Up-regulation of immunolabeled alpha2A-adrenoceptors, Gi coupling proteins, and regulatory receptor kinases in the prefrontal cortex of depressed suicides

Alpha-2-adrenoreceptors in depressed suicide attempters: relationship with medical lethality of the attempt

Several lines of evidence tend to suggest a role for noradrenaline, and more specifically alpha-2-adrenoreceptors, in the biology of suicidal behavior. The purpose of this study was to assess the growth hormone (GH) response to clonidine, an alpha-2-adrenergic agonist, in majorly depressed inpatients with a history of highly lethal suicide attempt compared to depressed patients with a history of low lethal suicide attempt and nonattempters. Our sample included 20 male depressed inpatients with a history of suicide attempt compared to 20 male depressed nonattempters. We did not observe any significant difference between suicide attempters and nonattempters for GH peak values (2.4 +/- 2.9 vs. 4.1 +/- 3.7 ng/ml; F = 2.52, d.f. = 1, 38, p = 0.12). Moreover, GH peak responses to clonidine were not related to the degree of lethality of the attempt. The results of the present study do not support a major role for noradrenaline in the biology of suicidal behavior.

Acute and chronic effects of desipramine and clorgyline on alpha(2)-adrenoceptors regulating noradrenergic transmission in the rat brain: a dual-probe microdialysis study

1. The effects of desipramine (3 mg kg(-1) i.p.) and clorgyline (1 mg kg(-1) i.p.) on extracellular noradrenaline (NA) in the locus coeruleus (LC) and cingulate cortex were assessed in freely-moving rats by dual-probe microdialysis. Functional activities of alpha(2)-adrenoceptors regulating NA release in the LC and cingulate cortex were determined by systemic (0.3 mg kg(-1) i.p.) or local (0.1 - 100 microM) clonidine administration. 2. Extracellular NA was increased in the LC and cingulate cortex following acute desipramine but not clorgyline treatment. Systemic clonidine decreased NA similarly in desipramine-, clorgyline-, and saline-treated animals, in both brain areas. 3. Long-term (twice daily, 14 days) but not short-term (twice daily, 7 days) desipramine, and long-term clorgyline (once daily, 21 days) treatments increased NA (3 fold) in cingulate cortex but not in the LC. Following long-term treatments, responses of NA to systemic clonidine were attenuated in the LC and cingulate cortex. 4. Clonidine perfusion by reverse dialysis into the cingulate cortex decreased local NA (-55 +/- 9%). The effect was attenuated by long-term desipramine (-31 +/- 9%) and clorgyline (-10 +/- 2%) treatments. 5. Clonidine perfusion by reverse dialysis into the LC decreased NA in the LC (-89 +/- 2%) and in cingulate cortex (-52 +/- 12%). This effect was attenuated in the LC following long-term desipramine (-72 +/- 4%) and clorgyline (-62 +/- 12%) treatments but it was not modified in the cingulate cortex (-57 +/- 10% and -68 +/- 6%, respectively). 6. These findings demonstrate that chronic desipramine or clorgyline treatments increase NA in noradrenergic terminal areas and desensitize alpha(2)-adrenoceptors modulating local NA release at somatodendritic and terminal levels. However, somatodendritic alpha(2)-adrenoceptors that control LC firing activity are not desensitized.

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.

Abnormalities in the cAMP signaling pathway in post-mortem brain tissue from the Stanley Neuropathology Consortium

There is an established relationship between the monoaminergic neurotransmitter system and mood disorders. In an attempt to define further the pathophysiology of mood disorders, research is focussing on intracellular second messenger systems, including cyclic adenosine 3',5'-monophosphate (cAMP) and the polyphosphoinositol generated second messengers. The availability of tissue from the Stanley Foundation Neuropathology Consortium has offered us the opportunity to make a number of observations with respect to these second messenger systems in tissue from patients with major depressive disorder and bipolar affective disorder. There is evidence that antidepressants stimulate components of the cAMP pathway in patients with depression while mood stabilizers blunt the same pathway in patients with bipolar disorder. Furthermore, downstream targets of this pathway appear to be altered in patients with mood disorders. The relations between changes in second messenger systems, gene transcription, and clinical effects of current therapeutic regimens has implications for development of novel treatments of mood disorders.

Cyclic AMP-mediated signaling components are upregulated in the prefrontal cortex of depressed suicide victims

The components of cyclic AMP signaling cascade (catalytic (Calpha) subunit of cyclic AMP-dependent protein kinase (PKA) and cyclic AMP response element binding protein (CREB)) were quantitated by Western blotting in the prefrontal cortex of depressed suicide victims (n=23) and their matched controls (n=14). There was a significant increase in the levels of CREB, both in total (tCREB; 121+/-8% (mean+/-S.E.M.), P<0.02) and phosphorylated (pCREB; 128+/-9%, P<0.01) forms, but not in PKA Calpha levels (109+/-9%, ns), in brains of depressed suicides compared to those in control subjects. The increases in CREB were specifically observed in antidepressant drug-free subjects (tCREB: 137+/-11%, P<0.01; pCREB: 136+/-12%, P<0.02; n=9), but not in the antidepressant-treated subjects (tCREB: 108+/-18%, ns; pCREB: 111+/-17%, ns; n=8). There were significant correlations between the levels of PKA and those of tCREB and pCREB in the prefrontal cortex of depressed suicides. These results indicate that the components of cyclic AMP signaling are upregulated in a coordinated manner in brains of depressed suicides and that this alteration is not related to antidepressant treatment.

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.

Implications of the cAMP signaling pathway in psychiatric disorders: a systematic review of the evidence

The last decade has seen a shift in the theoretical framework addressing the pathophysiology of psychiatric disorders. During this period, research endeavors have been directed toward investigating the biochemical mechanisms involved in the transduction of information from the cell surface to the cell interior. The emerging picture, supported by growing evidence, is that in addition to neurotransmitters and their receptors, various signal transduction pathways may be linked to the pathophysiology of major psychiatric disorders. In this review, the role of one such pathway--the cyclic adenosine monophosphate (cAMP) signaling pathway--will be highlighted. We review data suggesting the involvement of the upstream and downstream components of this system in the pathophysiology of psychiatric disorders.

Noradrenergic dysfunction in the prefrontal cortex in depression: an [15O] H2O PET study of the neuromodulatory effects of clonidine

BACKGROUND

Noradrenergic dysfunction has been consistently implicated in depression. Much of the evidence, though, has been indirect, such as an attenuated growth hormone response to the alpha2-adrenoceptor agonist clonidine. To more directly examine central functioning of the noradrenergic system in depression, we have used [15O] H2O positron emission tomography (PET) to measure cerebral blood flow (rCBF) in combination with clonidine as a neuromodulatory probe.

METHODS

Subjects were six depressed and six healthy women, medication free and matched for age and phase of menstrual cycle. Two PET scans were acquired at baseline and two scans at 20 and 35 min following an intravenous clonidine infusion of 1.4 microg/kg while subjects performed a sustained attention task.

RESULTS

The growth hormone response did not show a significant difference between groups. However, PET results revealed a difference in the right superior prefrontal cortex that was resolved as an interaction from decreased rCBF in healthy control subjects but increased rCBF in the depressed group, which was not accounted for by differences in task performance.

CONCLUSIONS

This differential effect of clonidine in the right prefrontal cortex provides in vivo evidence of noradrenergic dysfunction in depression, which we postulate arises from functionally impaired presynaptic alpha2-adrenoceptors as well as regionally "supersensitive" postsynaptic cortical alpha2-adrenoceptors.

Protein kinase A and Rap1 levels in platelets of untreated patients with major depression

We have recently reported altered levels of protein kinase A and Rap1 in patients with bipolar disorder. The purpose of the current investigation was to assess the levels of these proteins in platelets from untreated euthymic and depressed patients with major unipolar depression. Platelets were collected from 45 drug-free unipolar patients (13 euthymic and 32 depressed) and 45 healthy subjects. The levels of protein kinase A and Rap1 were assessed by Western blot analysis, immunostaining and computer-assisted imaging. The immunolabeling of the regulatory subunit type II of protein kinase A and that of Rap1 was significantly lower in untreated depressed patients compared with untreated euthymic patients and healthy subjects. No significant differences were found in the immunolabeling of both the regulatory type I and the catalytic subunits of protein kinase A among groups. Levels of the regulatory subunit type II of protein kinase A and Rap1 are altered in platelets of unipolar depressive patients. These findings may provide new insight about the relationship between components of cAMP signaling and affective disorders.

Post-receptor signaling pathways in the pathophysiology and treatment of mood disorders

The molecular medicine revolution has resulted in a more complete understanding about the etiology and pathophysiology of a variety of illnesses. This remarkable progress reflects in large part the elucidation of the basic mechanisms of signal transduction, and the application of the powerful tools of molecular biology to the study of human disease. Although we have yet to identify the specific abnormal genes in mood disorders, recent studies have implicated signal transduction pathways, in particular the stimulatory guanine nucleotide binding protein (Gs)/cyclic AMP and protein kinase C pathways, in the pathophysiology and treatment of mood disorders. Recent studies have also shown that mood stabilizers exert neurotrophic and neuroprotective effects not only in preclinical paradigms, but also in humans. Together, these studies suggest that mood disorders may be associated with impaired neuroplasticity and cellular resiliency, findings that may have major implications for our understanding of mood disorders, and for the development of improved therapeutics.

Identifying a series of candidate genes for mania and psychosis: a convergent functional genomics approach

We have used methamphetamine treatment of rats as an animal model for psychotic mania. Specific brain regions were analyzed comprehensively for changes in gene expression using oligonucleotide GeneChip microarrays. The data was cross-matched against human genomic loci associated with either bipolar disorder or schizophrenia. Using this convergent approach, we have identified several novel candidate genes (e.g., signal transduction molecules, transcription factors, metabolic enzymes) that may be involved in the pathogenesis of mood disorders and psychosis. Furthermore, for one of these genes, G protein-coupled receptor kinase 3 (GRK3), we found by Western blot analysis evidence for decreased protein levels in a subset of patient lymphoblastoid cell lines that correlated with disease severity. Finally, the classification of these candidate genes into two prototypical categories, psychogenes and psychosis-suppressor genes, is described.

Molecular Abnormalities in Brains of Depressed Patients

Studies on the molecular pharmacology of antidepressants have lead to a reinterpretation of earlier models of the neuropathology of depression. Noradrenergic and serotonergic hypotheses of depression have been expanded to include postsynaptic intracellular signal transduction pathways and regulation of gene expression. Because much of this evidence was obtained from postmortem brain, there has been increased interest in the use of this tissue to study depression. In the following pages, we will review the postmortem brain studies in depressed individuals focusing on neurotransmitter systems, signal transduction, and structural abnormalities.

Regulation of nonphosphorylated and phosphorylated forms of neurofilament proteins in the prefrontal cortex of human opioid addicts

The neurofilament (NF) proteins (NF-H, NF-M, and NF-L for high, medium, and low molecular weights) play a crucial role in the organization of neuronal shape and function. In a preliminary study, the abundance of total NF-L was shown to be decreased in brains of opioid addicts. Because of the potential relevance of NF abnormalities in opioid addiction, we quantitated nonphosphorylated and phosphorylated NF in postmortem brains from 12 well-defined opioid abusers who had died of an opiate overdose (heroin or methadone). Levels of NF were assessed by immunoblotting techniques using phospho-independent and phospho-dependent antibodies, and the relative (% changes in immunoreactivity) and absolute (changes in ng NF/microg total protein) amounts of NF were calculated. Decreased levels of nonphosphorylated NF-H (42-32%), NF-M (14-9%) and NF-L (30-29%) were found in the prefrontal cortex of opioid addicts compared with sex, age, and postmortem delay-matched controls. In contrast, increased levels of phosphorylated NF-H (58-41%) and NF-M (56-28%) were found in the same brains of opioid addicts. The ratio of phosphorylated to nonphosphorylated NF-H in opioid addicts (3.4) was greater than that in control subjects (1.6). In the same brains of opioid addicts, the levels of protein phosphatase of the type 2A were found unchanged, which indicated that the hyperphosphorylation of NF-H is not the result of a reduced dephosphorylation process. The immunodensities of GFAP (the specific glial cytoskeletol protein), alpha-internexin (a neuronal filament related to NF-L) and synaptophysin (a synapse-specific protein) were found unchanged, suggesting a lack of gross changes in glial reaction, other intermediate filaments of the neuronal cytoskeletol, and synaptic density in the prefrontal cortex of opioid addicts. These marked reductions in total NF proteins and the aberrant hyperphosphorylation of NF-H in brains of opioid addicts may play a significant role in the cellular mechanisms of opioid addiction.

No influence of adrenergic receptor polymorphisms on schizophrenia and antipsychotic response

The adrenergic system plays an important role in psychiatric disorders such as depression and schizophrenia. Antagonism of the adrenergic receptor subtypes alpha1A and alpha2A has been found to have an antipsychotic effect. Genetic mutations in these receptors could be related to the alterations in the adrenergic system observed in psychiatric patients and to failure to respond to drug antagonism. We have studied one polymorphism in the alpha1A-adrenergic receptor (Arg492Cys) and two polymorphisms in the promoter region of the alpha2A-adrenergic receptor (-1291-C/G and -261-G/A) in a sample of clozapine-treated schizophrenic patients and controls. No clear differences were observed between the different groups suggesting that these polymorphisms did not play an important role in the aetiology of the disorder or in determining antipsychotic response.

Regulation of signal transduction pathways and gene expression by mood stabilizers and antidepressants

OBJECTIVE

To determine whether the currently available evidence supports the hypothesis that antidepressants and mood stabilizers may bring about some of their long-term therapeutic effects by regulating signal transduction pathways and gene expression in the central nervous system.

METHODS

To address this question, we reviewed the evidence showing that chronic administration of antidepressants and mood stabilizers involves alterations in signaling pathways and gene expression in the central nervous system.

RESULTS

A large body of data has shown that lithium and valproate exert effects on the protein kinase C signaling pathway and the activator protein 1 family of transcription factors; in contrast, antidepressants affect the cyclic adenosine monophosphate pathway and may bring about their therapeutic effects by modulating cyclic adenosine monophosphate-regulated gene expression in the central nervous system.

CONCLUSIONS

Given the key roles of these signaling cascades in the amplification and integration of signals in the central nervous system, the findings have clear implications not only for research into the etiology and pathophysiology of the severe mood disorders but also for the development of novel and innovative treatment strategies.

The alkylating agent EEDQ facilitates protease-mediated degradation of the human brain alpha2A-adrenoceptor as revealed by a sequence-specific antibody

An antibody against a sequence from the divergent third intracellular loop of the human alpha2A-adrenoceptor, amino acids 262-276, was produced. The antiserum was tested, along with the preimmune serum, by means of ELISA and dot blot assays which demonstrated that the alpha2A-peptide used for the antibody production was recognized by the immune serum. The antibody also recognized the alpha2A-adrenoceptor protein in the human brain (immunoblot analysis). In cortical membranes a major immunoreactive peptide of approximately 70 kDa (mature glycosylated receptor) was detected and after treatment with N-glycosidase F only a approximately 50 kDa peptide (non-glycosylated receptor) was immunodetected. This antibody was used to demonstrate that a chemical modification of the alpha2A-adrenoceptor induced by the alkylating agent EEDQ facilitates the protease-mediated receptor degradation. Thus in vitro, normal receptor degradation (24-44% at 2-4 h) was enhanced by EEDQ (10(-6) M) (38-71% at 2-4 h) but in the presence of protease inhibitors this effect was almost abolished.