Platelet adenylate cyclase responses in depression: implications for a receptor defect

Gαs, adenylyl cyclase, and their relationship to the diagnosis and treatment of depression

The relationship between depression, its etiology and therapy, and the cAMP signaling system have been studies for decades. This review will focus on cAMP, G proteins and adenylyl cyclase and depression or antidepressant action. Both human and animal studies are compared and contrasted. It is concluded that there is some synteny in the findings that cAMP signaling is attenuated in depression and that this is reversed by successful antidepressant therapy. The G protein that activates adenylyl cyclase, Gα_s, appears to have diminished access to adenylyl cyclase in depression, and this is rectified by successful antidepressant treatment. Unfortunately, attempts to link specific isoforms of adenylyl cyclase to depression or antidepressant action suffer from discontinuity between human and animal studies.

Cyclic-AMP response element binding protein (CREB) in the neutrophils of depressed patients

Cyclic-AMP response element binding (CREB) protein regulates the expression of many genes involved in the pathophysiology of depression. Increased CREB levels were found in the brain of antidepressant-treated rats and decreased protein and mRNA expression of CREB was reported in the postmortem brain of depressed suicide victims. We determined CREB protein expression, using Western blot technique, and CRE-DNA binding, using gel shift assay, in neutrophils obtained from 22 drug-free patients with major depressive disorder (MDD) and 23 normal control subjects. Diagnosis of patients was based on Diagnostic and Statistical Manual of Mental Disorders DSM-IV criteria; severity of illness was rated by Hamilton Depression Rating Scale (HDRS). We found that the CRE-DNA binding activity and CREB protein expression were significantly decreased in the neutrophils of drug-free MDD patients compared with normal control subjects. Our findings suggest that CREB may play an important role in the pathophysiology of depression and that it may be an important target for the therapeutic action of antidepressant drugs. Neutrophil CREB levels may also serve as a useful biomarker for patients with MDD.

Beta adrenergic receptor function in depression and the effect of antidepressant drugs

It has been suggested that alterations of monoamine receptor sensitivity in the central nervous system may be associated with some forms of affective illness. It has been observed by several investigators that chronic treatment with antidepressant drugs causes down regulation of NE receptor coupled adenylate cyclase and beta adrenergic receptor binding in rat brain. This observation has led to the suggestion that the therapeutic effects of antidepressant drugs may be related to the changes in the responsivity of beta adrenergic receptors. In order to examine if depressive illness may be associated with altered beta adrenergic function, we studied adenylate cyclase and its responsiveness to norepinephrine and isoproterenol in the leukocytes obtained from patients with psychiatric illness and normal controls as an index of beta adrenergic receptor function. We also studied the effects of antidepressant drugs, in vitro, on isoproterenol sensitive leukocyte adenylate cyclase. We observed that norepinephrine and isoproterenol sensitive leukocyte adenylate cyclase in depressed patients are significantly decreased as compared to normal controls. Our results appear to have been replicated by another group of investigators. We also observed that certain antidepressant drugs potentiate isoproterenol stimulated accumulation of cyclic AMP in human leukocytes. This potentiation was most pronounced in the case of iprindole. These results thus indicated a decreased beta adrenergic receptor function in patients with depressive illness. Whether or not such decreased receptor function is associated with depressive illness or is a manifestation of some other changes unrelated to the illness is not clear. Our results also indicate that some antidepressant drugs may enhance adrenergic transmission by potentiating the effects of neurotransmitters on beta adrenergic receptors.

Adenylyl cyclase-cyclicAMP signaling in mood disorders: role of the crucial phosphorylating enzyme protein kinase A

Mood disorders are among the most prevalent and recurrent forms of psychiatric illnesses. In the last decade, there has been increased understanding of the biological basis of mood disorders. In fact, novel mechanistic concepts of the neurobiology of unipolar and bipolar disorders are evolving based on recent pre-clinical and clinical studies, most of which now focus on the role of signal transduction mechanisms in these psychiatric illnesses. Particular investigative emphasis has been given to the role of phosphorylating enzymes, which are crucial in regulating gene expression and neuronal and synaptic plasticity. Among the most important phosphorylating enzyme is protein kinase A (PKA), a component of adenylyl cyclase-cyclic adenosine monophosphate (AC-cAMP) signaling system. In this review, we critically and comprehensively discuss the role of various components of AC-cAMP signaling in mood disorders, with a special focus on PKA, because of the interesting observation that have been made about its involvement in unipolar and bipolar disorders. We also discuss the functional significance of the findings regarding PKA by discussing the role of important PKA substrates, namely, Rap-1, cyclicAMP-response element binding protein, and brain-derived neurotrophic factor. These studies suggest the interesting possibility that PKA and related signaling molecules may serve as important neurobiological factors in mood disorders and may be relevant in target-specific therapeutic interventions for these disorders.

Epinephrine- and thrombin-stimulated high-affinity GTPase activity in platelet membranes from patients with psychiatric disorders

Although heterotrimeric guanine nucleotide-binding regulatory (G) proteins have been implicated in the pathophysiology of mental illnesses (especially mood disorders), direct evidence has been scarce. This study was designed to reveal possible abnormalities of receptor-coupled G protein function in platelets in patients with psychiatric disorders such as depression and schizophrenia. The functional status of alpha(2A)-adrenergic receptor-coupled G(i2) and thrombin receptor-coupled G proteins (G(i2)+G(q)) was determined by the increase in high-affinity GTPase activity in response to epinephrine and thrombin, respectively, in platelet membranes from 18 patients with mood disorders (15 unipolar and three bipolar subtype), 13 schizophrenic patients, four neurotic patients and 29 healthy control subjects. Neither alpha(2A)-adrenergic receptor-coupled G(i2) nor thrombin receptor-coupled G(q) was functionally altered in platelets from psychiatric patients compared with control subjects. No significant correlation was observed between these biochemical measures in platelets and severity of psychopathological symptoms. The functional coupling efficiency of G proteins with receptors appears intact, at least between alpha(2A)-adrenergic receptors and G(i2), and between thrombin receptors and G(q), in platelets from patients with psychiatric disorders.

Subsensitivity of adenylyl cyclase-coupled receptors on mononuclear leukocytes from drug-free inpatients with a major depressive episode

Previous studies have demonstrated blunted beta-adrenergic responsivity in leukocytes from depressed patients. We sought to determine if this blunted cyclic adenosine monophosphate (AMP) response is specific for beta-adrenergic receptors (homologous), or whether other adenylyl cyclase-coupled receptors are also involved (heterologous), in order to localize this effect at the level of the receptor versus the coupling protein or the transducer, adenylyl cyclase. We studied adenylyl cyclase-mediated responses in peripheral blood mononuclear cells from 95 drug-free patients with a major depressive episode and 69 healthy controls. We found a similar degree of decrease in the peak cyclic AMP response to activation of the beta-adrenergic receptor (28%) and the prostaglandin receptor (34%) in the depressed patients, which indicated heterologous desensitization. Forskolin cyclic AMP responses were not blunted. Blunting of cyclic AMP responses to isoproterenol did not appear to correlate with levels of plasma norepinephrine and epinephrine or hypothalamic-pituitary-adrenocortical function. The absence of a decrease in the peak forskolin-generated cyclic AMP response, which involves direct activation of adenylyl cyclase, suggests an abnormality at the level of the coupling protein in these adenylyl-coupled receptors in depressed patients. Future studies need to determine whether this leukocyte signal transduction defect in depression also involves brain adenylyl cyclase-coupled receptors.

Forskolin-stimulated platelet adenylyl cyclase activity is lower in persons with major depression

We investigated platelet adenylyl cyclase activity in 17 subjects with a history of major depression ("depressed subjects") and 20 controls. Forskolin was used to directly activate adenylyl cyclase, while guanine nucleotides (Gpp(NH)p) and fluoride ions were used to measure adenylyl cyclase activity modulated through the G proteins. Forskolin-stimulated adenylyl cyclase was significantly lower in the depressed subjects (p < 0.0005). There was a statistically significant difference in basal adenylyl cyclase activity between male depressed subjects and male controls. The basal adenylyl cyclase activity was also lower in female depressed subjects, but this difference did not reach statistical significance (p < 0.2). The adenylyl cyclase activity measured after stimulation with a guanine nucleotide or cesium fluoride did not differ between control and depressed male or female subjects. Severity of current depression and the current use of antidepressant medication were not related to the lower forskolin-stimulated enzyme activity in the depressed subjects. The difference in forskolin-stimulated adenylyl cyclase activity appears to reflect a qualitative difference in the adenylyl cyclase enzyme activity in persons with a history of major depression.

CNS signal transduction in the pathophysiology and pharmacotherapy of affective disorders and schizophrenia

Until recently, research on the neurochemical basis of affective disorders (AD) and schizophrenia (SCZ) focused on detecting postulated disturbances in presynaptic neurotransmitter release and metabolism, or postsynaptic receptor function. New insights into the molecular mechanisms involved in the propagation of neurotransmitter signals across biological membranes and in the regulation of neuronal responses have allowed the development of novel hypotheses, which may explain the altered postsynaptic neuroreceptor responsivity thought to be integral to the pathophysiology of these disorders. In this review we evaluate evidence from both basic science and clinical research implicating disturbances in postreceptor signal transduction in the pathophysiology and pharmacotherapy of AD and SCZ. Specific findings regarding potential postreceptor sites of pathophysiology are highlighted in each of these disorders, together with the growing body of data on the possible postreceptor loci of psychotropic drug action, especially lithium and antidepressants.

Platelet adenylate cyclase activity in depression and after clomipramine and lithium treatment: relation to serotonergic function

Adenylate cyclase activity was measured in platelet membranes from 10 healthy controls, 12 depressed patients, and the same patients after treatment with clomipramine (CMI) followed by lithium carbonate (Li) supplementation, in an attempt to determine whether any evidence for an effect on the serotonergic system could be obtained in peripheral cells. There were no differences in basal, NaF-, PGE1-, or forskolin-stimulated activity either between the control subjects and depressed patients or between activities in the patients measured before treatment, after CMI, and after CMI+Li. The degree of inhibition of forskolin-stimulated adenylate cyclase by 5-HT, an effect putatively mediated by a 5-HT1A-like receptor, was not different in the depressed patients compared to controls or affected by CMI treatment, but was significantly reduced after Li supplementation.

Clinical and biochemical aspects of depressive disorders: I. Introduction, classification, and research techniques

The present review focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. In addition to integrating these data, problems and future directions in this research are discussed. The review is presented in three parts. This study, Part I, describes diagnostic classification schemes for depressive disorders, some epidemiological and biological correlates of the classifications, and research techniques for investigating depressive disorders. Research techniques include animal models, human biochemical techniques, and Positron Emission Tomography. In a future issue, Part II will discuss various transmitter/receptor theories of depressive disorders, e.g., noradrenergic, serotonergic, cholinergic, and dopaminergic, GABAergic, and peptidergic theories. Also in a future issue, Part III will discuss treatments for depression and some of the controversies in the field.

Increased 3H-clonidine binding in the platelets of patients with depressive and schizophrenic disorders

To examine whether alpha 2-adrenergic receptor function is altered in affective and schizophrenic disorders, we determined 3H-clonidine binding in platelets obtained from 33 normal control subjects and from 24 patients with depressive, 22 patients with schizophrenic, 18 with bipolar, and 8 patients with schizoaffective disorders during a drug-free period. The maximum number of binding sites (Bmax) and apparent dissociation constant (Kd) for high affinity 3H-clonidine binding was computed by Scatchard analysis. Comparison of the diagnostic groups indicated that the Bmax in depressed, schizophrenic, and schizoaffective patients was significantly higher than in normal controls, but there were no significant Bmax differences between bipolar patients and controls. Comparison of the Kd among the diagnostic groups indicated no significant differences among the groups or between patient diagnostic groups and normal controls. Baseline Bmax in schizophrenic patients was significantly correlated with the decrease in Brief Psychiatric Rating Scale (BPRS) scores after treatment, suggesting a relationship between baseline Bmax and clinical response. Treatment with lithium caused a significant decrease in the baseline Bmax, whereas treatment with desipramine or trifluoperazine did not cause significant changes in the baseline Bmax. Our results thus indicate an increase in the number of alpha 2-adrenergic receptors in depressed and schizophrenic patients as compared to normal controls.

Modulation of second messenger function in rat brain by in vivo alteration of receptor sensitivity: relevance to the mechanism of action of electroconvulsive therapy and antidepressants

1. The second messengers cyclic AMP and inositol triphosphate are the intracellular mediators for a number of neurotransmitters for which receptors exist on brain neurons. 2. Up- or down-regulation of these receptors in general produce corresponding changes in the associated second messenger systems. 3. Chronic administration of antidepressants including electroconvulsive shock to rats produces a number of changes in cerebral receptors, notably down-regulation of beta-adrenergic and serotonin 5-HT2 receptors and up-regulation of alpha-1 adrenergic receptors. 4. The changes in receptor number induced by such antidepressant treatments are in general accompanied by corresponding changes in the associated second messenger reactions. 5. Antidepressant administration has also been shown to induce increased post-receptor mediated adenylate cyclase activity in cortical membranes, and similar effects have also been reported in striatum after chronic administration of neuroleptics. The relevance of these effects to the mechanism of action of the drugs is discussed.

Platelet alpha-2-receptor binding and adenylate cyclase activity in panic disorder

The function of the alpha-2-receptor and intracellular effector systems was examined in 39 panic disorder patients and 30 healthy subjects using the platelet as a model system. Alpha-2-receptor density, as reflected by 3H-yohimbine binding, was not different between the two groups. Platelet alpha-2-receptor affinity was decreased (higher Kd) in the panic disorder patients. Other significant abnormalities in the patients included a decreased basal adenylate cyclase activity, reduced EC50 for the epinephrine inhibition of adenylate cyclase activity, and decreased stimulation of adenylate cyclase activity by prostaglandin E1 and sodium fluoride. These results are consistent with a dysfunction in some panic disorder patients at the level of the stimulatory GTP binding regulatory protein, Gs, or the adenylate cyclase catalytic unit. The relationship of these findings to previous studies of noradrenergic function in panic disorder patients is discussed.

Rapid antidepressant response to alprazolam in depressed patients with high catecholamine output and heterologous desensitization of platelet adenylate cyclase

The present study examined the relationship between 24-hr urinary catecholamine (norepinephrine and epinephrine) output and measures of platelet adenylate cyclase (AC) activity in depressed patients (n = 17) and control subjects (n = 10). In both groups, significant inverse correlations were observed when 24-hr urinary catecholamine levels were examined in relation to measures of both receptor-mediated (prostaglandin D2 and alpha 2-adrenergic) and postreceptor-mediated (NaF) platelet AC enzyme activities, suggesting that circulating catecholamines may regulate platelet AC by heterologous (agonist-nonspecific) desensitization of the AC enzyme complex. Depressed patients who had favorable antidepressant responses to alprazolam had significantly higher pretreatment urinary catecholamine output and lower receptor-mediated platelet AC enzyme activities than control subjects, whereas the nonresponders did not. After 8 days of treatment with alprazolam, urinary catecholamine levels declined significantly. In responders, receptor-mediated measures of platelet AC activity increased significantly by day 8 to values comparable to those in control subjects; but similar changes were not observed in nonresponders. Prior to treatment, responders showed a strict linear relationship between receptor-mediated (prostaglandin D2) and postreceptor-mediated (NaF) stimulation of platelet AC activity through the stimulatory guanine nucleotide regulatory protein (Ns), whereas nonresponders did not. This suggests the presence of two distinct coupling interactions between platelet prostaglandin D2 receptors and the stimulatory guanine nucleotide regulatory protein in responders and nonresponders to the antidepressant effects of alprazolam prior to treatment. The authors propose that catecholamines, possibly acting through prostaglandins, may regulate platelet AC enzyme activity by heterologous desensitization occurring through postreceptor mechanisms.

Platelet alpha 2-adrenergic receptor function in psychiatric disorders

The inhibitory effects of norepinephrine (NE) on the cyclic adenosine-3',5'-monophosphate (cAMP) response to prostaglandin E1 (PGE1), a measure of alpha 2-adrenergic receptor function, have been compared in platelets from drug-free schizophrenic patients, depressive patients, and normal controls. The absolute value of the inhibition by NE of the cAMP response to PGE1 was smaller in platelets from schizophrenic and depressive patients than in controls. However, this result was secondary to the smaller baseline platelet cAMP response to PGE1 in patients with these disorders. Effects of NE on cAMP production did not discriminate between actively ill and remitted patients with either schizophrenia or depression. Platelet alpha 2-receptor sensitivity, as measured by the effects of NE on cAMP production, does not appear to be altered in these psychiatric disorders.

Evaluation of studies on platelet alpha 2 adrenoreceptors in depressive illness

Discrepant results have been reported from at least ten laboratories regarding the status of platelet alpha 2 adrenoreceptors in depressed patients. Using a statistical test to combine those studies which utilized radioligand binding techniques, we find the overall data support an elevation in density of platelet alpha 2 adrenoreceptors from drug-free depressed patients (p less than 0.05) and suggest a normalization to lower binding values following antidepressant drug treatment (0.05 less than p less than 0.10). However, these positive results are attributable to highly significant findings by only three laboratories. Much of the discrepancy may be attributable to numerous methodological variables which distinguish the studies. Foremost amongst these variables are the use of different platelet size populations, the use of different medium, and the choice of radioactive ligand and competitor (non-radioactive ligand) in the assay. We present a rationale for the proper choice of each methodological condition used in the clinical assessment of platelet alpha 2 adrenoreceptor status, hoping that improved experimental designs will resolve the current controversy.

Reduced sensitivity of lymphocyte beta-adrenergic receptors in patients with endogenous depression and psychomotor agitation

It has been suggested that there are altered levels of norepinephrine or other neurotransmitters at functionally important receptors in patients with depressive disorders. This hypothesis is difficult to study in the human central nervous system. However, noradrenergic function can be assessed indirectly with peripheral-blood lymphocytes used as a model of the beta-adrenergic receptor complex. We found that drug-free inpatients with endogenous depression had lower isoproterenol-stimulated cyclic AMP levels in intact lymphocytes than did healthy control subjects (3.9 +/- 0.5 vs. 7.4 +/- 1.0 pmol per 10(6) cells, P less than 0.01). The density and affinity of beta-adrenergic receptors were similar in controls and depressed subjects (beta-receptor number, 5.4 +/- 0.7 and 5.3 +/- 0.8 fmol per 10(6) cells; binding affinity, 106 +/- 7.6 vs. 99.2 +/- 11.4 pM, respectively). When the depressed patients were subdivided by psychomotor manifestations, binding characteristics were indistinguishable among the subgroups. However, a significant reduction in beta-adrenergic responsiveness was observed in patients with psychomotor agitation, as compared with controls (2.6 +/- 0.5 vs. 7.4 +/- 1.0 pmol per 10(6) cells, P less than 0.01), but not in patients with psychomotor retardation (5.8 +/- 1.1 pmol per 10(6) cells, P less than 0.05). Thus, the desensitization of beta-adrenergic receptors was correlated more closely with the severity of psychomotor agitation than with the overall severity of depression.

Enhanced signal transduction by adenylate cyclase in platelet membranes of patients showing antidepressant responses to alprazolam: preliminary data

The triazolobenzodiazepine, alprazolam, was administered to 11 depressed patients over a period of six weeks, and six patients showed a favorable antidepressant response. There were no significant differences between responders and nonresponders in age, pretreatment Hamilton Depression Rating Scores, 4 p.m. postdexamethasone plasma cortisol levels, or platelet monoamine oxidase activities. Blood levels of alprazolam were not meaningfully different in responders and nonresponders when measured on treatment day 8. However, on treatment day 8, significantly enhanced prostaglandin D2-stimulated platelet adenylate cyclase activity, greater suppression of prostaglandin D2-stimulated platelet adenylate cyclase activity by epinephrine, and enhanced sodium fluoride-stimulated platelet adenylate cyclase activity were seen in the six patients who went on to respond to alprazolam, but not in the five nonresponders. In contrast, there were no significant changes in prostaglandin D2, (-)-isoproterenol, or fluoride ion-stimulated leukocyte adenylate cyclase activity in responders or nonresponders. No meaningful changes were observed in the mean densities of either the high-affinity platelet alpha 2-adrenergic receptor (for 3H-p-aminoclonidine) or the leukocyte beta-adrenergic receptor (for 3H-dihydroalprenolol) in responders or nonresponders. The present findings, taken in conjunction with findings from other recent studies, suggest that enhanced coupling between certain neurotransmitter or hormone receptors and adenylate cyclase through the guanine nucleotide regulatory proteins may help explain the antidepressant effects of alprazolam and possibly other forms of antidepressant treatment.

Platelet alpha-adrenergic binding and biochemical responsiveness in depressed patients and controls

In a study of platelet alpha 2-adrenergic receptor number in depressed patients, binding of tritiated dihydroergocriptine (3H-DHE) to platelet membranes was measured in 23 depressed patients and 51 controls. To examine the functional responsiveness of the platelet alpha 2-adrenergic receptor, basal cyclic adenosine 3',5'-monophosphate (cAMP) production, prostaglandin E1 (PGE1) stimulation of cAMP production, and norepinephrine (NE) inhibition of PGE1-stimulated cAMP production were measured in 23 depressed patients and 53 control subjects. Finally, plasma NE concentration was measured in 20 patients to explore the possible relationship between this endogenous agonist and platelet alpha 2-adrenergic receptor function. 3H-DHE binding to platelet membranes was significantly increased in the depressed patients compared to control subjects. Both the PGE1-stimulated cAMP response and the inhibition of this response by NE were significantly reduced in the depressed patients compared to the control subjects. Thus, an apparent dissociation between alpha 2-adrenergic receptor binding and functional responsiveness was observed. Plasma NE concentrations were neither significantly different in the depressed patients than in the controls nor correlated with any of the measures of cAMP responsiveness. They were, however, significantly negatively correlated with 3H-DHE binding in depressed patients with adequate PGE1 stimulation of cAMP production.

Clinical studies of monoamine receptors in the affective disorders and receptor changes with antidepressant treatment

Pre-clinical and clinical studies suggest that the responsiveness of monoamine and cholinergic receptors may be altered in the affective disorders and that antidepressants may modify the sensitivity of these receptors. The growth hormone response to clonidine is reduced in depressed patients compared to controls according to several independent studies, suggesting that post-synaptic alpha 2-adrenergic receptors may be less responsive in depressed patients. The cortisol response to clonidine is enhanced in depressed patients compared to controls in our study raising the possibility that cortisol hypersecretion in depressed patients may be related to noradrenergic dysfunction. The hypotensive response to clonidine is blunted in patients on chronic antidepressant treatment with either clorgyline or desipramine suggesting that pre-synaptic alpha 2-adrenergic receptors may subsensitize with chronic antidepressant treatment. The prolactin increase in response to fenfluramine is less in depressed patients compared to controls suggesting decreased functional activity of the serotonergic system in depression. Platelet alpha 2-adrenergic receptor number as measured by tritiated dihydroergocriptine (3H-DHE) binding is increased in depressed patients compared to controls, while cyclic 3'-5' adenosine monophosphate (cAMP) production in response to prostaglandin E1 (PGE1) and norepinephrine (NE) inhibition of PGE1-stimulated cAMP production are reduced in the platelets of depressed patients. Thus, it is not clear that increased 3H-DHE binding reflects increased functional responsiveness and might in fact be compensatory to decreases in functional responses of alpha 2-adrenergic receptors.

Presynaptic noradrenergic regulation during depression and antidepressant drug treatment

A specific testable hypothesis in which supersensitive alpha-2-adrenoreceptors play an important role in the etiology and maintenance of affective illness is presented based on the following observations: (1) published findings of changes in adrenergic receptors in the periphery and brains of rats in response to antidepressant regimens; (2) new studies of the monoamine oxidase type A-inhibiting antidepressant clorgyline, specifically relating to adaptation in the alpha-adrenergic presynaptic negative feedback system; (3) human peripheral alpha-adrenergic receptor changes from studies of patients with affective illness; and (4) observations from animals and humans experiencing stress and withdrawal from chronic amphetamine and opiate administration, suggesting that the development of supersensitive alpha-2-adrenoreceptors may lead to affective illness in vulnerable individuals. Old and new pharmacologic treatments are then discussed in terms of their capacity to specifically alter adrenergic receptor state.

Changes in lymphocyte beta-adrenergic receptors in depression and mania

The beta-adrenergic receptors were studied in vitro in lymphocytes obtained from patients with major affective disorders and controls. Specific L-[3H]-dihydroalprenolol binding was decreased in both depressed and manic patients compared to controls and euthymic patients. Isoproterenol-stimulated, but not prostaglandin El-stimulated, cyclic adenosine-3',5'-monophosphate production was decreased in manic and depressed patients. These results suggest decreased lymphocyte beta-receptor functioning in depression and mania. This decrease may be an index of changes in brain beta-receptors in mania and depression, or may simply reflect homeostatic regulation of peripheral beta-receptors in response to stress-induced increases in circulating catecholamines.

Studies on human blood platelets in affective disorder

Platelets were examined to enable a simultaneous investigation to be made of indolylamine and electrolyte metabolism in affective disorder. No significant differences were detected in either platelet membrane ATPase or adenyl cyclase specific activity in any of the groups of patients studied, when compared with appropriate controls. A reduced Vmax and y for the 5-hydroxy-tryptamine uptake process into platelets was observed in both unipolar and bipolar depressed groups. The Km for this process was not significantly different in any of the patients from that found in control subjects. Lithium therapy was shown not to influence significantly any of the platelet parameters examined. It is suggested that membrane enzyme changes found in some peripheral cells in patients suffering from affective disorder, i.e. reduced Na+ + K+ - ATPase activity in erythrocytes in depression, is not common to all peripheral cells and may or may not reflect central nervous system changes.