Adrenocortical steroids modify neurotransmitter-stimulated cyclic AMP accumulation in the hippocampus and limbic brain of the rat

Glucocorticoids and depression

Depression has been associated with impaired mineralocorticoid receptor function, restrained glucocorticoid receptor feedback at the level of the hypothalamic-pituitary-adrenal (HPA) axis, raised cortisol level and increased corticotropin-releasing factor activity, which may act in concert to induce the signs and symptoms of the disorder. Pre-clinical and clinical evidence suggests that both genetic and environmental factors contribute to the development of these HPA axis abnormalities in depressed patients. Support for this view derives from models using genetically modified animals and/or chronic stress exposure at different developmental stages, although all of the current approaches have to be viewed within their limitations to model the disease. However, both animal and human studies challenging the HPA system show at least some neuroendocrine and behavioural changes comparable to those seen in depression, suggesting that some of the depressive symptoms can be attributed to HPA axis hyperactivity. Moreover, normalization of the neuroendocrine function following chronic antidepressant drug treatment seems to be a prerequisite for stable remission of depressive psychopathology, i.e. that normalization of HPA function is critical for relief of the clinical symptomatology of this disorder.

Regulation of gene expression by corticoid hormones in the brain and spinal cord

Glucocorticoids (GC) and mineralocorticoids (MC) have profound regulatory effects upon the central nervous system (CNS). Hormonal regulation affects several molecules essential to CNS function. First, evidences are presented that mRNA expression of the alpha3 and beta1-subunits of the Na,K-ATPase are increased by GC and physiological doses of MC in a region-dependent manner. Instead, high MC doses reduce the beta1 isoform and enzyme activity in amygdaloid and hypothalamic nuclei, an effect which may be related to MC control of salt appetite. The alpha3-subunit mRNA of the Na,K-ATPase is also stimulated by GC in motoneurons of the injured spinal cord, suggesting a role for the enzyme in GC neuroprotection. Second, we provide evidences for hormonal effects on the expression of mRNA for the neuropeptide arginine vasopressin (AVP). Our data show that GC inhibition of AVP mRNA levels in the paraventricular nucleus is sex-hormone dependent. This sexual dimorphism may explain sex differences in the hypothalamic-pituitary-adrenal axis function between female and male rats. Third, steroid effects on the astrocyte marker glial fibrillary acidic protein (GFAP) points to a complex regulatory mechanism. In an animal model of neurodegeneration (the Wobbler mouse) showing pronounced astrogliosis of the spinal cord, in vivo GC treatment down-regulated GFAP immunoreactivity, whereas the membrane-active steroid antioxidant U-74389F up-regulated this protein. It is likely that variations in GFAP protein expression affect spinal cord neurodegeneration in Wobbler mice. Fourth, an interaction between neurotrophins and GC is shown in the injured rat spinal cord. In this model, intensive GC treatment increases immunoreactive low affinity nerve growth factor (NGF) receptor in motoneuron processes. Because GC also increases immunoreactive NGF, this mechanism would support trophism and regeneration in damaged tissues. In conclusion, evidences show that some molecules regulated by adrenal steroids in neurons and glial cells are not only involved in physiological control, but additionally, may play important roles in neuropathology.

Steroid Regulation of Vasoactive Intestinal Peptide (VIP)

The present review is dedicated to the work of B.S. Mc Ewen on the regulatory effects of steroid hormones on peptidergic neurotransmission in the brain and pituitary. The focus is on the discoveries encompassing almost two decades of work on the central and neuroendocrine regulation of vasoactive intestinal peptide (VIP) by both corticosteroids and estrogens.

Corticosterone alters G protein alpha-subunit levels in the rat hippocampus

The hypothalamic-pituitary-adrenal axis regulates the synthesis and secretion of corticosteroid hormones. The hippocampus, a component of the limbic system, contains the highest concentration of corticosteroid receptors in the brain and may play an important role in regulating hypothalamic-pituitary-adrenal axis activity and mediating physiological responses to stress. The corticosteroid hormone corticosterone alters the response elicited by activation of several different G protein-linked neurotransmitter receptors in the hippocampus. In the present study we used Western blot and immunohistochemical techniques to determine the effects of chronic adrenalectomy (ADX), low basal (CT) and high (HCT) corticosterone treatments on Gs, Gi1 and 2 and Go alpha-subunit levels and intracellular location in the rat hippocampus. CT treatment increased Gs alpha-subunit levels and HCT treatment increased the levels of Gs, Gi1 and 2 and Go alpha-subunits when compared to sham as detected on Western blots. No change in the intracellular location of the G protein alpha-subunits was detected using immunohistochemistry. Based on our results, we conclude that corticosterone alters G protein alpha-subunit levels in the rat hippocampus without altering their intracellular location. These results provide an important piece of information towards understanding how corticosteroids alter G protein-linked neurotransmitter receptor-mediated responses.

Distribution of glucocorticoid receptor immunoreactivity and mRNA in the rat brain: an immunohistochemical and in situ hybridization study

The localization of glucocorticoid receptor (GR) immunoreactivity and mRNA in the adult rat brain was examined by light microscopic and electron microscopic immunohistochemistries, and in situ hybridization. For the purpose of detailed investigation of the distribution and comparison of GR immunoreactivities and mRNAs, specific polyclonal antibodies against a part of the transcription modulation (TR) domain of rat GR were used in the immunohistochemistry, whereas fluorescein-labeled RNA probes, complementary to the TR domain in the GR cDNA were used in the in situ hybridization. In the rat brain, GR immunoreactivity was predominantly localized in the cell nucleus, and the expression of GR mRNA was detected in the cytoplasm. GR-immunoreactive and GR mRNA-containing cells were widely distributed from the olfactory bulb of the forebrain to the gracile-cuneate nuclei of the medulla oblongata. The highest densities of GR-immunoreactive and mRNA-containing cells were observed in the subfields of cerebral cortex, olfactory cortex, hippocampal formation, amygdala, septal region, dorsal thalamus, hypothalamus, trapezoid body, cerebellar cortex, locus coeruleus and dorsal nucleus raphe. The distributional pattern of GR immunoreactivity in many regions was well-correlated with that of GR mRNA, but in the CA3 and CA4 pyramidal layers of the hippocampus, different localization was noted. The present study provides the groundwork for elucidating the role of GRs in brain function.

Mineralocorticoid and glucocorticoid receptors in the brain. Implications for ion permeability and transmitter systems

In this review we have argued that corticosteroid hormones represent an endocrine signal that can influence neuronal communication. The steroids bind to intracellular receptors in the brain, resulting in slow effects that involve gene transcription, but they may also evoke rapid effects via membrane receptors. The signal carried by the corticosteroids is therefore divergent with respect to the dimension of space and time. Within the rat brain, at least two intracellular receptor subtypes, i.e. MRs and GRs, bind corticosterone. The affinity, density and localization of the MRs is different from the GRs, although the actual properties may vary somewhat depending on the condition of the animal. In general, due to the difference in affinity, low corticosteroid levels result in a predominant MR occupation, while higher steroid levels additionally occupy GRs. Recent studies indicate that predominant MR occupation is important for the maintenance of ongoing transmission in certain brain regions and for neuroprotection. By contrast, additional GR occupation (for a limited period of time) results in an attenuation of local excitability; yet, prolonged exposure to high steroid levels may become an endangering condition for neurons. Since predominant MR occupation on the one hand and additional GR occupation on the other hand induce different cellular actions, the ratio of MR/GR occupation is an important factor determining the net effect of corticosteroid hormones in the brain. How coordinated MR- and GR-mediated effects control neuronal communication under various physiological and pathological conditions will be a challenge for future research.

Adrenalectomy increases phosphoinositide hydrolysis induced by norepinephrine or excitatory amino acids in rat hippocampal slices

Phosphoinositide hydrolysis induced by norepinephrine, quisqualate, or trans-1-amino-1,3-cyclopentanedicarboxylic acid (ACPD), but not by carbachol, was approximately 50% greater in hippocampal slices from adrenalectomized (14 days) rats compared with controls. These changes appeared to be selective for the hippocampus because no effects of adrenalectomy on phosphoinositide hydrolysis were detected in cortical or striatal slices. The enhanced response to norepinephrine in hippocampal slices after adrenalectomy was observed throughout the effective concentration range of norepinephrine, was not influenced by in vitro addition of corticosterone, was not mimicked or altered by incubation with dibutyryl cyclic adenosine 3',5'-monophosphate (AMP), and did not appear to be due to impaired inhibition of the response to norepinephrine which was elicited by activation of protein kinase C or by inclusion of an inhibitory concentration of quisqualate. These findings indicate that adrenalectomy either removes an inhibitory influence of glucocorticoids on the phosphoinositide system in the hippocampus or that the neurodegeneration of granule cells in the dentate gyrus following adrenalectomy is associated with neurotransmitter-selective increases in phosphoinositide hydrolysis. These data provide further evidence that glucocorticoids modify signal transduction in the brain and extends their known influence to the phosphoinositide second messenger system.

Hypothalamic-pituitary-adrenocortical function in mixed and pure mania

There is little information about hypothalamic-pituitary-adrenocortical (HPA) axis function in mania, particularly in mixed states. We therefore investigated HPA function and its relationship to clinical state in 19 hospitalized manic patients meeting Schedule for Affective Disorders and Schizophrenia - Research Diagnostic Criteria for acute manic episodes, compared patients with and without a mixed presentation, and examined correlations between HPA activity and behavior. Data were available from 13-16 patients. Behavioral and biochemical analyses were conducted during a 15-d placebo period. Patients with mania had elevated cerebrospinal fluid (CSF) and urinary free cortisol excretion compared with healthy subjects, and did not differ from depressed patients in any cortisol measures. Mixed manics had significantly higher morning plasma cortisol, postdexamethasone plasma cortisol and CSF cortisol than pure manics. Five of 7 mixed manics and 3 of 9 pure manics were dexamethasone suppression test (DST) nonsuppressors. Afternoon plasma cortisol and CSF cortisol correlated significantly with depressed mood; urinary free cortisol correlated with anxiety. None of the cortisol measures correlated with mania or agitation scores. These data suggest that increased cortisol secretion is a characteristic of the depressed state in mixed manics, although pure manics may also have increased DST nonsuppression.

Diurnal differences and adrenal involvement in calmodulin stimulation of hippocampal adenylate cyclase activity

Abstract Calciam/calmodulin-dependent processes are altered by manipulations of the hypothalamic-pituitary-adrenal axis, and are associated with changes in synaptic efficacy in the hippocampus, such as long-term potentiation. Recent evidence indicates that there are diurnal variations in the threshold for long-term potentiation, as well as diverse effects of the adrenals and of adrenal steroids on electrical activity related to long-term potentiation. In order to probe possible mechanisms underlying these observations, we investigated the effects of the diurnal cycle, as well as adrenalectomy (ADX) and adrenal demedullation on adenylate cyclase activity. In hippocampal, but not cortical, membranes the adenylate cyclase response to calmodulin was higher during the beginning of the dark phase of the cycle, when endogenous corticosterone levels are high. Basal and forskolin-stimulated adenylate cyclase activity did not exhibit diurnal variation in either brain region. ADX (6 and 14 days) depressed the adenylate cyclase response to calmodulin in hippocampal membranes, and abolished the diurnal difference. ADX had smaller effects on this response in cortical membranes. ADX also attenuated basal and forskolin-stimulated adenylate cyclase activity, but these changes were less striking than effects on calmodulin-stimulated activity. Demedullation (14 days), generating corticosterone levels in the low physiological range, mirrored the effects of ADX on hippocampal adenylate cyclase activity. Corticosterone (20 to 25 mug/ml in the drinking water) did not consistently prevent ADX effects on adenylate cyclase activity. These results demonstrate that adrenal effects on adenylate case activity are regionally specific within the brain, and they suggest that other adrenal secretions besides glucocorticoids may be involved in the feedback of the diurnal rhythm on the hippocampus. Taken together with our recent finding that chronic stress or corticosterone injection selectively attenuated the adenylate cyclase response to calmodulin in cortical, but not hippocampal membranes our findings provide further support for a role of the pituitary-adrenal axis in modulating neural calmodulin-dependent adenylate cyclase activity.

Calmodulin involvement in stress- and corticosterone-induced down-regulation of cyclic AMP-generating systems in brain

Manipulation of the hypothalamic-pituitary-adrenal axis selectively alters alpha-adrenergic potentiation of the cyclic AMP response to beta-adrenergic receptor stimulation in rat cerebral cortex. Calcium has been implicated in this alpha-receptor-mediated response, which may involve activation of phospholipases A2 and C and/or calmodulin-dependent adenylate cyclase. We therefore investigated the effects of stress and corticosterone (CORT) on membrane calmodulin-dependent adenylate cyclase and noradrenaline-stimulated cyclic AMP accumulation in brain slices. Repeated stress for 21 days selectively attenuated the adenylate cyclase response to calcium/calmodulin in cerebral cortex membranes, without affecting basal or forskolin-stimulated enzyme activity. There was no such effect in hippocampal membranes. The same pattern of response was elicited by daily CORT injection (50 mg/kg s.c.) for 21 days, while vehicle injection had no effect. CORT in the drinking water (400 micrograms/ml) elicited the same reduction of body weight as CORT injections, but had no effect on calmodulin adenylate cyclase. In parallel with calmodulin adenylate cyclase, cyclic AMP accumulation elicited by noradrenaline in slices of cerebral cortex was suppressed by both stress and daily CORT injections, with smaller effects observed with CORT in the drinking water. Unlike calmodulin adenylate cyclase, noradrenaline-stimulated cyclic AMP accumulation in hippocampus showed the same suppression as that in cerebral cortex. These results are discussed in relation to the differential mode of coupling of alpha-adrenergic receptors to cyclic AMP-generating systems between brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

VIP neurons in the cerebral cortex

VIP-containing cells in the neocortex are intrinsic neurons of the bipolar type, which release VIP through mechanisms that involve Ca2+ and lipoxygenase metabolites. VIP receptors are coupled to cAMP-generating systems that are amplified by various neurotransmitters such as noradrenaline, histamine and GABA. Pierre Magistretti reviews the evidence that VIP neurons play an important role in the local regulation of metabolism in the cerebral cortex by stimulating glycogenolysis and altering cortical blood flow.

Charting of type II glucocorticoid receptor-like immunoreactivity in the rat central nervous system

The rat brain and spinal cord have been mapped for Type II glucocorticoid receptor-like immunoreactivity in neurons and glia, using a monoclonal antibody, BUGR2, which recognizes an epitope close to the DNA-binding domain of the rat Type II receptor. The study revealed a widespread distribution of Type II-like immunoreactive neurons and glia, and a heterogeneity of densities and intensities of immunoreactive elements. Our results corresponded to a large extent with previous immunocytochemical mapping using Ig2a, a monoclonal antibody against a different epitope in the variable domain, with some notable differences in the hippocampus, hypothalamus and cerebellum. There was also a good correlation between immunocytochemical mapping and binding studies, [3H]steroid autoradiography and mRNA localization of the Type II receptor.

Behavioral sensitization to amphetamine is dependent on corticosteroid receptor activation

Thirty rats received 3 amphetamine injections (1.5 mg/kg, s.c.) 6 days apart and the locomotor response was measured. One day before the second injection they were adrenalectomized or sham operated. Corticosteroid replacement treatments (500 micrograms/kg, s.c.) were given every evening. Sham adrenalectomized animals exhibited behavioral sensitization to successive injections of amphetamine, which was prevented by adrenalectomy. Treatment with corticosterone or deoxycorticosterone did not reverse the effect of adrenalectomy, whereas dexamethasone completely restored and even potentiated sensitization to amphetamine. These results demonstrate that corticosteroids are necessary for sensitization of the dopaminergic system to occur and that they most probably act through the type II (or glucocorticoid) receptor subtype.

New perspectives on the molecular pharmacology of affective disorders

Research with antidepressants has emphasized the importance of a delayed deamplification of the linked serotonin (5HT)/norepinephrine (NE) receptor coupled adenylate cyclase system in brain. The basic phenomena of regulation of receptor number and function of the beta adrenoceptor linked adenylate cyclase system in brain are well established, with NE regulating beta adrenoceptors in the high agonist affinity conformation (linked to adenylate cyclase and down-regulated by antidepressants), and with 5HT regulating those receptors in the low agonist affinity conformation. The biochemical effector systems of NE and 5HT are discussed and it is concluded that the final common pathway of signal transduction is protein kinase mediated phosphorylation of cellular proteins. Glucocorticoid receptors are located in the perikarya of aminergic cell bodies and may exert their effects by modifying the genomic expression of the diffusely projecting stress-responsive monoamine systems. The molecular neurobiology of beta adrenoceptors, with its implication for genetic and immunologic investigations, is briefly discussed and further research on stimulus-transcription coupling and regulation of gene expression in brain is suggested as an exciting new direction in central receptor research relevant to the psychopharmacology of affective and other disorders.

Glucocorticoids modify differentially dopamine- and prostaglandin E1-mediated cyclic AMP formation by the cultured human astrocytoma clone D384

The effects of steroid hormones on the cyclic AMP responses to stimulation of human astrocytoma cells (D384) by dopamine, prostaglandin E1 (PGE1), and isoprenaline were investigated. Incubation of D384 cells with dexamethasone resulted in a potentiation of the PGE1 and isoprenaline responses and a marked attenuation of the dopamine response. The time courses of the effects of dexamethasone on dopamine and PGE1 responses were similar, requiring long-term (at least 18 h) incubation of cells with the steroid. Concentration-response curves of dexamethasone effects on dopamine and PGE1 responses yielded similar Ka apparent values, suggesting a common mechanism. Cycloheximide, a protein synthesis inhibitor, prevented the effects of dexamethasone. Only steroids with glucocorticoid activity reproduced the dexamethasone effects. Direct stimulation of Gs with 5-guanylylimidodiphosphate and adenylate cyclase with forskolin revealed no significant differences in their activities in dexamethasone-treated and untreated cells. Furthermore, a comparison of the dopamine and PGE1 concentration-response curves obtained from dexamethasone-treated and untreated cells suggested that the affinity of the receptors for their agonists remained unchanged. These results suggest that glucocorticoids may alter protein synthesis and thereby the number of receptors expressed by D384 cells.

Corticosterone differentially regulates the expression of Gs alpha and Gi alpha messenger RNA and protein in rat cerebral cortex

The possibility that glucocorticoids regulate specific guanine nucleotide binding regulatory proteins (G proteins) was investigated in rat cerebral cortex. Corticosterone was administered to normal and bilaterally adrenalectomized rats, and hormone regulation of individual G-protein subunits was investigated in cerebral cortex in three ways: (i) immunoblot analysis of subunit protein, (ii) hybridization blot analysis of subunit mRNA, and (iii) ADP-ribosylation analysis of stimulatory G protein (Gs alpha) subunits. Chronic (7 days) corticosterone administration to normal rats increased levels of Gs alpha immunoreactivity, mRNA, and ADP-ribosylation but decreased levels of inhibitory G protein (Gi alpha) mRNA and tended to decrease levels of Gi alpha immunoreactivity. In contrast, levels of Go alpha and G beta immunoreactivity and mRNA were not influenced by corticosterone treatment. In adrenalectomized rats, corticosterone treatment produced a 25-50% increase in the levels of Gs alpha immunoreactivity, mRNA, and ADP-ribosylation, whereas the hormone produced a 20-35% decrease in the levels of Gi alpha immunoreactivity and mRNA. Adrenalectomy, without corticosterone replacement, produced the opposite effects on Gs alpha and Gi alpha compared to sham-operated controls, indicating that these G proteins are regulated by this class of steroid hormone under physiological conditions in vivo. The results indicate that specific G-protein subunits--namely, Gs alpha and Gi alpha--are under the coordinated control of glucocorticoids in rat brain and demonstrate that G proteins are physiological targets of glucocorticoids in vivo. Possible roles played by these G-protein responses in mediating the effects of glucocorticoids on brain function are discussed.

Corticosteroids in cancer: neuropsychiatric complications

The addition of corticosteroids in the early 1950s to the treatment armamentarium provided cure of some diseases and control of many. They have become an integral part of many cancer treatment regimens. Early reports of severe affective disorders appear less frequent today in patients receiving steroids, though controlled studies are rare. Minor mood changes are common, ranging from the euphoria of initial treatment to depressive symptoms on withdrawal. The most common severe disturbances seen clinically in cancer patients are the organic mood disorders and delirium. Studies are needed, especially in cancer, which control for prior psychiatric history, cancer site, cancer treatment, pain regimen, coexisting cancer complications, especially central nervous system complications, and physical performance status. DSM-III-R terminology must be used as the diagnostic classification for reliable investigation. A more careful clinical delineation of the mental changes with steroids is desirable not only for the clinical relevance, but for the potential understanding of the etiology of mood disorders and mental changes seen in delirium.

Dexamethasone and adrenalectomy alter brain (Na+,K+)-ATPase responses to noradrenergic stimulation or depletion

We investigated the effects of adrenalectomy or dexamethasone treatment on the regulation of brain (Na+,K+)-ATPase by noradrenaline. Noradrenergic stimulation was produced by repeated injections of yohimbine, and noradrenaline depletion by an injection of the selective toxin DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine). Adrenalectomy had no effect on the number of ouabain binding sites in cerebral cortex, but increased the number of sites synergistically with noradrenergic stimulation. Dexamethasone prevented the decrease in ouabain binding in rats treated with DSP4, but did not itself alter ouabain binding. Neither dexamethasone nor adrenalectomy altered the changes in beta-receptor binding associated with the noradrenergic manipulations. Changes in exposure to corticosteroids may alter the coupling between adrenoceptor binding and second messenger activation in a way that affects (Na+,K+)-ATPase regulation.