HTR1A, HTR1B, HTR2A, HTR2C and HTR6 Gene Polymorphisms and Extrapyramidal Side Effects in Haloperidol-Treated Patients with Schizophrenia.

Schizophrenia is a serious, chronic psychiatric disorder requiring lifelong treatment. Extrapyramidal side effects (EPS) are common adverse reactions to antipsychotic medications. In addition to the dopaminergic system, serotonergic mechanisms, including serotonin (5-HT) receptors, might be involved in EPS development. This study aimed to examine molecular associations of HTR1A, HTR1B, HTR2A, HTR2C and HTR6 gene polymorphisms with acute EPS in 229 male schizophrenia patients, following two weeks of haloperidol monotherapy. The Simpson-Angus Rating Scale for Extrapyramidal Side Effects (SAS), Barnes Akathisia Rating Scale (BARS) and Extrapyramidal Symptom Rating Scale (ESRS) were used to evaluate EPS severity. Genotyping was performed using real-time PCR, following extraction of blood DNA. Significant acute EPS appeared in 48.03% of schizophrenia patients. For the rs13212041 HTR1B gene polymorphism, affecting microRNA regulation of HTR1B gene expression, a higher frequency of TT carriers was found among haloperidol-treated patients with akathisia when compared to the group without akathisia symptoms. In comparison to C-allele carriers, patients carrying the TT genotype had higher akathisia severity, as determined by the SAS, BARS and ESRS scales. These molecular findings suggest potential involvement of 5-HT1B receptors in akathisia development following haloperidol treatment, as well as possible epigenetic mechanisms of serotonergic modulation associated with antipsychotic-induced EPS.

Remission Is not Associated with DRD2 rs1800497 and DAT1 rs28363170 Genetic Variants in Male Schizophrenic Patients after 6-months Monotherapy with Olanzapine.

BACKGROUND: Symptomatic remission is an achievable goal in the treatment of schizophrenia. The type of antipsychotic medication and particular genetic variants of the dopaminergic system might be associated with remission. Potential pharmacogenetic markers of the treatment response to antipsychotic medication are missing. This study assessed the possible association between dopamine receptor type 2 (DRD2 rs1800497) and dopamine transporter (DAT1 rs28363170) gene variants with symptomatic remission in schizophrenia. SUBJECTS AND METHODS: Olanzapine (5-20 mg/d) monotherapy was administered for 6 months to 150 male Caucasian subjects with schizophrenia. Remission was evaluated according to "Remission in Schizophrenia Working Group" criteria. Genotyping was performed by PCR-RFLP. RESULTS: Symptomatic remission was found in 31% of patients. DRD2 rs1800497 and DAT1 rs28363170 gene variants were not significantly associated with symptomatic remission. The limitations are a relatively small sample size of patients with schizophrenia (N=150), especially of group with symptomatic remission (N=45). However, the study had moderate but adequate sample sizes for most of the comparisons. Only two dopaminergic polymorphisms were analyzed, and plasma concentration of olanzapine was not determined. CONCLUSION: These results revealed a lack of association between DRD2 rs1800497 and DAT1 rs28363170 genetic variants and symptomatic remission in male patients treated with olanzapine, suggesting that these genetic variants could not be used to predict symptomatic remission to olanzapine monotherapy. Negative results should be further confirmed or rejected in the larger samples, including haplotype analyses, to detect clinically useful and easy obtainable pharmacogenetic markers that might predict therapeutic response or remission in schizophrenia.

Monoaminergic and Histaminergic Strategies and Treatments in Brain Diseases.

The monoaminergic systems are the target of several drugs for the treatment of mood, motor and cognitive disorders as well as neurological conditions. In most cases, advances have occurred through serendipity, except for Parkinson's disease where the pathophysiology led almost immediately to the introduction of dopamine restoring agents. Extensive neuropharmacological studies first showed that the primary target of antipsychotics, antidepressants, and anxiolytic drugs were specific components of the monoaminergic systems. Later, some dramatic side effects associated with older medicines were shown to disappear with new chemical compounds targeting the origin of the therapeutic benefit more specifically. The increased knowledge regarding the function and interaction of the monoaminergic systems in the brain resulting from in vivo neurochemical and neurophysiological studies indicated new monoaminergic targets that could achieve the efficacy of the older medicines with fewer side-effects. Yet, this accumulated knowledge regarding monoamines did not produce valuable strategies for diseases where no monoaminergic drug has been shown to be effective. Here, we emphasize the new therapeutic and monoaminergic-based strategies for the treatment of psychiatric diseases. We will consider three main groups of diseases, based on the evidence of monoamines involvement (schizophrenia, depression, obesity), the identification of monoamines in the diseases processes (Parkinson's disease, addiction) and the prospect of the involvement of monoaminergic mechanisms (epilepsy, Alzheimer's disease, stroke). In most cases, the clinically available monoaminergic drugs induce widespread modifications of amine tone or excitability through neurobiological networks and exemplify the overlap between therapeutic approaches to psychiatric and neurological conditions. More recent developments that have resulted in improved drug specificity and responses will be discussed in this review.

The serotonergic system and cognitive function.

Symptoms of cognitive dysfunction like memory loss, poor concentration, impaired learning and executive functions are characteristic features of both schizophrenia and Alzheimer's disease (AD). The neurobiological mechanisms underlying cognition in healthy subjects and neuropsychiatric patients are not completely understood. Studies have focused on serotonin (5-hydroxytryptamine, 5-HT) as one of the possible cognitionrelated biomarkers. The aim of this review is to provide a summary of the current literature on the role of the serotonergic (5-HTergic) system in cognitive function, particularly in AD and schizophrenia. The role of the 5-HTergic system in cognition is modulated by the activity and function of 5-HT receptors (5-HTR) classified into seven groups, which differ in structure, action, and localization. Many 5-HTR are located in the regions linked to various cognitive processes. Preclinical studies using animal models of learning and memory, as well as clinical in vivo (neuroimaging) and in vitro (post-mortem) studies in humans have shown that alterations in 5-HTR activity influence cognitive performance. The current evidence implies that reduced 5-HT neurotransmission negatively influences cognitive functions and that normalization of 5-HT activity may have beneficial effects, suggesting that 5-HT and 5-HTR represent important pharmacological targets for cognition enhancement and restoration of impaired cognitive performance in neuropsychiatric disorders.

Neurotransmitter measures in the cerebrospinal fluid of patients with Alzheimer's disease: a review.

BACKGROUND: Alzheimer's disease (AD) is a severe neurodegenerative disorder characterized by progressive cognitive and functional decline, as well as by a variety of neuropsychiatric and psychological symptoms and behavioral dysfunctions. Various studies proposed the role of different neurotransmitter systems not only in AD-related cognitive, but also psychotic symptoms and behavioral and emotional deficits. Due to the close proximity, pathological neurochemical changes in brain occurring in AD are likely to be reflected in the cerebrospinal fluid (CSF). The purpose of this review is to provide a summary of the CSF neurotransmitter correlates of AD in order to get further insights into the potential role of altered neurotransmitters in the pathophysiology of AD and to offer novel AD biomarkers. METHODS: PubMed and MEDLINE data bases were searched for English-language articles by using "Alzheimer's disease", "CSF" and "neurotransmitter" as primary terms. No time or article type constraints were applied. Moreover, the lists of references were searched manually for additional articles. RESULTS: Changes in various correlates of cholinergic, monoaminergic and amino acid neurotransmitter systems, as well as neuropeptides, have been observed in CSF of AD patients. However, as the results of these studies have been controversial, the importance of CSF neurotransmitter parameters as potential biomarkers in AD remains quite unclear. The observed discrepancies could be bypassed by implementation of new sensitive methods, such as novel proteomics approaches that include protein separation techniques, mass spectroscopy and targeted multiplex panels of specific analytes. CONCLUSION: Although no individual CSF neurotransmitter correlate was demonstrated as suitable biomarker of AD, a combined profile of several CSF neurochemical parameters might show enhanced sensitivity and specificity and thus contribute to earlier and more accurate diagnosis of AD, crucial for application of effective treatments.

Serotonin risk factors for the development of hypertension in pregnancy.

PURPOSE: To determine platelet serotonin (5-HT) concentrations and genotype and allele frequencies of serotonergic type 2A receptor gene (HTR2A) and 5-HT transporter gene (SLC6A4) in women with pre-eclampsia, gestational hypertension without proteinuria (PIH) and in control normotensive pregnant women. METHODS: The study included 96 control women, 131 women with PIH and 84 women with pre-eclampsia (ICD-10 criteria) in the last trimester of pregnancy. Variants of the HTR2A T102C (rs6313) and SLC6A4 (5-HTTLPR and rs25531) were determined by the PCR and real-time PCR procedures. Platelet 5-HT concentrations were analyzed by the spectrofluorimetric method. RESULTS: The frequency of the 5HTTLPR and of HTR2A T102C genotypes or alleles was similar between three groups of pregnant women and was not associated with low platelet 5-HT concentrations observed in pregnant women with PIH or pre-eclampsia. CONCLUSIONS: The results confirm alterations in the peripheral 5-HT system in pregnancy-induced hypertension. Low platelet 5-HT concentration is a common feature of both PIH and pre-eclampsia. The results did not support the hypothesis that hypertension in pregnancy is a trait associated with polymorphic variants of the HTR2A and SLC6A4 or that they have a role in the predisposition to hypertensive disorders in pregnancy. The further studies are necessary to elucidate the role of 5-HT and genetic factors in the development of hypertensive disorders in pregnancy.

Update on the core and developing cerebrospinal fluid biomarkers for Alzheimer disease.

Alzheimer disease (AD) is a complex neurodegenerative disorder, whose prevalence will dramatically rise by 2050. Despite numerous clinical trials investigating this disease, there is still no effective treatment. Many trials showed negative or inconclusive results, possibly because they recruited only patients with severe disease, who had not undergone disease-modifying therapies in preclinical stages of AD before severe degeneration occurred. Detection of AD in asymptomatic at risk individuals (and a few presymptomatic individuals who carry an autosomal dominant monogenic AD mutation) remains impractical in many of clinical situations and is possible only with reliable biomarkers. In addition to early diagnosis of AD, biomarkers should serve for monitoring disease progression and response to therapy. To date, the most promising biomarkers are cerebrospinal fluid (CSF) and neuroimaging biomarkers. Core CSF biomarkers (amyloid ß1-42, total tau, and phosphorylated tau) showed a high diagnostic accuracy but were still unreliable for preclinical detection of AD. Hence, there is an urgent need for detection and validation of novel CSF biomarkers that would enable early diagnosis of AD in asymptomatic individuals. This article reviews recent research advances on biomarkers for AD, focusing mainly on the CSF biomarkers. In addition to core CSF biomarkers, the potential usefulness of novel CSF biomarkers is discussed.

Association of gene polymorphisms encoding dopaminergic system components and platelet MAO-B activity with alcohol dependence and alcohol dependence-related phenotypes.

The present study aimed to evaluate the association of alcohol dependence and alcohol dependence-related phenotypes with platelet monoamine oxidase type B (MAO-B) activity, Val108/158Met of catechol-o-methyltransferase (COMT), variable number of tandem repeats (VNTR) in the third exon of dopamine receptor D4 (DRD4) gene, VNTR in the 3'-untranslated region of dopamine transporter (DAT) gene, -1021C/T of dopamine beta-hydroxylase (DBH) and MAO-B intron 13 polymorphisms. The study included 1270 Caucasian men and women of Croatian origin: 690 patients with alcohol dependence and 580 healthy controls. Patients with alcohol dependence were subdivided according to the presence or absence of withdrawal symptoms, aggressive behavior, severity of alcohol dependence, delirium tremens, comorbid depression, suicidal behavior, lifetime suicide attempt and early/late onset of alcohol abuse. The results, corrected for multiple testing, revealed increased platelet MAO-B activity in patients with alcohol dependence, subdivided into those with or without alcohol-related liver diseases, compared to control subjects (P<0.001). In addition, we found an increased frequency of the COMT Met/Met genotype among suicidal (P=0.002) and patients who attempted suicide (P<0.001) and an increased frequency of COMT Val/Val genotype in patients with an early onset of alcohol dependence (P=0.004). This study provides data from a sample of ethnically homogeneous unrelated Caucasian subjects for future meta-analyses and suggests that the increased platelet MAO-B activity might be used as independent peripheral indicator of alcohol dependence, while COMT Val108/158Met polymorphism is associated with increased suicidality and early onset of alcohol dependence.

Decreased platelet serotonin concentration in Alzheimer's disease with involuntary emotional expression disorder.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder manifested by progressive decline in cognitive functions. A variety of behavioral disturbances appear very often in AD which might be associated with altered function of serotoninergic system. The aim of the study was to determine platelet serotonin (5-HT) concentrations in 49 patients with AD (NINCDS-ADRDA and DSM-IV-TR criteria) subdivided in three groups: (a) patients with aggressive behavior, (b) patients with involuntary emotional expression disorder (IEED) and (c) patients without aggression or IEED (controls). Platelet 5-HT concentrations were measured using ELISA. Platelet 5-HT concentrations were significantly lower in patients with AD and co-existing IEED compared to AD patients with aggressive behavior or control patients. No significant difference in platelet 5-HT concentrations was found between patients expressing aggressive behavior and controls. Our results suggest disruptions in serotoninergic system in AD patients with comorbid IEED but not with aggressive behavior and support the presumption that platelet 5-HT concentration is a suitable and easy measured peripheral indicator of some behavioral and psychological symptoms of AD.

Association between the brain-derived neurotrophic factor Val66Met polymorphism and therapeutic response to olanzapine in schizophrenia patients.

RATIONALE: Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a major role in neurogenesis and neuroplasticity, and in the modulation of several neurotransmitter systems including the dopaminergic system. There are mixed reports about the association between the BDNF Val66Met polymorphism, schizophrenia, and treatment response to antipsychotic drugs. OBJECTIVES: The present study evaluated the association of the BDNF Val66Met polymorphism with treatment response to atypical antipsychotic olanzapine in schizophrenia and the possible predictive value of the BDNF Val66Met genotype status in treatment response to antipsychotic medication. METHODS: The study included 590 ethnically homogenous Caucasian patients with schizophrenia (diagnosed using the SCID), 40.2 ± 12.0 years old, treated with olanzapine monotherapy (10-20 mg/day), or with other antipsychotics such as risperidone (3-6 mg/day), clozapine (100-500 mg/day), haloperidol (3-115 mg/day), fluphenazine (4-25 mg/day), and quetiapine (50-800 mg/day). Patients were subdivided into responders and non-responders according to a 50 % reduction in the Positive and Negative Syndrome Scale (PANSS) total and subscale scores after 8 weeks of treatment. RESULTS: The results, corrected for possible effects of gender and age, showed a significant association between the BDNF Val66Met polymorphism and treatment response to olanzapine in patients. The Val/Val genotype was observed more frequently in treatment responders to olanzapine, and this genotype was associated with an improvement in clinical symptoms. CONCLUSIONS: Our results suggest that BDNF Val66Met variants might influence the response to 8 weeks of monotherapy with olanzapine, in a relatively large sample of patients with schizophrenia.

The association study of polymorphisms in DAT, DRD2, and COMT genes and acute extrapyramidal adverse effects in male schizophrenic patients treated with haloperidol.

Extrapyramidal symptoms (EPSs) are common adverse effects of antipsychotics. The development of acute EPSs could depend on the activity of dopaminergic system and its gene variants. The aim of this study was to determine the association between dopaminergic type 2 receptor (DRD2) dopamine transporter (SLC6A3) and catechol-O-methyltransferase (COMT) gene polymorphisms and acute EPSs in 240 male schizophrenic patients treated with haloperidol (15-mg/d) over a period of 2 weeks. Acute EPSs were assessed with Simpson-Angus Scale. Three dopaminergic gene polymorphisms, the DRD2 Taq1A, the SLC6A3 VNTR, and the COMT Val158Met, were determined. Extrapyramidal symptoms occurred in 116 (48.3%) of patients. Statistically significant associations were found for SLC6A3 VNTR and COMT Val158Met polymorphisms and EPS susceptibility. Patients with SLC6A3 9/10 genotype had almost twice the odds to develop EPSs compared with those with all other SLC6A3 genotypes (odds ratio, 1.9; 95% confidence interval, 1.13-3.30), and patients with COMT Val/Met genotype had 1.7 times greater odds to develop EPSs than those with all other COMT genotypes (odds ratio, 1.7; 95% confidence interval, 1.01-2.88). There was no statistically significant association between genotype and allele frequencies of DRD2, SLC6A3, or COMT polymorphisms and the development of particular EPSs.In conclusion, the results of the present study showed for the first time the association between acute haloperidol-induced EPSs and SLC6A3 VNTR and COMT Val158Met polymorphisms. Although the precise biological mechanisms underlying these findings are not yet understood, the results suggest that the dopaminergic gene variations could predict the vulnerability to the development of the acute EPSs in haloperidol-treated schizophrenic patients.

Lack of association between brain-derived neurotrophic factor Val66Met polymorphism and body mass index change over time in healthy adults.

Obesity is becoming the epidemic health problem worldwide with a very complex etiology. The interaction between diverse genetic and environmental factors contributes to development of obesity. Among myriad of functions in central and peripheral tissues, brain-derived neurotrophic factor (BDNF) also regulates energy homeostasis, food intake and feeding behavior, and has a role in obesity and increased body mass index (BMI). BDNF Val66Met (rs6265) polymorphism is associated with BMI gain, but both positive associations and non-replications are reported. Since BMI changes over time and since genetic influences on BMI vary with age, the aim of the study was to evaluate association between BDNF Val66Met polymorphism and BMI gain in healthy subjects with middle or old age. The study included a cohort of 339 adult healthy Caucasians of Croatian origin, free of eating and metabolic disorders, evaluated in three time periods in the year 1972, 1982 and 2006, when the subjects were around 40, 50 and 70 years old, respectively. The results revealed a significant effect of smoking on BMI, but a lack of significant association between BDNF Val66Met polymorphism and overweight or obesity, and no significant association between BDNF Val66Met and BMI changes over time. These results did not confirm the major role of BDNF Val66Met in the regulation of BMI changes in adult and old healthy subjects.

The association between the catechol-O-methyltransferase Val108/158Met polymorphism and hyperactive-impulsive and inattentive symptoms in youth.

RATIONALE: Hyperactivity, impulsivity, and inattention are major symptoms occurring in attention-deficit/hyperactivity disorder. This disorder is highly heritable, multifactorial, polygenic, and associated primarily with dysfunctions of dopaminergic, noradrenergic, and serotonergic systems. OBJECTIVES: The present study tested the possible association of the catechol-O-methyltransferase (COMT) Val108/158Met (rs4680) polymorphism with hyperactive-impulsive and inattentive symptoms in male youth. METHOD: Polymorphism COMT Val108/158Met was analyzed in 807 male unrelated Caucasian young subjects: 231 healthy controls, 195 subjects with moderate hyperactive symptoms and 254 subjects with moderate inattentive symptoms, 111 subjects with severe hyperactive symptoms and 90 subjects with severe inattentive symptoms, all evaluated using Swanson, Nolan, and Pelham Questionnaire IV criteria. RESULTS: The frequency of the COMT genotypes, alleles, and the homozygous Met/Met genotype versus Val carriers (χ²) test with standardized residuals) differed significantly between subjects without and subjects with hyperactive-impulsive and inattentive symptoms. In addition, significantly higher hyperactive-impulsive and inattentive scores were found in subjects with the Met/Met genotype compared to carriers of other COMT genotypes. These significant results were due to the more frequent occurrence of Met/Met genotype or the Met allele in subjects with moderate and severe hyperactive-impulsive and inattentive symptoms compared to matched controls. CONCLUSION: These results suggest that the Met/Met genotype or the Met allele of the COMT Val108/158Met, contributing to higher dopaminergic activity, are significantly overrepresented in subjects with moderate or severe hyperactive-impulsive and inattentive symptoms, and that this polymorphism is significantly associated with hyperactive-impulsive and inattentive symptoms in young boys and adolescents.

The lack of association between components of metabolic syndrome and treatment resistance in depression.

RATIONALE: Although a number of studies investigated the link between major depressive disorder (MDD) and metabolic syndrome (MetS), the association between MetS and treatment-resistant depression (TRD) is still not clear. OBJECTIVES: The aim of the study was to investigate the relationship between TRD and MetS and/or components of MetS and cardiovascular risk factors. Given the high prevalence of both conditions, the hypothesis was that TRD would be significantly associated with MetS. METHODS: This cross-sectional study included 203 inpatients with MDD, assessed for the treatment resistance, MetS and its components, and severity of MDD. Diagnoses and evaluations were made with SCID based on DSM-IV, National Cholesterol Education Program Adult Treatment Panel III criteria, and the Hamilton Depression Rating Scale. RESULTS: TRD prior to study entry was found in 26.1 % of patients, while MetS was observed in 33.5 % of patients. The prevalence of MetS did not differ significantly between TRD and non-TRD patients. In addition, the frequency of the altered values of particular components of the MetS or cardiovascular risk factors was not associated with treatment resistance in depressed patients. Patients with TRD were older, had a higher number of lifetime episodes of depression and suicide attempts, and longer duration of MDD compared to non-TRD patients. CONCLUSIONS: The occurrence of either MetS or the particular components of the MetS and other cardiovascular risk factors was similar between TRD and non-TRD patients. Although there is a bidirectional relationship between depression and MetS, neither MetS nor its components appear to influence treatment resistance to antidepressants.

Genotype-independent decrease in plasma dopamine beta-hydroxylase activity in Alzheimer's disease.

The noradrenergic system is involved in the etiology and progression of Alzheimer's disease (AD) but its role is still unclear. Dopamine beta-hydroxylase (DBH) as a catecholamine-synthesizing enzyme plays a central role in noradrenaline (NA) synthesis and turnover. Plasma DBH (pDBH) activity shows wide inheritable interindividual variability that is under genetic control. The aim of this study was to determine pDBH activity, DBH (C-970T; rs1611115) and DBH (C1603T; rs6271) gene polymorphisms in 207 patients with AD and in 90 healthy age-matched controls. Plasma DBH activity was lower, particularly in the early stage of AD, compared to values in middle and late stages of the disease, as well as to control values. Two-way ANOVA revealed significant effect of both diagnosis and DBH (C-970T) or DBH (C1603T) genotypes on pDBH activity, but without significant diagnosis×genotype interaction. No association was found between AD and DBH C-970T (OR=1.08, 95% CI 1.13-4.37; p=0.779) and C1603T (OR=0.89; 95% CI 0.36-2.20; p=0.814) genotypes controlled for age, gender, and ApoE4 allele. The decrease in pDBH activity, found in early phase of AD suggests that alterations in DBH activity represent a compensatory mechanism for the loss of noradrenergic neurons, and that treatment with selective NA reuptake inhibitors may be indicated in early stages of AD to compensate for loss of noradrenergic activity in the locus coeruleus.

Brain-derived neurotrophic factor Val66Met polymorphism and alcohol-related phenotypes.

Alcoholism is a chronic psychiatric disorder affecting neural pathways that regulate motivation, stress, reward and arousal. Brain-derived neurotrophic factor (BDNF) regulates mood, response to stress and interacts with neurotransmitters and stress systems involved in reward pathways and addiction. Aim of the study was to evaluate the association between a single nucleotide polymorphism (BDNF Val66Met or rs6265) and alcohol related phenotypes in Caucasian patients. In ethnically homogenous Caucasian subjects of the Croatian origin, the BDNF Val66Met genotype distribution was determined in 549 male and 126 female patients with alcohol dependence and in 655 male and 259 female healthy non-alcoholic control subjects. Based on the structured clinical interview, additional detailed clinical interview, the Brown-Goodwin Scale, the Hamilton Rating Scale for Depression and the Clinical Global Impression scores, alcoholic patients were subdivided into those with or without comorbid depression, aggression, delirium tremens, withdrawal syndrome, early/late onset of alcohol abuse, prior suicidal attempt during lifetime, current suicidal behavior, and severity of alcohol dependence. The results showed no significant association between BDNF Val66Met variants and alcohol dependence and/or any of the alcohol related phenotypes in either Caucasian women, or men, with alcohol dependence. There are few limitations of the study. The overall study sample size was large (N=1589) but not well-powered to detect differences in BDNF Val66Met genotype distribution between studied groups. Healthy control women were older than female alcoholic patients. Only one BDNF polymorphism (rs6265) was studied. In conclusion, these data do not support the view that BDNF Val66Met polymorphism correlates with the specific alcohol related phenotypes in ethnically homogenous medication-free Caucasian subjects with alcohol dependence.

The involvement of noradrenergic mechanisms in the suppressive effects of diazepam on the hypothalamic-pituitary-adrenal axis activity in female rats.

AIM: To elucidate the involvement of noradrenergic system in the mechanism by which diazepam suppresses basal hypothalamic-pituitary-adrenal (HPA) axis activity. METHODS: Plasma corticosterone and adrenocorticotropic hormone (ACTH) levels were determined in female rats treated with diazepam alone, as well as with diazepam in combination with clonidine (α(2)-adrenoreceptor agonist), yohimbine (α(2)-adrenoreceptor antagonist), alpha-methyl-p-tyrosine (α-MPT, an inhibitor of catecholamine synthesis), or reserpine (a catecholamine depleting drug) and yohimbine. RESULTS: Diazepam administered in a dose of 2.0 mg/kg suppressed basal HPA axis activity, ie, decreased plasma corticosterone and ACTH levels. Pretreatment with clonidine or yohimbine failed to affect basal plasma corticosterone and ACTH concentrations, but abolished diazepam-induced inhibition of the HPA axis activity. Pretreatment with α-MPT, or with a combination of reserpine and yohimbine, increased plasma corticosterone and ACTH levels and prevented diazepam-induced inhibition of the HPA axis activity. CONCLUSION: The results suggest that α(2)-adrenoreceptors activity, as well as intact presynaptic noradrenergic function, are required for the suppressive effect of diazepam on the HPA axis activity.