Regulation of 5-HT receptors and the hypothalamic-pituitary-adrenal axis. Implications for the neurobiology of suicide

Nutrient insufficiencies and deficiencies involved in the pathogenesis of bruxism (Review)

Stress has been well-documented to have a significant role in the etiopathogenesis of bruxism. Activation of the hypothalamic-pituitary-adrenal axis (HPA) and subsequent release of corticosteroids lead to increased muscle activity. Neurological studies have demonstrated that chronic stress exposure induces neurodegeneration of important neuronal structures and destabilization of the mesocortical dopaminergic pathway. These disruptions impair the abilities to counteract the overactivity of the HPA axis and disinhibit involuntary muscle activity, while at the same time, there is activation of the amygdala. Recent evidence shows that overactivation of the amygdala under stressful stimuli causes rhythmic jaw muscle activity by over activating the mesencephalic and motor trigeminal nuclei. The present review aimed to discuss the negative effects of certain vitamin and mineral deficiencies, such as vitamin D, magnesium, and omega-3 fatty acids, on the central nervous system. It provides evidence on how such insufficiencies may increase stress sensitivity and neuromuscular excitability and thereby reduce the ability to effectively respond to the overactivation of the sympathetic nervous system, and also how stress can in turn lead to these insufficiencies. Finally, the positive effects of individualized supplementation are discussed in the context of diminishing anxiety and oxidative stress, neuroprotection and in the reversal of neurodegeneration, and also in alleviating/reducing neuromuscular symptoms.

Suicide: Allostatic regulation and resilience

Suicide is a complex public health problem that is the result of a number of intertwined biopsychosocial factors. The diathesis-stress model suggests that suicide is the result of an interaction between genetic vulnerability and environmental stressors. Chronic stress and trauma contribute to biologic adaptations, including hypothalamus-pituitary-adrenal axis dysregulation, that contribute to the degradation of regulatory mechanisms and promote wear and tear the body, represented by allostatic load (AL). AL has been associated with a number of negative outcomes, including mental health problems and suicide. Fortunately, there are pharmacological and non-pharmacological interventions that are effective at reducing AL and reversing its effects. Thus, AL may provide a construct for supporting early risk identification, prevention, and treatment of suicide. AL biomarkers that are amenable to measurable change, effective treatments to reduce AL and perhaps help prevent suicide, and how to best tailor them to the individual and societal levels are important avenues of therapeutic inquiry.

Research on potential biomarker correlates for suicidal behavior: A review

Suicide is a world health priority. Studies over the last few decades have revealed the complexity underlying the neurobiological mechanisms of suicide. Researchers have found dysregulations in the serotonergic system, the stress system, neural plasticity, lipid metabolism, and cell signaling pathways in relation to suicidal behaviors. These findings have provided more insight into the final path leading to suicide, at which medical intervention should be applied to prevent the action. However, because these molecular mechanisms have been implicated in both depression and suicide, the specificity of the mechanisms has been obscured. In this review, we summarize the main findings of studies on molecular mechanisms of suicidal behavior from the last 2 decades, with particular emphasis on the potential, independent role of each mechanism that is not contingent upon an underlying psychopathology, such as depression. The act of suicide is multifactorial; no single molecular mechanism is sufficient to fully account for the act. Knowledge of the reciprocal interactions among these molecular mechanisms and studying them in the context of brain circuitry by using neuroimaging techniques will provide a better understanding of the neurobiology of suicide.

Adrenergic and noradrenergic regulation of poultry behavior and production

Norepinephrine and epinephrine (noradrenaline and adrenaline) are integral in maintaining behavioral and physiological homeostasis during both aversive and rewarding events. They regulate the response to stressful stimuli through direct activation of adrenergic receptors in the central and sympathetic nervous systems, hormonal activity and through the interaction of the brain, gut, and microbiome. The multiple functions of these catecholamines work synergistically to prepare an individual for a "fight or flight" response. However, hyper-reactivity of this system can lead to increased fearfulness and aggression, decreased health and productivity, and a reduction in overall well-being. Behaviors, such as aggression and certain fear-related behaviors, are a serious problem in the poultry industry that can lead to injury and cannibalism. For decades, catecholamines have been used as a measure of stress in animals. However, few studies have specifically targeted the adrenergic systems as means to reduce behaviors that are damaging or maladapted to their rearing environments and improve animal well-being. This article attempts to address our current understanding of specific, adrenergic-regulated behaviors that impact chicken well-being and production.

Multi-Level Risk Factors for Suicidal Ideation Among at-Risk Adolescent Females: The Role of Hypothalamic-Pituitary-Adrenal Axis Responses to Stress

Adopting a multi-level approach, this study examined risk factors for adolescent suicidal ideation, with specific attention to (a) hypothalamic-pituitary-adrenal (HPA) axis stress responses and (b) the interplay between HPA-axis and other risk factors from multiple domains (i.e., psychological, interpersonal and biological). Participants were 138 adolescent females (M(age) = 14.13 years, SD = 1.40) at risk for suicidal behaviors. At baseline, lifetime suicidal ideation and a number of risk factors were assessed (i.e., depressive symptoms, impulsiveness, pubertal status and peer stress). Participants were exposed to a psychosocial stress task and HPA-axis responses were assessed by measuring cortisol levels pre- and post-stressor. At 3 months post-baseline, suicidal ideation again was assessed. Using group-based trajectory modeling, three groups of cortisol stress-response patterns were identified (i.e., hyporesponsive, normative, and hyperresponsive). As compared to females in the normative and hyporesponsive group, females in the hyperresponsive group were more likely to report a lifetime history of suicidal ideation at baseline, above and beyond the effects of the other predictors. Moreover, as compared to females in the normative group, females in the hyperresponsive group were at increased risk for reporting suicidal ideation 3 months later, after controlling for prior ideation. No interactions between cortisol group and the other risk factors were significant, with the exception of a non-significant trend between impulsiveness and cortisol group on lifetime suicidal ideation. Findings highlight the importance of HPA-axis responses to acute stressors as a risk factor for suicidal ideation among adolescents.

Role of 5-HT3 receptor on food intake in fed and fasted mice

Background

Many studies have shown that 5-hydroxytryptamine (5-HT) receptor subtypes are involved in the regulation of feeding behavior. However, the relative contribution of 5-HT₃ receptor remains unclear. The present study was aimed to investigate the role of 5-HT₃ receptor in control of feeding behavior in fed and fasted mice.

Methodology/Principal Findings

Food intake and expression of c-Fos, tyrosine hydroxylase (TH), proopiomelanocortin (POMC) and 5-HT in the brain were examined after acute treatment with 5-HT₃ receptor agonist SR-57227 alone or in combination with 5-HT₃ receptor antagonist ondansetron. Food intake was significantly inhibited within 3 h after acute treatment with SR 57227 in fasted mice but not fed mice, and this inhibition was blocked by ondansetron. Immunohistochemical study revealed that fasting-induced c-Fos expression was further enhanced by SR 57227 in the brainstem and the hypothalamus, and this enhancement was also blocked by ondansetron. Furthermore, the fasting-induced downregulation of POMC expression in the hypothalamus and the TH expression in the brain stem was blocked by SR 57227 in the fasted mice, and this effect of SR 57227 was also antagonized by ondansetron.

Conclusion/Significance

Taken together, our findings suggest that the effect of SR 57227 on the control of feeding behavior in fasted mice may be, at least partially, related to the c-Fos expression in hypothalamus and brain stem, as well as POMC system in the hypothalamus and the TH system in the brain stem.

Depressed suicidal adolescent males have an altered cortisol response to a pharmacological challenge

Dysregulation of the HPA axis and the dysfunction of the central serotonin (5HT) system are the most replicated biomarkers of depression and suicidal ideation and behavior. However, few studies have examined the two systems simultaneously. In this study, cortisol response was measured in depressed adolescents, following the administration of a central serotonin receptor agonist, meta-chlorphenylpiprazine (mCPP). Adolescents with major depression (MDD; n = 44; males = 15, females = 29; mean age ± SD = 15.5 ± 1.5) were divided into two groups: non-suicidal or those who reported passive suicidal ideation (n = 21), and those who had either threatened suicide or engaged in suicidal acts (n = 23). Sequential infusions of normal saline and mCPP were administered, and serial blood samples were collected for cortisol response. A differential time by group pattern of cortisol response following mCPP was found in the entire group (F(6,242) = 2.6, p=0.018). However, this was mostly attributed to males (F(6,73) = 2.3, p = 0.043) who had threatened or engaged in suicidal acts and displayed a higher cortisol response at 10 and 25 min after the infusion of mCPP, which was not affected by the severity of depression. This differential pattern of cortisol secretion in response to a serotonergic agonist may be a biomarker for more severe forms of suicidal ideation and behavior in adolescent males.

5-HT(1A) [corrected] receptors in mood and anxiety: recent insights into autoreceptor versus heteroreceptor function

RATIONALE

Serotonin (5-HT) neurotransmission is intimately linked to anxiety and depression and a diverse body of evidence supports the involvement of the main inhibitory serotonergic receptor, the serotonin-1A (5-HT(1A)) subtype, in both disorders.

OBJECTIVES

In this review, we examine the function of 5-HT(1A) receptor subpopulations and re-interpret our understanding of their role in mental illness in light of new data, separating both spatial (autoreceptor versus heteroreceptor) and the temporal (developmental versus adult) roles of the endogenous 5-HT(1A) receptors, emphasizing their distinct actions in mediating anxiety and depression-like behaviors.

RESULTS

It is difficult to unambiguously distinguish the effects of different populations of the 5-HT(1A) receptors with traditional genetic animal models and pharmacological approaches. However, with the advent of novel genetic systems and subpopulation-selective pharmacological agents, direct evidence for the distinct roles of these populations in governing emotion-related behavior is emerging.

CONCLUSIONS

There is strong and growing evidence for a functional dissociation between auto- and heteroreceptor populations in mediating anxiety and depressive-like behaviors, respectively. Furthermore, while it is well established that 5-HT(1A) receptors act developmentally to establish normal anxiety-like behaviors, the developmental role of 5-HT(1A) heteroreceptors is less clear, and the specific mechanisms underlying the developmental role of each subpopulation are likely to be key elements determining mood control in adult subjects.

Altered expression of synapse and glutamate related genes in post-mortem hippocampus of depressed subjects

Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.

Gene expression changes in the prefrontal cortex, anterior cingulate cortex and nucleus accumbens of mood disorders subjects that committed suicide

Suicidal behaviors are frequent in mood disorders patients but only a subset of them ever complete suicide. Understanding predisposing factors for suicidal behaviors in high risk populations is of major importance for the prevention and treatment of suicidal behaviors. The objective of this project was to investigate gene expression changes associated with suicide in brains of mood disorder patients by microarrays (Affymetrix HG-U133 Plus2.0) in the dorsolateral prefrontal cortex (DLPFC: 6 Non-suicides, 15 suicides), the anterior cingulate cortex (ACC: 6NS, 9S) and the nucleus accumbens (NAcc: 8NS, 13S). ANCOVA was used to control for age, gender, pH and RNA degradation, with P≤0.01 and fold change±1.25 as criteria for significance. Pathway analysis revealed serotonergic signaling alterations in the DLPFC and glucocorticoid signaling alterations in the ACC and NAcc. The gene with the lowest p-value in the DLPFC was the 5-HT2A gene, previously associated both with suicide and mood disorders. In the ACC 6 metallothionein genes were down-regulated in suicide (MT1E, MT1F, MT1G, MT1H, MT1X, MT2A) and three were down-regulated in the NAcc (MT1F, MT1G, MT1H). Differential expression of selected genes was confirmed by qPCR, we confirmed the 5-HT2A alterations and the global down-regulation of members of the metallothionein subfamilies MT 1 and 2 in suicide completers. MTs 1 and 2 are neuro-protective following stress and glucocorticoid stimulations, suggesting that in suicide victims neuroprotective response to stress and cortisol may be diminished. Our results thus suggest that suicide-specific expression changes in mood disorders involve both glucocorticoids regulated metallothioneins and serotonergic signaling in different regions of the brain.

Extracellular signal-regulated kinase 2 signaling in the hippocampal dentate gyrus mediates the antidepressant effects of testosterone

BACKGROUND

Human and animal studies suggest that testosterone may have antidepressant effects. In this study, we sought to investigate the molecular mechanisms underlying the antidepressant effects of testosterone within the hippocampus, an area that is fundamental in the etiology of depression.

METHODS

The effects of testosterone replacements in gonadectomized adult male rats were investigated using the sucrose preference and forced swim tests. We explored possible effects of testosterone on hippocampal neurogenesis and gene expression of stress-related molecules. Through the use of viral vectors, we pursued the antidepressant molecular mechanism(s) of testosterone in mediating anhedonia and manipulated extracellular signal-regulated kinase 2 (ERK2) expression in the dentate gyrus in gonadectomized rats with testosterone replacements.

RESULTS

Testosterone had antidepressant effects, likely mediated by aromatization to estrogen metabolites, in the sucrose preference and forced swim tests despite having no effects on hippocampal cell proliferation or survival. We found a testosterone-dependent regulation of hippocampal ERK2 expression. Functionally, reducing ERK2 activity within the dentate gyrus induced anhedonia in gonadectomized rats receiving testosterone supplementation, whereas the overexpression of ERK2 rescued this behavior in gonadectomized rats.

CONCLUSIONS

These results implicate a role for ERK2 signaling within the dentate gyrus area of the hippocampus as a key mediator of the antidepressant effects of testosterone.

Implications of hypothalamic-pituitary-adrenal axis functioning in posttraumatic stress disorder

BACKGROUND

Cortisol secretions serve as the barometer of the hypothalamic-pituitary-adrenal (HPA) axis, which regulates and controls responses to stress. Studies of cortisol secretions in patients with posttraumatic stress disorder (PTSD) reveal inconsistent results.

PURPOSE

Current research on HPA axis functioning in PTSD is examined to elucidate the neuroendocrine contributions in the disorder, identify current treatment's impact on the HPA axis, and consider implications for nursing care and areas for future research.

FINDINGS

There is evidence for HPA dysregulation in PTSD, which contributes to widespread impairment in functions such as memory and stress reactivity and to physical morbidity via processes such as allostatic load. There is limited, but building, evidence that dehydroepiandrosterone (DHEA), which is released simultaneously with cortisol, may provide anti-glucocorticoid and neuroprotective effects.

CONCLUSION

Current treatments such as selective serotonin reuptake inhibitors and psychotherapy may have a beneficial impact on the HPA axis in PTSD populations. Somatic approaches to treating PTSD have not yet been studied in relation to their impact on HPA axis parameters in PTSD patients. Treatment studies of DHEA or glucocorticoids have not yet used HPA axis endpoints. PTSD treatment studies that include measures of HPA axis target mechanisms and consider HPA axis regulation as an additional treatment outcome are warranted.

Alterations on monoamines concentration in rat hippocampus produced by lipoic acid

The purposes of the present study were to verify monoamines (dopamine (DA), norepinephrine (NE), serotonin (5-HT)), and their metabolites (3,4-hydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA)) contents in rat hippocampus after lipoic acid (LA) administration. Wistar rats were treated with 0.9% saline (i.p., control group) and LA (10, 20 or 30 mg/kg, i.p., LA10, LA20 and LA30 groups, respectively). After the treatments all groups were observed for 24 h. The NE and DA levels were increased only in 20 mg/kg dose of LA in rat hippocampus. Serotonin content and in their metabolite 5-HIAA levels was decreased in same dose of LA. On the other hand, in DOPAC and HVA levels did not show any significant change. The alterations in hippocampal monoamines can be suggested as a possible of brain mechanism of action from this antioxidant. The outcome of the study may have therapeutic implications in the treatment of neurodegenerative diseases.

Stress, genetics and epigenetic effects on the neurobiology of suicidal behavior and depression

Alterations in a number of neurobiological systems have been associated with suicidal behavior including the serotonergic and noradrenergic systems and the hypothalamic-pituitary-adrenal axis. Altered functioning of these systems may stem from both genetic and developmental causes. Adversity in early-life has developmental consequences on these systems that persist into adulthood. Genetic differences may also contribute to alterations in functioning of neurobiological systems. Moreover, the interaction of early-life experiences of adversity and genetic vulnerability is increasingly thought to play a role, including via epigenetic mechanisms.

Lipoic acid effects on lipid peroxidation level, superoxide dismutase activity and monoamines concentration in rat hippocampus

The purposes of the present work were to verify lipid peroxidation level, superoxide dismutase (SOD) activity and monoamines (dopamine (DA), norepinephrine (NE), serotonin (5-HT)), and their metabolites (3,4-hydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA)) contents in rat hippocampus after lipoic acid (LA) administration. Wistar rats were treated with 0.9% saline (i.p., control group) and LA (10, 20 or 30 mg/kg, i.p., LA10, LA20 and LA30 groups, respectively). After the treatments all groups were observed for 24h. In LA20 group only there was a significant decrease in lipid peroxidation level. However, no alteration was observed in SOD activity in groups treated with LA. The NE and DA levels were increased only in 20mg/kg dose of LA in rat hippocampus. Serotonin content and their metabolite 5-HIAA levels was decreased in same dose of LA. On the other hand, DOPAC and HVA levels did not show any significant change. The reduction in lipid peroxidation level and alterations in hippocampal monoamines can be suggested as a possible brain mechanism from this antioxidant. The outcome of the study may have therapeutic implications in the neurodegenerative diseases.

Influence of sex and corticotropin-releasing factor pathways as determinants in serotonin sensitivity

Stress sensitivity and sex are predictive factors in affective disorder susceptibility. Serotonin (5-HT) pathway recruitment by corticotropin-releasing factor (CRF) during stress is necessary in adaptive coping behaviors, but sex differences in such responses have not been investigated. Using selective 5-HT reuptake inhibitor (SSRI) administration to acutely elevate 5-HT in a genetic model of stress sensitivity, we examined behavioral and physiological responses in male and female stress-sensitive CRF receptor-2-deficient (R2KO) mice. Chronic SSRI treatment was used to confirm outcomes were specific to acute 5-HT elevation and not antidepressant efficacy. We hypothesized that R2KO mice would show a greater sensitivity to acute changes in 5-HT and that, because females typically are more stress sensitive, R2KO females would be the most responsive. Our results supported this hypothesis because females of both genotypes and R2KO males showed a greater sensitivity to an acute 10 mg/kg dose of citalopram in a tail suspension test, displaying decreased immobile time and increased latency to immobility. Furthermore, acute citalopram promoted significant anxiogenic-like effects that were specific to R2KO females in the elevated plus maze and light-dark box tests. Chronic citalopram did not produce these behavioral changes, supporting specificity to acute 5-HT modulation. Mechanistically, females had decreased hippocampal 5-HT transporter (SERT) levels, whereas R2KO mice showed reduced SERT in the prefrontal cortex, supporting a possible intersection of sex and genotype where R2KO females would have the lowest SERT to be blocked by the SSRI. This sensitivity to 5-HT-mediated anxiety in females may underlie a heightened vulnerability to stress-related affective disorders.

Differential regulation of the serotonin 1 A transcriptional modulators five prime repressor element under dual repression-1 and nuclear-deformed epidermal autoregulatory factor by chronic stress

Chronic stress is known to affect brain areas involved in learning and emotional responses. These changes, thought to be related to the development of cognitive deficits are evident in major depressive disorder and other stress-related pathophysiologies. The serotonin-related transcription factors (Freud-1/CC2D1A; five prime repressor element under dual repression/coiled-coil C2 domain 1a, and NUDR/Deaf-1; nuclear-deformed epidermal autoregulatory factor) are two important regulators of the 5-HT1A receptor. Using Western blotting and quantitative real-time polymerase chain reaction (qPCR) we examined the expression of mRNA and proteins for Freud-1, NUDR, and the 5-HT1A receptor in the prefrontal cortex (PFC) of male rats exposed to chronic restraint stress (CRS; 6 h/day for 21 days). After 21 days of CRS, significant reductions in both Freud-1 mRNA and protein were observed in the PFC (36.8% and 32%, respectively; P<0.001), while the levels of both NUDR protein and mRNA did not change significantly. Consistent with reduced Freud-1 protein, 5-HT1A receptor mRNA levels were equally upregulated in the PFC, while protein levels actually declined, suggesting post-transcriptional receptor downregulation. The data suggest that CRS produces distinct alterations in the serotonin system specifically altering Freud-1 and the 5-HT1A receptor in the PFC of the male rat while having no effect on NUDR. These results point to the importance of understanding the mechanism for the differential regulation of Freud-1 and NUDR in the PFC as a basis for understanding the related effects of chronic stress on the serotonin system (serotonin-related transcription factors) and stress-related disorders like depression.

Screening for maternal depression in the neonatal ICU

Postpartum depression is common in women with infants in the neonatal ICU. Maternal depression can affect infant health and development adversely. A screening program for depression in the neonatal ICU could identify women who have depressive symptoms and facilitate their referral for follow-up services.

Decline in serotonergic firing activity and desensitization of 5-HT1A autoreceptors after chronic unpredictable stress

Chronic stressful life events are risk factors for contracting depression, the pathophysiology of which is strongly associated with impairments in serotonergic (5-HT) neurotransmission. Indeed, in rodents, exposure to chronic unpredictable stress (CUS) produces depressive-like behaviours such as behavioural despair and anhedonia. To date, there have not been many studies that especially explore in vivo changes in 5-HT neurotransmission associated with CUS in the rat. Therefore, using in vivo electrophysiology, we evaluated whether CUS that induces anhedonia-like behaviours concurrently impairs midbrain raphe 5-HT neuronal activity. Unlike unstressed and acutely stressed rats, CUS produced progressive reductions in sucrose intake and preference (anhedonia-like). These were associated with a decrease in the spontaneous firing activity (35.4%) as well as in the number of spontaneously active 5-HT neurons, and a desensitization of somatodendritic 5-HT1A autoreceptors in the dorsal raphe. These results suggest that CUS dramatically decreases 5-HT neural activity and 5-HT1A autoreceptor sensitivity, and may represent endophenotypic features of depressive-like states.

Neurotrophin receptor activation and expression in human postmortem brain: effect of suicide

BACKGROUND

The physiological functions of neurotrophins occur through binding to two receptors: pan75 neurotrophin receptor (p75(NTR)) and a family of tropomyosin receptor kinases (Trks A, B, and C). We recently reported that expression of neurotrophins and TrkB were reduced in brains of suicide subjects. This study examines whether expression and activation of Trk receptors and expression of p75(NTR) are altered in brain of these subjects.

METHODS

Expression levels of TrkA, B, C, and of p75(NTR) were measured by quantitative reverse transcription polymerase chain reaction and Western blot in prefrontal cortex (PFC) and hippocampus of suicide and normal control subjects. The activation of Trks was determined by immunoprecipitation followed by Western blotting using phosphotyrosine antibody.

RESULTS

In hippocampus, lower mRNA levels of TrkA and TrkC were observed in suicide subjects. In the PFC, the mRNA level of TrkA was decreased, without any change in TrkC. However, the mRNA level of p75(NTR) was increased in both PFC and hippocampus. Immunolabeling studies showed similar results as observed for the mRNAs. In addition, phosphorylation of all Trks was decreased in hippocampus, but in PFC, decreased phosphorylation was noted only for TrkA and B. Increased expression ratios of p75(NTR) to Trks were also observed in PFC and hippocampus of suicide subjects.

CONCLUSIONS

Our results suggest not only reduced functioning of Trks in brains of suicide subjects but also that increased ratios of p75(NTR) to Trks indicate possible activation of pathways that are apoptotic in nature. These findings may be crucial in the pathophysiology of suicide.

Serum BDNF levels in suicide attempters related to psychosocial stressors: a comparative study with depression

Although many studies have examined the neurobiological aspects of suicide, the molecular mechanisms and pathophysiologic mechanisms associated with suicide remain unclear. In this study, it is aimed to investigate whether there is a difference in serum brain-derived neurotrophic factor (BDNF) levels among suicide attempters without a major psychiatric disorder, compared to major depressive disorder patients and healthy subjects. It was undertaken with the hypothesis that suicide per se lowers serum BDNF levels, since it is a source of stress. The study was carried out in Celal Bayar University Hospital, Manisa, Turkey. Ten suicide attempters, 24 patients with major depressive disorder and 26 subjects without any psychiatric diagnosis and any psychiatric treatment were included in the study. All subjects were asked to give their written consent. Blood samples were collected at the baseline. Serum BDNF was kept at -70 degrees C before testing, and assayed with an ELISA kit (Promega; Madison, Wisc., USA) after dilution with the block and sample solution provided with the kit. The data were subjected to the Kruskal-Wallis test for nonparametric analysis of variance. Mean serum BDNF levels were significantly lower in the suicide group (21.2 +/- 12.4 ng/ml) and the major depressive disorder group (21.2 +/- 11.3 ng/ml) than the control group (31.4 +/- 8.8 ng/ml; p = 0.004). These results suggest that BDNF may play an important role in the neurobiology of suicidal behavior. BDNF levels may be a biological marker for suicidal behavior. To investigate the role of BDNF in suicide, further studies with a wider sample size and a variety of psychiatric diagnoses accompanying suicide attempt are needed.

Prenatal alcohol exposure: foetal programming, the hypothalamic-pituitary-adrenal axis and sex differences in outcome

Prenatal exposure to alcohol has adverse effects on offspring neuroendocrine and behavioural functions. Alcohol readily crosses the placenta, thus directly affecting developing foetal endocrine organs. In addition, alcohol-induced changes in maternal endocrine function can disrupt the normal hormonal interactions between the pregnant female and foetal systems, altering the normal hormone balance and, indirectly, affecting the development of foetal metabolic, physiological and endocrine functions. The present review focuses on the adverse effects of prenatal alcohol exposure on offspring neuroendocrine function, with particular emphasis on the hypothalamic-pituitary-adrenal (HPA) axis, a key player in the stress response. The HPA axis is highly susceptible to programming during foetal and neonatal development. Here, we review data demonstrating that alcohol exposure in utero programmes the foetal HPA axis such that HPA tone is increased throughout life. Importantly, we show that, although alterations in HPA responsiveness and regulation are robust phenomena, occurring in both male and female offspring, sexually dimorphic effects of alcohol are frequently observed. We present updated findings on possible mechanisms underlying differential effects of alcohol on male and female offspring, with special emphasis on effects at different levels of the HPA axis, and on modulatory influences of the hypothalamic-pituitary-gonadal hormones and serotonin. Finally, possible mechanisms underlying foetal programming of the HPA axis, and the long-term implications of increased exposure to endogenous glucocorticoids for offspring vulnerability to illnesses or disorders later in life are discussed.

Neurobiology of suicidal behavior. An integration of biological and clinical findings

Suicide is among the top ten leading causes of death in individuals of all ages. An explanatory model for suicidal behavior that links clinical and psychological risk factors or endophenotypes, to the underlying neurobiological abnormalities associated with suicidal behavior may enhance prediction, help identify treatment options and have heuristic value. Our explanatory model proposes that developmental factors that are biological (genetics) and psychological or clinical (early childhood adversity) may have causal relevance to the disturbances found in subjects with suicidal behavior. In this way, our model integrates findings from several perspectives in suicidology and attempts to explain the relationship between various neurobiological, genetic, and clinical observations in suicide research, offering a comprehensive hypothesis to facilitate understanding of this complex outcome.

Regulation of serotonin-1A receptor function in inducible brain-derived neurotrophic factor knockout mice after administration of corticosterone

BACKGROUND

We examined the effects of a forebrain-specific reduction in brain-derived neurotrophic factor (BDNF) on the regulation of serotonin-1A (5-HT1A) receptor function in serotonergic cell body areas as well as in limbic and cortical structures of mice chronically treated with corticosterone.

METHODS

5-HT1A receptor function, at the level of receptor-G protein interaction, was assessed with quantitative autoradiography of [35S]GTPgammaS binding stimulated by the 5-HT1A receptor agonist 8-OH-DPAT. 5-HT1A receptor number was assessed by measuring the binding of the antagonist radioligand [3H] WAY100635.

RESULTS

We observed a significant attenuation of 5-HT1A receptor function, in the absence of a change in receptor number, in the dorsal hippocampus of BDNF knockout versus control mice. There was no difference between control and BDNF knockout mice in 5-HT1A receptor number or function in the dorsal or median raphe nuclei or medial prefrontal cortex or anterior cingulate cortex. Corticosterone treatment of control mice decreased 5-HT1A receptor function in the dorsal and median raphe but not in hippocampus or frontal cortical areas. The regulation of 5HT1A receptor number or function in the dorsal and median raphe by corticosterone was lost in BDNF knockout mice.

CONCLUSIONS

Attenuation of BDNF expression in forebrain regions produces differential effects on distinct 5-HT1A receptor populations and on the regulation of these receptor populations by corticosterone.

Physiological mechanisms involved in religiosity/spirituality and health

During the last two decades of the 20th century, psychological science rediscovered religiosity/spirituality (R/S) as a legitimate subject matter in understanding the human experience. In large measure, this renewed interest was motivated by the positive association between this variable and health (physical and mental) reported in much of the literature. If the described relationship between R/S and health is accurate, the question of how such an influence might be realized becomes important and subject to empirical investigation. The present paper develops a rationale for why such an outcome might be expected and describes various physiological mechanisms that could mediate the effect of R/S on health.

Alterations in stress reactivity after long-term treatment with paroxetine in women with posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is typically accompanied by both acute and chronic alterations in the stress response. These alterations have mostly been described in individuals under baseline conditions, but studies have also used a challenge model to assess the role of the hypothalamic-pituitary-adrenal (HPA) axis in the stress response. The purpose of this article was to assess the effect of long-term treatment with the selective reuptake inhibitor (SSRI), paroxetine, on stress reactivity in patients with PTSD. We assessed diurnal salivary cortisol and urinary cortisol as well as cortisol, heart rate, and behavioral responses to a standardized cognitive stress challenge, in 13 female patients with chronic PTSD before and after 12 months of paroxetine treatment. Treatment resulted in a significant decrease in PTSD symptoms. Twenty-four-hour urinary cortisol was lower compared to base line after successful treatment. Treatment resulted in a decrease of salivary cortisol levels on all time points on a diurnal curve. Despite similar stress perception, cortisol response to the cognitive stress challenge resulted in a 26.5% relative decrease in stress-induced salivary cortisol with treatment. These results suggest that successful treatment with SSRI in chronic PTSD is associated with a trend for a decrease in baseline diurnal cortisol and with reduced cortisol reactivity to stress.

Hypoactivity of the hypothalamo-pituitary-adrenocortical axis during recovery from chronic variable stress

Chronic stress induces both functional and structural adaptations within the hypothalamo-pituitary-adrenocortical (HPA) axis, suggestive of long-term alterations in neuroendocrine reactivity to subsequent stressors. We hypothesized that prior chronic stress would produce persistent enhancement of HPA axis reactivity to novel stressors. Adult male rats were exposed to chronic variable stress (CVS) for 1 wk and allowed to recover. Plasma ACTH and corticosterone levels were measured in control or CVS rats exposed to novel psychogenic (novel environment or restraint) or systemic (hypoxia) stressors at 16 h, 4 d, 7 d, or 30 d after CVS cessation. Plasma ACTH and corticosterone responses to psychogenic stressors were attenuated at 4 d (novel environment and restraint) and 7 d (novel environment only) recovery from CVS, whereas hormonal responses to the systemic stressor were largely unaffected by CVS. CRH mRNA expression was up-regulated in the paraventricular nucleus of the hypothalamus (PVN) at 16 h after cessation of CVS, but no other alterations in PVN CRH or arginine vasopressin mRNA expression were observed. Thus, in contrast to our hypothesis, reductions of HPA axis sensitivity to psychogenic stressors manifested at delayed recovery time points after CVS. The capacity of the HPA axis to respond to a systemic stressor appeared largely intact during recovery from CVS. These data suggest that chronic stress selectively targets brain circuits responsible for integration of psychogenic stimuli, resulting in decreased HPA axis responsiveness, possibly mediated in part by transitory alterations in PVN CRH expression.

Corticotropin-releasing hormone, arginine vasopressin, gastrin-releasing peptide, and neuromedin B alterations in stress-relevant brain regions of suicides and control subjects

BACKGROUND

Postmortem levels of several stress- and depression-relevant neuropeptides were assessed in brain regions of depressed suicides relative to control subjects that had died of other causes.

METHODS

Brains of suicides and those that died from other causes were collected soon after death (typically <6 hours). Immunoreactivity levels (ir) of corticotropin-releasing hormone (CRH-ir) and arginine vasopressin (AVP-ir), and the bombesin analogs, gastrin-releasing peptide (GRP-ir), and neuromedin B (NMB-ir), were assessed.

RESULTS

Levels of CRH-ir among suicides were elevated in the locus coeruleus (LC), frontopolar, dorsolateral prefrontal (DMPFC) and ventromedial prefrontal cortices, but were reduced at the dorsovagal complex (DVC). The concentration of AVP-ir was elevated at the paraventricluar hypothalamic nucleus, LC, and DMPFC, and reduced at the DVC. Finally, GRP and NMB variations, which might influence anxiety states, were limited, although GRP-ir within the LC of suicides was higher than in control subjects, while NMB-ir was reduced at the DVC of suicides.

CONCLUSIONS

The data show several neuropeptide changes in relation to suicide, although it is premature to ascribe these outcomes specifically to the suicide act versus depression. Likewise, it is uncertain whether the neuropeptide alterations were etiologically related to suicide/depression or secondary to the depressive state.

Effect of neonatal handling on serotonin 1A sub-type receptors in the rat hippocampus

Serotonin 1A sub-type receptors play an important role in the etiopathogenesis of depression, which is known to occur more often in females than males. Early experiences can be a predisposing factor for depression; however, the underlying cellular processes remain unknown. In an effort to address such issues, we employed neonatal handling, an experimental model of early experience, which has been previously shown to render females more vulnerable to display enhanced depression-like behavior in response to chronic stress, while it increases the ability of males to cope. In rat pre-pubertal (30 days of age) and adult (90 days) hippocampus, of both males and females, the effect of neonatal handling on serotonin 1A sub-type receptor mRNA and protein levels was determined by in situ hybridization and immunohistochemistry, respectively, while the number of binding sites was determined by in vitro autoradiography using [(3)H]8-hydroxy-2(di-n-propylamino)tetralin as the ligand. Our results revealed a significant sex difference in serotonin 1A sub-type receptor mRNA, protein and binding sites, with females having higher levels than males. Handling resulted in statistically significant decreased numbers of cells positive for serotonin 1A sub-type receptor mRNA or protein, as well as [(3)H]8-hydroxy-2(di-n-propylamino)tetralin binding sites in the area 4 of Ammon's horn and dentate gyrus of both pre-pubertal males and females. In adult animals the number of serotonin 1A sub-type receptor mRNA positive cells was increased as a result of handling in the area 1 of Ammon's horn, area 4 of Ammon's horn and dentate gyrus of males, while it was decreased only in the area 4 of Ammon's horn of females. Furthermore, the number of serotonin sub-type 1A receptor immunopositive cells, as well as [(3)H]8-hydroxy-2(di-n-propylamino)tetralin binding sites was increased in the area 1 of Ammon's horn, area 4 of Ammon's horn and dentate gyrus of handled males, whereas it was decreased in these same brain areas in the handled females. We can thus infer that neonatal handling results in alterations in postsynaptic serotonergic neurotransmission, which may contribute to the sex dimorphic effects of handling as to the vulnerability toward depression-like behavior in response to chronic stressful stimuli.

Maternal separation alters serotonergic transporter densities and serotonergic 1A receptors in rat brain

RATIONALE

The basic mechanisms underlying the association between early life maternal separation and adulthood psychiatric disorders are largely unknown. One possible candidate is the central serotonergic system, which is also abnormal in psychiatric illnesses. Neuroadaptational changes in serotonergic transporter and serotonergic 1A receptors may underlie links between early life stress and adulthood psychiatric disorders.

OBJECTIVE

The aim of this study was to investigate the consequences of a rat model of maternal separation on serotonergic transporter and serotonergic 1A receptor densities and function in adult rat forebrain.

METHODS

Rat pups were separated from dams from postnatal day 2 to postnatal day 14, each day, for zero time, 15 min and 180 min to determine the time-course of effects. A non-handled group was added to control for the effects of handling by an experimenter compared with the animal facility-reared group. Quantitative [(125)I]3beta-(4-iodophenyl)tropan-2beta-carboxylic acid methyl ester and [(125)I]-mPPI autoradiography was used to determine serotonergic transporter and serotonergic 1A densities, respectively. Adult rats were challenged with saline or serotonergic 1A agonist (+) 8-hydroxy-2-(di-n-propylamino)tetralin, 0.4 mg/kg, s.c.) and plasma adrenocorticotropic hormone and corticosterone were determined.

RESULTS

serotonergic transporter and serotonergic 1A densities were significantly lower in the non-handled group in the paraventricular, arcuate, dorsomedial and ventromedial nuclei of the hypothalamus. The non-handled group also displayed lower serotonergic transporter and serotonergic 1A densities in the basolateral anterior, basolateral ventral and basomedial amygdaloid nuclei. Serotonergic transporter densities were also decreased in the CA3 area of the hippocampus in the non-handled group. In contrast, the maternal separation 15 min group displayed the highest serotonergic transporter and serotonergic 1A densities in the basomedial nucleus of amygdala, basolateral anterior nucleus of amygdala, basolateral ventral nucleus of amygdala and basomedial nucleus of amygdala amygdaloid nuclei.

CONCLUSIONS

Early life maternal separation and the extent of handling can alter adult brain serotonergic transporter and serotonergic 1A levels and function in the forebrain. Alterations in these serotonergic systems by early rearing conditions might increase vulnerability for behavioral disorders in adulthood.

Suicide brain is associated with decreased expression of neurotrophins

BACKGROUND

Neurotrophins mediate diverse biological responses, including maintenance and growth of neurons and synaptic plasticity in adult brain. This study examined whether suicide brain is associated with changes in the expression of neurotrophins.

METHODS

Messenger ribonucleic acid (mRNA) levels of nerve growth factor (NGF), neurotrophin (NT)-3, NT-4/5, and of cyclophilin and neuron-specific enolase (NSE) were measured by quantitative reverse transcriptase polymerase chain reaction, whereas protein levels of neurotrophins were determined by enzyme-linked immunosorbent assay, in prefrontal cortex (PFC) and hippocampus from 28 suicide victims and 21 control subjects.

RESULTS

In hippocampus of suicide subjects compared with control subjects mRNA levels of NGF (p < .001), NT-3 (p < .001), and NT-4/5 (p < .001) were decreased, whether or not they were expressed as a ratio to cyclophilin or NSE. This was accompanied by a decrease in their respective protein levels (NGF [p < .001], NT-3 [p < .001], and NT-4/5 [p < .001]). In PFC, however, mRNA (p = .001) and protein (p < .001) levels of NT-4/5 and only protein level of NGF (p < .001) were decreased; NT-3 levels were unchanged.

CONCLUSIONS

Given the role of neurotrophins in synaptic plasticity and maintenance of adult neurons, our findings of altered expression of neurotrophins in postmortem brain of suicide victims suggest that these molecules might play a vital role in the pathophysiology of suicide.

5-HT1A receptor expression in pyramidal neurons of cortical and limbic brain regions

We studied expression of the 5-HT(1A) receptor in cortical and limbic areas of the brain of the tree shrew. In situ hybridization with a receptor-specific probe and immunocytochemistry with various antibodies was used to identify distinct neurons expressing the receptor. In vitro receptor autoradiography with (3)H-8-OH-DPAT ((3)H-8-hydroxy-2-[di-n-propylamino]tetralin) was performed to visualize receptor-binding sites. In the prefrontal, insular, and occipital cortex, 5-HT(1A) receptor mRNA was expressed in pyramidal neurons of layer 2, whereas (3)H-8-OH-DPAT labeled layers 1 and 2 generating a columnar-like pattern in the prefrontal and occipital cortex. In the striate and ventral occipital cortex, receptor mRNA was present within layers 5 and 6 in pyramidal neurons and Meynert cells. Pyramid-like neurons in the claustrum and anterior olfactory nucleus also expressed the receptor. Principal neurons in hippocampal region CA1 expressed 5-HT(1A) receptor mRNA, and (3)H-8-OH-DPAT labeled both the stratum oriens and stratum radiatum. CA3 pyramidal neurons displayed low 5-HT(1A) receptor expression, whereas granule neurons in the dentate gyrus revealed moderate expression of this receptor. In the amygdala, large pyramid-like neurons in the basal magnocellular nucleus strongly expressed the receptor. Immunocytochemistry with antibodies against parvalbumin, calbindin, and gamma aminobutyric acid (GABA) provided no evidence for 5-HT(1A) receptor expression in GABAergic neurons in cortical and limbic brain areas. Our data agree with previous findings showing that the 5-HT(1A) receptor mediates the modulation of glutamatergic neurons. Expression in the limbic and cortical areas suggested an involvement of 5-HT(1A) receptors in emotional and cognitive processes.

Behavioural and neurochemical effects induced by chronic mild stress applied to two different rat strains

Chronic mild stress (CMS) has been reported to induce an anhedonic-like state in rats that resembles some of the symptoms of endogenous depression in humans. In the present study, CMS-induced behavioural responses along with neurochemical alterations in dopaminergic and serotonergic function in prefrontal cortex, striatum, hypothalamus and hippocampus were examined following treatment with imipramine in Wistar and Sprague-Dawley rats. The CMS procedure lasted 7 weeks in total. Once per week, a 1-h preference test for 1% sucrose solution was conducted. Treatment with imipramine (10mg/kg i.p., once daily) commenced after experimental week 3. CMS induced significant reductions in absolute and relative sucrose intake and sucrose preference in both rat strains but their temporal pattern was different especially during the weeks 0-3. These effects were reversed by IMI. An increase in the dopaminergic and a decrease in the serotonergic activity were observed in the prefrontal cortex in both rat strains following CMS. A decrease in the striatal dopaminergic activity and an increased hippocampal serotonergic activity were also seen in both rat strains following CMS. In Wistar rats, dopaminergic and serotonergic activities were enhanced in the hypothalamus whereas in Sprague-Dawley rats no such stress-induced changes were observed. Notably, the clear decrease in sucrose consumption observed in stressed Wistar rats could be directly associated with a respective increase in the dopaminergic hypothalamic activity. Chronic treatment with imipramine normalized all neurochemical alterations induced by CMS. Our results suggest that a specific and regionally differentiated serotonin-dopamine interaction is directly related to the observed stress-induced anhedonia.

Serotonin 5-HT1A, 5-HT1B, and 5-HT2A receptor mRNA expression in subjects with major depression, bipolar disorder, and schizophrenia

BACKGROUND

Alterations of serotonin neurotransmission are implicated in both mood disorders and schizophrenia. Specific serotonin-receptor-based abnormalities in these psychiatric illnesses have been intensively studied; however, it has been difficult to draw any conclusions because of a lack of consensus. These inconsistencies have most likely arisen from the unavailability of selective ligands.

METHODS

Our study used in situ hybridization to quantify 5-HT(1A), 5-HT(1B), and 5-HT(2A) mRNA levels in the hippocampus (HC) and 5-HT(1A) and 5-HT(2A) mRNA levels in the dorsolateral prefrontal cortex (DLPFC) of subjects with a history of major depression disorder (MDD), bipolar disorder (BPD), schizophrenia, and a normal comparison group (15 subjects per group).

RESULTS

In the DLPFC, there is a significant decrease in 5-HT(1A) mRNA of subjects with MDD and in 5-HT(2A) mRNA of subjects with BPD. Subjects with MDD have a significant decrease in 5-HT(1A) mRNA in the HC; subjects with BPD and schizophrenia had increased 5-HT(1B) mRNA levels and a significant decrease in 5-HT(2A) mRNA levels in the hippocampal formation.

CONCLUSIONS

Alterations in 5-HT(1A,) 5-HT(1B), and 5-HT(2A) mRNA levels in the brains of subjects with both mood disorders and schizophrenia add further support for hypothesis of dysregulation of the serotonergic system in these psychiatric disorders.

Conditioned taste aversion: modulation by 5-HT receptor activity and corticosterone

Two experiments were designed to elucidate the involvement of the hypothalamic-pituitary-adrenal axis and the 5-hydroxytryptamine (5-HT) system in the acquisition of lithium chloride-conditioned taste aversion. In Experiment 1, rats were administered either vehicle or 50 mg/kg nefazodone daily for 4 weeks. Rats were treated with 22 mg/kg of lithium chloride in order to produce conditioned taste aversion to a sucrose solution. Three days later, nefazodone completely blocked the lithium chloride-conditioned taste aversion. In Experiment 2, the effects of chronic corticosterone administration on lithium chloride-conditioned taste aversion were investigated. Twenty male rats received either corticosterone at a dose of (50 mg/kg) or vehicle injections over a period of 14 consecutive days. Lithium chloride-conditioned taste aversion was potentiated in rats treated with corticosterone. Additionally, corticosterone-treated animals required more trials to reach extinction. These results suggest the involvement of both the 5-HT system and the hypothalamic-pituitary-adrenal axis in lithium chloride-conditioned taste aversion.

Impact of maternal deprivation on brain corticotropin-releasing hormone circuits: prevention of CRH receptor-2 mRNA changes by desipramine treatment

Corticotropin-releasing hormone (CRH) acts within the brain and pituitary to coordinate the overall endocrinological and behavioral stress response. From postnatal day (PND) 4 to 14, the infant rat displays minimal adrenal response to mild stress. However, maternal deprivation alters the pituitary-adrenal system such that the infants become responsive to specific stimuli. We hypothesized that maternal deprivation would also affect CRH brain circuits. Since tricyclic antidepressants have been shown to decrease the adrenal response to stress in adult rats, we hypothesized that CRH-related changes induced by maternal deprivation would be prevented by this treatment. Thus, we investigated CRH-related molecules on animals that were maternally deprived on PND 13 compared with nondeprived animals. We found that maternal deprivation caused alterations in the gene expression of both CRH receptors (CRHr) 1 and 2 in specific brain regions, and that some of these effects were augmented by chronic isotonic saline injections. There was a significant increase in CRH, CRHr1, and r2 mRNA in the cortex. In amygdala, CRHr1 and r2 mRNAs were decreased. CRHr2 mRNA was also decreased in the ventromedial nucleus of the hypothalamus, whereas an increase was detected in the hippocampal pyramidal cells. One week of desipramine (DES) administration preceding the maternal deprivation event prevented all the deprivation-induced changes in CRHr2 mRNA, regardless of the direction of the original change. We also found that chronic injection treatments enhanced the adrenocortical response and improved the efficiency of negative feedback in maternal deprivation animals. These results demonstrate that maternal deprivation elicits modifications of CRH brain circuits in a site-specific manner, and that the regulation of CRHr2 gene expression is mediated by mechanisms different from those involved with the modulation of CRHr1 in the infant rat.

Suicide: life span considerations

Although the daily hassles of living are challenging and stressful to most people, suicide is a cry for help that often reflects tremendous emotional pain and distress. When one's normal adaptive coping skills or developmental capacities fail to manage these situations effectively, some youth and adults resort to suicide as a means of managing intense overwhelming negative emotional states. This article has discussed suicide among older adults and children and adolescents. The role of the nurse in recognizing high-risk groups, analyzing assessment data, and implementing treatment interventions that integrate holistic concepts and reflect cultural sensitivity has been described. The ultimate goal of nurses working with the suicidal patient is prevention. Prevention of suicide requires an understanding of the emotional pain that precludes this act. Through preventive measures, the nurse has the opportunity to establish a therapeutic relationship that enhances adaptive coping skills, restores homeostasis of biologic process, and facilitates an optimal level of functioning in all age groups.

Norepinephrine-gamma-aminobutyric acid (GABA) interaction in limbic stress circuits: effects of reboxetine on GABAergic neurons

BACKGROUND

Reboxetine is a selective norepinephrine (NE) reuptake inhibitor that exerts significant antidepressant action. The current study assessed norepinephrine-gamma-aminobutyric acid (GABA)-ergic mechanisms in reboxetine action, examining glutamic acid decarboxylase (GAD) mRNA expression in limbic neurocircuits following reboxetine within the context of chronic stress.

METHODS

Male rats received 25 mg/kg reboxetine/day, p.o. Reboxetine and vehicle animals were exposed to 1 week of variable stress exposure or handling. Behavioral responses to stress (open field) were tested on day 7, and animals were killed on day 8 to assess neuroendocrine stress responses and limbic GAD65/67 mRNA regulation (in situ hybridization).

RESULTS

Reboxetine significantly decreased behavioral reactivity in the open field. Reboxetine administration did not affect expression of GAD65/67 mRNA in handled rats; however, administration to stressed animals reduced GAD67 (but not GAD65) mRNA in the medial amygdaloid nucleus, posteromedial bed nucleus of the stria terminalis, and dentate gyrus. In contrast, GAD65 mRNA expression was increased by reboxetine in the lateral septum of stressed animals.

CONCLUSIONS

Norepinephrine pathways appear to modulate synthesis of GABA in central limbic stress circuits. Decreases in GABA synthetic capacity suggest reduced activation of stress-excitatory pathways and enhanced activation of stress-inhibitory circuits, and is consistent with a role for GABA in the antidepressant efficacy of NE reuptake inhibitors.

The 5-HT1A serotonin receptor is located on calbindin- and parvalbumin-containing neurons in the rat brain

The 5-HT(1A) receptor is a well-characterized serotonin receptor playing a role in many central nervous functions and known to be involved in depression and other mental disorders. In situ hybridization, immunocytochemical, and binding studies have shown that the 5-HT(1A) receptor is widely distributed in the rat brain, with a particularly high density in the limbic system. The receptor's localization in the different neuronal subtypes, which may be of importance for understanding its role in neuronal circuitries, is, however, unknown. In this study we show by immunocytochemical double-labeling techniques, that the 5-HT(1A) receptor is present on both pyramidal and principal cells, and calbindin- and parvalbumin-containing neurons, which generally define two different subtypes of interneurons. Moreover, semiquantitative analysis showed that the receptor's distribution in the different neuronal types varies between brain areas. In cortex, hippocampus, hypothalamus, and amygdala the receptor was located on both principal cells and calbindin- and parvalbumin-containing neurons. In septum and thalamus, the receptor was mostly present on calbindin- and parvalbumin-containing cells. Especially in the medial septum and thalamic reticular nucleus, the receptor highly colocalized with parvalbumin-positive neurons. These results suggest a diverse function of the 5-HT(1A) receptor in modulating neuronal circuitry in different brain areas, that may depend on the type of neuron the receptor is predominantly located on.

Corticosterone modulation of somatodendritic 5-HT1A receptor function in mice

Corticosteroid modulation of serotonergic function may play a central role in mood disorders. 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) produces a hypothermia in mice that serves as an in-vivo model of somatodendritic 5-HT1A autoreceptor function. Daily injections (s.c.) of 50 mg/kg of corticosterone (CORT) for 3 days attenuates 8-OH-DPAT hypothermia tested 24 h later. This study sought to further clarify the nature of the CORT-mediated attenuation of somatodendritic 5-HT1A receptor function. Mice underwent various CORT manipulations prior to an 8-OH-DPAT challenge. Neither 14-day bilateral adrenalectomy (ADX), nor CORT 50 mg/kg/day, administered continuously by osmotic minipump over 72 h had any effect on the 8-OH-DPAT hypothermic response. In contrast, daily injections of CORT over three consecutive days caused a significant attenuation in 8-OH-DPAT hypothermia when tested 24 h later. However, administration of an additional dose of CORT 2 h prior to the 8-OH-DPAT challenge occluded this CORT-mediated attenuation in a dose-dependent fashion. The findings demonstrate that CORT modulates somatodendritic 5-HT1A receptor function in a complex manner. Attenuation is seen only after intermittent administration of CORT. In addition, the degree of attenuation depends on CORT concentrations at the time of testing. These findings may have implications regarding mechanisms of adaptation to stress.

Brain 5-HT receptor system in the stressed infant rat: implications for vulnerability to substance abuse

Clinical and epidemiological studies have found an association between aversive experiences early in life and an increased risk for depression, anxiety and substance abuse. In order to elucidate the mechanisms by which adverse life events are translated into behavioral and psychological abnormalities, we used a rat model to study the impact of chronic injection and 24 h maternal deprivation on the developing rat brain. Specifically, we investigated the regulation of molecules related to the 5-HT (5-HT) system and studied the effect of desipramine administration on animals that were maternally deprived (DEP) on day 13 of life compared with non-deprived animals. We found that maternal deprivation caused an enhanced corticosterone response to an acute stress. Maternally deprived animals also showed a decrease in corticosteroid receptors and an increase in 5-HT 1A and 1B receptors restricted to the CA1 region of the hippocampus. Desipramine prevented the maternal deprivation induced up-regulation of the 5-HT 1B receptor and the enhanced adrenocortical response observed in these animals. Interestingly, non-deprived animals receiving chronic injections showed a decrease in hippocampal 5-HT1B receptor mRNA. At 80 days of age, a group of animals that were treated as infants were given the option of drinking from two identical water bottles, one bottle contained tap water, while the second contained ethanol at increasing concentrations. Animals that received chronic injections during the newborn period consumed more alcohol than those that were not injected. On the other hand, maternal deprivation did not have an impact on alcohol consumption. Alcohol preference has implications to the organism since studies of drug self-administration in laboratory animals have shown that ethanol ingestion is positively related to the use of other drugs, principally opioids and psychostimulants. Our findings suggest that the quality and/or chronicity of early life stressors can influence the neurobiological substrates that may trigger and/or predispose individuals to substance abuse in adulthood.