Alcoholism and the dopaminergic system: a review

Early life social complexity shapes adult neural processing in the communal spiny mouse Acomys cahirinus

RATIONALE

Early life social rearing has profound consequences on offspring behavior and resilience. Yet, most studies examining early life development in rodents use species whose young are born immobile and do not produce complex social behavior until later in development. Furthermore, models of rearing under increased social complexity, rather than deprivation, are needed to provide alternative insight into the development of social neural circuitry.

OBJECTIVES

To understand precocial offspring social development, we manipulated early life social complexity in the communal spiny mouse Acomys cahirinus and assessed long-term consequences on offspring social behavior, exploration, and neural responses to novel social stimuli.

METHODS

Spiny mouse pups were raised in the presence or absence of a non-kin breeding group. Upon adulthood, subjects underwent social interaction tests, an open field test, and a novel object test. Subjects were then exposed to a novel conspecific and novel group and neural responses were quantified via immunohistochemical staining in brain regions associated with social behavior.

RESULTS

Early life social experience did not influence behavior in the test battery, but it did influence social processing. In animals exposed to non-kin during development, adult lateral septal neural responses toward a novel conspecific were weaker and hypothalamic neural responses toward a mixed-sex group were stronger.

CONCLUSIONS

Communal species may exhibit robust behavioral resilience to the early life social environment. But the early life environment can affect how novel social information is processed in the brain during adulthood, with long-term consequences that are likely to shape their behavioral trajectory.

Linking Ethanol-Addictive Behaviors With Brain Catecholamines: Release Pattern Matters

Using a variety of animal models that simulate key features of the alcohol use disorder (AUD), remarkable progress has been made in identifying neurochemical targets that may contribute to the development of alcohol addiction. In this search, the dopamine (DA) and norepinephrine (NE) systems have been long thought to play a leading role in comparison with other brain systems. However, just recent development and application of optogenetic approaches into the alcohol research field provided opportunity to identify neuronal circuits and specific patterns of neurotransmission that govern the key components of ethanol-addictive behaviors. This critical review summarizes earlier findings, which initially disclosed catecholamine substrates of ethanol actions in the brain and shows how the latest methodologies help us to reveal the significance of DA and NE release changes. Specifically, we focused on recent optogenetic investigations aimed to reveal cause-effect relationships between ethanol-drinking (seeking and taking) behaviors and catecholamine dynamics in distinct brain pathways. These studies gain the knowledge that is needed for the better understanding addiction mechanisms and, therefore, for development of more effective AUD treatments. Based on the reviewed findings, new messages for researches were indicated, which may have broad applications beyond the field of alcohol addiction.

After-effects of self-control: The reward responsivity hypothesis

Exercising self-control can be phenomenologically aversive. Insofar as individuals strive to maintain a positive emotional state, one consequence of exercising self-control may thus be a temporarily tuning toward or amplification of reward-related impulses (perhaps arising to countermand the aversive feelings that stem from self-control). Reward-relevant after-effects are relatively underappreciated in self-control research. In the current paper, we review theory and research pertaining to the idea that exercising self-control increases reward responsivity. First, we review theoretical models of self-control focusing on the relationship between control systems and reward systems. Second, we review behavioral studies regarding the effects of exercising self-control on subsequent reactivity to food, money, drugs, and positive emotional images. Third, we review findings from functional neuroimaging and electroencephalographic research pertaining to the reward responsivity hypothesis. We then call for additional research to integrate how, when, and under what circumstances self-control exertion influences reward processing. Such an endeavor will help to advance research and theory on self-control by offering a more precise characterization of the dynamic interactions between control systems and reward systems.

Spatial navigation deficits in amnestic mild cognitive impairment with neuropsychiatric comorbidity

AIMS

To find out whether neuropsychiatric comorbidity (comMCI) influences spatial navigation performance in amnestic mild cognitive impairment (aMCI).

METHODS

We recruited aMCI patients with (n = 21) and without (n = 21) neuropsychiatric comorbidity or alcohol abuse, matched for global cognitive impairment and cognitively healthy elderly participants (HE, n = 22). They completed the Mini-Mental State Examination and a virtual Hidden Goal Task in egocentric, allocentric, and delayed recall subtests.

RESULTS

In allocentric navigation, aMCI and comMCI performed significantly worse than HE and similarly to each other. Although aMCI performed significantly worse at egocentric navigation than HE, they performed significantly better than patients with comMCI.

CONCLUSIONS

Despite the growing burden of dementia and the prevalence of neuropsychiatric symptoms in the elderly population, comMCI remains under-studied. Since trials often assess "pure" aMCI, we may underestimate patients' navigation and other deficits. This finding emphasizes the importance of taking account of the cognitive effects of psychiatric disorders in aMCI.

Perspectives on fronto-fugal circuitry from human imaging of alcohol use disorders

Descriptions of the cognitive functions affected by alcohol use disorders (AUD) often highlight dysfunction of executive processes such attention, inhibitory control, working memory, and cognitive flexibility. Such complex cognitive functions have historically been ascribed to the prefrontal cortex. AUD, however, disrupts extensive areas of the brain. Structural and functional MRI studies suggest a central role for degradation of circuitry originating in the prefrontal cortex including nodes in widespread brain regions. This review features fronto-fugal circuits affected by AUD including frontocerebellar, frontolimbic, and frontostriatal networks and their relations to the salient, enduring, and debilitating cognitive and motor deficits reported in AUD. This article is part of the Special Issue entitled "Alcoholism".

Are Alcohol Anti-relapsing and Alcohol Withdrawal Drugs Useful in Cannabinoid Users?

Cannabinoids are still classified as illegal psychoactive drugs despite their broad and increasingly acknowledged therapeutic potential. These substances are most famous for their wide recreational use, particularly among young adults to either alter the state of consciousness, intensify pleasure induced by other psychoactive substances or as an alternative to the previously abused drugs. It is important to emphasize that cannabinoids are often taken together with a variety of medications intended for the treatment of alcohol use disorder (AUD) or alcohol withdrawal syndrome (AWS). These medications include disulfiram, acamprosate, and naltrexone. In this paper, we summarize recent advances in the knowledge of possible beneficial effects and interactions between cannabinoids and drugs commonly used for treatment of AUD and AWS either comorbid or existing as a separate disorder.

[The 444G/A and -1021 C/T polymorphisms of the dopamine-beta-hydroxylase gene modulate the trajectory of alcohol dependence development]

AIM

To study the influence of 444 G/A (rs 1108580) and -1021 C/T (rs 1611115) polymorphisms of the dopamine beta-hydroxylase (DBH) gene on clinical parameters of the trajectory of alcohol dependence.

MATERIAL AND METHODS

Authors studied 548 male inpatients, of Slavic ethnicity, with ICD-10 diagnosis of «alcohol dependence» (F-10.2).

RESULTS

The effects of DBH * 444 G/A on the rate of formation of alcohol withdrawal syndrome (AWS), and DBH *-1021C/T on the age of onset of alcohol abuse with significant role of the age of first alcohol use were identified. In 444 G/A GG carriers, the development of AWS was accelerated since the beginning of alcohol abuse compared with AA carriers (p=0.026), AG carriers occupied an intermediate position. In 22.5% of GG carriers, AWS developed within 2 years (AA: 8.11%, p=0.005; AG: 17.67%, p=0.04). According to the results of linear regression analysis, in AG carriers the alcohol abuse (p=0.037) and the AWS (p=0.049) developed earlier than in AA carriers if the first alcohol use occured at the age of about 15 years. Among -1021C/T genotype carriers who began to abuse alcohol at an early age (before 20 years), there were 23.45% patients with CC genotype and only 11.97% with a T allele (genotypes CT+TT) (p=0.03), but T carriers began to abuse alcohol earlier than others (p=0.05) if the first alcohol use occurred at the age of about 16 years.

CONCLUSION

The results can be used to search for genetic markers for prognosis of alcohol dependence development.

Quetiapine mitigates the ethanol-induced oxidative stress in brain tissue, but not in the liver, of the rat

Quetiapine, an atypical antipsychotic, has been employed to treat alcoholic patients with comorbid psychopathology. It was shown to scavenge hydroxyl radicals and to protect cultured cells from noxious effects of oxidative stress, a pathophysiological mechanism involved in the toxicity of alcohol. This study compared the redox status of the liver and the brain regions of prefrontal cortex, hippocampus, and cerebellum of rats treated with or without ethanol and quetiapine. Ethanol administration for 1 week induced oxidative stress in the liver and decreased the activity of glutathione peroxidase and total antioxidant capacity (TAC) there. Coadministration of quetiapine did not protect glutathione peroxidase and TAC in the liver against the noxious effect of ethanol, thus was unable to mitigate the ethanol-induced oxidative stress there. The ethanol-induced alteration in the redox status in the prefrontal cortex is mild, whereas the hippocampus and cerebellum are more susceptible to ethanol intoxication. For all the examined brain regions, coadministration of quetiapine exerted effective protection on the antioxidants catalase and total superoxide dismutase and on the TAC, thus completely blocking the ethanol-induced oxidative stress in these brain regions. These protective effects may explain the clinical observations that quetiapine reduced psychiatric symptoms intensity and maintained a good level of tolerability in chronic alcoholism with comorbid psychopathology.

Downregulation of dopamine D₁ receptors and increased neuronal apoptosis upon ethanol and PTZ exposure in prenatal rat cortical and hippocampal neurons

The objective of this study was to evaluate the effect of ethanol and pentylenetetrazol (PTZ) on the expression of dopamine receptors (D1R) and to observe the apoptotic neurodegeneration in prenatal rat cortical and hippocampal neurons at gestational days (GD) 17.5. In the present study, ethanol (100 mM) and PTZ (15 mM) were exposed to the prenatal rat cortical and hippocampal neuronal cell cultures for 1 h. For mRNA RT-PCR and for protein Western blot analysis was done to elucidate D1R, Bax, Bak, Bcl-2 and cleaved caspase-3 expression upon ethanol and PTZ exposure in neuronal cell cultures. Furthermore, ethanol and PTZ-induced apoptotic neurodegeneration was also observed using TUNEL staining and propidium iodide (PI) used as counter stain under confocal microscopy. The results of present study showed that ethanol and PTZ exposure significantly decreased D1R expression and induced neuronal death by significantly increasing the expression of pro-apoptotic Bax, Bak and decreasing anti-apoptotic protein Bcl-2 leading to the apoptosis by increasing cleaved caspase-3 expression in cortical and hippocampal primary neuronal cell cultures. Our findings indicated that ethanol and PTZ exposure to the prenatal neurons showed not only downregulation of D1R but also causes neuronal apoptosis in the developing rat brain. Further, this explains the possibility of higher risk of developmental disturbances and malformations during early developmental stage.

Resting state functional connectivity of the nucleus accumbens in youth with a family history of alcoholism

Adolescents with a family history of alcoholism (FHP) are at heightened risk for developing alcohol use disorders (AUDs). The nucleus accumbens (NAcc), a key brain region for reward processing, is implicated in the development of AUDs. Thus, functional connectivity of the NAcc may be an important marker of risk in FHP youth. Resting state functional magnetic resonance imaging (rs-fcMRI) was used to examine the intrinsic connectivity of the NAcc in 47 FHP and 50 family history negative (FHN) youth, ages 10-16 years old. FHP and FHN adolescents showed significant group differences in resting state synchrony between the left NAcc and bilateral inferior frontal gyri and the left postcentral gyrus (PG). Additionally, FHP youth differed from FHN youth in right NAcc functional connectivity with the left orbitofrontal cortex (OFC), left superior temporal gyrus, right cerebellum, left PG, and right occipital cortex. These results indicate that FHP youth have less segregation between the NAcc and executive functioning brain regions, and less integration with reward-related brain areas, such as the OFC. The findings of the current study highlight that premorbid atypical connectivity of appetitive systems, in the absence of heavy alcohol use, may be a risk marker in FHP adolescents.

[Comparative characteristics of glucose metabolism in the liver of rats under acute alcohol and morphine intoxication]

The comparative analysis effect of acute alcohol and morphine intoxications on rats on hepatic glycolysis and pentose phosphate pathway was done. The dose-dependent inhibitory effect of ethanol on activity of limiting enzymes of these metabolic ways, as well as anaerobic reorientation of glucose metabolism was recognised with the increase of the dose of the intake alcohol. Morfine (10 mg/kg) activated enymes of glycolysis and pentose phosphate pathway, but in contrast to ethanol it did not influence these parameters at the dose 20 or 40 mg/kg.

Complete suppression of craving in alcohol-dependent individuals: is it possible?

A recent preliminary, single-case report suggested that baclofen not only reduces but may completely suppress craving in alcohol-dependent individuals. The current article summarizes the neurobiological basis of drug craving, and the pharmacological targets that have been shown to be involved in modulating such craving. The potential usefulness of agents that suppress craving is discussed. However, beyond individual case reports, no evidence is available to indicate that targeting a single neurobiological pathway will be sufficient to completely suppress craving in unselected individuals. Nevertheless, subgroups that carry specific characteristics associated with single receptor dysfunction might benefit from a targeted treatment. Further research is needed to enable clinicians to detect these subgroups.

D2 dopamine receptor (DRD2) gene, P300, and personality in children of alcoholics

The D2 dopamine receptor (DRD2) gene has been associated with alcoholism and other drug use disorders. Reduced P300 amplitude has been noted in individuals with psychiatric disorders. Personality variables are also associated with reduced P300 amplitude. The current study was conducted to determine whether variants of the DRD2 would show differential relationships among P300 amplitude and personality traits. The study consisted of 101 adolescent children of alcoholics; 39 carried the A1(+) genotype (A1A1, A1A2) and 62 carried the A1(-) genotype (A2A2). The A1(+) genotype group had higher IQ and Self-Directedness scores than the A1(-) genotype group. As predicted, the negative relationship between Novelty Seeking and Harm Avoidance was present in A1(-) but not A1(+) participants. Additionally, in A1(+) but not in A1(-) participants, there was a negative relationship between Novelty Seeking and Self-Directedness and a positive relationship between P300 amplitude and Cooperativeness. The results suggest that in adolescent children of alcoholics, dopaminergic genetic determinants are critical modifiers of the relationship between neurocognitive and personality endophenotypes proposed as vulnerability markers for substance use disorders.

Imaging of opioid receptors in the central nervous system

In vivo functional imaging by means of positron emission tomography (PET) is the sole method for providing a quantitative measurement of mu-, kappa and delta-opioid receptor-mediated signalling in the central nervous system. During the last two decades, measurements of changes to the regional brain opioidergic neuronal activation--mediated by endogenously produced opioid peptides, or exogenously administered opioid drugs--have been conducted in numerous chronic pain conditions, in epilepsy, as well as by stimulant- and opioidergic drugs. Although several PET-tracers have been used clinically for depiction and quantification of the opioid receptors changes, the underlying mechanisms for regulation of changes to the availability of opioid receptors are still unclear. After a presentation of the general signalling mechanisms of the opioid receptor system relevant for PET, a critical survey of the pharmacological properties of some currently available PET-tracers is presented. Clinical studies performed with different PET ligands are also reviewed and the compound-dependent findings are summarized. An outlook is given concluding with the tailoring of tracer properties, in order to facilitate for a selective addressment of dynamic changes to the availability of a single subclass, in combination with an optimization of the quantification framework are essentials for further progress in the field of in vivo opioid receptor imaging.

Ethanol Preference Is Inversely Correlated With Ethanol-Induced Dopamine Release in 2 Substrains of C57BL/6 Mice

BACKGROUND

The C57BL/6 mouse model has been used extensively in alcohol drinking studies, yet significant differences in ethanol preference between substrains exist. Differences in ethanol-induced dopamine release in the ventral striatum could contribute to this variability in drinking behavior as dopamine has been implicated in the reinforcing properties of ethanol.

METHODS

A 2-bottle choice experiment investigated the difference in ethanol preference between C57BL/6J and C57BL/6NCrl animals. Microdialysis was used to determine dopamine release and ethanol clearance in these 2 substrains after intraperitoneal injections of 1.0, 2.0 and 3.0 g/kg ethanol or saline.

RESULTS

C57BL/6J mice exhibited significantly greater ethanol preference and less ethanol-stimulated dopamine release compared with C57BL/6NCrl mice. The intraperitoneal injections of ethanol caused a significant increase in dopamine in both substrains at all 3 doses with significant differences between substrains at the 2 highest alcohol doses. Saline injections had a significant effect on dopamine release when given in a volume equivalent to the 3 g/kg ethanol dose. Ethanol pharmacokinetics were similar in the 2 substrains at all 3 doses.

CONCLUSIONS

Ethanol-induced dopamine release in the ventral striatum may contribute to the differences in alcohol preference between C57BL/6J and C57BL/6NCrl mice.

The efficacy of the dopamine D2/D3 antagonist tiapride in maintaining abstinence: a randomized, double-blind, placebo-controlled trial in 299 alcohol-dependent patients

In this investigation, the hypothesis was tested whether the selective dopamine D2/D3 receptor antagonist tiapride is effective in maintaining abstinence after detoxification in alcohol-dependent patients. The rationale of the study was based on the relevance of the dopaminergic system for addictive behaviour as well as some preliminary studies. A multi-centre, randomized, double-blind, placebo-controlled, parallel-group study was conducted. A total of 299 detoxified alcohol-dependent patients (ICD-10: F10.2) received either tiapride (300 mg/d) or placebo over a 24-wk study period. Subjects with severe comorbid psychiatric disorder such as schizophrenia or Wernicke-Korsakoff syndrome were excluded. Primary outcome variable was the time to first relapse with relapse defined as any alcohol consumption after detoxification. Data analysis was done with Kaplan-Meier estimates with log-rank test (one-sided, p<0.05). Tiapride was not superior to placebo in maintaining abstinence. The time to first relapse was 71 d in the tiapride group and 92 d in the placebo group (log-rank test, p=0.9895). Relapse rate was higher in the intervention group (54.4%) than in the control group (40.7%). Like the dopamine antagonist flupenthixol, tiapride was not effective in maintaining alcohol abstinence. Regarding the high success rate in the placebo group the influence of psychosocial treatment in studies investigating drug effects on the course of alcohol dependence has to be considered.

Effects of chronic alcohol exposure on dopamine uptake in rat nucleus accumbens and caudate putamen

RATIONALE

Existing data strongly suggest that alcohol affects dopamine (DA) neurotransmission in the brain. However, many questions remain about the effects of alcohol on the delicate equilibrium between such neurochemical processes as DA release and uptake. Dysregulation of these processes in the mesolimbic and nigrostriatal systems after chronic alcohol ingestion could be a neuroadaptation contributing to dependence.

OBJECTIVES

In the present study, we have employed an alcohol vapor inhalation model to characterize the effects of chronic alcohol exposure on DA dynamics in rat nucleus accumbens (NAc) and caudate putamen (CP) using fast-scan cyclic voltammetry (FSCV) in brain slices. This method provides a unique view of real-time, spatially resolved changes in DA concentration.

RESULTS

We found that chronic alcohol exposure enhanced DA uptake rates in rat NAc and CP. These changes would have the effect of down-regulating extracellular DA levels, presumably a compensatory effect related to increased DA release by repeated alcohol exposure. The sensitivity of terminal release-regulating DA autoreceptors was not different in alcohol-exposed rats compared with alcohol-naïve animals.

CONCLUSIONS

The DA uptake changes after chronic alcohol exposure documented here using FSCV may be associated with a compensatory response of the DA system aimed at decreasing DA signaling. Alterations in autoreceptor function may require relatively long lasting alcohol exposure.

A double-blind, placebo-controlled pilot trial of quetiapine for the treatment of Type A and Type B alcoholism

BACKGROUND

Atypical antipsychotics may be useful in the treatment of alcohol dependence. Human trials suggest that atypical antipsychotics may reduce alcohol craving and consumption, especially among patients with comorbid psychopathology. Therefore, these medications may be more useful for treating more severely affected alcoholics, such as patients with Type B alcoholism. Type B alcoholics are characterized by an early age of onset of problem drinking, high severity of alcohol dependence, increased psychopathology, and treatment-resistance. Quetiapine is an atypical antipsychotic with a favorable side effect profile, and may be a promising medication for the treatment of alcohol dependence, particularly Type B alcoholism.

METHODS

Male and female alcoholics (33 Type A and 28 Type B) were included in a 12-week, double-blind, placebo-controlled trial. After detoxification, patients were randomized to receive quetiapine (n = 29), 400 mg/d at bedtime, or placebo (n = 32). The primary outcome measure was the quantity and frequency of alcohol consumption, measured by the timeline follow back.

RESULTS

Forty-seven patients (77%) completed the trial, with no significant between-group differences in treatment retention. Nine quetiapine-treated patients (31%) maintained complete abstinence compared with 2 placebo-treated patients (6%) (chi(2) = 6.3, P = 0.012). There was a significant interaction between quetiapine and alcoholic subtype. As predicted, quetiapine- versus placebo-treated Type B alcoholics had significantly fewer days of drinking and fewer days of heavy drinking. Alcohol craving was also significantly reduced in quetiapine-treated compared with placebo-treated Type B alcoholics. Among Type A alcoholics, quetiapine provided no advantage over placebo in improving drinking outcomes.

CONCLUSIONS

Quetiapine may be effective for the treatment of alcohol dependence, particularly in the more complicated Type B, early-onset alcoholics.

Decreased dopamine D(2) receptor function in cerebral cortex and brain stem: their role in hepatic ALDH regulation in ethanol treated rats

Ethanol exerts numerous pharmacological effects through its interaction with various neurotransmitters. The dopaminergic pathway is associated with cognitive, endocrine, and motor functions, and reinforcement of addictive substances or behaviours. Aldehyde dehydrogenase (ALDH) is a vital enzyme involved with alcohol metabolism and detoxification. In the present study, we investigated the role of cerebral cortex and brain stem dopamine D(2) receptors in the functional regulation on ALDH enzyme activity, in ethanol administrated rats. Two groups of rats were selected viz. control and alcoholic. Cerebral cortex, brain stem and the liver dopamine content was decreased significantly (P < 0.05, 0.05, 0.001, respectively) and homovanillic acid/dopamine (HVA/DA) ratio has significantly increased (P < 0.05, 0.001 and 0.001), respectively in ethanol treated rats when compared to control. Scatchard analysis of [(3)H]YM-09151-2 binding to synaptic membrane preparations of cerebral cortex and brain stem showed a significant decrease (P < 0.001, 0.05, respectively) in B (max) in ethanol treated rats compared to control and the K (d) also decreased significantly (P < 0.05). The ALDH analysis showed a significant increase (P < 0.05) in V (max) in cerebral cortex, plasma and liver of experimental rats when compared with control without having significant change in brain stem but with decreased K (m) (P < 0.001). Our results suggest that decreased function of dopamine mediated through DA D(2) receptor in the cerebral cortex and brain stem enhanced the brain, plasma and liver ALDH activity in ethanol treated rats. This ALDH regulation has significance to correct alcoholics from addiction due to allergic reaction observed in aldehyde accumulation.

Test of association between TaqIA A1 allele and alcohol use disorder phenotypes in a sample of adolescent patients with serious substance and behavioral problems

Several studies have demonstrated a significant association between the A1 allele of the TaqIA polymorphism and various phenotypes of alcoholism, others have not, and two studies have shown the reversed association, where the A2 allele was associated with higher levels of alcohol consumption. We sought to test for an association between early onset (in childhood or adolescence) alcohol use disorders and the DRD2 TaqIA polymorphism and to resolve some of the hypothesized explanations for previous negative results, utilizing a larger sample than many previous studies.

METHODS

We selected individuals with a lifetime alcohol abuse or dependence (n=239) diagnosis from a clinically ascertained sample of youth (ages 13-19) with serious conduct and substance problems (about 90% also met criteria for conduct disorder and a cannabis use disorder) and compared them with individuals without a lifetime alcohol use disorder diagnosis ascertained from (1) community adolescent controls (n=151), (2) siblings of patients (n=87) and (3) other adolescent patients (n=92). Cases were compared with each control group, separately, by genotype using the chi(2)-test. Using 78 adolescent patients with an alcohol use disorder where genotypic information was available for both parents, we conducted the transmission disequilibrium test (TDT).

RESULTS

Case-control results were non-significant using the entire community control sample (chi(2)(2)=1.92; p=0.38) and when restricting the sample to Caucasians (chi(2)(2)=3.81; p=0.15) or Hispanics (chi(2)(2)=1.70; p=0.43). Case-control results using the other comparison groups and TDT results were also non-significant.

DISCUSSION

We did not find support for an association between the TaqIA polymorphism and early onset alcohol use disorders.

Dorsal hippocampal dopamine receptors are involved in mediating ethanol state-dependent memory

In the present study, the effects of bilateral injections of dopaminergic agents into the hippocampal CA1 regions (intra-CA1) on ethanol (EtOH) state-dependent memory were examined in mice. A single-trial step-down passive avoidance task was used for the assessment of memory retention in adult male NMRI mice. Pre-training intra-peritoneal (i.p.) administration of EtOH (0.25, 0.5 and 1 g/kg) dose dependently induced impairment of memory retention. Pre-test administration of EtOH (0.5 g/kg)-induced state-dependent retrieval of the memory acquired under pre-training EtOH (0.5 g/kg) influence. Intra-CA1 administration of the dopamine D(1) receptor agonist, SKF 38393 (0.5, 1 and 2 g/mouse) or the dopamine D(2) receptor agonist, quinpirole (0.25, 0.5 and 1 microg/mouse) alone cannot affect memory retention. While, pre-test intra-CA1 injection of SKF 38393 (2 microg/mouse, intra-CA1) or quinpirole (0.25, 0.5 and 1 microg/mouse, intra-CA1) improved pre-training EtOH (0.5 g/kg)-induced retrieval impairment. Moreover, pre-test administration of SKF 38393 (0.5, 1 and 2 microg/mouse, intra-CA1) or quinpirole (0.5 and 1 microg/mouse, intra-CA1) with an ineffective dose of EtOH (0.25 g/kg) significantly restored the retrieval and induced EtOH state-dependent memory. Furthermore, pre-training injection of the dopamine D(1) receptor antagonist, SCH 23390 (4 microg/mouse), but not the dopamine D(2) receptor antagonist, sulpiride, into the CA1 regions suppressed the learning of a single-trial passive avoidance task. Pre-test intra-CA1 injection of SCH 23390 (2 and 4 microg/mouse, intra-CA1) or sulpiride (2.5 and 5 microg/mouse, intra-CA1) 5 min before the administration of EtOH (0.5 g/kg, i.p.) dose dependently inhibited EtOH state-dependent memory. These findings implicate the involvement of a dorsal hippocampal dopaminergic mechanism in EtOH state-dependent memory and also it can be concluded that there may be a cross-state dependency between EtOH and dopamine.

Effect of ethanol on 24-h hormonal changes in prolactin release mechanisms in growing male rats

This study analyzes the effect of chronic ethanol feeding on 24-h variation of hypothalamic-pituitary mechanisms involved in prolactin regulation in growing male Wistar rats. Animals were maintained under a 12:12 h light/dark photoperiod (lights off at 2000 h), and they received a liquid diet for 4 wk, starting on d 35 of life. The ethanol-fed group received a similar diet to controls except that maltose was isocalorically replaced by ethanol. Ethanol replacement provided 36% of the total caloric content of the diet. Rats were killed at six time intervals every 4 h, beginning at 0900 h. Mean concentration of serum prolactin in ethanol-fed rats was 58.7% higher than in controls. Peak circulating prolactin levels occurred at the early phase of the activity span in both groups of rats, whereas a second peak was found late in the resting phase in ethanol-fed rats only. In control rats, median eminence dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and taurine levels exhibited two maxima, the major one preceding prolactin release and a second one during the first part of the resting phase. Median eminence DA and 5-HT turnover (as measured by 3,4-dihydroxyphenylacetic acid, DOPAC/DA, and 5-hydroxyindoleacetic acid, 5-HIAA/5-HT ratio) showed a single maximum preceding prolactin, at 0100 h. Ethanol treatment did not affect median eminence DA or 5-HT levels but it decreased significantly their turnover rate. The midday peak in DA and 5-HT levels (at 1300 h) was abolished and the night peak (at 0100 h) became spread and blunted in the ethanol-fed rats. This was accompanied with the disappearance of the 0100 h peak in DA and 5-HT turnover and the occurrence of a peak in 5-HT turnover at 1700 h. Ethanol intake suppressed the night peak in median eminence GABA and taurine (at 0100 h) as well as the midday peak of GABA. Ethanol augmented pituitary levels of DOPAC and 5-HIAA. The results indicate that chronic ethanol administration affects the mechanisms that modulate the circadian variation of prolactin release in growing male rats.

Reward-aversion circuitry in analgesia and pain: implications for psychiatric disorders

Sensory and emotional systems normally interact in a manner that optimizes an organism's ability to survive using conscious and unconscious processing. Pain and analgesia are interpreted by the nervous system as aversive and rewarding processes that trigger specific behavioral responses. Under normal physiological conditions these processes are adaptive. However, under chronic pain conditions, functional alterations of the central nervous system frequently result in maladaptive behaviors. In this review, we examine: (a) the interactions between sensory and emotional systems involved in processing pain and analgesia in the physiological state; (b) the role of reward/aversion circuitry in pain and analgesia; and (c) the role of alterations in reward/aversion circuitry in the development of chronic pain and co-morbid psychiatric disorders. These underlying features have implications for understanding the neurobiology of functional illnesses such as depression and anxiety and for the development and evaluation of novel therapeutic interventions.

Behavioral and neurochemical effects on rat offspring after prenatal exposure to ethanol

The work studied behavioral and neurochemical alterations in 21-day-old pups, from both sexes (26 g on average) born from female Wistar rats administered daily with ethanol (0.5 or 4.0 g/kg, p.o.), for 30 days before mating, and throughout their gestational period. Ethanol administration continued from delivery up to weaning. The open field, elevated plus maze and forced swimming tests were used to evaluate effects of ethanol on locomotion, anxiety and depression, respectively. Binding assays were used to identify dopaminergic (D1- and D2-like) and muscarinic (M1 plus M2) receptors. Results of the plus maze test indicated significant and dose-dependent increases in the number of entrances in the open arms and in the time of permanence in the open arms, in the prenatally ethanol-exposed offspring, as compared to controls, indicating an anxiolytic effect. In the open field test, this group presented decreases in spontaneous locomotor activity as well as in the occurrences of rearing and grooming. Offspring also showed dose-dependent increases in their immobility time in the forced swimming test, characterizing despair behavior. Decreases in the hippocampal (D2: 32%; D1: 25%) and striatal (D2: 30%; D1: 52%) dopaminergic binding were detected in ethanol-exposed offspring. On the other hand, significant increases were observed in muscarinic binding in the hippocampus (40%) as well as in the striatum (42%). This study shows evidence that in utero ethanol exposure produces a long-lasting effect on development and pharmacological characteristics of brain systems that may have important implications in behavioral and neurochemical responsiveness occurring in adulthood.

Local effects of acute ethanol on dopamine neurotransmission in the ventral striatum in C57BL/6 mice

In this study, fast-scan cyclic voltammetry in brain slices was used to evaluate the effects of acute ethanol on dopamine terminal release and uptake in the nucleus accumbens of C57BL/6 mice. We found that pharmacologically relevant concentrations of ethanol (20 and 100 mM) did not alter electrically evoked dopamine release, while the highest concentration (200 mM) significantly decreased release (approximately 45%). No significant changes were observed in the rate of dopamine uptake after ethanol (20, 100 or 200 mM). In addition, it was established that a moderate dose (2 g/kg, i.p.) of ethanol did not alter the rate of dopamine synthesis, measured as L-dihydroxyphenylalanine (L-DOPA) accumulation. However, a high dose (5 g/kg, i.p.) of ethanol significantly increased the levels of L-DOPA to 60% above the control value. These data are consistent with earlier findings obtained in brain slices from rats; dopamine release, but not clearance, is affected by acute ethanol.

Neuroprotective and abstinence-promoting effects of acamprosate: elucidating the mechanism of action

Acamprosate is an abstinence-promoting drug widely used in the treatment of alcohol dependence but which has a mechanism of action that has remained obscure for many years. Recently, evidence has emerged that this drug may interact with excitatory glutamatergic neurotransmission in general and as an antagonist of the metabotropic glutamate receptor subtype 5 (mGluR5) in particular. These findings provide, for the first time, a satisfactory, unifying hypothesis that can bring together and explain the diverse neurochemical effects of acamprosate. Glutamic acid is involved in several aspects of alcohol dependence and withdrawal, many of which can be modified by acamprosate. For example, during chronic exposure to alcohol, the glutamatergic system becomes upregulated, leaving the brain exposed to excessive glutamatergic activity when alcohol is abruptly withdrawn. The surge in glutamic acid release that occurs following alcohol withdrawal can be attenuated by acamprosate. The elevated extracellular levels of glutamic acid observed in withdrawal, together with supersensitivity of NMDA receptors, may expose vulnerable neurons to excitotoxicity, possibly contributing to the neuronal loss sometimes observed in chronic alcohol dependence. In vitro studies suggest that the excitotoxicity produced by ethanol can effectively be blocked by acamprosate. Moreover, glutamatergic neurotransmission plays an important role in the acquisition of cue-elicited drinking behaviours, which again can be modulated by acamprosate. In conclusion, the glutamatergic hypothesis of the mechanism of action of acamprosate helps explain many of its effects in human alcohol dependence and points the way to potential new activities, such as neuroprotection, that merit exploration in the clinic.

A three-axes approach of subtyping the alcohol dependence syndrome

Subtyping of alcoholics according to specific characteristics has a long tradition in alcoholism research with a number of different typologies that emerged in the literature. The goal of the present study was to test a multidimensional approach of subtyping with characteristics from different axes. Therefore, male inpatients meeting ICD-10 criteria for alcohol dependence were rated on three axes by assessing their degree of sensation seeking (personality axis), age of alcoholism onset (clinical axis) and level of dopamine activity (neurobiological axis). By using a configuration frequency analysis, we identified a subtype that was characterized by high sensation seeking early age of alcoholism onset and high dopamine activity. This subtype, which is in accordance with clinical experience and cannot be explained by antisocial personality disorder, embodied a significantly greater proportion of alcoholics than expected. The result emphasizes the usefulness of multidimensional approaches integrating personality, clinical and neurobiological characteristics.

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.

Pharmacotherapy of alcohol dependence: a review of the clinical data

Over the last 20 years, the role of adjuvant pharmacotherapy in optimising outcome in rehabilitation programmes for alcohol-dependent patients has become increasingly evident. New avenues for rational drug treatment have arisen from better understanding of the neurobiological substrates of alcohol dependence, including adaptive changes in amino acid neurotransmitter systems, stimulation of dopamine and opioid peptide systems, and, possibly, changes in serotonergic activity. Disulfiram, naltrexone and acamprosate are currently the only treatments approved for the management of alcohol dependence. However, there is still no unequivocal evidence from randomised controlled clinical trials that disulfiram improves abstinence rates over the long term. Aversive therapy with disulfiram is not without risk for certain patients, and should be closely supervised. Both naltrexone and acamprosate improve outcome in rehabilitation of alcohol-dependent patients, but seem to act on different aspects of drinking pathology. Naltrexone is thought to decrease relapse to heavy drinking by attenuating the rewarding effects of alcohol. However, data from the naltrexone clinical trial programme are somewhat inconsistent, with several large studies being negative. Acamprosate is believed to maintain abstinence by blocking the negative craving that alcohol-dependent patients experience in the absence of alcohol. The clinical development programme has involved a large number of patients and studies, of which the vast majority have shown a beneficial effect of acamprosate on increasing abstinence rates. Both drugs are generally well tolerated; nausea is reported by around 10% of patients treated with naltrexone, while the most frequent adverse effect reported with acamprosate is diarrhoea. Another opioid receptor antagonist, nalmefene, has shown promising activity in pilot studies, and may have a similar profile to naltrexone. Data from studies of SSRIs in alcohol dependence are somewhat heterogeneous, but it appears that these drugs may indirectly improve outcome by treating underlying depression rather than affecting drinking behaviour per se. Similarly, the anxiolytic buspirone may act by ameliorating underlying psychiatric pathology. Dopaminergic neuroleptics, benzodiazepines and antimanic drugs have not yet demonstrated evidence of activity in large controlled clinical trials. Trials with drugs acting at serotonin receptors have yielded disappointing results, with the possible exception of ondansetron. Because the biological basis of alcohol dependence appears to be multifactorial, the future of management of alcoholism may be combination therapy, using drugs acting on different neuronal pathways, such as acamprosate and naltrexone. Pharmacotherapy should be used in association with appropriate psychosocial support and specific treatment provided for any underlying psychiatric comorbidities.

Alcohol Activates a Sucrose-Responsive Gustatory Neural Pathway

A strong positive association exists between the ingestion of alcohol and sweet-tasting solutions. The neural mechanisms underlying this relationship are unknown, although recent data suggest that gustatory substrates are involved. Here, we examined the role of sweet taste receptors and central neural circuits for sugar taste in the gustatory processing of ethanol. Taste responses to ethanol (3, 5, 10, 15, 25, and 40% vol/vol) and stimuli of different taste qualities (e.g., sucrose, NaCl, HCl, and quinine-HCl) were recorded from neurons of the nucleus of the solitary tract in anesthetized rats prior to and after oral application of the sweet receptor blocker gurmarin. The magnitude of ethanol-evoked activity was compared between sucrose-responsive ( n = 21) and sucrose-unresponsive ( n = 20) neurons and the central neural representation of ethanol taste was explored using multivariate analysis. Ethanol produced robust concentration-dependent responses in sucrose-responsive neurons that were dramatically larger than those in sucrose-unresponsive cells. Gurmarin selectively and similarly inhibited ethanol and sucrose responses, leaving NaCl, HCl, and quinine responses unaltered. Across-neuron patterns of response to ethanol were most similar to those evoked by sucrose, becoming increasingly more so as the ethanol concentration was raised. Results implicate taste receptors for sucrose as candidate receptors for ethanol and reveal that alcohol and sugar taste are represented similarly by gustatory activity in the CNS. These findings have important implications for the sensory and reward properties of alcohol.

Lower CSF homovanillic acid levels in depressed patients with a history of alcoholism

Major depression and alcoholism are often comorbid, resulting in more impairment and more suicidal behavior compared with either diagnosis alone. This study compared clinical features and cerebrospinal fluid (CSF) monoamine metabolites in depressed subjects with and without a history of alcoholism and healthy volunteers. We hypothesized that depressed subjects with a history of alcoholism would be more aggressive, impulsive, and suicidal than depressed subjects without a history of alcoholism, and would have lower CSF monoamine metabolite levels. We compared 63 subjects with a current major depressive episode (MDE) and a history of alcoholism, 72 subjects with a current MDE but without a history of alcoholism, and 22 healthy volunteers. Participants with a history of alcoholism were in remission for at least 6 months. All subjects were free from prescribed medications known to affect brain serotonin, dopamine, or norepinephrine systems for a minimum of 14 days. Depressive symptoms, lifetime aggression, impulsivity, Axis II disorders, and suicidal behavior were assessed. CSF was sampled and homovanillic acid (HVA), 5-hydroxyindolacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were assayed by high-performance lipid chromatography with electrochemical detection. Depressed subjects with a history of alcoholism did not differ from depressed subjects without a history of alcoholism in current severity of depressive symptoms, or in past suicidal behavior. Depressed subjects with a history of alcoholism had lower CSF HVA levels, and higher lifetime aggression and current suicide ideation scale scores and were more likely to be tobacco smokers compared with depressed subjects without a history of alcoholism. Low HVA was present after adjustment for sex, aggression and depression scores, cigarette smoking, antisocial and borderline personality disorders, psychomotor retardation, and delusions. Controls had CSF HVA levels intermediate between the two depressed groups. We found no group difference in CSF 5-HIAA and MHPG levels. In individuals with current MDE, those with a history of comorbid alcoholism had lower CSF HVA levels compared with those without a history of alcoholism. Low CSF HVA suggests that impaired dopaminergic activity is associated with a history of alcoholism in persons with current MDE.

Genetic polymorphisms of the promoter region of dopamine D2 receptor and dopamine transporter genes and alcoholism among four aboriginal groups and Han Chinese in Taiwan

This study aims to examine the relationship between the functional polymorphism at the promoter region of the dopamine D2 receptor (DRD2) gene (i.e. -141C Ins/Del) and variable number of tandem repeat polymorphism at the 3' untranslated region of the dopamine transporter (DAT) gene (SLC6A3) with alcoholism in a case-control study. The cases (n = 203) were alcohol dependents with withdrawal symptoms, and the controls (n = 213) were sex- and ethnicity-matched individuals who were screened to exclude those with alcohol problems among four aboriginal groups (Atayal, Ami, Bunun, and Paiwan) and Han Chinese in Taiwan. To control for potential confounding factors, we excluded tobacco abusers from control subjects in part of the analysis and compared the distribution of the genetic polymorphisms in alcoholics with severe medical complications versus those with less severe medical complications. There were no differences in allele and genotype frequencies of these two distinct genetic markers between alcoholics and control subjects in these five different ethnic groups. There was no significant linkage disequilibrium between the -141C polymorphism and two other DRD2 polymorphisms (TaqI A and NcoI). The results remained unchanged when cases were limited to alcoholics with more severe medical complications or when tobacco abusers were excluded from control subjects. The results suggest that both the DRD2 promoter region and the DAT gene do not play a significant role in conferring vulnerability to alcoholism.

Haplotypes at the DRD2 locus and severe alcoholism

Association studies of the minor TaqI A allele of the D(2) dopamine receptor (DRD2) gene with alcoholism have produced conflicting findings. Failure to assess alcoholics for severity of their disorder and to screen controls for substance use have been proposed as causes for the discrepant results. In the present study, five diallelic sites spanning the DRD2 gene were determined in combined Caucasian (non-Hispanic) studies of more severe alcoholics (n = 92) and controls screened for substance use (n = 85). The frequency of the minor alleles at the 3'-untranslated site (TaqI A) and two intronic sites (TaqI B and intron 6) of the DRD2 gene were each strongly associated with alcoholism. Moreover, the alcoholics compared with the controls at these three sites had a significantly higher frequency of the minor/major allele heterozygote haplotype combination (A1/A2 B1/B2 T/G) than the major allele homozygote haplotype combination (A2/A2 B2/B2 G/G). However, exon 7 and promoter alleles were not associated with alcoholism. In neither the alcoholics nor in the controls were there departures from Hardy-Weinberg equilibrium at any of the five sites examined. The most significant diallelic composite genotypic disequilibria were found when comparisons were made between TaqI A and TaqI B, TaqI A and intron 6, and TaqI B and intron 6 sites. Weaker but still significant disequilibria were observed when TaqI A and exon 7, TaqI B and exon 7, intron 6 and exon 7, and promoter and exon 7 sites were compared. However, no significant disequilibria were noted when TaqI A and promoter, TaqI B and promoter, and intron 6 and promoter sites were compared. In sum, the study found significant evidence for association of the minor alleles in the untranslated sites of the DRD2 gene and their haplotypes with the more severe alcoholic phenotype.

Reappraisal of the association between the DRD2 gene, alcoholism and addiction

We analysed the impact of the TaqI A1 allele of the D2 dopamine receptor gene on the risk for alcoholism, trying to depict three explanations frequently proposed to explain discrepancies in association and linkage studies: that the A1 allele may act as a marker rather than as a vulnerability factor, that stratification biases and unevaluated controls may explain positive results, and that the A1 allele is modifying the phenotype rather than increasing the risk for alcoholism. We thus tested another (dinucleotide STRP) marker within the DRD2 gene, selected a new homogenous sample of 113 alcoholic patients and 49 unaffected controls strictly matched for ethnic origins, and systematically assessed both samples with a semi-structured interview to detect (in both samples) alcohol dependence, but also such related traits as specificities of complications. The frequency of the A1 allele was not significantly different between alcoholics and controls but when comparing different subgroups of alcoholics, the A1 allele was significantly more frequent in alcoholic patients with somatic complications (OR = 3.00, CI[1.37-6.62]), social and professional complications (OR = 2. 72, CI[1.25-5.90]), or with co-morbid dependence (OR = 2.88, 95% IC [1.16-7.15]). The association for co-morbid dependence and somatic complications was also positive when taking into consideration both STRP and TaqIA polymorphisms. The A1 allele does not increase the risk for alcoholism per se in our sample, but may be involved in a related trait which is partially dependent on the diagnosis of alcoholism, through a disequilibrium with another close mutation.

Addiction and its reward process through polymorphisms of the D2 dopamine receptor gene: a review

Since 1990, association studies have amassed strong evidence implicating the D(2) dopamine receptor (DRD2) gene in alcoholism. Specifically, the TaqI A minor (A1) allele of the DRD2 gene has been associated with alcoholism. The DRD2 gene has also been found to be involved in other substance use disorders including cocaine, nicotine and opioid dependence, and obesity. Beyond association studies, pharmacologic studies have shown reduced brain D(2) dopamine receptor numbers in A1(+) allele carriers (A1A1 and A1A2 genotypes) compared to A1(-) allele carriers (A2A2 genotype). Through a number of other approaches, different phenotypes have also been identified in subjects with the A1(+) and A1(-) alleles. These include metabolic, neurophysiological, neuropsychological, personality, stress and treatment studies. It is hypothesized that in an effort to compensate for deficiencies in the dopaminergic system, substance abusers may seek to stimulate the mesocorticolimbic circuits of the brain, long thought to be important in behavioral reward and reinforcement. In effect, one form of the DRD2 gene, the A1 allele, renders the dopaminergic system inefficient and rewards substance abuse that increases brain dopamine levels.

Lack of association of the dopamine D4 receptor gene polymorphism with alcoholism in a Brazilian population

The dopaminergic system has been implicated in alcoholism, but most of the past investigations concentrated on the dopamine D2 receptor (DRD2), with conflicting results. The dopamine D4 receptor gene (DRD4) is in the same class as DRD2, but presents different pharmacological properties. This gene has an expressed highly variable 48 base pair (bp) tandem repeat polymorphism (VNTR), which could be of functional relevance.We screened 100 Caucasians and 100 Afro-Brazilians to determine the allele distribution of this polymorphism in a southern Brazilian population. The allele frequencies observed are significantly different from those described in the literature except when Afro-Brazilians and African Bantus are compared. A group of 136 male alcoholics, classified according to DSM-III-R criteria for alcohol dependence, was also ascertained. The results of the association study were negative for comparisons between white and black alcoholics and controls, and no association was disclosed when either subtypes of alcoholics and different aspects of this condition were considered. These results, together with those available in the literature for other ethnic groups, suggest a minor role, if any, of the DRD4 gene in the susceptibility to alcoholism.