Evidence for Reduced Dopamine D2 Receptor Sensitivity in Postwithdrawal Alcoholics

Dopamine D2 receptor sensitivity was assessed in the postwithdrawal period in alcoholics. Growth hormone (GH) responses to dopamine D2 agonist bromocriptine were measured in eight DSM-III-R alcohol-dependent subjects who were 2 weeks or more postalcohol withdrawal. Their responses were compared with eight nonalcoholic controls. After an overnight fast, each subject received 1.25 mg of bromocriptine orally, and serial samples of GH were taken over a 3-hr period. There was a significantly blunted delta GH response (mean ± SE) in the alcoholic group, 2.3 mU/liter (±1.4) relative to controls, 7.7 mU/liter (±1.2) ( t = 2.96, df = 14, p = 0.01). There was a significantly blunted peak GH response (mean ± SE) in the alcoholic group, 5.36 mU/liter (±2.1) relative to controls, 9.04 mU/liter (±5.0). This difference also reached statistical significance ( t = 2.32, df = 14, p = 0.035). A repeated-measures ANOVA yielded a significant within-subjects effect of time [ F (4,54) = 4.08, p = 0.0057], a significant with-in-subjects effect of group [ F (1,14) = 5.6, p = 0.0329], and an almost significant group x time interaction [ F (4,54) = 2.45, p = 0.056]. This result implies a relative dopamine D2 receptor subsensitivity in alcoholics in the postwithdrawal period.     

A Family-Based Analysis of the Association of the Dopamine D2 Receptor (DRD2) with Alcoholism

The possible association of the DRD2 locus, and in particular the 7aql-A1 allele, with alcoholism remains controversial, in part because of differences in allele frequencies among populations. To avoid problems associated with differences in allele frequencies in different populations, we tested whether the DRD2 locus is associated with alcohol dependence in a large family-based sample. Neither the transmission/disequilibrium test nor the Affected Family-Based Controls test provide any evidence of linkage or association between the DRD2 locus and alcohol dependence.     

Association Study Between the 441C Ins/Del and TaqI A Polymorphisms of the Dopamine D2 Receptor Gene and Alcoholism

Dopamine D2 receptors have been implicated in the biology of alcohol preference. We examined the-141 C Ins/Del polymorphism in the promoter region of the dopamine D2 receptor gene (DRD2) and the DRD2 Taql A polymorphisms in 209 Japanese alcoholics and 152 age- and sex-matched Japanese controls. The Ins allele was significantly increased in the alcoholics, compared with the controls ( p < 0.002, odds ratio = 1.82). The Taql A1 allele tended to be more frequent in the alcoholics than in the controls ( p < 0.04). Linkage disequilibrium between these two polymorphisms was weak (a maximum δ value = 0.13). The -141 C Ins/Del polymorphism may affect the vulnerability for alcoholism presumably through different expression of DRD2 in the Japanese.     

No Association of the Structural Dopamine D2 Receptor (DRD2) Variant 311Cys with Alcoholism

The human dopamine D2 receptor (DRD2) has been implied in the vulnerability for alcoholism and/or the modification of its severity. This is supported through animal experimental and pharmacological data. We analyzed the DRD2 ³¹¹Ser/Cys polymorphism in 312 German alcoholics and 131 ethnically matched controls to investigate the association of genetic DRD2 variants with alcoholism or clinical characteristics of homogeneous subgroups of alcoholics. We observed no association between the ³¹¹Cys variant and alcoholism, and none of the clinical characteristics evaluated was significantly associated with ³¹¹Cys. The allele frequencies of the ³¹¹Cys variant were 0.026 and 0.031 in the alcoholics and controls, respectively. These are the highest reported ³¹¹Cys frequencies in Caucasians. The DRD2 Taq I A1/A2 restriction fragment length polymorphism was analyzed simultaneously in our samples. In most cases, the ³¹¹Cys allele is associated with the Taq I A2-allele. Data do not suggest a clinical relevance of the ³¹¹Cys variant in alcoholism. However, the relevance of this variant in other diseases or the existence of other DRD2 variants with altered receptor function or expression cannot be excluded.     

Tyrosine Hydroxylase and Dopamine D4 Receptor Allelic Distribution in Scandinavian Chronic Alcoholics

Associations of polymorphic genetic markers at the tyrosine hydroxylase (TH) and dopamine D4 receptor (DRD4) loci were examined in Scandinavian chronic alcoholics ( n = 72) and control subjects ( n = 67). Patients were divided into subgroups with regard to the presence of parental alcoholism and age of onset. Neither the TH nor the DRD4 allele distributions were significantly different when alcoholic samples were compared with control subjects. However, a tendency to high prevalence for 1 of the 5 TH alleles assayed (TH-K3) was observed in a subsample of 44 alcoholics characterized by late onset when compared with control subjects (27.3% vs. 10.6%, p = 0.041). Results suggest that no major influence on alcoholism is exerted through genes associated with the DRD4 or TH allelic markers examined.     

Alcoholism and the D2 Receptor Gene

The allelic association of the human dopamine D2 receptor gene and alcoholism was evaluated in 20 male alcoholics and 20 controls (sex, race, and geographic place of birth matched). This study further examines the issue of alcoholism severity and A1 allele frequency. No difference in A1 allele frequency was observed between these two groups. Similarly, no relationship between alcoholism severity and A1 frequency within the alcoholics was demonstrated.     

DRD2 Dopamine Receptor Genotype, Linkage Disequilibrium, and Alcoholism in American Indians and Other Populations

We defined interpopulation differences in the frequency of the dopamine D2 receptor DRD2/Taq1 A1 allele, which has previously been associated with alcoholism. Frequencies of the A1 allele in unrelated subjects were 0.18 to 0.20 (se = 0.02 to 0.03) in several Caucasian populations previously assessed, 0.38 (±0.05) in American Blacks ( n = 44), 0.63 (±0.07) in Jemez Pueblo Indians ( n = 23), and 0.80 (± 0.04) in Cheyenne Indians ( n = 52). The existence of large interpopulation differences in the frequency of the Taq1 alleles suggests that associations to disease status could readily be generated or masked if disease and control groups were uneven in ethnic composition. To address the possibility that the 4-fold higher frequency of the A1 allele in Cheyenne Indians was related to an increased vulnerability to alcoholism in that population, 47 Cheyenne Indians were psychiatrically interviewed and blind-rated. However, there was no significant difference between interviewed controls (0.73 ± 0.06, n = 24), subjects with alcoholism and/or drug abuse (0.74 ± 0.06, n = 23) and noninterviewed population controls (0.87 ± 0.05, n = 20). Legitimate association of the DRD2/Taq1 allele to alcoholism would presumably require it to be in linkage disequilibrium (nonrandom association) with a functional mutation at DRD2 or elsewhere. The level of disequilibrium would vary between populations and could place an upper bound on the strength of an association. To provide a model for the extent and variation of disequilibrium at DRD2, the level of linkage disequilibrium between the Taq1 RFLP and a second DRD2 polymorphism, the SSCP variant in the immediate 3'region of the gene, was determined in three populations. The normalized disequilibrium values were 0.36 In U.S. Caucasians ( n = 48), 0.34 in Finns ( n = 86), and 0.78 in Cheyenne Indians ( n = 34).     

No Association Between the Dopamine D2 Receptor Taq I A1 Allele and Earlier Age of Onset of Alcohol Dependence According to Different Specified Criteria

BACKGROUND: The presence of the A1 allele of the dopamine D2 receptor TaqI restriction fragment length polymorphism has been reported to be associated with an earlier age of onset of alcohol dependence as a marker for severity. METHODS: We tested this hypothesis with special regard to the definition of the age of onset of alcoholism in 243 patients with alcohol dependence, according to DSM-IV criteria assessed by the standardized interview Münchner Composite International Diagnostic Interview (M-CIDI), consecutively admitted for detoxification. Additionally, the Addiction Severity Index (ASI) was performed. The TaqIA polymorphism was amplified by polymerase chain reaction (PCR), and the PCR product was digested by the restriction enzyme TaqI. Patients were subsequently divided into an A1 (presence of at least one A1 allele, n = 88) and an A2 group (absence of an A1 allele, n = 155). The following criteria for different definitions of age of onset were used: (1) age of onset of the first occurring symptom necessary for the diagnosis of alcohol dependence according to M-CIDI; (2) age of onset of the last symptom of alcohol dependence according to M-CIDI; (3) age of onset of more than 3 drinking days per week on a regular basis according to ASI; (4) age of onset of more than 3 drinking days-of more than five drinks per drinking day-or at least one binge drinking episode per week on a regular basis according to ASI. RESULTS: The frequency of the A1 allele in our patient sample was 0.208. No statistically significant association between the A1 allele and the age of onset of alcoholism was found. The mean age of onset according to criterion 1 was 30.4 +/- 10.8 years for the A1 group and 30.2 +/- 10.2 years for the A2 group (p = 0.89); for criterion 2, it was 33.3 +/- 10.0 years for the A1 group and 33.9 +/- 10.2 years for the A2 group (p = 0.77); for criterion 3, it was 18.0 +/- 7.5 years for the A1 group and 18.1 +/- 6.1 years for the A2 group (p = 0.92); and for criterion 4, it was 22.3 +/- 9.7 years for the A1 group and 21.8 +/- 8.5 years for the A2 group (p = 0.76). CONCLUSIONS: No association was found between the A1 polymorphism and age at onset of alcohol dependence according to different specified criteria.     

The Interaction of Reward Genes With Environmental Factors in Contribution to Alcoholism in Mexican Americans

Background: Alcoholism is a polygenic disorder resulting from reward deficiency; polymorphisms in reward genes including serotonin transporter (5‐HTT)‐linked polymorphic region (5‐HTTLPR), A118G in opioid receptor mu1 (OPRM1), and ?141C Insertion/Deletion (Ins/Del) in dopamine receptor D2 (DRD2) as well as environmental factors (education and marital status) might affect the risk of alcoholism. Objective of the current study was to examine the main and interacting effect of these 3 polymorphisms and 2 environmental factors in contribution to alcoholism in Mexican Americans. Methods: Genotyping of 5‐HTTLPR, OPRM1 A118G, and DRD2‐141C Ins/Del was performed in 365 alcoholics and 338 nonalcoholic controls of Mexican Americans who were gender‐ and age‐matched. Alcoholics were stratified according to tertiles of MAXDRINKS, which denotes the largest number of drinks consumed in one 24‐hour period. Data analysis was done in the entire data set and in each alcoholic stratum. Multinomial logistic regression was conducted to explore the main effect of 3 polymorphisms and 2 environmental factors (education and marital status); classification tree, generalized multifactor dimensionality reduction (GMDR) analysis, and polymorphism interaction analysis version 2.0 (PIA 2) program were used to study factor interaction. Results: Main effect of education, OPRM1, and DRD2 was detected in alcoholic stratum of moderate and/or largest MAXDRINKS with education ≤12 years, OPRM1 118 A/A, and DRD2 ?141C Ins/Ins being risk factors. Classification tree analysis, GMDR analysis, and PIA 2 program all supported education*OPRM1 interaction in alcoholics of largest MAXDRINKS with education ≤12 years coupled with OPRM1 A/A being a high risk factor; dendrogram showed synergistic interaction between these 2 factors; dosage‐effect response was also observed for education*OPRM1 interaction. No definite effect of marital status and 5‐HTTLPR in pathogenesis of alcoholism was observed. Conclusions: Our results suggest main effect of education background, OPRM1 A118G, and DRD2 ?141C Ins/Del as well as education*OPRM1 interaction in contribution to moderate and/or severe alcoholism in Mexican Americans. Functional relevance of these findings still needs to be explored.     

多巴胺受体D1基因多态性与原发性高血压的相关性研究

目的:探讨多巴胺受体D1(DRD1)基因(-48A／G)多态性与原发性高血压的相关性。方法:采用多聚酶链式反应结合限制性内切酶片段长度多态性分析方法检测330例原发性高血压患者(高血压组) 和195例健康人(对照组)DRD1基因(-48A／G)多态性,并对两组人群的血压及各项临床指标进行测定。结果:高血压患者中,DRD1基因(-48A／G)多态性各基因型之间的收缩压、舒张压及平均动脉压有显著差异。其中, AG基因型的诊室舒张压、24h舒张压及24h平均动脉压显著高于AA基因型(P<0．05);GG基因型的诊室收缩压、诊室舒张压、诊室平均动脉压及24h舒张压、24h平均动脉压均显著高于AA基因型(P<0．05);AG基因型与GG基因型之间的收缩压、舒张压及平均动脉压均无显著差异(P>0．05)。结论:北京地区汉族人群中DRD1基因(-48A／G)多态性与原发性高血压明显相关。     

Lack of Allelic Association of Dopamine D1 and D2 (TaqIA) Receptor Gene Polymorphisms with Reduced Dopaminergic Sensitivity in Alcoholism

Our study tested the hypothesis of whether the sensitivity of central dopamine receptors corresponds to the genotypic constitution of DNA-polymorphisms of the dopamine D1 and D2 receptor (DRD1, DRD2) genes and is associated with poor treatment outcome. Therefore, 97 alcohol-dependent patients were assessed according to their sensitivity of central dopamine receptors (apomorphine-induced secretion of growth hormone), clinical outcome during a 6-month observation period, and genotypic constitution of the Taq IA restriction fragment length polymorphism (RFLP) at the DRD2 locus and of the Bsp 12861 RFLP at the DRD1 locus. On the 1st day of detoxification, dopamine receptor hyposensitivity was found in treatment nonresponders, but not in responders. Apomorphine-induced growth hormone release did not differ significantly in alcoholics with different genotypes of the DRD1 and DRD2 RFLPs. Neither did we find a significant allelic association with treatment response. Thus, we did not find evidence for a genetic determination of dopamine receptor hyposensitivity in alcoholics with poor treatment outcome.     

Investigation of Genetic Risk Factors Associated with Alcoholism

Alcoholism is a multifactorial disease influenced by genetic-environmental interaction. Genetic variation of the receptor may be associated with alcohol dependence due to its modified function in behavioral and physiological responses. In the present study, polymorphic alleles of cholecystokinin B receptor (CCKBR), serotonin 1A receptor (HT1AR) genes, and mitochondrial DNA were analyzed. DNAs were isolated from the blood samples of 112 healthy controls and 106 alcoholics. Genetic variation was detected by SSCP analysis, followed by direct sequencing of polymerase chain reaction product as well as restriction fragment-length polymorphism. Three different mutations were found in the exon 3 sequence of CCKBR: His (CAT) at aa207 → His (CAC) (5.4%), Arg (CGC) at aa215 → His (CAC) (4.5%), and Val (GTG) at aa138 → Met (ATG) (0.9%) in controls. Genotypic distribution of alcoholics was not significantly different with that in controls. A proline (CCG) to leucine (CTG) substitution at amino acid 16 of HT1AR was found in alcoholics (4.5%) and in controls (4.7%). This mutation site of HT1AR was different in comparison with the variants reported by Nakhai et al. ( Biochem Biophys. Res.Commun. 210:530 -536,1995). Analysis of the mitochondrial DNA showed that a 491 bp deletion in the sequence of ATPase exists as heteroplasmy in 58% of alcoholics, but not in controls. Heteroplasmic deletion of mitochondrial DNA may be a useful marker for alcohol abuse. Further study is undergoing to elucidate the cause and significance of this deletion in alcoholics.     

The Effects of Chronic Ethanol Consumption on the Mesolimbic and Nigrostriatal Dopamine Systems

Both the mesolimbic dopamine system, which is involved with the rewarding properties of several drugs of abuse, and the nigrostriatal dopamine system, which is involved with motor function, appear to be sensitive to the effects of ethanol. In order to determine which components of the mesolimbic and nigrostriatal dopamine systems are adversely affected by chronic ethanol consumption, we assessed dopamine and DOPAC (3,4-dihydroxyphenylacetic acid) concentration and D1 and D2 receptors in several dopaminergic brain areas. These studies demonstrated that consumption of a 6.6% (v/v) ethanol-containing lipid diet for 1 month affected several components of the mesolimbic dopamine system in 3-month-old Fisher 344 rats and fewer components of the nigrostriatal dopamine system. Specifically, there was a 1.6- to 2.6-fold increase in the concentration of DOPAC in the nucleus accumbens (NA), frontal cortex (FCX), ventral tegmental area (VTA), and substantia nigra (SN). While the increase in DOPAC in the FCX and VTA was paralleled by a similar increase in dopamine, there was a significant deficiency of dopamine in the SN. These results suggest that there is an increase in dopamine turnover in the FCX, VTA, NA, and SN, which is accompanied by increased dopamine synthesis in the former two regions. Studies of dopamine receptors in control and ethanol-fed rats demonstrated a 25% loss of D1 receptors in the NA. No significant differences were found in D1 receptors in the striatum or globus pallidus. In addition, there were no differences in the number of total D2 receptors or in the conversion of the high to low affinity state of D2 receptors in the nucleus accumbens and striatum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Combined Scopolamine and Ethanol Treatment Results in a Locomotor Stimulant Response Suggestive of Synergism That is Not Blocked by Dopamine Receptor Antagonists

Background: Muscarinic acetylcholine receptors (mAChRs) are well positioned to mediate ethanol’s stimulant effects. To investigate this possibility, we examined the effects of scopolamine, a receptor subtype nonselective mAChR antagonist, on ethanol‐induced stimulation in genotypes highly sensitive to this effect of ethanol. We also investigated whether the dopamine D1‐like receptor antagonist, SCH‐23390 or the dopamine D2‐like receptor antagonist, haloperidol, could block the extreme stimulant response found following co‐administration of scopolamine and ethanol. Methods: Scopolamine (0, 0.0625, 0.125, 0.25, or 0.5 mg/kg) was given 10 minutes prior to saline or ethanol (0.75 to 2 g/kg) to female FAST (Experiment I) or DBA/2J (Experiment II) mice that were then tested for locomotion for 30 minutes. In Experiments III and IV, respectively, SCH‐23390 (0, 0.015, or 0.03 mg/kg) was given 10 minutes prior, and haloperidol (0, 0.08, or 0.16 mg/kg) was given 2 minutes prior, to scopolamine (0 or 0.5 mg/kg), followed 10 minutes later by saline or ethanol (1.5 g/kg) and female DBA/2J mice were tested for locomotion for 30 minutes. Results: FAST and DBA/2J mice displayed a robust enhancement of the locomotor effects of ethanol following pretreatment with scopolamine that was suggestive of synergism. SCH‐23390 had no effect on the response to the scopolamine + ethanol drug combination, nor did it attenuate ethanol‐ or scopolamine‐induced locomotor activity. Haloperidol, while attenuating the effects of ethanol, was not able to block the effects of scopolamine or the robust response to the scopolamine‐ethanol drug combination. Conclusions: These results suggest that while muscarinic receptor antagonism robustly enhances acute locomotor stimulation to ethanol, dopamine receptors are not involved in the super‐additive interaction of scopolamine and ethanol treatment. They also suggest that in addition to cautions regarding the use of alcohol when scopolamine is clinically prescribed due to enhanced sedative effects, enhanced stimulation may also be a concern.     

Neuroendocrine Evidence for Reduced Serotonergic Neurotransmission During Heavy Drinking

A fenfluramine (60-mg oral dose) challenge test was performed in 19 male heavy drinkers (mean daily consumption 88 g of pure alcohol). Twelve healthy males served as controls. The prolactin and temperature responses to fenfluramine were significantly reduced in the group of heavy drinkers. The results suggest impaired central serotonergic neurotransmission in alcoholism, possibly involving subsensitivity in various serotonin receptor subtypes.     

Glycine Receptors Involved in Acamprosate's Modulation of Accumbal Dopamine Levels: An In Vivo Microdialysis Study

Background:  Glycine receptors (GlyRs) in the nucleus accumbens (nAc) and nicotinic acetylcholine receptors (nAChRs) in the ventral tegmental area (VTA) have been suggested to be involved in the positive reinforcing and dopamine elevating effects of ethanol. Recent studies have also shown that ethanol high-preferring rats substantially decrease their ethanol intake when treated with a glycine transporter 1 inhibitor (ORG 25935). Acamprosate, a drug used for relapse prevention in treatment of alcohol dependence, has also been demonstrated to elevate extracellular dopamine levels in the nAc. However, the underlying mechanism of action of acamprosate is not fully understood. Here we investigated whether acamprosate interferes with a neuronal circuitry that previously has been demonstrated to be involved in the dopamine elevating effects of ethanol and taurine.
Methods:  In vivo microdialysis in freely moving rats was used to assess accumbal dopamine levels before and during local (nAc) or systemic administration of acamprosate.
Results:  Perfusion of 0.5 mM acamprosate in the nAc significantly increased dopamine levels. Pretreatment either with 10 μM strychnine in the nAc or 100 μM mecamylamine in the VTA, completely antagonized the acamprosate-induced elevation of accumbal dopamine levels. Also, systemic acamprosate administration elevated accumbal dopamine output, an effect that was abolished by local (nAc) pretreatment with 10 μM strychnine.
Conclusions:  These results suggest that both systemic and local application of acamprosate elevate extracellular dopamine levels in the nAc by activating accumbal GlyRs, and, secondarily, tegmental nAChRs.     

Neuroendocrine assessment of serotonergic, dopaminergic, and noradrenergic functions in alcohol-dependent individuals

Background: Alcohol dependence has been associated with reduced function of serotonin, dopamine as well as noradrenaline activities in several neuroendocrine studies. To our knowledge, there is, however, no study investigating all these 3 systems with the use of neuroendocrine methods in one and the same alcohol‐dependent individual. Methods: Alcohol‐dependent individuals (n = 42) and controls (n = 28) participated in the neuroendocrine test series. Central serotonergic neurotransmission was assessed by the prolactin (PRL) response to citalopram (CIT). The postsynaptic DRD2 function was measured by the growth hormone (GH) response to apomorphine (APO) and the postsynaptic α2‐adrenoceptor function by GH response to clonidine (CLON). Results: In the alcohol‐dependent individuals, the PRL concentrations were significantly lower at the time points 240 minutes and 300 minutes after CIT administration and mean delta PRL value was significantly reduced by 45% in comparison with controls. There were no significant differences in APO‐GH and CLON‐GH concentrations at any time points or in mean delta GH values between the groups. An impaired monoaminergic profile, including all 3 systems, was significantly more frequent in alcohol‐dependent individuals than controls (43% vs. 6% respectively). Conclusions: The monoaminergic dysfunction was restricted to an impairment of the serotonergic system, suggesting that this system is especially vulnerable to long‐term and excessive alcohol consumption. Moreover, impaired monoaminergic profiles, including low responses in 2 or 3 systems, were more frequently observed in alcohol‐dependent individuals than in controls. Such impaired profiles may be of clinical importance, but further studies are needed.     

Pharmacotherapies for Alcoholism: Promising Agents and Clinical Issues

The past 10 years have witnessed important advances in research on pharmacotherapy for alcoholism. Promising drugs are discussed under six headings: agents to treat alcohol withdrawal; anticraving agents; agents that make drinking an aversive experience; agents to alleviate concomitant psychiatric problems; agents to treat concurrent drug abuse; and amethystic ("sobering-up") agents. Research on the drug classes is summarized and clinical issues surrounding specific agents and alcoholism pharmacotherapy in general are discussed. Finally, long-range therapeutic implications of recent findings on the actions of alcohol on basic mechanisms of the brain are offered.