEO-PI were genotyped at 5-HTTLPR and Pro385Ser. Associations between polymorphisms and both alcohol use and personality domains were tested.

RESULTS

The 5-HTTLPR short allele (p =.008) and Pro385Ser Pro allele (p =.003) are associated with higher neuroticism scores. The 5-HTTLPR long allele (p =.006), but not Pro385Ser, is also associated with an increased presence of alcohol use. In addition, there is a nonsignificant suggestion of an interaction: the effect of 5-HTTLPR on neuroticism might be dependent on the Pro385Ser genotype.

CONCLUSIONS

These findings support a role for the serotonin transporter and GABA(A) alpha6 subunit in depression-related traits.

Alcoholism and seasonal affective disorder

Seasonal changes in mood and behavior (seasonality) may be closely related to alcoholism. Some patients with alcoholism have a seasonal pattern to their alcohol misuse. They may be self-medicating an underlying seasonal affective disorder (SAD) with alcohol or manifesting a seasonal pattern to alcohol-induced depression. Both genetic and environmental factors play a role in the etiology and pathogenesis of alcoholism and SAD, operating, at least in part, through the brain serotonergic system. Family and molecular genetic studies suggest that there may be a genetic link between seasonality and alcoholism. Certain environmental and social factors may contribute to the development of seasonality in patients with alcoholism. The fact that SAD and alcoholism may be comorbid shows the importance of a thorough diagnostic interview. Both mental health and drug and alcohol professionals should be provided with education to assist with appropriate identification, management, and referral of patients presenting with comorbid alcoholism and SAD.

Pharmacogenomics of alcohol response and addiction

Alcoholism is a complex psychiatric disorder that has high heritability (50-60%) and is relatively common; in the US the lifetime prevalence of alcohol dependence is 20% in men and 8% in women. Current psychosocial and pharmacological therapies have relatively modest effects. Treatment is complicated by the fact that alcoholism is often co-morbid with other disorders, including anxiety, depression, and antisocial personality disorder. Approximately 80% of alcoholics smoke cigarettes and there is considerable genetic overlap between nicotine and alcohol addiction. Convergent evidence supports the classification of alcoholics into two broad categories: type 1 - later onset with feelings of anxiety, guilt, and high harm avoidance; and type 2 - early age of onset, usually men, impulsive, antisocial, and with low levels of brain serotonin. The pharmacogenomics of alcohol response is well established; genetic variants for the principal enzymes of alcohol metabolism influence drinking behavior and protect against alcoholism. Vulnerability to alcoholism is likely to be due to multiple interacting genetic loci of small to modest effects. First-line therapeutic targets for alcoholism are neurotransmitter pathway genes implicated in alcohol use. Of particular interest are the 'reward pathway' (serotonin, dopamine, GABA, glutamate, and beta endorphin) and the behavioral stress response system (corticotrophin-releasing factor and neuropeptide Y). Common functional polymorphisms in these genes are likely to be predictive (although each with small effect) of individualized pharmacological responses. Genetic studies, including case-control association studies and genome wide linkage studies, have identified associations between alcoholism and common functional polymorphisms in several candidate genes. Meanwhile, the current pharmacological therapies for alcoholism are effective in some alcoholics but not all. Some progress has been made in elucidating the pharmacogenomic responses to these drugs, particularly in the context of the type 1/type 2 classification system for alcoholics.

Linkage disequilibrium and haplotype analysis between serotonin receptor 1B gene variations and subtypes of alcoholism

A number of studies have reported a possible association between serotonergic pathway genes and alcoholism. A silent polymorphism (G to C substitution) in the gene encoding the autoreceptor 5-HT1B was linked to antisocial alcoholism in Finnish and an American Indian populations [Lappalainen et al., 1998: Arch Gen Psychiatry 55:989-994]. Several other polymorphisms of this gene have been investigated for their association with neuropsychiatric disorders. In the present study, a sample of 133 alcoholics without and 39 alcoholics with medical complications, and 88 normal controls was screened for three single nucleotide polymorphisms (SNPs), G861C, G261T, and C129T, in the 5-HT1B gene. The goal was to investigate their association with the disease, to measure the strength of linkage disequilibrium (LD) between the SNPs, and to compare haplotype frequencies between alcoholic groups and normal controls. Data was also analyzed on the basis of Type I (n = 47) and Type II (n = 85) alcoholism. There was no significant difference in the allele frequencies or the genotype distribution between any alcoholic groups, alcoholic subgroups, and controls for any polymorphism. G861C and C129T polymorphisms were in complete LD. The pattern of distribution of haplotypes was similar in patients and controls. It is concluded that these SNPs are not playing any direct role in the development of susceptibility to alcoholism in our patient sample.

Ethanol consumption and serotonin-1A (5-HT1A) receptor function in heterozygous BDNF (+/-) mice

Heterozygous brain-derived neurotrophic factor (BDNF) (+/-) mice display abnormalities in central serotonergic neurotransmission, develop decrements in serotonergic innervation of the forebrain, and exhibit enhanced intermale aggressiveness. As disturbances of serotonin neurotransmission are implicated in alcohol abuse and aggression, we have examined in BDNF (+/-) mice alcohol drinking behavior, as well as central 5-hydroxytryptamine (5-HT)1A receptor function at the level of 5-HT1A receptor-G protein interaction. BDNF (+/-) mice displayed increased ethanol intake in a two-bottle choice procedure. There was no difference in the preference ratio for non-alcoholic tastants (i.e. quinine or saccharin) between genotypes. In the brains of alcohol-naive mice, we measured [35S]GTP gamma S binding stimulated by the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-dipropyl-aminotetralin hydrobromide (8-OH-DPAT; 1 microM). In BDNF (+/-) versus wild-type (WT) mice, 5-HT1A receptor-stimulated [35S]GTP gamma S binding was significantly attenuated in the median raphe nucleus. There was a decrease in (+/-)8-OH-DPAT-stimulated [35S]GTP gamma S binding in the dorsal raphe, which did not reach statistical significance. In the hippocampus, 5-HT1A receptor-stimulated [35S]GTP gamma S binding was significantly attenuated in BDNF (+/-) mice. 5-HT1A receptor-stimulated [35S]GTP gamma S binding was attenuated in the anterior cingulate cortex and lateral septum, although these reductions did not reach statistical significance. 5-HT1A receptor number was not different between genotypes in any area of brain examined, suggesting that 5-HT1A receptor function, specifically the capacity of the 5-HT1A receptor to activate G proteins, is attenuated in BDNF (+/-) mice.

Serotonin transporter gene variation is associated with alcohol sensitivity in rhesus macaques exposed to early-life stress

BACKGROUND

Decreased sensitivity to alcohol has been demonstrated to be a predictor of alcoholism in humans, and variation in the gene-linked polymorphic region of the serotonin transporter (5-HTTLPR) is associated with the response to the motor-impairing effects of alcohol. In a nonhuman primate model of excessive alcohol intake, we have shown that decreased serotonin turnover is associated with both lower initial sensitivity to alcohol and higher prospective alcohol consumption using rhesus macaques. In addition, we have demonstrated that macaques separated from their mothers and reared in peer-only groups are more likely to consume alcohol as adults.

METHOD

To examine the relationship between serotonin transporter genotype, early rearing experience, and initial sensitivity to alcohol, peer- and mother-reared, adolescent, alcohol-naive rhesus macaques (n = 123) were rated for intoxication after intravenous administration of ethanol (2.2 g/kg and 2.0 g/kg for males and females, respectively) during two testing periods. Serotonin transporter (rh5-HTTLPR) genotype was determined using polymerase chain reaction followed by gel electrophoresis, and data were analyzed using ANOVA and the Mann-Whitney U test.

RESULTS

Our analyses demonstrate an effect of serotonin transporter gene variation on ethanol sensitivity, such that animals homozygous for the l allele exhibited decreased sensitivity to the ataxic and sedating effects of alcohol. This effect remained after correction for blood ethanol concentrations and birth cohort. When animals were segregated according to rearing condition, serotonin transporter gene variation predicted intoxication scores among peer-reared animals.

CONCLUSIONS

As in some human reports, this study demonstrates a diminution in the response to alcohol in animals homozygous for the l rh5-HTTLPR allele. The phenotypic expression of this genotype in l/s animals, however, is environmentally dependent.

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

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

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.

Association study of novel human serotonin 5-HT(1B) polymorphisms with alcohol dependence in Taiwanese Han

BACKGROUND

Abnormal serotonergic pathways are implicated in numerous neuropsychiatric disorders, such as depression, anxiety, migraine, substance abuse, and alcoholism. The human serotonin receptor 1B, encoded by the HTR1B gene, is a presynaptic serotonin autoreceptor that plays a role in regulating serotonin synthesis and release. Because the linkage of antisocial alcoholism to the HTR1B gene was recently reported in two populations, it was of interest to identify genetic variants at the HTR1B locus and study their association with alcoholism in the Taiwanese Han population.

METHODS

We sequenced DNA from Taiwanese Han to screen for genetic variation in the coding, promoter, and partial 3' untranslated regions of the HTR1B locus of 158 alcohol-dependent cases with withdrawal symptoms and 149 control subjects, who either never drank or drank only occasionally and in low quantities.

RESULTS

Seven variants were identified. Positive associations were found between variant A-161T and alcohol dependence at both the allelic and genotypic level. In addition, an expression study showed that the A-161T variant affected reporter gene activity.

CONCLUSIONS

Our results support an association between HTR1B and alcohol dependence. The HTR1B A-161T polymorphism may be valuable both as a functional and as an anonymous genetic marker for HTR1B.

The Fawn-Hooded (FH/Wjd) rat: a genetic animal model of comorbid depression and alcoholism

The Fawn-Hooded (FH/Wjd) rat is an inbred strain of rat that has been reported to exhibit both high immobility in the forced swim test and high voluntary ethanol intake, measures that have been periodically linked with depression and alcoholism in humans. The present paper will first present a survey of the literature and previously unpublished findings that bear on the question of whether FH/Wjd rats should be considered genetic animal models of depression and alcoholism. Subsequently, behavioral studies of the FH/Wjd rats, the non-drinking ACI/N strain, and their F1 and F2 intercrosses will be described. Under free choice conditions, the FH/Wjd rat drinks up to 6 g/kg 10% ethanol per day. This intake was sufficient to render the rats tolerant to the hypothermic effects of injected ethanol (2.5 g/kg). Rats that had been voluntarily drinking for at least 6 weeks also exhibited withdrawal-induced anxiety in the social interaction, elevated plus maze, and ultrasonic vocalization tasks. The FH/Wjd rat exhibits a 25-30% increase in alcohol intake when the alcohol is returned after a 24-h period of deprivation. It responds to drugs that are effective in humans with a reduction in alcohol intake. Therefore, the FH/Wjd rat meets most of the criteria for an animal model of alcoholism. Chronic antidepressant treatments correct several of the abnormalities exhibited by the FH/Wjd rats, including the exaggerated immobility in the forced swim test. Therefore, the FH/Wjd rats also fulfill some of the criteria for an animal model of depression. On the contrary, inbred ACI/N rats do not drink much alcohol voluntarily and are quite active in the forced swim test. The FH/Wjd and ACI/N rats were intercrossed to obtain the F1 and F2 progenies, which were then tested for alcohol intake and immobility. Alcohol intake and immobility were distributed in different patterns in the F1 and F2 progenies. Alcohol intake was intermediate in the F1 progeny, while immobility was closer to the FH/Wjd parents. In the F2 progeny, chi-square analyses indicated that the distributions were significantly different. In addition, there were no significant litter effects, indicating that maternal effects did not appear to occur. There were also no significant differences among rats with different coat colors, suggesting that the Fawn-Hooded phenotype can be separated from the measures of alcohol intake and immobility. We conclude that the FH/Wjd rat is a genetic animal model of depression and alcoholism, but that the two measures reflective of these states are under separate genetic controls.

Dopaminergic dysfunction in alcoholism and schizophrenia--psychopathological and behavioral correlates

Dysfunction of central dopaminergic neurotransmission has been implicated in the pathogenesis of schizophrenia as well as drug and alcohol dependence. Different drugs of abuse stimulate dopamine release in the ventral striatum and thus reinforce drug consumption. Increased subcortical dopamine release has also been associated with the pathogenesis of positive symptoms in schizophrenia and may be driven by a prefrontal dopaminergic dysfunction. These seemingly heterogeneous findings may be explained by recent research in non-human primates. According to these studies, reward anticipation but not anticipated reward consumption is accompanied by a phasic dopamine release in the striatum and prefrontal cortex. In the striatum, phasic dopamine release primarily affects motivation, psychomotor activation and reward craving, while in the prefrontal cortex, dopaminergic stimulation is involved in the activation of working memory and reward anticipation. In alcoholism, previously neutral stimuli that have been associated with alcohol intake can become conditioned cues which activate phasic dopamine release and reward craving. In schizophrenia, stress-induced or chaotic activation of dopamine release may attribute incentive salience to otherwise irrelevant stimuli and thus be involved in the pathogenesis of delusional mood and other positive symptoms. Studies in humans and non-human primates emphasize the role of dopaminergic neurotransmission in reward anticipation and its dysfunction in different neuropsychiatric diseases.

Biological markers for suicidal behavior in alcohol dependence

Alcohol-dependent populations have a high lifetime suicide rate (between 7 and 15%, relative risk = 7), and alcoholism is one of the two psychiatric disorders most frequently found in suicidal cases (between 15 and 25%). Biological factors that would detect patients at risk could thus be of value. Carbohydrate-deficient transferrin, monoamine oxidase B, soluble interleukin-2 receptor and cholesterol have been proposed as markers of suicidal risk in alcohol-dependent patients, although nonspecific and with low predictive value. On the other hand, there is large and convergent data stressing the importance of serotonin dysregulation as increasing the risk for aggressive behaviour toward the self, although it is not clear whether serotonin is involved through the altered behavior inhibition system, enhancement of anxiety and depression, or association with specific subtypes of alcohol-dependence, such as early-onset type II alcoholism. Considering the complex but significant impact of alcohol on serotonin metabolism and turnover, it is likely that serotonin mediates a large part of the proneness of ethanol to commit impulsive-aggressive behavior.