Serotonergic dysfunction in addiction: effects of alcohol, cigarette smoking and heroin on platelet 5-HT content

Multi-omics study reveals associations among neurotransmitter, extracellular vesicle-derived microRNA and psychiatric comorbidities during heroin and methamphetamine withdrawal

Despite decades of research in the field of substance withdrawal, molecular biomarkers and related mechanistic study have generally been lacking. In addition to known neurotransmitters, circulating miRNAs are found in small vesicles known as exosomes within blood that have diagnostic potential and are known to contribute to psychiatric disorders. The aim of this work was to characterize the changes in neurotransmitter and exosomal miRNA profiles during heroin and methamphetamine withdrawal using a cross-sectional study design, and to determine their associations to psychiatric comorbidities in a large group of patients with substance use disorders (SUDs). Using weighted gene co-expression network analysis, a series of known, conserved, and novel exosomal miRNAs were identified as being associated with the severity of anxiety and depression, as well as the concentrations of neurotransmitters GABA, choline, and serotonin. Bioinformatics analyses established that the differences in the miRNA profile target signaling pathways are significantly associated with developmental and intellectual abnormalities. Notably, a set of dysregulated miRNA signatures including hsa-mia-451a and hsa-mir-21a resulted in an AUC of 0.966 and 0.861, respectively, for predicting the patients with SUDs. Furthermore, hsa-miR-744a-5p was positively correlated with serotonin, and its important role in maintaining neuronal development and function was revealed using an in vitro human induced pluripotent stem cells derived neuronal model. Our results suggest that the miRNA content of circulating exosomes represent a biomolecular "fingerprint" of the progression of substance withdrawal and may uncover the putative mechanism of how these exosomal miRNAs contribute to psychiatric symptoms.

Alcohol-related phenotypes and platelet serotonin concentration

Alcohol dependence is a chronic relapsing mental disorder with heterogeneous and complex underlying biology. It is frequently associated with nicotine dependence, severity of alcohol dependence symptoms, and diverse alcohol-related phenotypes, including the presence of delirium tremens and withdrawal symptoms, early or late onset of alcohol abuse, aggression, suicidal behavior, and anxiety. While searching for peripheral biomarkers of altered serotonergic (5-HT) function in alcohol dependence and alcohol-related behaviors, we determined a peripheral biomarker, i.e., platelet 5-HT concentration in a large group of Caucasian subjects with alcohol dependence subdivided according to the presence of specific alcohol-related phenotypes and smoking status. Individuals with alcohol dependence (n = 661) of both sexes were evaluated using Structural Clinical Interview based on DSM-IV criteria, while platelet 5-HT concentration was determined using the spectrophotofluorimetric method. Smoking is significantly associated, while sex and age are not, with platelet 5-HT concentration. Severe alcohol dependence and lack of withdrawal symptoms were associated with significantly decreased platelet 5-HT concentration in alcohol-dependent non-smokers. In smokers, significantly lower platelet 5-HT concentration was found in patients with the late onset of alcohol abuse. These results suggested that platelet 5-HT concentration might be used as a peripheral marker of different alcohol-related phenotypes, after controlling for the effects of smoking and sex.

The association between HTR1B gene rs13212041 polymorphism and onset of alcohol abuse

BACKGROUND

Alcohol dependence displays a wide variety of clinical phenotypes. Various typology classifications of alcoholism include age of onset of alcohol abuse as one of the major phenotypic features. Serotonergic changes have been associated with alcoholism, while serotonin receptors type 1B (5-HT1B) play an important role in regulating serotonergic neurotransmission. The rs13212041 polymorphism modulates the expression of HTR1B gene coding for 5-HT1B receptor. This study examined the association of platelet serotonin (5-HT) and HTR1B gene with the onset of alcohol abuse in alcohol-dependent subjects.

MATERIALS AND METHODS

Determination of platelet 5-HT concentration and genotyping of rs13212041 HTR1B gene polymorphism were performed in 613 alcohol-dependent patients, subdivided according to early/late onset (before/after 25 years of age) of alcohol abuse.

RESULTS

Alcohol-dependent individuals with CC genotype were more frequent in the group with early onset of alcohol abuse compared to carriers of T allele. Besides HTR1B genotype, age and gender, but not platelet 5-HT, were major variables associated with the onset of alcohol abuse. Platelet 5-HT concentration was not significantly different between patients with early and late onset of alcohol abuse, or patients carrying various HTR1B genotypes. Although we observed no influence of co-variables such as age, gender, or somatic and psychiatric comorbidities, platelet 5-HT concentration was significantly affected by smoking.

CONCLUSION

These findings support potential involvement of 5-HT1B receptors in the onset of alcohol abuse and development of alcohol dependence. Additionally, the results of our study emphasize the importance of controlling for smoking status, as one of the significant confounding factors influencing platelet 5-HT concentration.

A Genetic Animal Model of Alcoholism for Screening Medications to Treat Addiction

The purpose of this review is to present up-to-date pharmacological, genetic, and behavioral findings from the alcohol-preferring P rat and summarize similar past work. Behaviorally, the focus will be on how the P rat meets criteria put forth for a valid animal model of alcoholism with a highlight on its use as an animal model of polysubstance abuse, including alcohol, nicotine, and psychostimulants. Pharmacologically and genetically, the focus will be on the neurotransmitter and neuropeptide systems that have received the most attention: cholinergic, dopaminergic, GABAergic, glutamatergic, serotonergic, noradrenergic, corticotrophin releasing hormone, opioid, and neuropeptide Y. Herein, we sought to place the P rat's behavioral and neurochemical phenotypes, and to some extent its genotype, in the context of the clinical literature. After reviewing the findings thus far, this chapter discusses future directions for expanding the use of this genetic animal model of alcoholism to identify molecular targets for treating drug addiction in general.

Probing the Serotonin Transporter Availability Among Male Cigarette Smokers: A SPECT Study With [123I] ADAM

OBJECTIVE

Genetic studies have suggested that the serotonin transporter (SERT) could be associated with cigarette smoking. However, evidence from neuroimaging is scarce. The aim of the present study was to examine the SERT availability among cigarette smokers by using single-photon emission computed tomography (SPECT).

METHODS

Sixteen male smokers and 32 controls were enrolled. The SERT availability was measured by SPECT with a radiotracer, [I] ADAM, which is highly sensitive and specific to SERT.

RESULTS

No significant difference in SERT availability was found between 2 groups in the midbrain (smokers: 2.12 ± 0.70, nonsmokers: 2.13 ± 0.63; P = 0.86), basal ganglia (smokers: 0.83 ± 0.30, nonsmokers:0.90 ± 0.39; P = 0.95), or thalamus (smokers: 1.14 ± 0.41, nonsmokers: 1.20 ± 0.38; P = 0.88). No significant association was found between the SERT availability, and either the breath carbon monoxide level or the score of the Fagerström Test for Nicotine Dependence.

CONCLUSIONS

Whether the SERT availability in the brain is altered in smokers remains unclear.

The 5-HT7 receptor as a potential target for treating drug and alcohol abuse

Alcohol and drug abuse take a large toll on society and affected individuals. However, very few effective treatments are currently available to treat alcohol and drug addiction. Basic and clinical research has begun to provide some insights into the underlying neurobiological systems involved in the addiction process. Several neurotransmitter pathways have been implicated and distinct reward neurocircuitry have been proposed—including the mesocorticolimbic dopamine (MCL-DA) system and the extended amygdala. The serotonin (5-HT) neurotransmitter system is of particular interest and multiple 5-HT receptors are thought to play significant roles in alcohol and drug self-administration and the development of drug dependence. Among the 5-HT receptors, the 5-HT7 receptor is currently undergoing characterization as a potential target for the treatment of several psychiatric disorders. Although this receptor has received only limited research regarding addictive behaviors, aspects of its neuroanatomical, biochemical, physiological, pharmacological, and behavioral profiles suggest that it could play a key role in the addiction process. For instance, genomic studies in humans have suggested a link between variants in the gene encoding the 5-HT7 receptor and alcoholism. Recent behavioral testing using high-affinity antagonists in mice and preliminary tests with alcohol-preferring rats suggest that this receptor could mediate alcohol consumption and/or reinforcement and play a role in seeking/craving behavior. Interest in the development of new and more selective pharmacological agents for this receptor will aid in examining the 5-HT7 receptor as a novel target for treating addiction.

Serotonin and mental disorders: a concise review on molecular neuroimaging evidence

Serotonin is one of the most important neurotransmitters influencing mental health and, thus, is a potential target for pharmaco-logical treatments. Functional neuroimaging techniques, such as positron-emission tomography (PET) and single photon emission computed tomography (SPECT), could provide persuasive evidence for the association between mental disorders and serotonin. In this concise review, we focus on evidence of the links between serotonin and major depressive disorders, as well as other mood disorders, anxiety disorders, schizophrenia, addiction, attention deficit hyperactivity disorder (ADHD), and autism.

Serotonin transporter gene promoter polymorphism (5-HTTLPR) and alcohol use in general population: interaction effect with birth cohort

RATIONALE AND OBJECTIVE

Prevalence of alcohol use is markedly influenced by socioeconomic conditions and is therefore subject to cohort effects. The common genetic variation 5-HTTLPR (serotonin transporter gene-linked polymorphic region) has been related to several aspects of alcohol use and addiction but with mixed results, probably due to different environmental interaction effects. We aimed at assessing whether the association between alcohol use and 5-HTTLPR genotype is subject to cohort effects as birth cohorts may be raised in significantly different environments.

METHODS

We used the database of the Estonian Children Personality Behaviour and Health Study (beginning in 1998). Cohorts of initially 9-year-old (recalled at ages 15 and 18) and 15-year-old (recalled at ages 18 and 25) children provided self-reports on their alcohol use in all data collection waves (complete data available n = 1,075).

RESULTS

A significant genotype × gender × cohort interaction effect on the age of consuming the first alcoholic drink was found [F(2, 1,063) = 7.2, p < 0.001]. Females with the s/s genotype in the older cohort were the latest experimenters with alcohol, while the s/s females of younger cohort had tried alcohol earlier than any other group. In males, there was no significant cohort × genotype interaction, but the 5-HTTLPR genotype was associated with alcohol use, the s/s subjects reporting the highest consumption.

CONCLUSION

Expression of genetic vulnerability to alcohol use is influenced by birth cohort effects. The 5-HTTLPR genotype is associated with alcohol consumption in general population, but the effect depends on gender and birth cohort.

Effects of Tai Chi on the protracted abstinence syndrome: a time trial analysis

While exercise has been shown to reduce the negative effects of substance withdrawal symptoms, no research has investigated if Tai Chi, a traditional Chinese exercise, has similar effects. Here, we observed the physiological effects of Tai Chi on protracted abstinence syndrome (PAS) in female heroin addicts by comprehensively inspecting their immune system function, complete blood count, hepatic function and renal function. To determine the psychological effects, we used the Hamilton Rating Scale for Depression (HRSD) and the rating scale of heroin withdrawal symptoms. We recruited 70 heroin-addicted young women beginning to undergo withdrawal and randomly assigned them into two groups: one group received one-hour Tai Chi exercise every two days (Tai Chi group, n = 36) and the other group did not (control group, n = 34). Thirty-three patients finished this six-month trial. Numerous significant physiological differences were observed between all heroin-addicted subjects (n = 70) and age-matched healthy individuals (n = 18), suggesting a deleterious effect of drug addiction. There were improvements for certain physical parameters between the Tai Chi group (n = 17) and the control group (n = 16), although the differences were not statistically significant. We observed a small significant difference in psychological effects near the 60-day mark between the two groups. Taken together, our results suggest that Tai Chi might have a positive effect on PAS, which future studies can confirm by using an expanded sample size, longer trial time, and more sensitive and specific indicators of psychological and physiological health.

Effects of acute combined serotonin and dopamine depletion on cue-induced drinking intention/desire and cognitive function in patients with alcohol dependence

BACKGROUND

Alcohol cues can precipitate the desire to drink and cause relapse in recovering alcohol-dependent patients. Serotonin and dopamine may play a role in alcohol cue-induced craving. Acute combined tryptophan (Trp), tyrosine (Tyr), and phenylalanine (Phe) depletion (CMD) in the diet attenuates the synthesis of serotonin and dopamine in the human brain. However, no study of the effects of acute CMD has been previously conducted. Therefore, we investigated whether the attenuation of serotonin and dopamine synthesis changes cue-induced alcohol craving in recently abstinent alcoholics.

METHODS

In this double-blind, randomized, placebo-controlled, crossover design, 12 male patients who met the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria for alcohol dependence were divided into two conditions: (1) monoamine depletion (i.e., consumption of a concentrated amino acid beverage that resulted in a rapid and significant decrease in plasma-free Tyr/Phe/Trp) and (2) balanced condition (i.e., consumption of a similar beverage that contained Tyr/Phe/Trp). The participants were scheduled for two experimental sessions, with an interval of ≥7 days. The cue-induced craving test session was conducted 6h after each amino acid beverage administration. Drinking urge, blood pressure, heart rate, working memory, and attention/psychomotor performance were assessed before and after administration.

RESULTS

Compared with the balanced condition, the monoamine depletion condition significantly increased drinking intention/desire and diastolic blood pressure. Cognitive performance was not different between the two conditions.

CONCLUSIONS

Acute combined serotonin and dopamine depletion may increase drinking intention/desire and diastolic blood pressure without influencing cognitive function.

Suicide attempt, smoking, comorbid depression, and platelet serotonin in alcohol dependence

The risk of suicide in patients with alcoholism increases if alcoholism is related to comorbid depression. Both alcoholism and suicidal behavior are associated with reduced serotonin (5-hydroxytryptamine [5-HT]) function. Because suicide is enormous public health problem worldwide, to prevent suicide attempts, it is important to find peripheral marker of suicidal behavior. The aim of this study was to assess whether platelet 5-HT concentration is altered in alcoholic patients with or without suicide attempt. Platelet 5-HT concentration was evaluated in 397 male and 108 female ethnically homogenous medication-free patients with alcoholism, subdivided according to smoking status, comorbid depression, and a history of suicide attempt and in 450 male and 139 female healthy control (nonsuicidal) subjects. Suicide attempt was assessed by two measures: according to the score 4 on the item 3 from the Hamilton Rating Scale for Depression and according to the Structured Clinical Interview regarding suicidal attempt during lifetime. Both male and female patients with alcoholism who were nonsmokers had significantly lower platelet 5-HT concentration than the corresponding healthy subjects. Multifactor analyses of variance revealed the significant effects of alcoholism and smoking, but the lack of significant effects of suicide attempt, sex, or comorbid depression, and no interactions between variables, on platelet 5-HT concentration. Platelet 5-HT concentration did not differ significantly between suicidal patients compared with nonsuicidal patients with alcoholism. Because the results from the present study showed similar platelet 5-HT values between patients with or without a history of suicide attempt, our data did not support the hypothesis that platelet 5-HT concentration might be used as a peripheral marker of the pronounced suicidal behavior in alcoholism.

Dopamine and serotonin transporter availability in chronic heroin users: a [¹²³I]β-CIT SPECT imaging study

Dopamine (DA) and serotonin (5-HT) transporter availability in heroin users and healthy controls was measured using [¹²³I]β-CIT and SPECT imaging. Heroin users had statistically similar striatal DA and brainstem and diencephalon 5-HT transporter availability compared with controls. No associations between transporter availability and heroin use characteristics were found.

Smoking and suicide: a brief overview

This article provides a brief overview of the rationales, possible mechanisms and epidemiological data on the association of smoking, smoking cessation and cessation medications with suicide. Current smoking is reliably associated with suicide both in case-control and cohort studies. The three most plausible (but relatively untested) explanations for the association are that smokers have pre-existing conditions that increase their risk for suicide, smoking causes painful and debilitating conditions that might lead to suicide, and smoking decreases serotonin and monoamine oxidase levels. Stopping smoking appears to lead to major depression in some smokers; thus, it could induce suicide; however, smoking cessation has not been associated with suicide in the few studies available. Regulatory agencies have stated bupropion, rimonabant and varenicline appear to be associated with suicide; however, the data for these statements have not been presented in sufficient detail to assess their validity. Most prior data have come from post hoc analyses. Studies that a priori focus on understanding smoking and suicide are now needed.

Peri-operative decreased cAMP levels in long-term alcoholic patients

Long-term alcoholic patients have a five-fold higher risk of post-operative bleeding complications compared with nonalcoholic individuals. Serotonin increases and cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) decrease platelet aggregation. We examined the platelet-rich plasma levels of these substances and agonist-induced platelet aggregation in long-term alcoholic patients before and after surgery. Thirty-three consecutive patients (13 long-term alcoholics and 20 non-alcoholics) scheduled for tumour resections of the upper digestive tract were included in the study. The levels of cAMP were significantly decreased before and after surgery in long-term alcoholic patients, but there were no significant differences in cGMP and serotonin levels in alcoholic compared with non-alcoholic patients. In contrast to previous studies, no significantly altered aggregation responses in long-term alcoholics were found. A possible explanation is decreased inhibition through diminished cAMP levels; cGMP and serotonin do not seem to influence peri-operative haemostasis.

Influence of clozapine on platelet serotonin, monoamine oxidase and plasma serotonin levels

The purpose of this study was to investigate the influence of clozapine on plasma serotonin, platelet serotonin and monoamine oxidase (MAO) levels in schizophrenic patients and to compare their results with those of unmedicated healthy controls. Groups of 20 outpatients with schizophrenia and 20 healthy controls matched for age, sex and smoking status were recruited for the study. Psychopathology, neurocognitive functioning, plasma serotonin, platelet serotonin and MAO levels were assessed after 1-week drug free interval, and 8 weeks after initiation of clozapine treatment in an open design. The mean clozapine dose at week 8 was 382.5+/-96.4 (range: 250-600) mg/day. In the patient group, at baseline, plasma serotonin and platelet MAO levels were significantly lower, and platelet serotonin levels were significantly higher than in controls. After 8 weeks of clozapine treatment, plasma serotonin and platelet MAO levels increased significantly, while a significant decrease in platelet serotonin levels was detected compared with baseline values. Baseline platelet MAO levels explained 22% of the variance in Clinical Global Impression - Improvement (CGI-I) and improvement in attention, while baseline platelet serotonin predicted 23% of the variance in the improvement in positive symptoms during clozapine treatment. Our data indicate that clozapine may be reversing or compensating for a pre-existing alteration in serotonergic neurotransmission in schizophrenic patients. The prediction of response to clozapine through peripheral biochemical markers may have important clinical implications if repeated in larger samples.

Elevated platelet vesicular monoamine transporter 2 in former heroin addicts maintained on methadone

The brain vesicular monoamine transporter (VMAT2) is essential for neuronal monoamine storage and regulation of monoaminergic neurotransmission. We demonstrated previously a high degree of similarity between the pharmacodynamic characteristics of platelet and brain VMAT2. Opioids induce increase of dopamine release in limbic structures. In the present study we assessed the VMAT2 pharmacodynamic characteristics using high affinity [(3)H]dihydrotetrabenazine (TBZOH) binding to platelets of former male heroin addicts maintained on methadone (n = 12) compared to age-matched healthy controls (n = 13). A significant increase (19%, p < 0.05) in platelet VMAT2 density (Bmax) was observed in the methadone treated patients compared to controls. There was no significant difference in the affinity of [(3)H]TBZOH to its platelet binding site. The increased VMAT2 density may reflect a compensatory attempt to prevent vesicular depletion due to chronic methadone exposure.

Platelet serotonin concentration in alcoholic subjects

Serotonin (5-hydroxytryptamine, 5-HT) is assumed to play a role in the pathophysiology of different psychiatric disorders including alcoholism. Since platelets and central serotonergic synaptosomes share similar pharmacodynamics of 5-HT, this study determined platelet 5-HT concentration in 148 male and 42 female drug-free subjects with alcohol dependency, according to the DSM-IV criteria, and in sex-and age-matched controls. Male and female alcoholics had significantly lower platelet 5-HT concentration than 110 male and 123 female healthy controls. Sex differences, i.e. higher platelet 5-HT concentration in men than in women, were found both in healthy and alcoholic subjects. Platelet 5-HT concentration differed significantly in male and female alcoholic subjects with or without different psychiatric comorbidities. Platelet 5-HT concentration was higher in male alcoholics with comorbid posttraumatic stress disorder (PTSD) than in male alcoholics with comorbid anxious-depressive disorder, or depression, or male alcoholics without any psychiatric comorbidities. Comorbid depression in female alcoholics slightly elevated platelet 5-HT levels but these values were still reduced compared to values in healthy women. Smoking status did not affect platelet 5-HT concentration either in healthy or in alcoholic subjects. The data from our study show sex differences, and reduced platelet 5-HT values, regardless of the nicotine dependence, in the large groups of male and female alcoholic subjects. Among male alcoholics the presence of comorbid PTSD partly normalized the decreased platelet 5-HT values. The results of the present study support the hypothesis that alterations in 5-HT system might be related to alcoholism.

Alcohol consumption and smoking status: the role of smoking cessation

Cigarette smoking is common among persons with alcohol dependence or abuse with as many as 80% of persons who are alcohol dependent also being smokers. Not only is smoking common in persons with heavy alcohol consumption, but also nicotine dependence appears more severe in smokers with a history of alcohol dependence. This combined exposure to both tobacco smoke and alcohol results in major health consequences including additive risks for some diseases such as head and neck cancers. Although modest alcohol consumption has some positive health benefits, smoking typically negates these benefits. The cellular mechanisms impacted by combined smoking and alcohol exposure are poorly understood, but molecular epidemiology approaches are providing insights regarding the importance of effects on oxidant/antioxidant pathways and on metabolic pathways involving the cytochrome P450 system. Given the prevalence of smoking in the alcohol dependent population, smoking cessation in this group has the potential for tremendous impact. In recent years, smoking cessation approaches have been initiated in this population, but much work remains in order to define the optimal smoking cessation strategies for persons in alcohol treatment programs.

Neuroendocrine correlates of antisocial personality disorder in abstinent heroin-dependent subjects

The function of the central alpha-adrenergic, serotoninergic and dopaminergic systems was investigated in 30 heroin-dependent subjects, 6 - 8 weeks after detoxification and in 22 psychophysically healthy controls (group C). Twelve heroin-dependent subjects with antisocial personality disorder (ASPD) (group A), 18 heroin-dependent subjects without other Axis I and II pathologies (group B) were included among abstinent substance abusers. The norepinephrine (NE) function was evaluated by the GH responses to acute stimulation with clonidine (clon); the serotonin (5-HT) function by the PRL and cortisol (CORT) responses to acute stimulation with d-fenfluramine (d-fen) and the dopamine (DA) function was investigated by growth hormone (GH) and prolactin (PRL) responses to acute administration of bromocriptine (brom). Alpha-adrenergic sensitivity, as measured by the GH-clon test, was found significantly reduced in A subjects (ASPD), in comparison with B subjects and controls. PRL and CORT responses to d-fen were significantly blunted both in A and B subjects, in comparison with control subjects. DA receptors sensitivity seems to be reduced significantly in ASPD (A subjects); in contrast, heroin addicts without open psychiatric co-morbidity showed unimpaired responses to brom challenge; a significantly lower GH response to brom and a lack of PRL suppression in ASPD subjects could express D2 postsynaptic receptor hyposensitivity possibly related to DA gene variants associated to co-morbid disorder. In sum, the study of central monoamine function revealed an alteration of the 5-HT system in all detoxified heroin-dependent subjects. A significant reduction of alpha-adrenergic receptors sensitivity and the hyposensitivity of postsynaptic DA receptors in ASPD subjects suggest once again that specific biological correlates of psychiatric co-morbidity may characterize substance abusers subtypes.

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.

Neuroendocrine correlates of depression in abstinent heroin-dependent subjects

The functions of the central alpha-adrenergic, serotoninergic and dopaminergic systems were investigated in 28 heroin-dependent subjects 6-8 weeks after detoxification, and in 22 healthy control subjects (group C). Fourteen heroin-dependent subjects with depressive comorbidity (group A), and 14 heroin-dependent subjects without other Axis I and II pathologies (group B) were included among abstinent substance abusers. Norepinephrine (NE) function was evaluated by growth hormone (GH) responses to acute stimulation with clonidine (clon); serotonin (5-HT) function by prolactin (PRL) and cortisol (CORT) responses to acute stimulation with D-fenfluramine (D-fen) and dopamine (DA) function by GH and PRL responses to acute administration of bromocriptine (brom). Central NE activity, as measured by the GH-clon test, seems to be well preserved both in A and B subjects. PRL and CORT responses to D-fen were significantly blunted both in A subjects and in B subjects, in comparison with control subjects (C); the PRL response in A subjects was significantly lower than in B subjects. The DA system of B subjects was found unimpaired; in contrast, a significantly higher GH response to brom in A subjects (depressed) could express D2 post-synaptic receptor hypersensitivity and, therefore, decreased pre-synaptic DA release. In sum, the study of central monoamine function revealed an alteration only of the 5-HT system in detoxified heroin-dependent subjects without psychiatric comorbidity, which might be a trait character of these subjects, possibly involved in the pathogenesis of the disorder. A more significant impairment of 5-HT function and the hypersensitivity of post-synaptic DA receptors in A subjects suggests that specific biological correlates of psychiatric comorbidity may characterize substance abuser subtypes.

The stimulating effects of ethanol consumption on synthesis of rat brain monoamine oxidases and their sensitivity to the irreversible inhibitor, pargyline

Administration of a large dose of pargyline (60mg/kg) caused total irreversible inhibition of brain monoamine oxidases (MAOs) in both control and alcoholised rats. During the first 50h the recovery of brain MAO-A (but not MAO-B) activity occurred faster in the alcoholised rats. A low dose of pargyline (10mg/kg) produced significantly higher inhibition of MAO-A in the alcoholised rats, whereas the degree of MAO-B inhibition was the same in both groups. Brain MAOs of control and alcoholised rats exhibited similar sensitivity to pargyline in vitro. Since chronic ethanol feeding reduced the content of reversible endogenous MAO inhibitor, tribulin, higher pargyline-induced inhibition of MAO-A in alcoholised rats may stem from a tribulin deficit. The data obtained suggest that chronic ethanol consumption increases turnover of MAO-A molecules in the brain and reduces the content of endogenous MAO(A) inhibitors.