Increase In Corticosterone Secretion Research Articles

Involvement of cAMP but not PKA in the increase of corticosterone secretion in rat zona fasciculata‐reticularis cells by aging

The effects and mechanisms of aging on corticosterone secretion in zona fasciculata-reticularis (ZFR) cells of ovariectomized (Ovx) rats were studied. Young (3-month) and old (24-month) female rats were Ovx for 4 days before decapitation. ZFR cells were isolated and incubated with different hormones or reagents at 37 degrees C for 30 min. Aging increased the basal secretion of corticosterone both in vivo and in vitro. The adrenocorticotropin (ACTH)-, forskolin-, 3-isobutyl-l-methylxanthine (IBMX)-, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP)-, and ovine prolactin (oPRL)-stimulated release of corticosterone by ZFR cells was greater in old than in young Ovx rats. H89, an inhibitor of protein kinase A (PKA), decreased the production of corticosterone in ZFR cells from young but not old Ovx rats. Forskolin-, or IBMX-induced production of cAMP was greater in old than in young Ovx animals, which correlated with the increase of corticosterone production by aging. The activity of 11 beta-hydroxylase that converts deoxycorticosterone (DOC, 10(-9) or 10(-8) M) to corticosterone in rat ZFR cells was decreased by age. However, the corticosterone production in response to high dose of DOC (10(-7) M) was indifferent between young and old groups. These results suggest that aging increases corticosterone production in Ovx rats via a mechanism in part associated with an increase of adenylyl cyclase activity and a decrease of phosphodiesterase activity, and then an increase of the generation of cAMP, but not related to either PKA activity or 11 beta-hydroxylase.

The role of adrenal corticosteroids in induction of micronuclei by morphine

It has previously been shown that morphine can increase the frequency of micronucleated splenocytes when administered to mice, but not when cells are exposed to the opiate in vitro. Morphine treatment is also known to increase circulating levels of glucocorticosteroids, which have been reported to produce genetic damage in vivo and in vitro. In order to determine whether adrenal hormones might mediate the genotoxic effects of morphine, adrenalectomized and sham-operated mice were treated with morphine sulfate. In sham-operated animals administration of morphine produced a dose-related increase in the frequency of micronucleated cells, whereas adrenalectomy abolished the effect. When plasma from morphine-treated mice was used to supplement growth medium of untreated splenocytes, the frequency of micronucleated cells increased, an effect partially blocked by the steroid antagonist RU 486. The N-methylmorphine, which does not stimulate the release of corticosterone from adrenal glands, induced micronuclei formation in splenocytes, and administration of metyrapone, an inhibitor of corticosterone biosynthesis, blocked the morphine-induced increase in corticosterone secretion, but had no effect on the frequency of micronuclei formation. These results indicate that basal levels of glucocorticosteroids are required for induction of micronuclei by morphine in murine splenocytes, but activation of the hypothalamo–pituitary–adrenal (HPA) axis by morphine does not contribute to the observed response.

Amygdala Is Critical for Stress-Induced Modulation of Hippocampal Long-Term Potentiation and Learning

Stress is a biologically significant factor shown to influence synaptic plasticity and memory functioning in the hippocampus. This study examined the role of the amygdala, a brain structure implicated in coordinating stress behaviors and modulating memory consolidation, in mediating stress effects on hippocampal long-term potentiation (LTP) and memory in rats. Electrolytic lesions of the amygdala effectively blocked the adverse physiological and behavioral effects of restraint and tailshock stress, without impeding the increase in corticosterone secretion to stress. Physiologically, hippocampal slices from stressed animals exhibited impaired LTP relative to slices from unstressed control animals, whereas hippocampal slices from stressed animals with amygdalar lesions exhibited normal LTP. Behaviorally, stressed animals were impaired in retention of a hippocampal-dependent hidden platform version of the Morris water maze task, and this impairment was blocked by amygdalar lesions. In a fixed location-visible platform water maze task that can be acquired by independent hippocampal and nonhippocampal memory systems, stress enhanced the use of nonhippocampal-based memory to acquire the task. These results indicate that an intact amygdala is necessary for the expression of the modulatory effects of stress on hippocampal LTP and memory.

Prevention of glucoprivic stimulation of corticosterone secretion by leptin does not restore high frequency luteinizing hormone pulses in rats.

We have previously determined that exogenous leptin prevents the inhibition of pulsatile luteinizing hormone (LH) release in the fasting rodent. The present study tested the hypothesis that the mechanism by which leptin facilitates high LH secretion is through an attenuation of the stress response produced by a deficit in energy. Because hypogonadotropism is associated with activation of the hypothalamic-pituitary-adrenal (HPA) axis during both metabolic stress and nonmetabolic stress, our approach included a comparison of whether exogenous leptin could prevent the rise in corticosterone produced by a nonmetabolic stress (immobilization for 2 h), as well as by a widely used metabolic stress (transient glucoprivation by 2-deoxyglucose, 2DG; 400 mg/kg, b.w., i.v.). Each stressor was applied to well-fed ovariectomized rats (n = 4-6 per group), 2 h after leptin (3 microg/g, b.w., i.p.) or vehicle administration. Blood samples were collected through an indwelling atrial cannula every 6 min for 1 h before and for 2 h after the stress treatment to measure LH, leptin and corticosterone. During metabolic stress (acute glucoprivation), circulating leptin decreased, corticosterone increased and LH decreased; leptin administration abolished the increase in corticosterone, but pulsatile LH secretion remained inhibited. In contrast, during nonmetabolic stress (immobilization), leptin secretion was unaffected, but circulating corticosterone increased and LH decreased; leptin treatment did not prevent either the increase in corticosterone or the decrease in LH secretion. An important overall finding is that leptin can differentially alter the HPA axis depending upon the type of stress. In addition, whether the pattern of leptin is altered depends upon the type of stress. Although a glucoprivic-induced decrease in endogenous leptin can be a stressor responsible for the increase in corticosterone secretion, a nonmetabolic stress-induced increase in corticosterone is not mediated by leptin. Moreover, our results reveal that the depression of LH secretion when leptin is low during reduced energy availability is not due to activation of the HPA axis. During an energy deficit, exogenous leptin could not restore high frequency LH secretion when HPA function was restored to normal. Finally, the inability of leptin to increase LH secretion in the face of 2DG supports the notion that the action of leptin is dependent upon the degree of glucose availability.

Hypothalamo-pituitary-adrenocortical dysregulation in aging F344/Brown-Norway F1 hybrid rats.

Hypothalamo-pituitary-adrenocortical (HPA) axis aging was studied in young (3 mo), middle aged (15 mo) and aged (30 mo) F344/Brown Norway hybrid rats. This strain was selected to obviate HPA-relevant pathologies found in other aging models. Aged, unstressed rats showed enhanced central HPA drive, marked by elevated ACTH release and decreased pituitary proopiomelanocortin and corticotropin-releasing factor receptor 1 (CRH-R1) mRNAs. Acute corticosterone responses to spatial novelty were exacerbated in aged rats; however, responses to restraint or hypoxia were not affected. Chronic stress exposure also differentially increased HPA drive in aged animals, marked by elevated paraventricular nucleus CRH peptide levels and pituitary proopiomelanocortin mRNA. Plasma ACTH and pituitary POMC and CRH-R1 mRNA expression in middle-aged rats were intermediate those of young and aged animals. Middle-aged animals responded to chronic stress with disproportionate increases in CRH mRNA levels, and increased corticosterone secretion following hypoxia but not novelty. The results suggest a gradual increase in HPA tone across the aging process, culminating in marked hyperresponsivity to both acute and chronic stress in senescence.

Irreversible Binding and Adrenocorticolytic Activity of the DDT Metabolite 3-Methylsulfonyl-DDE Examined in Tissue-Slice Culture

The persistent adrenocorticolytic DDT metabolite 3-methylsulfonyl-DDE (MeSO(2)-DDE) was originally identified in Baltic grey seals, a population suffering from adrenocortical hyperplasia. In mice, MeSO(2)-DDE induces mitochondrial degeneration and cellular necrosis in the adrenal zona fasciculata. In this study, we used precision-cut tissue slice culture to examine local CYP11B1-catalyzed irreversible binding of MeSO(2)-DDE in the murine adrenal cortex. We also examined effects on steroid hormone secretion, histology, and ultrastructure. As determined by microautoradiography, selective binding occurred in zona fasciculata of slices exposed to MeSO(2)-[(14)C]-DDE. Quantification of binding by phosphorautoradiography revealed a 3-fold reduction of binding in slices co-exposed to the CYP11B1 inhibitor metyrapone. As measured by HPLC, corticosterone and 11-deoxycorticosterone secretion to the medium increased linearly for at least 24 hr. Addition of the ACTH analog tetracosactide caused an 8-fold increase in corticosterone secretion. Addition of metyrapone reduced corticosterone secretion 4-fold. Exposure of slices to MeSO(2)-DDE (50 microM) reduced the rate of corticosterone secretion by 90% after 24 hr of incubation. As determined by electron microscopy, vacuolated mitochondria were present in zona fasciculata of slices exposed to MeSO(2)-DDE (50 microM) for 24 hr. Our findings show that all effects of MeSO(2)-DDE previously reported in vivo could be reproduced in adrenal slice culture ex vivo. This test system allows analysis of zone-specific irreversible binding and effects on steroid hormone secretion and target cell ultrastructure. We propose adrenal slice culture as a simple ex vivo test system with which to examine the adrenocorticolytic activity of xenobiotics in human and wild animal tissue.

Irreversible binding and adrenocorticolytic activity of the DDT metabolite 3-methylsulfonyl-DDE examined in tissue-slice culture.

The persistent adrenocorticolytic DDT metabolite 3-methylsulfonyl-DDE (MeSO(2)-DDE) was originally identified in Baltic grey seals, a population suffering from adrenocortical hyperplasia. In mice, MeSO(2)-DDE induces mitochondrial degeneration and cellular necrosis in the adrenal zona fasciculata. In this study, we used precision-cut tissue slice culture to examine local CYP11B1-catalyzed irreversible binding of MeSO(2)-DDE in the murine adrenal cortex. We also examined effects on steroid hormone secretion, histology, and ultrastructure. As determined by microautoradiography, selective binding occurred in zona fasciculata of slices exposed to MeSO(2)-[(14)C]-DDE. Quantification of binding by phosphorautoradiography revealed a 3-fold reduction of binding in slices co-exposed to the CYP11B1 inhibitor metyrapone. As measured by HPLC, corticosterone and 11-deoxycorticosterone secretion to the medium increased linearly for at least 24 hr. Addition of the ACTH analog tetracosactide caused an 8-fold increase in corticosterone secretion. Addition of metyrapone reduced corticosterone secretion 4-fold. Exposure of slices to MeSO(2)-DDE (50 microM) reduced the rate of corticosterone secretion by 90% after 24 hr of incubation. As determined by electron microscopy, vacuolated mitochondria were present in zona fasciculata of slices exposed to MeSO(2)-DDE (50 microM) for 24 hr. Our findings show that all effects of MeSO(2)-DDE previously reported in vivo could be reproduced in adrenal slice culture ex vivo. This test system allows analysis of zone-specific irreversible binding and effects on steroid hormone secretion and target cell ultrastructure. We propose adrenal slice culture as a simple ex vivo test system with which to examine the adrenocorticolytic activity of xenobiotics in human and wild animal tissue.

Exendin-4, a GLP-1 Receptor Agonist, Stimulates Rat Pituitary-Adrenocortical Axis

Preproglucagon-derived peptides, among which glucagon and glucagon-like peptide-1 (GLP-1), are known to modulate the activity of the hypothalamo-pituitary-adrenal (HPA) axis. Many effects of GPL-1, however, are preventedby its very short half-life. Hence we investigated in vivo and in vitro the effects on the rat HPA axis of the GLP-1-receptor agonist exendin-4 (EX4), which possesses a longer biological half-life than GLP-1. The bolus systemic administration of EX4 (12 nmol/kg) evoked significant rises in ACTH, aldosterone and corticosterone concentrations. EX4 (10 - 7 M) induced a weak but significant increase in corticosterone secretion from dispersed rat adrenocortical cells, and the effect was abrogated by the GLP-1-receptor antagonist exendin (9-39). Collectively, our findings indicate that EX4, acting via GLP-1 receptors, stimulates HPA axis in rats, acting on both its central (hypothalamo-pituitary) and peripheral (adrenocortical) branch.

Corticosterone facilitates begging and affects resource allocation in the black-legged kittiwake

Parent black-legged kittiwakes (Rissa tridactyla) and their dependent chicks respond to food shortages by increasing circulating levels of corticosterone. To examine the behavioral significance of corticosterone release, we experimentally increased levels of circulating corticosterone in parents and chicks up to the levels observed during food shortages. We found that corticosteroneimplanted chicks begged more frequently than sham-implanted controls. Corticosterone-implanted chicks in broods of two begged more frequently than singletons. Parent kittiwakes then responded to the increase in corticosterone levels in their chicks by increasing chick-feeding rates. However, feeding rates were not different among corticosterone-implanted chicks in broods of two and singletons. We also found that corticosterone-implanted parents spent more time away from the nest—perhaps foraging—and less time brooding/guarding chicks than sham-implanted controls. Untreated mates of the corticosterone-implanted bird did not compensate for the change in their partner’s behavior; consequently, chicks were left unattended about 20% of the time compared to 1% at the control nests. However, corticosterone-implanted parents did not decrease their chickfeeding rates. Our findings suggest two functional implications of the increased corticosterone secretion during food shortages in the black-legged kittiwake: it facilitates begging in chicks, and it affects time allocated by parents to guarding young at the nest. Thus, release of corticosterone might provide a mechanistic link between physiological condition and behavioral interactions among adults and their young. Key words: begging, corticosterone, food stress, kittiwakes, parent-offspring conflict, Rissa tridactyla, seabirds. [Behav Ecol 12:619–625 (2001)]

The influence of sex and gonadectomy on the growth hormone and corticosterone response to hexarelin in the rat

The present study is designed to investigate the role of sex and gonadal status in the growth hormone (GH) and corticosterone response to hexarelin (HEXA), a GH-releasing peptide, which also causes a stimulatory action on the hypothalamic-pituitary-adrenal (HPA) axis. HEXA (80μg/Kg) was administered intracarotid to anesthetized intact or gonadectomized male (ORC) and female (OVX) middle-aged rats. The GH stimulatory response to HEXA was gender-related since the GH increase was significantly (p< 0.001) higher in intact males (area under the curve, AUC= 12560 ± 1784 ng/ml.45 min) than in females (AUC= 4628 ± 257 ng/ml.45 min). This sex difference does not depend on circulating gonadal steroids since it persists in ORC (AUC = 11980 ± 1136 ng/ml.45 min) and OVX (AUC = 5539 ± 614 ng/ml.45 min) rats. The different effects of HEXA on corticosterone secretion detected in male and female rats are probably dependent on the prevailing activity of the HPA axis. In fact, in male rats that have low basal corticosterone levels, HEXA caused an increase in corticosterone secretion, which was significantly (p< 0.05) higher in ORC than in intact rats. The increase in corticosterone secretion by HEXA both in intact and OVX females was delayed, probably due to the elevated initial corticosterone levels, which could have activated the glucocorticoid negative feedback. We suggest that gender-specific patterns in the regulation of the hypothalamus-pituitary function could be responsible for the GH and corticosterone sexually differentiated responses to HEXA.

Magnolol stimulates steroidogenesis in rat adrenal cells.

1. This study investigated the effect of magnolol, a compound purified from Magnolia officinalis, on glucocorticoid production by primary adrenal cell culture. 2. Magnolol increased corticosterone secretion in a dose-dependent manner, this effect being maximal at 40 microM. A similar effect was seen in a minced adrenal gland system. 3. In magnolol-treated cells, the number and total area of cytoplasmic lipid droplets were reduced, suggesting a high utilization rate of cholesterol esters stored in lipid droplets. In control cells, the capsule of the lipid droplet was clearly delineated by immunostaining with antibody A2, whereas capsular staining was discontinuous or undetectable following magnolol treatment. The percentage of decapsulated cells increased significantly from 20% in the control group to 80% in the magnolol-treated group. 4. Magnolol-induced steroidogenesis was not mediated either via the traditional ACTH-cyclic AMP-protein kinase A pathway or by protein kinase C, since the intracellular cyclic AMP level did not change and inhibition of protein kinase A or C did not block the action of magnolol. Furthermore, calcium/calmodulin-dependent protein kinase II was not involved in magnolol-induced steroidogenesis. 5. The stimulatory effect of magnolol on steroidogenesis apparently requires new protein synthesis, since cycloheximide inhibited magnolol-induced corticosterone production by 50%. 6. Although other studies have shown that high concentrations of magnolol inhibit acyl-CoA: cholesterol acyltransferase and 11 beta-hydroxysteroid dehydrogenase in a cell-free system, our data show that, in adrenal cell cultures, low concentrations of magnolol have a stimulatory effect on steroidogenesis, and the glucocorticoid produced may explain the effective control of asthma by Magnolia officinalis.

Noradrenergic and Dopaminergic Activity in the Hypothalamic Paraventricular Nucleus after Naloxone-Induced Morphine Withdrawal

Previous research has shown an increase in hypothalamo-pituitary-adrenal axis activity following naloxone administration to morphine-dependent rats. In the present study, we investigated the adaptive changes in the noradrenaline (NA) and dopamine (DA) systems in the hypothalamic paraventricular nucleus (PVN) during morphine dependence and withdrawal. Additionally, we examined the possible change in 3′,5′-cyclic adenosine monophosphate (cAMP) levels in that nucleus under the same conditions. Rats were made dependent on morphine by morphine or placebo (naïve) pellet implantation for 7 days. On day 8, rat groups received an acute injection of saline or naloxone (1 mg/kg subcutaneously) and were decapitated 30 min later. NA and DA content as well as their metabolite production in the PVN were estimated by HPLC/ED. Both plasma corticosterone levels and cAMP concentration in the PVN were measured by RIA. Naloxone administration to morphine-dependent rats (withdrawal) induced a pronounced increase in the production of both the NA metabolite MHPG and the DA metabolite DOPAC and an enhanced NA and DA turnover. Furthermore, an increase in corticosterone secretion was observed in parallel to the changes in catecholamine turnover. However, no alterations in cAMP levels were seen during morphine withdrawal. These results raise the possibility that catecholaminergic afferents to the PVN could play a significant role in the alterations of PVN functions and consequently in the pituitary-adrenal response during morphine abstinence syndrome. These data provide further support for the idea of adaptive changes in catecholaminergic neurons projecting to the PVN during chronic morphine exposure.

Skeletal muscle damage following halothane anaesthesia in the domestic fowl: plasma biochemical responses

The effects of a short period (10 minutes) of halothane anaesthesia upon skeletal muscle have been examined in broiler chickens. Integrity of the muscle membrane was assessed by measurement of plasma activities of intracellular enzymes. Creatine kinase activity was greatly increased during the first 12 hours post-anaesthesia and remained elevated for at least 48 hours. Lactate dehydrogenase activity exhibited a similar pattern which was less pronounced. Halothane anaesthesia induced transient hypercapnic acidosis and hypokalemia and increased corticosterone secretion but there was no significant effect upon deep body temperature. It is proposed that halothane may act directly upon skeletal muscle, perhaps influencing intracellular calcium homeostasis, to alter membrane permeability and increase enzyme efflux reflecting a degree of post-anaesthetic muscle damage. The transient changes in electrolyte and acid-base balance may contribute to these effects. Precautions should be taken to minimise the incidence or extent of halothane induced myopathy in birds particularly in rapidly growing broiler chickens where susceptibility may be increased.

The inhibitor of phospholipase-A2, AACOCF3, stimulates steroid secretion by dispersed human and rat adrenocortical cells

AACOF3 is a trifluomethylketone analog of arachidonic acid, which inhibits phospholipase-A2 (PLA2). AACOCF3 was found to concentration-dependently increase basal aldosterone and corticosterone secretion by dispersed rat zona glomerulosa and zona fasciculata/reticularis cells, respectively, as well as aldosterone and cortisol production by dispersed human adrenocortical cells Maximal effective concentration was 10 −5M, and elicited about 2.5–3.0-fold rises in steroid output. 10 −5 M AACOCF3 also enhanced submaximally ( 10 −15 10 −12M ), but not maximally (10 −9 M) ACTH-stimulated hormonal secretion. Quantitative HPLC showed that 10 −5 M AACOCF3 evokes similar increases (from 2.0- to 3.0-fold) in the basal release of the entire spectrum of adrenocortical steroids ( i.e. both intermediate and definitive products of steroid synthesis), thereby suggesting that AACOCF3 acts on the early steps of steroid synthesis. Accordingly, when pregnenolone metabolism is prevented by cyanoketone, 10 −5 M AACOCF3 increased by about 8–10-fold the production of this steroid. In conclusion, we have demonstrated a side-effect of AACOCF3, which may become relevant in studies where this chemical is used to inhibit PLA2 in tissues able to convert cholesterol to pregnenolone.

Effect of nitric oxide on rat adrenal zona fasciculata steroidogenesis.

The present study was designed to investigate the role of nitric oxide (NO) in the regulation of adrenocortical function. Different NO donors, such as sodium nitroprusside (SNP), S-nitroso-L-acetyl penicillamine, diethylamine/NO complex sodium salt and diethylenetriamine NO adduct, significantly decreased corticosterone production both in unstimulated and in corticotropin-stimulated zone fasciculata adrenal cells, in a dose-dependent manner. The effect of SNP was reversed by ferrous hemoglobin. A selective inhibitor of NO synthase, L-NG-nitro-arginine significantly increased corticosterone secretion. The effect of SNP was not mediated by cGMP as permeable cGMP analogs did not reproduce its inhibitory effect. SNP significantly inhibited the steroidogenesis stimulated by 8Br-cAMP and 22(R)-OH-cholesterol, but was ineffective when corticosterone was produced in the presence of exogenously added pregnenolone. Moreover, the conversion of [3H]cholesterol to [3H]pregnenolone and the production of pregnenolone or progesterone (assessed by RIA) were significantly decreased by SNP. Taken together, these results suggest that NO may be a negative modulator of adrenal zona fasciculata steroidogenesis.

Galanin Stimulates Glucocorticoid Secretion in Rats through a Receptor-dependent Activation of the Adenylate Cyclase/Protein Kinase A-dependent Signaling Pathway

Galanin, a 29-amino acid peptide widely distributed in the central and peripheral nervous systems, was found to induce a concentration-dependent increase in corticosterone secretion and cyclic-AMP release by dispersed rat inner adrenocortical cells (maximal effective concentration, 10 −7M). The effect of 10 −7M galanin was blocked by 10 −6M galantide, a specific antagonist of galanin receptors. Galanin (10 −7M) also enhanced corticosterone and cyclic-AMP responses of dispersed cells to submaximal but not maximal (10 −9M) effective concentrations of ACTH, and again this effect was reversed by galantide. The ACTH-receptor antagonist corticotropin-inhibiting peptide (10 −6M) blocked corticosterone response of dispersed cells to 10 −9M ACTH but not to 10 −7M galanin; conversely, the specific protein kinase A inhibitor H-89 (10 −5M) annulled the secretory response to both ACTH and galanin. In light of these findings, we conclude that galanin stimulates adrenal glucocorticoid secretion in rats, acting through specific receptors, coupled, like those of ACTH, with the adenylate cyclase/protein kinase A-dependent signaling pathway.

Neurochemical and Neuroendocrine Effects of Ibogaine in Rats: Comparison to MK-801.

Ibogaine (IBO) is a naturally-occurring indole compound that is being evaluated as a potential medication for substance use disorders. Although the precise mechanism of IBO action is unclear, recent in vitro data show this drug displays properties similar to the noncompetitive N-methyl-d-aspartate (NMDA) antagonist MK-801. The purpose of the present work was to compare In Vivo neurobiological effects of IBO and MK-801 in rats. Groups of male rats (n = 6-8/group) were decapitated 30 and 60 min after receiving intraperitoneal (i.p.) IBO (10 & 100 mg/kg), MK-801 (0.1 & 1.0 mg/kg) or vehicle. Trunk blood was collected for the analysis of plasma prolactin and corticosterone; brains were harvested and dissected for determination of dopamine (DA), serotonin (5-HT) and their metabolites. Both IBO and MK-801 increased corticosterone secretion, but only IBO elevated plasma prolactin. IBO produced dramatic reductions in tissue DA levels with concurrent increases in the metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This profile of IBO-induced changes in DA transmission was observed in the striatum, olfactory tubercle, and hypothalamus. The effects of MK-801 on DA metabolism did not mimic IBO, as MK-801 tended to increase DA and its metabolites. Neither drug appreciably affected 5-HT systems. Our results suggest that the effects of IBO on neuroendocrine function and DA transmission are not due to MK-801-like properties of IBO. Thus, the In Vivo mechanism of IBO action cannot be explained simply on the basis of antagonism at NMDA receptors.

1996 Curt P. Richter Award. Effects of viral infection on corticosterone secretion and glucocorticoid receptor binding in immune tissues.

During an immune challenge it has been suggested that responding cells secrete cytokines which then stimulate the release of glucocorticoids. Glucocorticoids, in turn, are believed to bind to their receptors in target immune tissues and provide feedback inhibition on evolving immune responses. The foundations for this hypothesis have been drawn primarily from studies on animal models of autoimmune and/or inflammatory processes, and the relevance of these glucocorticoid-immune interactions to viral infections has not been extensively examined. Accordingly, we infected mice with lymphocytic choriomeningitis virus (LCMV) and measured plasma corticosterone and cytosolic glucocorticoid receptor (GR) binding at multiple time points throughout the day and throughout infection (days 3, 5, 7 and 10 post infection). Despite a vigorous immune response to this virus, LCMV infection was associated with minimal and transient increases in corticosterone secretion. Interestingly, however, significant decreases in cytosolic GR were found in immune tissues. Receptor decreases were characterized by a significant decrease in GR binding during the diurnal rise in corticosterone in the spleen and thymus of infected but not uninfected animals on days 5-10 post infection. In addition, in the morning on these days, GR binding in the spleen of infected mice was decreased compared to uninfected control mice. Following an acute injection of corticosterone on day 7 post infection, LCMV-infected animals exhibited a significantly greater decrease in splenic GR binding than uninfected control mice, suggesting an increased sensitivity to corticosterone in infected animals. No changes were found in the affinity (Kd) of the GR during infection, nor was there evidence of an infection-associated decrease in plasma corticosteroid binding globulin. The appearance of significant GR changes in the spleen and thymus, in the absence of significant elevations in corticosterone or decreases in its binding protein, suggests that cytokines and/or other factors produced within the immune tissues during infection either directly influenced GR number and/or function or influenced the local availability of corticosterone. Taken together, the results indicate that interactions between the neuroendocrine and immune systems can be modified at the level of the GR in the context of an ongoing immune response such as during a viral infection.

Activational effects of gonadal steroids on hypothalamo-pituitary-adrenal regulation in the rat disclosed by response to dexamethasone suppression.

Previous studies demonstrated that gonadal steroids secreted during perinatal life permanently 'organize' the mechanisms governing hypothalamo-pituitary-adrenal (HPA) function, leading to sexually differentiated patterns of pituitary-adrenal activity under basal and stress conditions. In this paper, we show that gonadal steroids can also exert 'activational' effects upon the HPA system. Examination of the ability of different doses of dexamethasone to suppress the nocturnal increase in corticosterone secretion and to attenuate the gene expression of CRH in the hypothalamic paraventricular nucleus of intact and gonadectomized male and female rats revealed that ovarian steroids make an important contribution to the higher sensitivity of the pituitary-adrenal axis in females to glucocorticoid suppression, whereas testicular steroids may be causal to the male's moderate responsiveness to glucocorticoid feedback. These findings may be implicated in a number of psychiatric and neurological disease states commonly associated with impaired HPA regulation, but which may be primarily rooted in altered gonadal steroid secretion.

Chromaffin cell depolarization results in modulation of corticosteroidogenesis in co-culture.

Previous morphological and physiological evidence indicates that the adrenal medulla can modulate adrenocortical steroidogenesis, most likely via paracrine or neuronal interactions. To study directly chromaffin-adrenocortical cellular interactions, we previously developed co-cultures of frog (Rana pipiens) adrenal (interrenal) cells. Importantly, chromaffin cells in these co-cultures extend processes that project toward or onto adrenocortical cells, thereby providing the substrate for direct autonomic regulation of adrenocortical function and also mimicking the organization in vivo. To test whether chromaffin cells in our co-cultures affect adrenocortical steroidogenesis, we used veratridine, a sodium ionophore, to depolarize chromaffin cells. Chronic veratridine (50 microM) results in increased corticosterone secretion on days 3 (950%), and 4 (350%). These results indicate that chromaffin cell activation results in the modulation of corticosteroidogenesis.