Further neuroendocrine evidence for reduced D2 dopamine receptor function in alcoholism

Pharmacogenetics of Addiction Therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies with response to treatment based on individual genetic makeup. In this chapter, we will discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The continued elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Sensation seeking, alcoholism and dopamine activity

Sensation seeking scale (SSS) scores were determined in 15 alcohol dependent men with a positive family history for alcoholism (FHP), in 15 alcohol dependent men with a negative family history for alcoholism (FHN) and in 15 well-matched healthy male controls (CONTR). Both FHPs and FHNs suffered from longlasting alcohol dependence meeting ICD-10 and DSM-III-R diagnostic criteria. Dopamine activity was neuroendocrinologically assessed by measuring the amount of growth hormone released after stimulation with the dopamine receptor agonist apomorphine. Planned comparisons within a one-way ANOVA yielded significantly elevated levels of boredom susceptibility (BOS) in both FHPs and FHNs against CONTRs. SSS total scores, while approaching statistical significance, were elevated in FHPs only. Partial correlations (controlling for age, body weight, alcohol intake and duration of dependence) were calculated to examine the relationship between SSS and dopamine activity. Among the SSS subtraits, BOS revealed the highest correlation in each group. However, only in CONTRs did the relationship between BOS and dopamine activity reach statistical significance.

Addiction pharmacogenetics: a systematic review of the genetic variation of the dopaminergic system

Substance use disorders have significant personal, familial, and societal consequences. Despite the serious consequences of substance use, only a few therapies are effective in treating substance use disorders, thus highlighting a need for improved treatment practices. Substance use treatment response depends on multiple factors such as genetic, biological, and social factors. It is essential that each component is represented in treatment plans. The dopaminergic system plays a critical role in the pharmacotherapy for addictions, and an understanding of the role of variation of genes involved in this system is essential for its success. This review adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement guidelines. A computerized literature search was conducted using PubMed and Scopus (all databases). Articles published up to April 2015 that examined the role of dopaminergic gene variation in the pharmacotherapy of alcohol, opioid, and cocaine use disorders were reviewed. Search terms were dopamine, gene, polymorphism, substance abuse, treatment, and response. Polymorphisms of the DRD2, ANKK1, DAT1, DBH, and DRD4 genes have been found to moderate the effects of pharmacotherapy of alcohol, opioid, and cocaine use disorders. The integration of genetic information with clinical data will inform health professionals of the most efficacious pharmacotherapeutic intervention for substance use disorders. More studies are needed to confirm and extend these findings.

Pharmacogenetics of addiction therapy

Drug addiction is a serious relapsing disease that has high costs to society and to the individual addicts. Treatment of these addictions is still in its nascency, with only a few examples of successful therapies. Therapeutic response depends upon genetic, biological, social, and environmental components. A role for genetic makeup in the response to treatment has been shown for several addiction pharmacotherapies. For several addiction pharmacotherapies, response to treatment varies based on individual genetic makeup. In this chapter, we discuss the role of genetics in pharmacotherapies, specifically for cocaine, alcohol, and opioid dependences. The elucidation of the role of genetics should aid in the development of new treatments and increase the efficacy of existing treatments.

Reward-related genes and personality traits in alcohol-dependent individuals: a pilot case control study

Components of the brain reward system, i.e. the mesolimbic dopamine, laterodorsal cholinergic and ghrelin signaling systems, have been implicated in alcohol reward in preclinical studies. Genetic variants of these systems have previously been linked to alcohol dependence. Here, we genotyped 31 single nucleotide polymorphisms (SNPs): 1 SNP in the dopamine D₂ receptor (DRD2) gene, 20 SNPs in 5 different nicotinic acetylcholine receptor subunit (CHRN*) genes, and 10 SNPs in the genes encoding pro-ghrelin (GHRL) and its receptor (GHSR), in a pilot study of type 1 alcoholics (n = 84) and healthy controls (n = 32). These individuals were characterized using the Temperament and Character Inventory. None of the SNPs were associated with risk of alcohol dependence in this population. The GG genotype of SNP rs13261190 in the CHRNB3 was associated with increased novelty seeking, while SNPs of the ghrelin signaling system were associated with decreased self-directedness (AA of rs495225, GHSR) and alterations in self-transcendence (AA of both rs42451 and rs35680, GHRL). In conclusion, this pilot study suggests that reward-related genes are associated with altered personality scores in type 1 alcohol dependence, which warrants future studies of these associations in larger study samples.

The role of polyunsaturated fatty acids (PUFAs) in development, aging and substance abuse disorders: review and propositions

The polyunsaturated fatty acids (PUFAs), especially omega-3 and -6, play an important role in the functioning of membranes. Therefore, changes in their physical properties might entail impairment of the neurotransmission between cells. Studies emphasize the importance of omega-3 intakes, but they also highlight the need of a balance between omega-6 and -3, whose ideal ratio should be 4:1. The Western diet has very high amounts of saturated fat and omega-6, which might contribute, at least partially, to physiopathologies and high incidence as well as prevalence of psychiatric and neurodegenerative diseases. This narrow review aimed at systematizing the studies on the importance of PUFAs in some particular cases, that is, the extremes of life: pre- and post-natal development, and cognitive aging. Additionally, it aimed at studying the association between PUFAs and substance abuse disorders. We used the databases LILACs, MEDLINE and PUBMED.

Alcohol consumption is associated with an interaction between DRD2 exon 8 A/A genotype and self-directedness in males

BACKGROUND

Both reduced postsynaptic dopamine D(2) receptor function and the character variable self-directedness (SDD) are related to the level of alcohol consumption. We examined for interactions between DRD2 exon 8(rs6276), a polymorphism which has been associated with various alcohol-related phenotypes, SDD and alcohol consumption.

METHODS

A total of 144 male and 186 female probands with alcohol dependence or abuse diagnoses and without were included in the study. All subjects were assessed with the alcohol section of the Semi-Structured Assessment for the Genetics of Alcoholism and the Temperament and Character Inventory.

RESULTS

Male probands with A/A genotype reported significantly higher alcohol consumption in a typical week (ANOVA; p = 0.024); those with A/A genotype and low SDD showed particularly high consumption levels (interaction DRD2 x SDD: p = 0.019). Alcohol dependence/abuse (DSM-IV) but not nicotine dependence was also relevant for higher alcohol consumption (trend: p = 0.052). In the female group, only alcohol disorders predicted alcohol consumption.

CONCLUSIONS

Our findings support a role for a gene-personality interaction of DRD2 exon 8 x SDD in alcohol consumption in males.

Neurobiochemical and clinical aspects of craving in alcohol addiction: a review

Craving plays an important role in the pathogenesis of alcohol dependence and relapse. In this review we have tried to analyse how many contrasting theories have been formulated in order to clarify the concept of craving. Many complex neurobiochemical mechanisms are implicated in the etiology of craving; these mechanisms involve several neurotransmitters, such us dopamine, opioids, glutamate, and serotonin. On the other hand comportamental and/or cognitive aspects could also play a role in the etiology of craving. The coexistence of many and often contrasting theories can indicate that different subtypes of patients could have different mechanisms at the basis of alcohol craving, suggesting that it could be advisable to personalize the anti-craving therapy.

Dopamine and alcoholism: neurobiological basis of ethanol abuse

The role of the dopamine (DA) system in brain reward mechanisms and the development of substance abuse has been well established. We review earlier animal and human studies on DA and alcoholism with some relevant issues relating to those studies. The present animal and human data suggest several alterations in the DA system in the context of alcoholism. Receptor studies imply that DA D(2) receptor density and function are lower at least among type 1 alcoholics, which suggests that they could benefit from drugs that enhance DAergic activity, such as partial DA agonists. These drugs could help to restore suboptimal levels of DAergic activity by reducing both the craving for alcohol in abstinence and the euphoria subsequent to alcohol's release of DA in the nucleus accumbens (NAC), thus providing negative reinforcement for relapse.

Neuroendocrinological and neuropsychological correlates of dopaminergic function in nicotine dependence

RATIONALE

There is multiple evidence that nicotine--as with ethanol and other drugs of abuse--stimulates dopamine release in the ventral striatum as a central part of the brain reward circuits. Chronic nicotine exposure leads to changes in these dopaminergic reward circuits. During nicotine withdrawal, an impaired dopaminergic function has been reported. On the behavioral level, this seems to result in motivational disturbances in abstaining smokers.

OBJECTIVES

To investigate the impact of smoking on dopaminergic function in humans both on a neuroendocrinological and on a neuropsychological level.

METHODS

Thirty-seven healthy smokers were assessed whilst smoking (test 1) and after abstaining overnight for 12 h (test 2). A control group of 18 non-smokers was also examined twice. Severity of nicotine dependence, incentive motivation, digit span and verbal fluency were assessed. The sensitivity of central dopamine (DA) D2 receptors was assessed with the apomorphine-induced growth hormone (GH) secretion.

RESULTS

ANOVA revealed that GH response was significantly lower in smokers than in non-smokers (P=0.04). The GH response was significantly inversely correlated with severity of nicotine dependence (r=-0.39). Neuropsychological performance was not influenced by smoking status. After overnight abstinence from nicotine GH response, digit span and verbal fluency were not affected, whereas incentive motivation was significantly impaired in smokers (P=0.04).

CONCLUSIONS

Smoking is significantly associated with a reduced sensitivity of central DA D2 receptors. This alteration of dopaminergic sensitivity is stable even after 12 h of abstinence from nicotine. Therefore, the hypothesis that the motivational impairment during withdrawal from nicotine is associated with an altered sensitivity of central DA D2 receptors cannot be supported.

Preclinical and clinical pharmacology of cyamemazine: anxiolytic effects and prevention of alcohol and benzodiazepine withdrawal syndrome

Several studies have suggested that the antipsychotic compound, cyamemazine, possesses anxiolytic properties in humans. The original pharmacological profile of cyamemazine (D(2), 5-HT(2A), 5-HT(2C), and 5-HT(3) receptor antagonist), which was established by binding, microdialysis and behavioral studies, is consistent with these observations. In the light/dark exploration test, cyamemazine demonstrated anxiolytic-like activity by acute, but not chronic administration. By chronic administration, however, cyamemazine increased the time spent in the open arms of the elevated plus maze (EPM) test demonstrating anxiolytic-like activity. The discrepancy between the results obtained in these tests by acute and chronic administration, could be due to a combination of dopamine D(2) receptor antagonism with antagonism of the 5-HT(2C) and 5-HT(3) receptors. The action of cyamemazine on both the dopaminergic system and 5-HT(3) receptors could also explain the activity of cyamemazine in the management of alcohol withdrawal demonstrated in preclinical studies. This potential indication for cyamemazine and its activity in benzodiazepine withdrawal syndrome have recently been investigated in clinical trials and the results of these studies are presented in this review.

Dopamine D2 receptors and transporters in type 1 and 2 alcoholics measured with human whole hemisphere autoradiography

Increasing evidence implies the involvement of the dopamine (DA) system in the pathogenesis of alcoholism. We measured striatal DA D(2) receptors in Cloninger type 1 and 2 alcoholics by using [(125)I]epidepride in human postmortem whole hemispheric autoradiography (WHA), which provides high-resolution images corresponding to positron emission tomographic (PET) studies. We also evaluated the correlation between transporter and receptor DA binding site densities and putative correlation of [(125)I]epidepride binding between the dorsal striatum and nucleus accumbens. In the type 1 alcoholics, the DA D(2) receptor density was 21.4-32.6% lower in all dorsal striatal structures (caudate, putamen, globus pallidus) when compared with the controls. Type 2 alcoholics had 19.6-21.4% lower binding in other dorsal striatal structures, except medial globus pallidus, where they were not significantly different from controls. The density of DA D(2) receptors and DAT had a significant positive correlation only in the putamen of type 1 alcoholics. The binding of [(125)I]epidepride showed also consistent and statistically significant positive correlation between nucleus accumbens and all dorsal striatal areas in type 1 alcoholics but not in the controls. In the type 2 alcoholics, the correlation was weaker than that observed in the type 1 alcoholics, and no correlation was observed between nucleus accumbens and globus pallidus. Our results show that these two subgroups of alcoholics have stark differences in their DA D(2) receptor binding characteristics. Type 2 alcoholics may have selective deficiency in the dorsal striatum, whereas in limbic structures they may not differ significantly from controls. Moreover, WHA provides a useful tool for detailed mapping of neuronal receptors in healthy as well as diseased brain, and can also be used in radioligand development for PET.

Alcoholism and the dopaminergic system: a review

Alcohol as well as other substances of abuse are reinforcing substances which manifest their effects through activation of the mesolimbic dopaminergic reward pathways of the brain. In animal genetic models of alcoholism, reduced dopamine levels and D2 dopamine receptor (DRD2) numbers have been found in the brains of alcohol-preferring animals. Dopamine receptor agonists reduce alcohol consumption, whereas antagonists, in general, show the opposite effect. Moreover, quantitative trait loci studies in animals suggest the DRD2 gene and the region proximate to this locus is a chromosomal "hot spot" for alcohol-related behaviors. Human studies provide additional support for connection between alcohol dependence and CNS dopaminergic function. In endocrinological studies, using dopamine receptor agonists, reduced dopaminergic activity has been found in more severe and more genetic types of alcoholics. Brain imaging studies are similarly revealing a diminished dopaminergic tone in alcoholics. Treatment of alcoholics with dopamine receptor agonists shows reduced alcohol consumption and improvements in other outcome measures. Molecular genetic studies in humans have identified an association of the Al allele of the DRD2 gene with alcoholism. Moreover, a diminished central dopaminergic function has been found in DRD2 A1 allele subjects using pharmacological, electrophysiological and neuropsychological studies. Further, treatment of alcoholics with a dopamine receptor agonist showed more salutary effects on alcoholics who carry than those who do not carry the DRD2 A1 allele. The A1 allele has also been associated with substance use disorders other than alcoholism, including and cocaine and nicotine dependence and polysubstance abuse. The emerging evidence suggests that the DRD2 is a reinforcement or reward gene. It could represent one of the most prominent single-gene determinants of susceptibility to severe substance abuse. However, the environment and other genes, when combined, still play the larger role.

Pharmacokinetic-pharmacodynamic study of apomorphine's effect on growth hormone secretion in healthy subjects

Apomorphine (APO) stimulates growth hormone (GH) release via dopamine D2 receptors (DRD2). There is no specific study assessing the relationship between APO pharmacokinetic (PK) and the pharmacodynamic (PD) response e.g. GH release. The objective of the study is the PK-PD modelling of APO in healthy subjects. This is a randomized crossover study with s.c. administration of 5, 10, and 20 micro g/kg of APO in 18 healthy subjects. APO concentrations were modelled according to both a bi-compartmental model with zero-order absorption and a bi-compartmental model with first-order absorption. PK-PD relationship was modelled in accordance with the Emax Hill equation using plasma concentrations of APO calculated according to the bi-compartmental model with zero-order absorption. Modelled parameters were very similar to the experimental parameters. PK of APO was linear and there was no significant difference between the tested doses for AUC0--> infinity and Cmax (normalised to the dose 1 micro g/kg), t1/2alpha and t1/2beta. These parameters expressed as mean (CV%: SD/mean) were: 17.2 (26.9) ng/mL.min, 0.26 (33.3) ng/mL, 17.1 (54.2) and 45.2 (20.6) min, respectively (n = 53). An anticlockwise hysteresis loop (effect function of APO plasma concentration) appeared for each dose and each subject. The predicted and measured GH concentrations for all subjects and times were similar whatever the dose (P > 0.27). Emax values were 246 (121), 180 (107), 205 (139) ng/mL, respectively, and EC50 were 0.98 (48.1), 1.70 (62.3), 3.67 (65.2) ng/mL, respectively at dose 5, 10, and 20 micro g/kg (P < 10-4). APO and GH concentrations were predicted with good accuracy using bi-compartmental with zero-order absorption PK model and sigmoid Emax PD model, respectively.

Outcome predictors in substance use disorders

Given the heterogeneous nature of substance abuse, it is notable that several predictors of response are independent of the primary drug of abuse or the treatment setting [208]. Although the strength of the relationship of predictor to outcome varies, the following factors have been identified consistently: severity of dependence or withdrawal; psychiatric comorbidity; substance-related problems; motivation (abstinence commitment); length of treatment; negative affective states; cognitive factors; personality traits and disorders; coping skills; multiple substance abuse; contingency contracting or coercion; genetic factors; sleep architecture; urges and craving; self-efficacy; and economic and social factors. Although it is well known that severity of dependence (including polysubstance abuse), serious psychiatric comorbidity, and social problems are associated with poor treatment response, only recently has research examined the efficacy of intervention strategies that specifically address these problems. Adequate treatment of psychiatric comorbidity and improvement in social, economic, and family functioning lead to better treatment outcomes. The development of specific techniques to enhance self-efficacy, motivation, coping skills, and functioning in the community are concrete examples of how the identification of factors associated with positive outcomes has led to the development of new treatments. Despite significant accomplishments, the field is left with many unanswered questions. Although several biologic markers, such as neuroendocrine response and sleep architecture, show promise as outcome predictors, it is not known whether these are critical factors in the initiation of substance use or its progression to dependence. Determining whether biologic markers are epiphenomena reflecting the amount and duration of substance abuse or are fundamental to the pathophysiology of dependence is a matter of urgent concern. With some exceptions, identification of biologic predictors has not led to innovative therapies. One of these exceptions is the development of naltrexone for the treatment of alcoholism, which was based in a solid theoretical rationale and followed by hypothesis-driven experiments. Similar opportunities should emerge from current basic science and clinical research. The application of pharmacogenetic techniques to the field of addiction also holds great promise. As future studies are undertaken, researchers and clinicians must be mindful that differences in outcome predictors across drugs of abuse and treatments may emerge as subgroups of individuals with addictive disorders and new therapies are identified. There is already evidence that early onset alcoholism is associated with poor response under some circumstances, yet may be a predictor of response to targeted pharmacotherapy with ondansetron [64, 112]. As the ability to subtype disorders based on meaningful biologic differences grows, it is anticipated that several relevant outcome predictors that are specific for pharmacotherapy will emerge.

Dopamine receptors and transporters in the brain reward circuits of type 1 and 2 alcoholics measured with human whole hemisphere autoradiography

The role of the dopamine system in brain reward mechanisms and development of substance abuse is well-established with nucleus accumbens as a key structure in mediating these effects. Several studies on alcoholism have indicated defects in dopaminergic neurotransmission and alterations in dopamine receptor densities. However, it has remained unclear if the substance abuse-related dopaminergic defect is specifically associated with a certain receptor subtype. The aim of this study was to compare putative alterations of dopamine D(1,) D(2), and D(3) receptors in nucleus accumbens, amygdala, and substantia nigra among alcoholics and controls. We studied the densities of dopamine D(1) and D(3) receptors in brains of 9 type 1 alcoholics, 8 type 2 alcoholics, and 10 healthy controls by using postmortem human whole hemisphere autoradiography. The mean densities of dopamine D(1) and D(3) receptors were at the same level in all study groups. Combining these with our previous results, our data suggest that among type 1 alcoholics dopamine transporters are lower in nucleus accumbens and dopamine D(2), but not D(1) or D(3) receptors in nucleus accumbens and amygdala. Further, the densities of all these dopamine-binding sites among type 2 alcoholics are at the level of healthy controls. The results suggest that lower dopamine receptor density is specific for D(2) receptor and for type 1 alcoholism, which supports Cloninger's neurogenetic model of two alcoholic subtypes, and indicates the importance of classifying these subgroups separately when issues related to dopaminergic activity are studied.

Effects of (+/-) 3,4-methylene-dioxymethamphetamine (ecstasy) on dopamine system function in humans

Twelve (+/-) 3,4-methylenedioxymethamphetamine (MDMA) users, who did not show other drug dependencies or prolonged alcohol abuse (group A), and 12 control subjects (group B) were included in the study. Prolactin (PRL) and growth hormone (GH) responses to the dopaminergic agonist bromocriptine (BROM) and psychometric measures were evaluated 3 weeks after MDMA discontinuation. PRL decreased both in A and B subjects after BROM suppression, without any significant difference between the two groups. PRL responses to BROM in MDMA users were in the normal range. In contrast, GH responses to BROM stimulation were found significantly reduced in ecstasy users, in comparison with control subjects (P < 0.001; F = 6.26). MDMA users showed higher scores on the Novelty Seeking (NS) scale at the Three dimensional Personality Questionnaire (TPQ), on direct aggressiveness subscale at Buss Durkee Hostility Inventory (BDHI), on subscale D (depression) at Minnesota Multiphasic Personality Inventory (MMPI 2) and on Hamilton Depression Rating Scale (HDRS) than control subjects. PRL areas under the curves (AUCs) showed a significant inverse correlation with NS scores both in A and B subjects. GH AUCs directly correlated with NS scores in healthy subjects, but not in MDMA users. No other psychometric measure correlated with hormonal responses. GH AUCs were inversely correlated with the measures of MDMA exposure (r = -0.48; P < 0.01). Lower GH response to BROM in A subjects (MDMA users) could reflect reduced D2 receptor sensitivity in the hypothalamus, possibly due to increased intrasynaptic dopamine concentration. Although the hypothesis of dopaminergic changes associated with a premorbid condition cannot be completely excluded, the inverse correlation between DA receptors sensitivity and the extent of ecstasy exposure may suggest a direct pharmacological action of MDMA on brain dopamine function in humans.

Lisuride, a dopamine D2 receptor agonist, and anticraving drug expectancy as modifiers of relapse in alcohol dependence

Due to a central role of dopamine in mediating ethanol intake and dependence, the authors tested lisuride, a dopamine D2 receptor agonist, for relapse prevention in alcoholics. Psychological and neuroendocrine determinants of outcome were also assessed within the study. This double-blind, placebo-controlled randomized study comprised 120 alcoholics who were subjected to an intend-to-treat analysis (ITT). After hospital detoxification, patients received an outpatient rehabilitation program and either the study medication or placebo for 6 months and follow-up for another 6 months without medication. Pharmacological and psychological effects on relapse and times to first drink were assessed using survival analysis and multivariate analysis of variance (ANOVA). Neuroendocrine assessments were made using growth hormone (GH) response to stimulation with dopamine D2 receptor agonist apomorphine. In contrast to our hypothesis, the pharmacological effects of lisuride shortened (effect size: 0.51) and the expectation of receiving the drug (while being on medication) prolonged the latency of relapse (effect size: 0.47) in weaned alcoholics. Lisuride was associated with side effects like dizziness and hypotension. Dopaminergic responsivity to apomorphine stimulation was reduced under lisuride. This study supports the view that alcoholics may relapse due to decreased dopamine function, resulting from intake of dopamine D2 receptor agonists. In particular, our data do not support the use of lisuride for relapse prevention in alcoholics. The favorable impact of anticraving drug expectancy on outcome was unrelated to this effect.

Is long-term heavy alcohol consumption toxic for brain serotonergic neurons? Relationship between years of excessive alcohol consumption and serotonergic neurotransmission

The relationship between years of excessive alcohol consumption and central serotonergic neurotransmission, as assessed by the prolactin (PRL) response to D-fenfluramine, was investigated in 22 male alcohol-dependent subjects. A negative correlation was obtained, that is, the longer duration of excessive alcohol consumption the lower PRL response to D-fenfluramine. It is therefore suggested that long duration of excessive alcohol consumption in alcohol-dependent subjects causes a reduction in central serotonergic neurotransmission, possibly by a toxic effect of alcohol on serotonin neurons. The relationship between depressive and anxiety symptoms during on-going drinking and the PRL response to D-fenfluramine was also investigated. No such correlations were obtained, suggesting that reduction in central serotonergic neurotransmission does not pre-dispose to the development of depressive and anxiety symptoms, at least in relation to on-going drinking in alcohol-dependent subjects.

Influence of the dopamine D2 receptor (DRD2) exon 8 genotype on efficacy of tiapride and clinical outcome of alcohol withdrawal

We tested the hypothesis that allelic variants of the human dopamine D2 receptor E8 genotype are associated with (i) dopamine D2 antagonist tiapride dose in treatment of alcohol withdrawal (n = 50) and (ii) with anxiety and depression in patients during alcoholism detoxification therapy (admission n = 87; discharge n = 50). DRD2 E8 A/A genotype was associated with increased dose of tiapride during a 9-day detoxification therapy and with increased anxiety and depression scores on admission and 2 weeks later. The findings suggest a pharmacogenetic influence of DRD2 E8 genotype on tiapride efficacy in alcohol withdrawal. In an earlier report, DRD2 E8 A/A genotype was associated with reduced responsiveness to the dopamine D2 agonist apomorphine; however, it is not clear whether both findings share the same biological basis. Earlier findings concerning association of DRD2 E8 A/A with increased anxiety and depression are replicated for the first time.

Dopamine D(2)/D(3)-receptor and transporter densities in nucleus accumbens and amygdala of type 1 and 2 alcoholics

Alcohol acts through mechanisms involving the brain neurotransmitter dopamine (DA) with the nucleus accumbens as the key zone for mediating these effects. We evaluated the densities of DA D(2)/D(3) receptors and transporters in the nucleus accumbens and amygdala of post-mortem human brains by using [(125)l]epidepride and [(125)I]PE2I as radioligands in whole hemispheric autoradiography of Cloninger type 1 and 2 alcoholics and healthy controls. When compared with controls, the mean binding of [(125)I]epidepride to DA D(2)/D(3) receptors was 20% lower in the nucleus accumbens and 41% lower in the amygdala, and [(125)I]PE2I binding to DA transporters in the nucleus accumbens was 39% lower in type 1 alcoholics. These data indicate that dopaminergic functions in these limbic areas may be impaired among type 1 alcoholics, due to the substantially lower number of receptor sites. Our results suggest that such a reduction may result in the chronic overuse of alcohol as an attempt to stimulate DA function.

Neuroendocrine correlates of temperament traits in abstinent opiate addicts

PURPOSE

Studies investigating temperament traits of drug abusers and their biological correlates have disclosed high rates of novelty seeking (NS) in opiate addicts, possibly based on dysfunctions of the dopaminergic (DA) system. The aims of the present study were to see whether or not the monoamine functions were impaired in detoxified addicts and whether or not these alterations were correlated with temperament traits, given the possibility that impairment of the biological and temperament parameters might be responsible for the development of addiction.

METHODS

We have investigated the DA, serotonergic (5-HT), and noradrenergic (NE) functions in 22 abstinent heroin addicts and 22 healthy controls by challenging the monoamine systems with the DA agonist bromocriptine (brom), the 5-HT agonist D-fenfluramine (D-fen), and the NE agonist clonidine (clon), respectively. We examined the temperament traits by measuring NS, harm avoidance (HA), and reward dependence (RD) using the "Three-Dimensional Personality Questionnaire" (TPQ).

RESULTS

Addicts showed higher than normal NS scores at TPQ blunted 5-HT function, and normal DA and NE activities, in response to the neuroendocrine challenges. NS correlated negatively with the DA function in both addicts and controls, and negatively with the 5-HT function only in addicts. HA correlated positively with 5-HT function in controls but not in addicts.

IMPLICATIONS

The impairment in 5-HT function observed in heroin addicts and the changes in the biological correlates of temperamental traits could increase the proneness to addiction and possible comorbid psychiatric disorders.

Different control of GH secretion by gamma-amino- and gamma-hydroxy-butyric acid in 4-year abstinent alcoholics

The present study attempted to establish whether long term abstinence from alcohol restores the stimulatory effects on GH secretion of gamma-aminobutyric acid (GABA) and gamma-hydroxybutyric acid (GHB) that are absent during the first month of alcohol withdrawal. Six 4-year abstinent alcoholic subjects--already tested with GHB 4 years earlier, and seven age- and weight-matched normal controls, were tested p.o. with 800 mg sodium valproate (a drug that enhances endogenous GABA activity), 10 mg baclofen (a GABA(B) receptor agonist), 25 mg/kg body-weight GHB, or a placebo. The blood samples for growth hormone (GH) assay were taken every 30 min for the next 150 min. Placebo administration did not modify GH secretion in any subject. All drugs induced a significant increase in serum GH levels in normal controls. GH secretion in abstinent alcoholics did not change after baclofen or sodium valproate administration, whereas the GH response to GHB was similar to that observed in normal controls. The data confirm previous observations which suggest that different neuroendocrine mechanisms underlie GABA and GHB control of GH secretion. The data also indicates that the GHB--but not the GABA--stimulated pathway returns to normal in alcoholics after 4 years abstinence.

Flupenthixol as a potential pharmacotreatment of alcohol and cocaine abuse/dependence

Preclinical and clinical studies suggest that the mesolimbic dopamine system plays a major role in mediating the reinforcing effects of drugs of abuse, including alcohol and psychostimulants, and that pharmacological blockade of dopamine D1 and/or D2 receptors may reduce intake of these drugs, as well as relapse rates. The neuroleptic flupenthixol, which has dopamine D1 and D2 receptor antagonist properties and which may be given intramuscularly in order to improve compliance, has been studied as a possible anti-craving drug in substance abuse disorders. Flupenthixol has been shown to attenuate the discriminative stimulus effects of psychostimulants, as well as their intake in animal models of drug abuse. In addition, the compound was found to reduce alcohol intake in a rat model of alcoholism, but the 'anti-alcohol' effect appeared to be only weakly selective and nonspecific. Clinically, the drug has been studied in alcoholics, cocaine addicts and in patients with comorbid psychiatric disorders. Although the data base is still limited and a number of recent trials have not been completely analyzed, these studies suggest that flupenthixol may be useful in decreasing cocaine consumption. Recent studies in alcoholism, however, have shown disappointing results. A number of pilot studies suggest that probably the most promising area may be the treatment of substance abuse/dependence in patients with comorbid psychiatric disorders. Future studies should focus on dosing issues, the differentiation between short- and long-term effects and the identification of subgroups of patients with particular psychopathology.

mu-opioid receptor variants and dopaminergic sensitivity in alcohol withdrawal

OBJECT

The endogenous opioid system plays an important role in the reinforcing properties of alcohol by an interconnected activation of the mesolimbic dopamine system. The Asn40Asp substitution polymorphism of the human mu-opioid-receptor (OPRM) influences binding of opioids and signal transduction and may, thereby, contribute to the development of alcoholism. The present study tested whether the Asn40Asp substitution polymorphism of the OPRM gene is associated with a variation in central dopaminergic sensitivity during alcohol withdrawal in alcoholics.

METHOD

Sensitivity of central dopamine receptors was assessed by apomorphine-induced growth hormone (GH) secretion in 97 alcohol-dependent patients before and 1 week after alcohol cessation, and in a subgroup of 19 alcoholics after 3 months of abstinence. GH response was defined as area under the hormone/time curve. Comparisons of the GH response were conducted between alcoholics carrying the Asn40Asp genotype versus those with the Asn40Asn genotype using U-test statistics.

RESULTS

Marginal differences in apomorphine-induced GH response were found between both genotype groups before detoxification (P = 0.799 (n = 97)/P = 0.459 (n = 19)) and after 3 months of abstinence (P = 0.331 (n = 19)). In contrast, the GH response measured seven days after alcohol withdrawal was significantly increased in alcoholics with the Asn40Asp genotype compared with those carrying the Asn40Asn genotype (P = 0.013 (n = 97)/P = 0.026 (n = 19)).

CONCLUSION

Our results suggest that genetic variation of the mu-opioid receptor modulates the central dopaminergic sensitivity during acute alcohol withdrawal.

Buspirone treatment of alcoholism: age of onset, and cerebrospinal fluid 5-hydroxyindolacetic acid and homovanillic acid concentrations, but not medication treatment, predict return to drinking

Disturbances in central nervous system serotonin (5-HT) have been implicated in the pathophysiology of alcoholism. To test the hypothesis that increasing 5-HT function could promote treatment compliance, we randomized patients who had completed a 5-week inpatient treatment program for alcoholism to receive either buspirone or placebo for 1 year. Ten of the 49 patients remained in the study for the entire year. The days to relapse did not differ significantly between patients receiving buspirone or placebo. Regardless of the medication, late-onset alcoholics had a longer time to relapse than early-onset alcoholics. Cerebrospinal fluid showed that patients with high concentrations of both the 5-HT metabolite, 5-hydroxyindoleacetic acid, and the dopamine metabolite, homovanillic acid, were more likely to relapse, compared with patients with low concentrations of cerebrospinal fluid 5-hydroxyindoleacetic acid and homovanillic acid.

Growth hormone response to placebo, apomorphine and growth hormone releasing hormone in abstinent alcoholics and control subjects

Abstinent alcoholics and control subjects were challenged with placebo (saline), growth hormone releasing hormone (GHRH) and apomorphine (APO). While both groups did not differ in their growth hormone response (HGH) to placebo and GHRH, the alcoholics revealed a significant lower HGH response to dopamine receptor stimulation with APO. These findings provide no evidence that in abstinent alcoholics HGH blunting after dopamine receptor stimulation could be related to an alteration at the pituitary level but they give neuroendocrinological support to the hypothesis of a lower dopamine receptor sensitivity in abstinent alcoholics.

Effects of thyrotropin-releasing hormone and metoclopramide on PRL secretion in normally cycling and amenorrheic alcoholic women

To assess the possible influence of alcoholism on the dopaminergic inhibitory control of prolactin (PRL) secretion, 10 mg of the dopaminergic antagonist metoclopramide (MTC), was injected i.v. in a group of eight healthy abstemious women (aged 28 +/- 6 (mean +/- S.E.) years) and in 16 aged-matched nondepressed female alcoholic subjects after 3-4 weeks of abstinence from alcohol. All normal controls and eight alcoholics had normal menstrual cycles and were tested in the early follicular phase (4-8 days), the remaining eight alcoholics were affected by amenorrhea (duration: 15 +/- 3 months). During the same period, all patients were also tested with TRH (200 micrograms in an i.v. bolus) to determine whether the pituitary PRL cell secretory capacity was preserved in alcoholics. The amenorrheic alcoholic group showed strikingly lower circulating estrogen levels than normally cycling groups. Similar basal PRL levels and PRL responses to TRH were observed in normal controls and normally cycling alcoholics, whereas basal and TRH-stimulated PRL levels were significantly higher in amenorrheic alcoholics. In contrast, the PRL response to MTC was significantly higher in cycling alcoholic patients than in normal controls and amenorrheic alcoholic subjects. However, when the statistical analysis of MTC test took into account the difference in estrogen levels among groups, the statistical differences in the PRL responses to MTC observed between normally cycling and amenorrheic alcoholics disappeared. These data suggest the presence of an enhanced dopaminergic inhibitory control of PRL secretion in 2-3 week abstinent alcoholics with normal menstrual cycles and normal circulating estrogen levels. In contrast, amenorrhea in abstinent alcoholics appears to be associated with an enhancement of PRL cell secretory activity.

Decreases in dopamine receptors but not in dopamine transporters in alcoholics

It has been hypothesized that ethanol's actions on the dopamine (DA) system may participate in addiction. The purpose of this study was to evaluate the DA system in the brain of alcoholics. We evaluated 10 alcoholics and 17 nonalcoholics using positron emission tomography and [11C]raclopride to measure DA D2 receptors. In addition, in 5 of the alcoholics and 16 of the nonalcoholics, we also measured DA transporters with [11C]d-threo methylphenidate. The ratio of the distribution volumes in striatum to that in cerebellum, which corresponds to Bmax/Kd + 1, was used as model parameter of DA D2 receptor and transporter availability. Dopamine D2 receptor availability (Bmax/Kd) was significantly lower in alcoholics (2.1 +/- 0.5) than in nonalcoholics (2.7 +/- 0.6) (p < 0.05) and was not correlated with days since last alcohol use. Alcoholics showed DA transporter values similar to those in nonalcoholics. The ratio of DA D2 receptor to transporter availability was significantly higher in nonalcoholics (1.4 +/- 0.1) than in alcoholics (1.1 +/- 0.1) (p < 0.005). Alcoholics showed significant reductions in D2 receptors (postsynaptic marker) but not in DA transporter availability (presynaptic marker) when compared with nonalcoholics. Because D2 receptors in striatum are mainly localized in gamma-aminobutyric acid (GABA) cells these results provide evidence of GABAergic involvement in the dopaminergic abnormalities seen in alcoholics.

Alcohol withdrawal and dopamine receptor sensitivity after prolonged abstinence

1. Forty-four male inpatients suffering from moderate to severe alcohol dependence (DSM-III-R and ICD-10) as well as 14 healthy controls entered this study. Individuals were classified according to the severity of their withdrawal symptoms during detoxification i.e. group 1) no withdrawal, group 2) autonomic hyperactivity, group 3) withdrawal delirium and group 4) controls. 2. During the 6th week of treatment, that is, when all patients were recovered, controlled abstinent, and several weeks away from the end of their withdrawal syndrome, dopamine receptor sensitivity was neuroendocrinologically assessed by stimulating human growth hormone (HGH) with apomorphine (APO). 3. In a repeated measures model ANOVA, the four groups differed significantly in their HGH release. However, when excluding the controls from the analysis and focusing on alcoholics only (group 1 - 3), the significant difference disappeared. Covariates such as age, weight, quantity of drinking and duration of dependence were not related to the dependent variable. 4. In conclusion, the first significant result (with controls) reflects a blunted HGH response in alcoholics. It confirms earlier reports. The second, non significant result with the alcohol dependents only, suggests that the severity of withdrawal is not reflected by the amount of HGH released. Therefore, in alcoholics, a reduced dopamine receptor function after six weeks of abstinence, as neuro-endocrinologically assessed with apomorphine, seems to be related to alcohol dependence rather than to the severity of alcohol withdrawal.

Lack of allelic association of dopamine D1 and D2 (TaqIA) receptor gene polymorphisms with reduced dopaminergic sensitivity to 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 TaqIA restriction fragment length polymorphism (RFLP) at the DRD2 locus and of the Bsp1286I 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.

Alcohol dependence, family history, and D2 dopamine receptor function as neuroendocrinologically assessed with apomorphine

Fifteen alcohol dependent men with an alcohol dependent first degree relative (i.e. family history positive or FHP), 15 well matched alcohol dependent men without a family history for alcohol dependence (i.e. family history negative or FHN), and 15 healthy controls (CONTR) participated in this study. The three groups were compared according to their postsynaptic D2 dopamine receptor function as assessed by growth hormone release after stimulation with the dopamine receptor agonist apomorphine. Statistical evaluation was done by planned comparisons within a one-way ANOVA. Alcohol dependent subjects significantly differed from CONTRs as long as family history was not taken into account (t(42) = 2.38; P = 0.022*). When differentiating according to family history, both FHPs and FHNs maintained a blunted growth hormone response. However, the difference between FHNs and CONTRs, though present, dropped out of statistical significance (t(42) = 1.65; P = 0.105); at the same time, the difference between FHPs and CONTRs became slightly stronger (t(42) = 2.47; p = 0.017*). In conclusion, our data give neuroendocrinological support to the assumption that a reduced D2 dopamine receptor function in alcohol dependent men is not only a state marker of residual heavy drinking but also a genetically determined trait marker.

Evidence for prolonged recovery of dopaminergic transmission after detoxification in alcoholics with poor treatment outcome

It has been hypothesized that dysfunction of dopaminergic neurotransmission is involved in the pathogenesis of alcohol addiction. Therefore, peripheral dopamine levels, sensitivity of central dopamine receptors (apomorphine-induced Growth Hormone (GH) secretion), and the inhibitory efficacy of G-proteins on adenylyl cyclase activity (as an indicator for dopamine D2-receptor coupled second messenger mechanisms) were measured in 45 alcohol-dependent patients before and after detoxification and in 10 healthy controls. The time needed to adjust to abstinence conditions differed between patients with good and poor treatment outcome. In subsequent abstainers, effects of alcohol withdrawal were already found during the first 24 hours of abstinence (normalisation of GH response, increases in dopamine levels and the inhibitory efficacy of G-proteins). During the next 7 days of abstinence, no more significant changes were observed in the assessed variables. In subsequent relapsers, no significant effect of acute ethanol withdrawal on the same measures was found. However, at day 8 of abstinence, increases in apomorphine-induced GH secretion (towards normalisation), in dopamine plasma levels, and in the inhibitory efficacy of G-proteins (towards above-normal levels) were observed. This retarded adjustment of dopaminergic signal transduction seems to reflect the relapse risk of treatment nonresponders.

Bromocriptine in the treatment of alcoholics with the D2 dopamine receptor A1 allele

Various types of alcoholics have been described and heredity has been shown to be involved in some of these types. An important role of the mesolimbic dopamine system has been suggested in the reinforcing effects of alcohol and recent molecular genetic studies are implicating the gene for the D2 dopamine receptor (DRD2) in alcoholism. In a double-blind study, bromocriptine, a DRD2 agonist, or placebo was administered to alcoholics with either the A1 (A1/A1 and A1/A2 genotypes) or only the A2 (A2/A2 genotype) allele of the DRD2 gene. The greatest improvement in craving and anxiety occurred in the bromocriptine-treated A1 alcoholics and attrition was highest in the placebo-treated A1 alcoholics. The feasibility of a pharmacogenetic approach in treating certain types of alcoholics is suggested.