Quantitative autoradiography of alpha 1- and alpha 2-adrenergic receptors in the cerebral cortex of controls and suicide victims

Homeostasis to Allostasis: Prefrontal Astrocyte Roles in Cognitive Flexibility and Stress Biology

In the intricate landscape of neurophysiology, astrocytes have been traditionally cast as homeostatic cells; however, their mechanistic involvement in allostasis-particularly how they modulate the adaptive response to stress and its accumulative impact that disrupts cognitive functions and precipitates psychiatric disorders-is now starting to be unraveled. Here, we address the gap by positing astrocytes as crucial allostatic players whose molecular adaptations underlie cognitive flexibility in stress-related neuropsychiatric conditions. We review how astrocytes, responding to stress mediators such as glucocorticoid and epinephrine/norepinephrine, undergo morphological and functional transformations that parallel the maladaptive changes. Our synthesis of recent findings reveals that these glial changes, especially in the metabolically demanding prefrontal cortex, may underlie some of the neuropsychiatric mechanisms characterized by the disruption of energy metabolism and astrocytic networks, compromised glutamate clearance, and diminished synaptic support. We argue that astrocytes extend beyond their homeostatic role, actively participating in the brain's allostatic response, especially by modulating energy substrates critical for cognitive functions.

Astrocytes in Post-traumatic Stress Disorder

Although posttraumatic stress disorder (PTSD) is on the rise, traumatic events and their consequences are often hidden or minimized by patients for reasons linked to PTSD itself. Traumatic experiences can be broadly classified into mental stress (MS) and traumatic brain injury (TBI), but the cellular mechanisms of MS- or TBI-induced PTSD remain unknown. Recent evidence has shown that the morphological remodeling of astrocytes accompanies and arguably contributes to fearful memories and stress-related disorders. In this review, we summarize the roles of astrocytes in the pathogenesis of MS-PTSD and TBI-PTSD. Astrocytes synthesize and secrete neurotrophic, pro- and anti-inflammatory factors and regulate the microenvironment of the nervous tissue through metabolic pathways, ionostatic control, and homeostatic clearance of neurotransmitters. Stress or trauma-associated impairment of these vital astrocytic functions contribute to the pathophysiological evolution of PTSD and may present therapeutic targets.

Noradrenergic α1-Adrenoceptor Actions in the Primate Dorsolateral Prefrontal Cortex

Noradrenergic (NE) α1-adrenoceptors (α1-ARs) contribute to arousal mechanisms and play an important role in therapeutic medications such as those for the treatment of posttraumatic stress disorder (PTSD). However, little is known about how α1-AR stimulation influences neuronal firing in the dorsolateral prefrontal cortex (dlPFC), a newly evolved region that is dysfunctional in PTSD and other mental illnesses. The current study examined the effects of α1-AR manipulation on neuronal firing in dlPFC of rhesus monkeys performing a visuospatial working memory task, focusing on the "delay cells" that maintain spatially tuned information across the delay period. Iontophoresis of the α1-AR antagonist HEAT (2-{[β-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone) had mixed effects, reducing firing in a majority of neurons but having nonsignificant excitatory effects or no effect in remaining delay cells. These data suggest that endogenous NE has excitatory effects in some delay cells under basal conditions. In contrast, the α1-AR agonists phenylephrine and cirazoline suppressed delay cell firing and this was blocked by coadministration of HEAT. These results indicate an inverted-U dose response for α1-AR actions, with mixed excitatory actions under basal conditions and suppressed firing with high levels of α1-AR stimulation such as with stress exposure. Immunoelectron microscopy revealed α1-AR expression presynaptically in axons and axon terminals and postsynaptically in spines, dendrites, and astrocytes. It is possible that α1-AR excitatory effects arise from presynaptic excitation of glutamate release, whereas postsynaptic actions suppress firing through calcium-protein kinase C opening of potassium channels on spines. The latter may predominate under stressful conditions, leading to loss of dlPFC regulation during uncontrollable stress.SIGNIFICANCE STATEMENT Noradrenergic stimulation of α1-adrenoceptors (α1-ARs) is implicated in posttraumatic stress disorder (PTSD) and other mental disorders that involve dysfunction of the prefrontal cortex, a brain region that provides top-down control. However, the location and contribution of α1-ARs to prefrontal cortical physiology in primates has received little attention. This study found that α1-ARs are located near prefrontal synapses and that α1-AR stimulation has mixed effects under basal conditions. However, high levels of α1-AR stimulation, as occur with stress, suppress neuronal firing. These findings help to explain why we lose top-down control under conditions of uncontrollable stress when there are high levels of noradrenergic release in brain and why blocking α1-AR, such as with prazosin, may be helpful in the treatment of PTSD.

The association between well-being and the COMT gene: Dispositional gratitude and forgiveness as mediators

BACKROUND

Previous studies have demonstrated the contributions of genetic variants and positive psychological traits (e.g. gratitude and forgiveness) to well-being. However, little is known about how genes interact with positive traits to affect well-being.

METHODS

To investigate to what extent the COMT Val158Met polymorphism modulates well-being and to what extent dispositional gratitude and forgiveness mediate the individual differences in well-being, 445 participants were recruited and required to complete a battery of questionnaires.

RESULTS

We found that individuals with a smaller number of the Met alleles reported greater well-being, less depressive symptoms, and greater tendencies for gratitude and forgiveness. Moreover, dispositional gratitude and forgiveness mediated the genotype effects on well-being and depressive symptoms. These results remained significant after controlling for non-genetic factors (socioeconomic status, religious beliefs, romantic relationship status, parenting style).

LIMITATION

The sample size limits the generalizability of results.

CONCLUSION

This study demonstrates the contribution of the COMT Val158Met polymorphism to individual differences in well-being and suggests a potential psychobiological pathway from dopaminergic and noradrenergic systems to happiness.

α2-adrenoceptor binding in Flinders-sensitive line compared with Flinders-resistant line and Sprague-Dawley rats

OBJECTIVES

Disturbances in the noradrenergic system, including alterations in the densities of α2-adrenoceptors, are posited to be involved in the pathophysiology of depression. In this study, we investigate the binding of α2-adrenoceptors in regions relevant to depression in an animal model of depression.

METHODS

Using in vitro autoradiography techniques and the selective α2-ligand, [3H]RX 821002, we investigated the density of α2-adrenoceptors in female Flinders-sensitive line (FSL) rats, a validated model of depression, and in two traditional control groups - female Flinders-resistant line (FRL) and Sprague-Dawley (SD) rats.

RESULTS

The α2-adrenoceptor density was increased in most regions of the FSL rat brain when compared with SD rats (10% across regions). Moreover, the α2-adrenoceptor density was further increased in the FRL rats compared with both FSL (10% across regions) and SD rats (24% across regions).

CONCLUSIONS

The increase in α2-adrenoceptor binding in cortical regions in the FSL strain compared with the SD control strain is in accord with α2-adrenoceptor post-mortem binding data in suicide victims with untreated major depression. However, the differences in binding observed in the two control groups were unexpected and suggest the need for further studies in a larger cohort of animals of both sexes.

The role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect

Depression is a serious global illness, becoming more and more common in developed countries. Because of specific symptoms it is considered as a leading cause of disability all over the world with a high death factor due to suicides. There are many antidepressants used in the therapy, but still more than 30% of patients do not respond to the treatment. The heterogeneous nature of the illness and its complex, unclear aetiology may be responsible for these difficulties. Next to the main monoaminergic hypothesis of depression there are also many other approaches connected with the pathophysiology of the disease, including hypothalamic-pituitary-adrenal axis dysregulation, dopaminergic, cholinergic, glutamatergic or GABA-ergic neurotransmission. Nevertheless, it can be unambiguously stated that serotonergic, noradrenergic and dopaminergic systems are precisely connected with pathogenesis of depression, and should be therefore considered as valuable targets in patients' treatment. Bearing that in mind, this review presents the role of serotonergic, adrenergic and dopaminergic receptors in antidepressant-like effect.

Toward a biosignature for suicide

OBJECTIVE

Suicide, a major cause of death worldwide, has distinct biological underpinnings. The authors review and synthesize the research literature on biomarkers of suicide, with the aim of using the findings of these studies to develop a coherent model for the biological diathesis for suicide.

METHOD

The authors examined studies covering a large range of neurobiological systems implicated in suicide. They provide succinct descriptions of each system to provide a context for interpreting the meaning of findings in suicide.

RESULTS

Several lines of evidence implicate dysregulation in stress response systems, especially the hypothalamic-pituitary-adrenal axis, as a diathesis for suicide. Additional findings related to neuroinflammatory indices, glutamatergic function, and neuronal plasticity at the cellular and circuitry level may reflect downstream effects of such dysregulation. Whether serotonergic abnormalities observed in individuals who have died by suicide are independent of stress response abnormalities is an unresolved question.

CONCLUSIONS

The most compelling biomarkers for suicide are linked to altered stress responses and their downstream effects, and to abnormalities in the serotonergic system. Studying these systems in parallel and in the same populations may elucidate the role of each and their interplay, possibly leading to identification of new treatment targets and biological predictors.

Lack of BDNF expression through promoter IV disturbs expression of monoamine genes in the frontal cortex and hippocampus

Brain-derived neurotrophic factor (BDNF) is implicated in the pathophysiology of psychiatric conditions including major depression and schizophrenia. Mice lacking activity-driven BDNF expression through promoter IV (knock-in promoter IV: KIV) exhibit depression-like behavior, inflexible learning, and impaired response inhibition. Monoamine systems (serotonin, dopamine, and noradrenaline) are suggested to be involved in depression and schizophrenia since many of the current antidepressants and antipsychotics increase the brain levels of monoamines and/or act on monoamine receptors. To elucidate the impact of activity-driven BDNF on the monoamine systems, we examined mRNA levels for 30 monoamine-related genes, including receptors, transporters, and synthesizing enzymes, in KIV and control wild-type mice by using quantitative reverse-transcription polymerase chain reaction (qRT-PCR). mRNA levels were measured in the frontal cortex and hippocampus, which are regions related to depression and schizophrenia and where promoter IV is active. The frontal cortex of KIV mice showed reduced levels of mRNA expression for serotonin receptors 1b, 2a, and 5b (5HTR1b, 5HTR2a, 5HTR5b), dopamine D2 receptors (DRD2), and adrenergic receptors alpha 1a and 1d (AdRα1a and AdRα1b), but increased levels for serotonin synthesizing enzyme, tryptophan hydroxylase (TPH), and dopamine D4 receptor (DRD4) when compared to control wild-type mice. The hippocampus of KIV mice showed decreased levels of 5HTR5b. Our results provide causal evidence that lack of promoter IV-driven BDNF disturbs expression of monoaminergic genes in the frontal cortex and hippocampus. These disturbed expression changes in the monoamine systems may mediate the depression- and schizophrenia-like behavior of KIV mice. Our results also suggest that antidepressant and antipsychotic treatments may actually interfere with and normalize the disturbed monoamine systems caused by reduced activity-dependent BDNF, while the treatment responses to these drugs may differ in the subject with reduced BDNF levels caused by stress and lack of neuronal activity.

The neurobiology of suicide - A Review of post-mortem studies

The neurobiology of suicidal behaviour, which constitutes one of the most serious problems both in psychiatry and general medical practice, still remains to a large degree unclear. As a result, scientists constantly look for new opportunities of explaining the causes underlying suicidality. In order to elucidate the biological changes occurring in the brains of the suicide victims, studies based on post-mortem brain tissue samples are increasingly being used. These studies employ different research methods to provide an insight into abnormalities in brain functioning on various levels, including gene and protein expression, neuroplasticity and neurotransmission, as well as many other areas. The aim of this paper to summarize the available data on the post-mortem studies, to provide an overview of main research directions and the most up-to-date findings, and to indicate the possibilities of further research in this field.

Autoradiographic evaluation of [3H]CUMI-101, a novel, selective 5-HT1AR ligand in human and baboon brain

[11C]CUMI-101 is the first selective serotonin receptor (5-HT1AR) partial agonist radiotracer for positron emission tomography (PET) tested in vivo in nonhuman primates and humans. We evaluated specific binding of [3H]CUMI-101 by quantitative autoradiography studies in postmortem baboon and human brain sections using the 5-HT1AR antagonist WAY-100635 as a displacer. The regional and laminar distributions of [3H]CUMI-101 binding in baboon and human brain sections matched the known distribution of [3H]8-OH-DPAT and [3H]WAY-100635. Prazosin did not measurably displace [3H]CUMI-101 binding in baboon or human brain sections, thereby ruling out [3H]CUMI-101 binding to α1-adrenergic receptors. This study demonstrates that [11C]CUMI-101 is a selective 5-HT1AR ligand for in vivo and in vitro studies in baboon and human brain.

α2 adrenergic receptor dysregulation in depressive disorders: implications for the neurobiology of depression and antidepressant therapy

Dysfunction in noradrenergic neurotransmission has long been theorized to occur in depressive disorders. The α2 adrenergic receptor (AR) family, as a group of key players in regulating the noradrenergic system, has been investigated for involvement in the neurobiology of depression and mechanisms of antidepressant therapies. However, a clear picture of the α2ARs in depressive disorders has not been established due to the existence of apparently conflicting findings in the literature. In this article, we report that a careful accounting of methodological differences within the literature can resolve the present lack of consensus on involvement of α2ARs in depression. In particular, the pharmacological properties of the radioligand (e.g. agonist versus antagonist) utilized for determining receptor density are crucial in determining study outcome. Upregulation of α2AR density detected by radiolabeled agonists but not by antagonists in patients with depressive disorders suggests a selective increase in the density of high-affinity conformational state α2ARs, which is indicative of enhanced G protein coupling to the receptor. Importantly, this high-affinity state α2AR upregulation can be normalized with antidepressant treatments. Thus, depressive disorders appear to be associated with increased α2AR sensitivity and responsiveness, which may represent a physiological basis for the putative noradrenergic dysfunction in depressive disorders. In addition, we review changes in some key α2AR accessory proteins in depressive disorders and discuss their potential contribution to α2AR dysfunction.

Neuron density and serotonin receptor binding in prefrontal cortex in suicide

Although serotonin receptor and cytoarchitectonic alterations are reported in prefrontal cortex (PFC) in suicide and depression, no study has considered binding relative to neuron density. Therefore, we measured neuron density and serotonin transporter (SERT), 5-HT1A and 5-HT2A binding in matched suicides and controls. Suicides and normal controls (n=15 matched pairs) were psychiatrically characterized. Neuron density and binding were determined in dorsal [Brodmann area (BA) 9] and ventral (BA 47) PFC by stereology and quantitative autoradiography in near-adjacent sections. Binding index was defined as the ratio of receptor binding to neuron density. Suicides had lower neuron density in the gyrus of both areas. The binding index was lower for SERT in BA 47 but not in BA9; the 5-HT1A binding index was higher in BA 9 but not in BA 47, while the 5-HT2A binding index was not different between groups. SERT binding was lower in suicides in BA 47 but not BA 9, while 5-HT1A binding was higher in BA 9 but not BA 47. SERT binding negatively correlated with 5-HT1A binding in BA 47 in suicides. Neuron density decreased with age. The 5-HT1A binding index was higher in females than males. We found lower neuron density and lower SERT binding index in both PFC regions in suicides. More 5-HT1A binding with less SERT binding and the negative correlation in depressed suicides suggests post-synaptic receptor up-regulation, and it is independent of the difference in neuron density. Thus, abnormalities in both cortical neurons and in their serotonergic innervation are present in suicides and future studies will need to determine whether cortical changes reflect the trophic effect of altered serotonin innervation.

No association between COMT val158met polymorphism and suicidal behavior: meta-analysis and new data

BACKGROUND

The polymorphism COMTval158met has been associated with suicidal behavior in case-control and meta-analysis studies, but results and conclusions remain controversial. The objective of this study was to examine the association between COMT val158met with suicidal behavior in a case-control study and to assess the combined evidence -this case-control study and available data from other related studies- we carried out a meta-analysis.

METHODS

We conducted a case-control study with 105 patients with suicide attempts and 236 controls. Subsequently, we performed a meta-analysis of published genetic association studies by searching through Medline, PubMed and Web of Science databases.

RESULTS

No significant differences were found in the distribution of alleles (χ2 = 0.33, 1 df, p = 0.56) or genotypes (χ2 = 2.36, 2 df, p = 0.26). The meta-analysis comprising 12 association studies (including the present one) showed that the risk COMTmet allele of COMTval158/met is not associated with suicidal behavior (OR: 1.09, 95% CI: 0.97-1.23), even in the absence of heterogeneity (OR: 1.09, 95% CI: 0.97-1.23).

CONCLUSION

Our results showed no association between COMTval158/met and suicidal behavior. However, more studies are necessary to determine conclusively an association between COMT and suicidal behavior.

Gender effect of catechol-O-methyltransferase Val158Met polymorphism on suicidal behavior

Genetic factors and catecholaminergic dysfunction have been suggested as the etiology of suicide. The catechol-O-methyltransferase (COMT) 158Val/Met polymorphism affects COMT activity; that is, the alleles encoding Val and Met are associated with relatively high and relatively low COMT activity, respectively. We aimed to identify the role of the COMT Val158Met polymorphism in suicidal attempt behavior. The COMT 158Val/Met polymorphisms were analyzed in 197 suicide attempters (male/female: 70/127), 170 control subjects (male/female: 85/85). All subjects were ethnic Korean. The Lethality Suicide Attempt Rating Scale (LSARS) and risk-rescue rating (RRR) system were explored. For the male subjects, there was a significant difference in genotype distributions and allele frequencies between control subjects and suicide attempters. That is, Val/Val genotype and Val carriers were more frequent in suicide attempters than in control subjects. For the female subjects, however, no significant difference was shown in genotype distributions and allele frequencies between control subjects and suicide attempters. There were no significant differences in LSARS and RRR according to the genotypes. The distribution of the COMT 158Val/Met polymorphism showed a biologically meaningful difference between control subjects and suicide attempters among the male subjects although selection bias should be considered.

Association study of a functional catechol-O-methyltransferase (COMT) Val108/158Met polymorphism and suicide attempts in patients with alcohol dependence

Alcohol dependence is frequently associated with aggressive and suicidal behaviour. Genetic factors contribute to both behaviours. Candidate genes, related to suicide and aggression, include genes involved in serotonin, norepinephrine and dopamine pathways. The enzyme catechol-O-methyl transferase (COMT) degrades dopamine, epinephrine and norepinephrine. The functional polymorphism (COMT Val108/158Met) affects COMT activity, with the valine (Val) variant associated with higher and the methionine (Met) variant with lower COMT activity. This polymorphism is associated with aggressive and suicidal behaviour, but the literature data on this relationship is contradictory and inconsistent. The hypothesis of this study was that Met allele carriers with alcohol dependence will have a higher frequency of suicide attempts compared to other genotypes. Participants were 312 male and 81 female medication-free patients with alcohol dependence and 487 male and 122 female unrelated, non-suicidal medication-free Caucasian healthy subjects. Our results showed significant (χ2 test with standardized residuals) differences in the frequencies of COMT variants in all alcoholics, alcoholics with different comorbid diagnoses, and in male but not in female alcoholics, with or without suicide attempts. Male alcoholic suicide attempters, compared to male non-attempters, had the higher frequency of Met/Met genotype or Met allele, and significantly (Kruskal-Wallis ANOVA on ranks and Mann-Whitney test) higher aggression and depression scores. These results confirmed the associations between Met allele and aggressive behaviour or violent suicide attempts in various psychiatric diagnoses, and suggested that Met allele of the COMT Val108/158 Met might be used as an independent biomarker of suicidal behaviour across different psychopathologies.

Behavioral and neurochemical effects of chronic L-DOPA treatment on nonmotor sequelae in the hemiparkinsonian rat

Depression and anxiety are the prevalent nonmotor symptoms that worsen quality of life for Parkinson's disease (PD) patients. Although dopamine (DA) cell loss is a commonly proposed mechanism, the reported efficacy of DA replacement therapy with L-DOPA on affective symptoms is inconsistent. To delineate the effects of DA denervation and chronic L-DOPA treatment on affective behaviors, male Sprague-Dawley rats received unilateral 6-hydroxydopamine or sham lesions and were treated daily with L-DOPA (12 mg/kg+benserazide, 15 mg/kg, subcutaneously) or vehicle (0.9% NaCl, 0.1% ascorbic acid) for 28 days before commencing investigations into anxiety (locomotor chambers, social interaction) and depression-like behaviors (forced swim test) during the OFF phase of L-DOPA. One hour after the final treatments, rats were killed and striatum, prefrontal cortex, hippocampus, and amygdala were analyzed through high-performance liquid chromatography for monoamine levels. In locomotor chambers and social interaction, DA lesions exerted mild anxiogenic effects. Surprisingly, chronic L-DOPA treatment did not improve these effects. Although DA lesion reduced climbing behaviors on day 2 of exposure to the forced swim test, chronic L-DOPA treatment did not reverse these effects. Neurochemically, L-DOPA treatment in hemiparkinsonian rats reduced norepinephrine levels in the prefrontal cortex, striatum, and hippocampus. Collectively, these data suggest that chronic L-DOPA therapy in severely DA-lesioned rats does not improve nonmotor symptoms and may impair nondopaminergic processes, indicating that long-term L-DOPA therapy does not exert necessary neuroplastic changes for improving affect.

Heterotrimeric g proteins: insights into the neurobiology of mood disorders

Mood disorders such as major depression and bipolar disorder are common, severe, chronic and often life-threatening illnesses. Suicide is estimated to be the cause of death in up to approximately 10-15% of individuals with mood disorders. Alterations in the signal transduction through G protein-coupled receptor (GPCR) pathways have been reported in the etiopathology of mood disorders and the suicidal behavior. In this regard, the implication of certain GPCR subtypes such as alpha(2A)-adrenoceptor has been repeatedly described using different approaches. However, several discrepancies have been recently reported in density and functional status of the heterotrimeric G proteins both in major depression and bipolar disorder. A compilation of the most relevant research topics about the implication of heterotrimeric G proteins in the etiology of mood disorders (i.e., animal models of mood disorders, studies in peripheral tissue of depressive patients, and studies in postmortem human brain of suicide victims with mood disorders) will provide a broad perspective of this potential therapeutic target field. Proposed causes of the discrepancies reported at the level of G proteins in postmortem human brain of suicide victims will be discussed.

Lower CSF MHPG predicts short-term risk for suicide attempt

Post-mortem studies document alterations in the central noradrenergic system in suicide. However, studies of non-fatal suicide attempts have, thus far, found no consistent relationship to the noradrenaline metabolite 3-methoxy-4-hydroxphenylglycol (MHPG) in cerebrospinal fluid (CSF). We therefore conducted a prospective study of CSF MHPG and suicidal acts in major depression and bipolar depression. CSF MHPG was assayed in 184 drug-free patients with DSM-IV major depressive disorder or bipolar disorder, presenting for treatment of a current depressive episode, who were then followed-up for up to 12 months. Survival analysis was conducted using Cox proportional hazards modelling to test association of CSF MHPG and future suicidal behaviour, and potential clinical mediators. Twenty-seven individuals made a suicide attempt (two fatal) in the follow-up period. Lower CSF MHPG predicted future suicide attempt or suicide (22% increase in hazard for each 10 pmol/ml lower MHPG, p=0.045). Lower CSF MHPG also correlated with higher medical lethality of future suicidal act (mean MHPG: 49+/-18 vs. 32+/-12 pmol/ml for low- vs. high-lethality, t=2.8, d.f.=25, p=0.009). Smoking and self-rated depression severity were also associated with lower CSF MHPG and with future suicide attempt, but were not statistically significant mediators in multivariate models. In conclusion, lower CSF MHPG is associated with short-term risk for future suicidal behaviour in the 12 months following a major depressive episode. Psychopathology that mediates the relationship between lower CSF MHPG and future suicidal behaviour needs to be identified.

Receptor mapping: architecture of the human cerebral cortex

PURPOSE OF REVIEW

Cytoarchitectonical brain mapping is of growing interest as a powerful tool for localization of activated brain regions in functional neuroimaging. Mapping of neurotransmitter receptors can provide novel molecular and functionally relevant information to the available cytoarchitectonical brain maps, because receptors are key molecules of neurotransmission. This review highlights the relation between cytoarchitectonical parcellations and the regionally inhomogeneous distribution of receptors. It will demonstrate the potential of receptor mapping for novel and functionally relevant insights into the regional organization of the human cortex.

RECENT FINDINGS

Mapping of a single receptor type can already reveal borders of functionally and cytoarchitectonically distinct cortical regions. The combined mapping of various receptors in each cortical area (receptor fingerprint) represents the balance between different neurotransmitter systems and often reveals hitherto unknown parcellations. Different brain regions are identified as parts of distinct functional systems.

SUMMARY

Receptor mapping of the human brain, particularly multireceptor mapping, provides a novel and multimodal view of its anatomical, functional and molecular organization. It reveals organizational principles of the segregation of cortical and subcortical structures. It improves our understanding of the brain's architecture beyond the limits of cytoarchitectonics and serves as a basis for clinical and pharmacological studies of brain diseases.

Suicide neurobiology

In this review, we examine the history of the neurobiology of suicide, as well as the genetics, molecular and neurochemical findings in suicide research. Our analysis begins with a summary of family, twin, and adoption studies, which provide support for the investigation of genetic variation in suicide risk. This leads to an overview of neurochemical findings restricted to neurotransmitters and their receptors, including recent findings in whole genome gene expression studies. Next, we look at recent studies investigating lipid metabolism, cell signalling with a particular emphasis on growth factors, stress systems with a focus on the role of polyamines, and finally, glial cell pathology in suicide. We conclude with a description of new ideas to study the neurobiology of suicide, including subject-specific analysis, protein modification assessment, neuroarchitecture studies, and study design strategies to investigate the complex suicide phenotype.

Global brain gene expression analysis links glutamatergic and GABAergic alterations to suicide and major depression

BACKGROUND

Most studies investigating the neurobiology of depression and suicide have focused on the serotonergic system. While it seems clear that serotonergic alterations play a role in the pathogenesis of these major public health problems, dysfunction in additional neurotransmitter systems and other molecular alterations may also be implicated. Microarray expression studies are excellent screening tools to generate hypotheses about additional molecular processes that may be at play. In this study we investigated brain regions that are known to be implicated in the neurobiology of suicide and major depression are likely to represent valid global molecular alterations.

METHODOLOGY/PRINCIPAL FINDINGS

We performed gene expression analysis using the HG-U133AB chipset in 17 cortical and subcortical brain regions from suicides with and without major depression and controls. Total mRNA for microarray analysis was obtained from 663 brain samples isolated from 39 male subjects, including 26 suicide cases and 13 controls diagnosed by means of psychological autopsies. Independent brain samples from 34 subjects and animal studies were used to control for the potential confounding effects of comorbidity with alcohol. Using a Gene Ontology analysis as our starting point, we identified molecular pathways that may be involved in depression and suicide, and performed follow-up analyses on these possible targets. Methodology included gene expression measures from microarrays, Gene Score Resampling for global ontological profiling, and semi-quantitative RT-PCR. We observed the highest number of suicide specific alterations in prefrontal cortical areas and hippocampus. Our results revealed alterations of synaptic neurotransmission and intracellular signaling. Among these, Glutamatergic (GLU) and GABAergic related genes were globally altered. Semi-quantitative RT-PCR results investigating expression of GLU and GABA receptor subunit genes were consistent with microarray data.

CONCLUSIONS/SIGNIFICANCE

The observed results represent the first overview of global expression changes in brains of suicide victims with and without major depression and suggest a global brain alteration of GLU and GABA receptor subunit genes in these conditions.

Family history of alcoholism is associated with lower 5-HT2A receptor binding in the prefrontal cortex

BACKGROUND

5-Hydroxytryptophan (5-HT(2A)) receptor involvement in alcoholism is suggested by less 5-HT(2A) binding in alcohol preferring rats, association of a 5-HT(2A) receptor gene polymorphism with alcohol dependence and reduced alcohol intake with 5-HT(2A) antagonists. We sought to determine postmortem whether 5-HT(2A) receptors are altered in the prefrontal cortex (PFC) of alcoholics.

METHODS

Brain tissue from 25 alcoholics and 19 controls was collected at autopsy. Diagnosis of DSM-IV alcoholism/abuse and other psychiatric disorders and the determination of family history of alcoholism were made by psychological autopsy. Specific binding to 5-HT(2A) ((3)H-ketanserin) receptors in the PFC was measured by quantitative autoradiography.

RESULTS

5-HT(2A) binding decreased with age [Brodmann areas (BA) 9, 46 gyrus; r = -0.381, -0.334, p < 0.05]. No differences in receptor binding between alcoholics and controls were detected in the gyrus or sulcus of any PFC area examined. Cases (controls or alcoholics) with a family history of alcoholism (n = 23) had less 5-HT(2A) binding throughout PFC than subjects without (n = 21) a family history of alcoholism (p < 0.05). 5-HT(2A) receptor binding in alcoholics without a family history of alcoholism (n = 7) did not differ from controls without a family history of alcoholism (n = 14). There was no association between alcoholism or alcohol rating and genotype. There was an association between genotype and the total amount of (3)H-ketanserin binding in BA46 with the TT genotype having more binding (TT>TC approximately CC).

CONCLUSIONS

Lower 5-HT(2A) receptor binding in the PFC of cases with a family history of alcoholism suggests a genetic predisposition to alcoholism. Alcohol abuse by itself did not have a significant effect on PFC 5-HT(2A) binding and as 5-HT(2A) binding in alcoholics is not different from controls and antagonists may be therapeutic, fewer receptors may result in downstream developmental effects on the brain resulting in a predisposition to alcoholism.

Power based association analysis (PBAT) of serotonergic and noradrenergic polymorphisms in bipolar patients with suicidal behaviour

BACKGROUND AND AIMS

Suicidality is a major health concern worldwide particularly in affective disorder patients. Attempted suicide is familial. There is strong neurobiological evidence showing that serotonergic and noradrenergic dysfunction is implicated in suicidal behaviours. We will apply now a new family based association strategy aimed to explain the genetic influence in suicidal behaviour by power based association test statistics (PBAT) in 336 bipolar patients assessed for suicidality within nuclear families.

METHODS

By use of conditional power calculations, the approach screens all possible null hypotheses without biasing the nominal significance level, and it identifies the subset of phenotypes that has optimal power when tested for association by either univariate or multivariate family based association test (FBAT). Using this statistical approach (PBAT) we investigated polymorphisms in serotonergic and noradrenergic genes, considering suicidal behaviour severity instead of the dichotomous phenotype (presence of suicide attempt).

RESULTS

COMT Val/Met polymorphism was not associated with suicide with high confidence (power=91%). On the other hand, the analysis of the other 12 markers in the adrenergic and serotonergic genes revealed that the TH allele tended towards association with higher severity of suicidal behaviour (p=0.060) but the power obtained was very low.

CONCLUSIONS

The marginal finding of association between TH and severe suicidal behaviour are convergent with previous reports. On the other hand, our sample has enough power to exclude the other polymorphisms investigated as major candidate for suicidality in bipolar disorder.

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.

Meta-analyses suggest association between COMT, but not HTR1B, alleles, and suicidal behavior

Several studies have suggested that suicidal behavior is at least partially determined by genetic factors, supporting a search for related genes. Two genes that have been highlighted in the literature as being involved are HTR1B, which codes for the serotonin 1B receptor, and COMT, which is related to the inactivation of catecholamines. In order to assess the combined evidence for the numerous studies that have been published relating suicidal behavior to these two genes, two different random effects meta-analyses were conducted utilizing seven studies related to HTR1B and six studies related to COMT. For HTR1B, the combined evidence from 789 case and 1,247 control subjects/participants, suggested that there was no significant association between the HTR1B G861C polymorphism and suicidal behavior. For COMT, based on the combined data from 519 cases and 933 control subjects, there was evidence of a significant association between the COMT 158Met polymorphism and suicidal behavior. Although the results for COMT were not influenced by publication bias, the significance of the combined results was not robust and was related to the gender of the case and control subjects. The results for COMT support past literature that has found a relationship between suicidal behavior and COMT, and has also found that the relationship differs for males and females. Given that in the United States a higher proportion of females attempt suicide, and the higher proportion of males successfully commit suicide, it is possible that COMT is related to the lethality of suicide attempts.

A review of prospective studies of biologic predictors of suicidal behavior in mood disorders

Predicting suicide is difficult due to the low base rate, even in high-risk groups, and the multi-causal nature of suicidal behavior. Clinical predictors have shown low specificity. Retrospective and cross-sectional studies have identified a number of biologic anomalies associated with suicide and suicide attempt. Prospective studies provide estimates of the predictive utility of biologic measures. Here we review prospective studies of suicidal behavior and serotonergic, noradrenergic, dopaminergic and hypothalamic-pituitary-adrenocortical axis function in mood disorders. The most promising biologic predictors are low CSF 5-HIAA and HPA axis dysfunction as demonstrated by dexamethasone non-suppression that are each associated with about 4.5 fold greater risk of suicide.

Increased plasma nitric oxide metabolites in suicide attempters

OBJECTIVE

To evaluate any correlation between plasma levels of nitric oxide metabolites (NO(x)) and suicide attempt.

METHOD

Plasma NO(x) levels were measured in 53 patients who had recently attempted suicide, 58 non-suicidal psychiatric patients, and 75 normal controls. The severity of suicidal behaviors was evaluated using Weisman and Worden's Risk-Rescue Rating Scale.

RESULTS

Plasma NO(x) levels were significantly higher in suicidal patients than non-suicidal psychiatric patients or normal control subjects (F=11.029, d.f.=2, 183, p<0.001). Among the patients with a diagnosis of major depression, suicidal depressive patients had significantly higher plasma NO(x) levels than non-suicidal depressive patients (t=-3.090, d.f.=84, p=0.003).

CONCLUSION

Our study suggests that increased NO production in plasma is associated with suicide attempt, especially in depressive patients.

Expression of the α1A-adrenergic receptor in schizophrenia

The alpha1-adrenergic receptors may contribute to cognitive functions relevant to schizophrenia. Following the discovery of an association between polymorphisms in the regulatory region of the alpha1A-adrenergic receptor and schizophrenia we investigated the expression of mRNA for this receptor between schizophrenics (n=19) and controls (n=19) using a TaqMan approach in post-mortem brains. No differences were found suggesting that mRNA levels are not altered in schizophrenia. Genotypic data for the subjects found that possession of the previously associated genotypes did not convey a difference in mRNA expression suggesting that these polymorphisms do not affect the level of transcription.

Gene-gene interaction between MAOA and COMT in suicidal behavior: analysis in schizophrenia

A large body of evidence suggests that suicidal behavior is associated with altered noradrenergic neurotransmission. Norepinephrine is degraded by monoamine oxidase A (MAOA) and catechol-O-methyl transferase (COMT). Our hypothesis is that the genes encoding MAOA and COMT might contain genetic variants conferring increased risk for suicidal behavior in schizophrenia and that both genes may interact each other. In order to test this hypothesis, we genotyped the promoter VNTR polymorphism in the MAOA gene and three COMT polymorphisms: -287A>G, Val/Met and 3'UTR C Ins/Del in a cohort of 270 schizophrenics in which 92 attempted suicide. No association between suicide attempt and the MAOA VNTR (P = 0.382), Val108/158Met (P = 0.788) or -287A>G (P = 0.420) polymorphisms was found, however, a slight significant finding was found for 3'UTR polymorphism (P = 0.050). Haplotype analysis for COMT gene revealed no association between suicide attempts and haplotype distribution (P = 0.451). As we tested for epistasis between MAOA VNTR and COMT Val/Met, we found no significant interaction in conferring risk for suicide attempts (P = 0.545). These results suggest that epistasis between MAOA and COMT genes may not influence suicidal behavior in patients with schizophrenia.

Serotonergic and Noradrenergic Neurobiology of Alcoholic Suicide

BACKGROUND

Alcoholism is associated with alterations in the serotonergic and noradrenergic systems. Alcoholics are at a significantly higher risk for suicide than the general population. Altered serotonin (5-HT) function is associated with suicide and serious suicide attempts. We hypothesized patterns of abnormality associated independently with suicide and with alcoholism.

METHODS

Quantitative autoradiographic experiments were performed in human postmortem brain tissue sections from alcoholics, alcoholic-suicide decedents, nonalcoholic suicide decedents, and normal controls diagnosed by psychological autopsy.

RESULTS

Binding to 5-HT1A receptors is lower in both alcoholic suicides and alcoholic nonsuicides, suggesting that this effect is related to alcoholism and not suicide. In nonalcoholic suicides, there is a localized increase in 5-HT1A binding in ventral prefrontal cortex, hypothesized to be a response to less serotonin input. Therefore, alcoholic suicides may fail to up-regulate ventral prefrontal 5-HT1A receptors in response to decreased serotonergic transmission, failing to mitigate the impact of less serotonin upon signal transduction and thereby increasing the risk of suicidal behavior. Binding to the serotonin transporter is low in alcoholic suicides but not in alcoholic nonsuicides, suggesting an association with suicide, as nonalcoholic suicides also have decreased binding compared with controls. Evidence of impaired serotonergic innervation associated with alcoholism is also manifested by less 5-HT1D terminal autoreceptor binding in alcoholics. Nonalcoholic suicides do not have lower 5-HT1D binding. In the noradrenergic system, alcoholics (suicide and nonsuicide) and nonalcoholic suicide victims all have fewer pigmented locus ceruleus neurons compared with controls, yet beta1-adrenergic binding is low in both alcoholic groups, whereas alpha1-and alpha2-adrenergic binding decreases are more pronounced in the alcoholic suicide group. These noradrenergic findings differ from those in nonalcoholic suicides, which have a common feature with alcoholics in having less alpha2-and beta1-adrenergic binding but more alpha1-adrenergic binding in ventrolateral and orbital cortex.

CONCLUSION

Extensive but different abnormalities in both the serotonergic and noradrenergic systems have been identified in alcoholics and suicides, suggesting two separate patterns: one related to alcoholism and the other related to suicide. The different patterns suggest different causes and homeostatic responses for alcoholism and suicide.

Higher postmortem prefrontal 5-HT2A receptor binding correlates with lifetime aggression in suicide

BACKGROUND

In vivo studies find altered serotonin function associated with aggressive and suicidal behaviors. Postmortem studies also reveal serotonergic alterations in suicide subjects but have not reported on the relationship between aggression and the serotonin system. We measured 5-hydroxytryptamine 2A (5-HT(2A)) receptor binding in prefrontal cortex of suicide and nonsuicide subjects and explored the relationship between 5-HT(2A) receptor binding, lifetime aggression, and suicide.

METHODS

The 5-HT(2A) receptor binding in coronal sections of prefrontal cortex was quantified by autoradiography with [(3)H] ketanserin in 37 suicide subjects and 73 nonsuicide subjects. The relationship between [(3)H] ketanserin binding and lifetime aggression, rated on the Brown-Goodwin Aggression History Scale, was assessed controlling for age and sex.

RESULTS

In suicide subjects, lifetime aggression scores correlated positively with [(3)H] ketanserin binding in all prefrontal Brodmann areas examined, after adjusting for age and sex. This was not the case in nonsuicide subjects. We found no significant differences in aggression scores or [(3)H] ketanserin binding between the suicide subjects and nonsuicide subjects.

CONCLUSIONS

The relationship between aggression and 5-HT(2A) receptor binding in suicide subjects, but not in nonsuicide subjects, may reflect differences in the regulation of the 5-HT(2A) receptor related to suicidal behavior and perhaps other proaggressive changes in brains of suicide subjects.

Endocannabinoid lipids and mediated system: implications for alcoholism and neuropsychiatric disorders

Several natural lipids have emerged as candidate modulators of central nervous system (CNS) functions. Fatty acid amides and their coupled signaling pathways are known to regulate several physiological and behavioral processes. Recent studies from our laboratory and others also have implicated endogenous marijuana-like brain constituents, endocannabinoids (ECs), and cannabinoid-1 (CB1) receptors in the neural circuitry that mediate drug addiction and neuropsychiatric disorders. Neuroadaptation to chronic ethanol (EtOH) has been shown to involve changes in the EC system. These changes include alterations in the synthesis of EC, their precursors, as well as density and coupling efficacy of CB1 receptors. The evidence for the participation of the EC system in the pathophysiology of various neuropsychiatric disorders is just beginning to evolve. It is of great interest to explore the components of EC system in different areas of the CNS for further understanding of its role in health and disease. This article presents a comprehensive overview of the currently available literature pertaining to the role of the EC system in alcoholism, schizophrenia, depression and/or suicide.

Polymorphisms in the promoter region of the alpha1A-adrenoceptor gene are associated with schizophrenia/schizoaffective disorder in a Spanish isolate population

BACKGROUND

Animal models have implicated the alpha(1)-adrenergic subtypes in cognitive functions relevant to schizophrenia, but no consensus exists with regard to the status of noradrenergic receptor populations in psychiatric patients. We focused on one alpha(1)-adrenergic subtype, the alpha(1A)-adrenergic receptor, and proposed that genetic variants within the regulatory region of this gene (ADRA1A) alter the expression of this receptor, influencing susceptibility toward schizophrenia.

METHODS

This study examined this proposal by testing the hypothesis that single nucleotide polymorphisms (SNPs) in the promoter region of the alpha(1A)-adrenergic gene were associated with schizophrenia by performing case-control association analysis on SNPs found in a 5' upstream region, which included the putative promoter region and 5' untranslated region. Our sample consisted of 103 schizophrenia and 14 schizoaffective disorder patients and 176 control subjects. All recruits were from a Spanish population isolate of Basque origin that is characterized by low heterogeneity, which was selected with the intent that it might facilitate the identification of disease-related polymorphisms.

RESULTS

A total of eight SNPs (-9625 G/A, -7255 A/G, -6274 C/T, -4884 A/G, -4155 C/G, -2760 A/C, -1873 G/A, and -563 C/T) were confirmed at a rare allele frequency of >5%. Association with schizophrenia and schizoaffective disorder was found for the -563 C/T SNP (p = .0005 for allele and p = .007 for genotype, Bonferroni corrected) and -9625 G/A SNP (p = .02 for allele and p = .03 for genotype, Bonferroni corrected). Significant differences in the 54 haplotypes formed by these eight SNPs were also found between patients and control subjects (p = .008, Bonferroni corrected).

CONCLUSIONS

Because of the strength of these results and the location of these SNPs in the regulatory region of this gene, functional studies investigating the possible influence of these SNPs on receptor expression levels in schizophrenia are warranted.

Gene–gene interaction between MAOA and COMT in suicidal behavior

Several lines of evidence suggest that suicidal behavior is associated with altered noradrenergic neurotransmission. Noradrenaline (NA) is catabolized by monoamine oxidase A (MAOA) and cathecol-O-methyl transferase (COMT). We hypothesized that the genes encoding MAOA and COMT might contain genetic variation conferring increased risk for attempted suicide. In order to test this hypothesis, we genotyped the 941T > G and the promoter VNTR polymorphisms in the MAOA gene and the Val 108/158 Met COMT polymorphism in 305 families with at least one member having bipolar disorder (BD). No association with history of suicide attempt was found either in the MAOA polymorphisms (VNTR:LRS = 1.90, d.f. = 1, p = 0.16; 941T > G:LRS = 1.39, d.f. = 1, p = 0.23), or with the Val 158 Met polymorphism (LRS = 1.61, d.f.=1, p = 0.20). When we performed the haplotype analysis for MAOA gene, we found no association between suicide attempt and haplotype distribution (LRS = 3.07, d.f. = 2, p = 0.21). As both genes are involved in degrading noradreanline, we also tested the hypothesis of epistasis between MAOA polymorphisms and Val158Met, however, no additive effect was found in conferring risk for suicide attempt. These findings suggest that MAOA and COMT genes may not influence suicidal behavior in patients with bipolar disorder.

Suicidal disorders: A nosological entity per se?

An extensive body of data has repeatedly shown in the past decades that suicidal behaviors are associated with several external validators such as low serotonergic activity in body fluids and in brains of suicide victims, genetic transmission of suicide risk independently of transmission of associated major psychiatric disorders, and more recently association with several serotonin-related genes. Despite these concordant findings, suicidal behaviors are still not considered as a nosological entity per se in standardized classification. The aim of this study is to review the existing literature establishing the validity of this entity through clinical, genetic, biochemical, and therapeutic arguments all leading to the need to recognizing suicidal behavior as an independent and possibly dimensional clinical entity.

Association between catechol-O-methyltransferase functional polymorphism and male suicide completers

Suicide has been suggested to involve catecholaminergic dysfunction and to be related to genetics. Catechol-O-methyltransferase (COMT) 158Val/Met polymorphism (GenBank Accession No. Z26491) is a polymorphism of the gene encoding COMT, a major enzyme in catecholamine inactivation. The COMT 158Val/Met polymorphism affects COMT activity, that is, the alleles encoding Val and Met are associated with relatively high and relatively low COMT activity, respectively. In this study, we hypothesized that the COMT 158Val/Met polymorphism is associated with suicide. The study population consisted of 163 suicide completers (112 males and 51 females). We found that the genotype distribution of the COMT 158Val/Met polymorphism was significantly different between male suicide completers and male controls (p=0.036), while the frequency of the Val/Val genotype, a high-activity COMT genotype, was significantly less in male suicide completers than in male controls (OR: 0.52; 95% CL: 0.31-0.89; p=0.016). However, this was not the case in females. Our results suggest that the Val/Val genotype is a protective factor against suicide in males.

Differential expression of alpha2-adrenoceptor vs. imidazoline binding sites in postmortem orbitofrontal cortex and amygdala of depressed subjects

Clonidine is a well established antihypertensive agent that is also used effectively to treat a variety of psychiatric disorders. Clonidine is a prototypic imidazoline compound that acts as an alpha(2)-adrenergic agonist but possesses nearly equivalent affinity for non-adrenergic imidazoline binding sites (I-sites). Receptor autoradiography of [(3)H]-clonidine binding presented herein compares densities of alpha(2)-adrenoceptors and I-sites (under a noradrenergic-mask) in Brodmann's area 47 of the left orbitofrontal cortex (OFC) and in six amygdaloid nuclei of subjects with major depression (n=12) vs. controls with no psychiatric history (n=11). Postmortem diagnoses were made from psychiatric interviews with next-of-kin. [(3)H]-Clonidine binding to alpha(2)-adrenoceptors in each of six OFC layers was lower, although not reaching statistical significance in any one layer by multivariate analysis, in depressives vs. control subjects. Binding to I-sites was conversely higher in depressives compared to control OFC layers, but did not reach statistical significance alone. However, the ratios of alpha(2)-adrenoceptor : I-sites in all six layers of OFC of depressed subjects were nearly half that of control subjects (P<0.008). In amygdalas from a different group of depressed patients there were no changes in alpha(2)-adrenoceptors or I-sites, or their ratios, compared with controls. The results support previous western blot data indicating a cortex-selective shift away from alpha(2)AR towards I-site preponderance in depressed patients.

Emerging evidence for a central epinephrine-innervated alpha 1-adrenergic system that regulates behavioral activation and is impaired in depression

Currently, most basic and clinical research on depression is focused on either central serotonergic, noradrenergic, or dopaminergic neurotransmission as affected by various etiological and predisposing factors. Recent evidence suggests that there is another system that consists of a subset of brain alpha(1B)-adrenoceptors innervated primarily by brain epinephrine (EPI) that potentially modulates the above three monoamine systems in parallel and plays a critical role in depression. The present review covers the evidence for this system and includes findings that brain alpha(1)-adrenoceptors are instrumental in behavioral activation, are located near the major monoamine cell groups or target areas, receive EPI as their neurotransmitter, are impaired or inhibited in depressed patients or after stress in animal models, and are restored by a number of antidepressants. This "EPI-alpha(1) system" may therefore represent a new target system for this disorder.

[3H]RX 821002 in human dorsolateral prefrontal cortex: no changes in postmortem tissue from subjects with schizophrenia

One of the major differences between the atypical antipsychotic drugs clozapine and olanzapine is that clozapine has a two-fold higher affinity for the alpha(2)-adrenoreceptors. As clozapine can have therapeutic benefits in individuals that do not respond to other antipsychotic drugs, this raises the possibility that changes in the alpha(2)-adrenoreceptors could be a marker for a predisposition to treatment resistance. A methodology has been optimised to measure the binding of [3H]RX 821002 to alpha(2)-adrenoreceptors in human postmortem CNS and has shown that these receptors are not altered in Brodmann's area 9 from subjects with schizophrenia. These data add to those of one other study that showed the alpha(2)-adrenoreceptors were not altered in Brodmann's area 10 and the hippocampus from subjects with schizophrenia, and do not support the hypothesis that changes in alpha(2)-adrenoreceptors are a marker for treatment resistance in schizophrenia.

Neurotransmitter receptor-mediated activation of G-proteins in brains of suicide victims with mood disorders: selective supersensitivity of alpha(2A)-adrenoceptors

Abnormalities in the density of neuroreceptors that regulate norepinephrine and serotonin release have been repeatedly reported in brains of suicide victims with mood disorders. Recently, the modulation of the [(35)S]GTPgammaS binding to G-proteins has been introduced as a suitable measure of receptor activity in postmortem human brain. The present study sought to evaluate the function of several G-protein coupled receptors in postmortem brain of suicide victims with mood disorders. Concentration-response curves of the [(35)S]GTPgammaS binding stimulation by selective agonists of alpha(2)-adrenoceptors, 5-HT(1A) serotonin, mu-opioid, GABA(B), and cholinergic muscarinic receptors were performed in frontal cortical membranes from 28 suicide victims with major depression or bipolar disorder and 28 subjects who were matched for gender, age and postmortem delay. The receptor-independent [(35)S]GTPgammaS binding stimulation by mastoparan and the G-protein density were also examined. The alpha(2A)-adrenoceptor-mediated stimulation of [(35)S]GTPgammaS binding with the agonist UK14304 displayed a 4.6-fold greater sensitivity in suicide victims than in controls, without changes in the maximal stimulation. No significant differences were found in parameters of 5-HT(1A) serotonin receptor and other receptor-mediated [(35)S]GTPgammaS binding stimulations. The receptor-independent activation of G-proteins was similar in both groups. Immunoreactive densities of G(alphai1/2)-, G(alphai3)-, G(alphao)-, and G(alphas)-proteins did not differ between suicide victims and controls. In conclusion, alpha(2A)-adrenoceptor sensitivity is increased in the frontal cortex of suicide victims with mood disorders. This receptor supersensitivity is not related to an increased amount or enhanced intrinsic activity of G-proteins. The new finding provides functional support to the involvement of alpha(2)-adrenoceptors in the pathogenesis of mood disorders.

Elevated agonist binding to alpha2-adrenoceptors in the locus coeruleus in major depression

BACKGROUND

Recent postmortem studies demonstrate disrupted neurochemistry of the noradrenergic locus coeruleus (LC) in major depression (MD). Increased levels of tyrosine hydroxylase and decreased levels of norepinephrine transporter implicate a norepinephrine deficiency in the LC in MD. Here we describe a study of alpha2-adrenoceptors in the LC and raphe nuclei of subjects with MD compared with psychiatrically normal control subjects.

METHODS

The specific binding of p-[125I]iodoclonidine to alpha2-adrenoceptors was measured at multiple levels along the rostrocaudal extent of the LC in postmortem tissue from 14 control and 14 MD subjects. In addition, p-[125I]iodoclonidine binding was measured in the dorsal and median raphe nuclei in the same tissue sections.

RESULTS

The specific binding of p-[125I]iodoclonidine to alpha2-adrenoceptors was significantly elevated throughout the LC from MD compared with matched control subjects. No significant differences were observed in p-[125I]iodoclonidine binding to alpha2-adrenoceptors in the raphe nuclei comparing MD and control subjects.

CONCLUSIONS

Given that alpha2-adrenoceptors are upregulated in laboratory animals by treatment with drugs that deplete norepinephrine, our findings implicate a premortem deficiency of brain norepinephrine in the region of the locus coeruleus in subjects with MD.

Understanding the neurobiology of suicidal behavior

Our current knowledge about the neurobiology of suicide is still limited. Technical limitations and the complexity of the CNS are major obstacles. However, there is evidence for a hereditary disposition to suicide, which appears to be independent of diagnosis. Clinical, postmortem, genetic, and animal studies suggest that serotonin has a central role. The main regions of interest in the CNS have been the dorsal and median raphe nuclei in the midbrain that host the main serotonergic cell bodies and the prefrontal cortex, particularly the ventral PFC, innervated by the serotonergic system. In vivo and postmortem studies indicate serotonergic hypofunction in suicide and serious suicide attempts. This deficiency in turn can lead to a predisposition to impulsive and aggressive behavior, probably due to a breakdown in the inhibitory function of the ventral prefrontal cortex as a result of less serotonin input. In the context of this predisposition and the development of mental illness or other life stressors, the individual is at risk of acting on suicidal thoughts. Such deficient serotonin input into the PFC may arise as a result of genetic, parenting, head injury, and other effects. Identifying psychiatric, social, and environmental predictors of suicide are studied to improve prediction and prevention of suicide. A better understanding of the neurobiology of suicide can help detect at risk populations and help develop better treatment interventions.

Depression as a spreading adjustment disorder of monoaminergic neurons: a case for primary implication of the locus coeruleus

A model for the pathophysiology of depression is discussed in the context of other existing theories. The classic monoamine theory of depression suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. More recent elaborations of the classic theory also implicitly include this postulate, other theories of depression frequently prefer to depart from the monoamine-based model altogether. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity, and concomitantly, exaggerated responses to acute increases in the presynaptic firing rate and transmitter release. It is proposed that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus (LC). Dysregulation of the LC projection activities may lead in turn to dysregulation of serotonergic and dopaminergic neurotransmission. Failure of the LC function could explain the basic impairments in the processing of novel information, intensive processing of irrational beliefs, and anxiety. Concomitant impairments in the serotonergic neurotransmission may contribute to the mood changes and reduction in the mesotelencephalic dopaminergic activity to loss of motivation, and anhedonia. Dysregulation of CRF and other neuropeptides such as neuropeptide Y, galanin and substance P may reinforce the LC dysfunction and thus further weaken the adaptivity to stressful stimuli.

Noradrenergic pathology in psychiatric disorders: postmortem studies

In this paper, we review research utilizing postmortem brain tissue in order to investigate the potential neuropathology of the noradrenergic system in psychiatric disorders. The postmortem tissue approach to the study of the noradrenergic system has been used primarily in investigations of the biology of suicide and depression. Findings from postmortem studies provide data generally consistent with the hypothesis that a norepinephrine deficiency exists in depression, and possibly in the victims of suicide. However, postmortem studies do not presently provide irrefutable evidence of noradrenergic neuropathology. Technical shortcomings, issues of reproducibility, and the strengths of postmortem research are reviewed. More rigorously performed postmortem research is needed to aid researchers in pinpointing specific neuropathologies associated with psychiatric disease.

Brain alpha(2)-adrenoceptors in monoamine-depleted rats: increased receptor density, G coupling proteins, receptor turnover and receptor mRNA

1. This study was designed to assess the molecular and cellular events involved in the up-regulation (and receptor supersensitivity) of brain alpha(2)-adrenoceptors as a result of chronic depletion of noradrenaline (and other monoamines) by reserpine. 2. Chronic reserpine (0.25 mg kg(-1) s.c., every 48 h for 6 - 14 days) increased significantly the density (B(max) values) of cortical alpha(2)-adrenoceptor agonist sites (34 - 48% for [(3)H]-UK14304, 22 - 32% for [(3)H]-clonidine) but not that of antagonist sites (11 - 18% for [(3)H]-RX821002). Competition of [(3)H]-RX821002 binding by (-)-adrenaline further indicated that chronic reserpine was associated with up-regulation of the high-affinity state of alpha(2)-adrenoceptors. 3. In cortical membranes of reserpine-treated rats (0.25 mg kg(-1) s.c., every 48 h for 20 days), the immunoreactivities of various G proteins (Galphai(1/2), Galphai(3), Galphao and Galphas) were increased (25 - 34%). Because the high-affinity conformation of the alpha(2)-adrenoceptor is most probably related to the complex with Galphai(2) proteins, these results suggested an increase in signal transduction through alpha(2)-adrenoceptors (and other monoamine receptors) induced by chronic reserpine. 4. After alpha(2)-adrenoceptor alkylation, the analysis of receptor recovery (B(max) for [(3)H]-UK14304) indicated that the increased density of cortical alpha(2)-adrenoceptors in reserpine-treated rats was probably due to a higher appearance rate constant of the receptor ((Delta)r=57%) and not to a decreased disappearance rate constant ((Delta)k=7%). 5. Northern- and dot-blot analyses of RNA extracted from the cerebral cortex of saline- and reserpine-treated rats (0.25 mg kg(-1), s.c., every 48 h for 20 days) revealed that reserpine markedly increased the expression of alpha(2a)-adrenoceptor mRNA in the brain (125%). This transcriptional activation of the receptor gene expression appears to be the cellular mechanism by which reserpine induces up-regulation in the density of brain alpha(2)-adrenoceptors.