Corticosterone: narrow range required for normal body and thymus weight and ACTH

Differential Hypothalamic-pituitary-adrenal Response to Stress among Rat Strains: Methodological Considerations and Relevance for Neuropsychiatric Research

The hormones of the hypothalamic-pituitary-adrenal (HPA) axis, particularly glucocorticoids (GCs), play a critical role in the behavioral and physiological consequences of exposure to stress. For this reason, numerous studies have described differences in HPA function between different rodent strains/lines obtained by genetic selection of certain characteristics not directly related to the HPA axis. These studies have demonstrated a complex and poorly understood relationship between HPA function and certain relevant behavioral characteristics. The present review first remarks important methodological considerations regarding the evaluation and interpretation of resting and stress levels of HPA hormones. Then, it presents works in which differences in HPA function between Lewis and Fischer rats were explored as a model for how to approach other strain comparisons. After that, differences in the HPA axis between classical strain pairs (e.g. High and Low anxiety rats, Roman high- and low-avoidance, Wistar Kyoto versus Spontaneously Hypertensive or other strains, Flinder Sensitive and Flinder Resistant lines) are described. Finally, after discussing the relationship between HPA differences and relevant behavioral traits (anxiety-like and depression-like behavior and coping style), an example for main methodological and interpretative concerns and how to test strain differences is offered.

Male long-Evans rats: An outbred model of marked hypothalamic-pituitary-adrenal hyperactivity

Rat and mouse strains differ in behavioral and physiological characteristics, and such differences can contribute to explain discrepant results between laboratories and better select the most appropriate strain for a particular purpose. Differences in the activity of the hypothalamic-pituitary-adrenal (HPA) axis are particularly important given the pivotal role of this system in determining consequences of exposure to stressors. In this regard, Long-Evans (LE) rats are widely used in stress research, but there is no specific study aiming at thoroughly characterizing HPA activity in LE versus other extensively used strains. In a first experiment, LE showed higher resting ACTH and corticosterone levels only at certain points of the circadian rhythm, but much greater ACTH responsiveness to stressors (novel environment and forced swim) than Sprague-Dawley (SD) rats. Accordingly, enhanced corticotropin-releasing hormone (CRH) expression in the paraventricular nucleus of the hypothalamus and reduced expression of glucocorticoid receptors were observed in the hippocampal formation. Additionally, they are hyperactive in novel environments, and prone to adopt passive-like behavior when compared to SD rats. Supporting that altered HPA function has a marked physiological impact, we observed in another set of animals much lower thymus weight in LE than SD rats. Finally, to demonstrate that LE rats are likely to have higher HPA responsiveness to stressors than most strains, we studied resting and stress levels of HPA hormones in LE versus Wistar and Fischer rats, the latter considered an example of high HPA responsiveness. Again, LE showed higher resting and stress levels of ACTH than both Wistar and Fischer rats. As ACTH responsiveness to stressors in LE rats is stronger than that previously reported when comparing other rat strains and they are commercially available, they could be an appropriate model for studying the behavioral and physiological implications of a hyper-active HPA axis under normal and pathological conditions.

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Strain differences in hypothalamic-pituitary-adrenal (HPA) function were studied.

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Long-Evans (LE) rats show greater HPA response to stressors than other strains.

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CRH expression in critical brain areas is greater in LE than Sprague-Dawley (SD) rats.

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Glucocorticoid receptor expression was lower in the hippocampal formation of LE rats.

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LE rats are more active in novel environments but showed more passive coping.

Glucocorticoids regulate adipose tissue protein concentration in a depot- and sex-specific manner

Preclinical and clinical findings indicate that glucocorticoids (GC) induce lipid accumulation in visceral depots, while inhibiting lipid stores from subcutaneous depots. Whereas some suggest that this is due to adipose depot specific concentration of glucocorticoid receptors (GR) or 11beta-hydroxysteroid dehydrogenase 1 (11β-HSD1), others demonstrate these events emerge from increases in interleukin-1 beta (IL-1β) from macrophages within distinct depots. Regardless of the mechanisms, most of these studies occur in males and thus lack evaluation of sex differences. Here, we examined the impact of 2-week corticosterone (CORT) (3 mg/kg/day) or saline treatment on GR, 11β-HSD1 and IL-1β protein concentration in intra-abdominal (epididymal/parametrial, and visceral) and subcutaneous (inguinal) depots in male and female Sprague Dawley rats. The objective was to examine if factors that regulate GC-induced adipose depot metabolism and distribution, differ between males and females. CORT inhibited, but did not decrease, body weight gain in both sexes. 11β-HSD1 was similar between the sexes in all adipose depots. CORT increased IL-1β in both sexes only in gonadal adipose tissue. Overall, males had greater GR protein concentration in all adipose depots, whereas females had more IL-1β in intra-abdominal adipose depots. Given the male-biased increase in intra-abdominal GR protein concentration, the data suggest that males may be more prone to CORT-induced increases in visceral obesity, which may have implications for increased risk for metabolic diseases. Overall, the data suggest that the effects of GC signaling in adipose tissue are multifaceted, dependent on sex, and the inherent adipocyte characteristics.Lay summaryResearch supports that glucocorticoids (GC) induce visceral adipose tissue accumulation, however few studies have examined if these GC-mediated outcomes are similar between males and females. This study investigates if female rats differentially respond to corticosterone treatment. Results indicate that male rats may have an increased susceptibility to CORT-induced accumulation of visceral adipose tissue compared with females, which may have implication for sex-specific risk for metabolic diseases.

Role of corticosterone in anxiety- and depressive-like behavior and HPA regulation following prenatal alcohol exposure

Prenatal alcohol exposure (PAE) is known to cause dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, including hyperresponsivity to stressors. Dysregulation of the HPA axis plays a role in vulnerability to stress-related disorders, such as anxiety and depression. Thus, the effects of PAE on HPA function may result in increased vulnerability to the effects of stress and, in turn, lead to the development of stress-related disorders. Indeed, individuals prenatally exposed to alcohol have an increased risk of developing anxiety and depression. However, it is unclear whether hypersecretion of corticosterone (CORT) in response to stress per se is involved with mediating differential effects of stress in PAE and control animals. To investigate the role of CORT in mediating effects of stress in both adult females and males following PAE, adrenalectomy with CORT replacement (ADXR) was utilized to produce similar CORT levels among prenatal treatment groups before exposure to chronic unpredictable stress (CUS). Anxiety-like behavior was evaluated using the open field and elevated plus maze, and depressive-like behavior was examined in the forced swim test. Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA expression was assessed in the medial prefrontal cortex (mPFC), amygdala, and hippocampal formation. Under the non-CUS condition, PAE alone differentially altered anxiety-like behavior in sham but not ADXR females and males, with females showing decreased anxiety-like behavior but males exhibiting increased anxiety-like behavior compared to their control counterparts. There were no effects of PAE alone on depressive-like in females or males. PAE also decreased GR mRNA expression in the hippocampal formation in females but had no effects on MR or GR mRNA expression in any brain region in males. CUS had differential effects on anxiety- and depressive-like behavior in PAE and control animals, and these effects were sex dependent. Importantly, ADXR unmasked differences between PAE and control animals, demonstrating that CORT may play a differential role in modulating behavior and HPA activity/regulation in PAE and control animals, and may do so in a sex-dependent manner.

A users guide to HPA axis research

Glucocorticoid hormones (cortisol and corticosterone - CORT) are the effector hormones of the hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine system. CORT is a systemic intercellular signal whose level predictably varies with time of day and dynamically increases with environmental and psychological stressors. This hormonal signal is utilized by virtually every cell and physiological system of the body to optimize performance according to circadian, environmental and physiological demands. Disturbances in normal HPA axis activity profiles are associated with a wide variety of physiological and mental health disorders. Despite numerous studies to date that have identified molecular, cellular and systems-level glucocorticoid actions, new glucocorticoid actions and clinical status associations continue to be revealed at a brisk pace in the scientific literature. However, the breadth of investigators working in this area poses distinct challenges in ensuring common practices across investigators, and a full appreciation for the complexity of a system that is often reduced to a single dependent measure. This Users Guide is intended to provide a fundamental overview of conceptual, technical and practical knowledge that will assist individuals who engage in and evaluate HPA axis research. We begin with examination of the anatomical and hormonal components of the HPA axis and their physiological range of operation. We then examine strategies and best practices for systematic manipulation and accurate measurement of HPA axis activity. We feature use of experimental methods that will assist with better understanding of CORT's physiological actions, especially as those actions impact subsequent brain function. This research approach is instrumental for determining the mechanisms by which alterations of HPA axis function may contribute to pathophysiology.

Genotype-related effect of crowding stress on blood pressure and vascular function in young female rats

This study investigated the influence of chronic crowding stress on nitric oxide (NO) production, vascular function and oxidative status in young Wistar-Kyoto (WKY), borderline hypertensive (BHR) and spontaneously hypertensive (SHR) female rats. Five-week old rats were exposed to crowding for two weeks. Crowding elevated plasma corticosterone (P<0.05) and accelerated BP (P<0.01 versus basal) only in BHR. NO production and superoxide concentration were significantly higher in the aortas of control BHR and SHR versus WKY. Total acetylcholine (ACh)-induced relaxation in the femoral artery was reduced in control SHR versus WKY and BHR, and stress did not affect it significantly in any genotype. The attenuation of ACh-induced relaxation in SHR versus WKY was associated with reduction of its NO-independent component. Crowding elevated NO production in all strains investigated but superoxide concentration was increased only in WKY, which resulted in reduced NO-dependent relaxation in WKY. In crowded BHR and SHR, superoxide concentration was either unchanged or reduced, respectively, but NO-dependent relaxation was unchanged in both BHR and SHR versus their respective control group. This study points to genotype-related differences in stress vulnerability in young female rats. The most pronounced negative influence of stress was observed in BHR despite preserved endothelial function.

Binge-like ethanol consumption increases corticosterone levels and neurodegneration whereas occupancy of type II glucocorticoid receptors with mifepristone is neuroprotective

Excessive ethanol (EtOH) use leads to impaired memory and cognition. Using a rat model of binge-like intoxication, we tested whether elevated corticosterone (Cort) levels contribute to the neurotoxic consequences of EtOH exposure. Rats were adrenalectomized (Adx) and implanted with cholesterol pellets, or cholesterol pellets containing Cort in order to achieve basal, medium, or high blood concentrations of Cort. Intragastric EtOH or an isocaloric control solution was given three times daily for 4 days to achieve blood alcohol levels ranging between 200 and 350 mg/dl. Mean 24-hour plasma levels of Cort were ∼110 and ∼40 ng/ml in intact EtOH-treated and intact control animals, respectively. Basal Cort replacement concentrations in EtOH-treated Adx animals did not exacerbate alcohol-induced neurodegeneration in the hippocampal dentate gyrus (DG) or the entorhinal cortex (EC) as observed by amino-cupric silver staining. In contrast, Cort replacement pellets resulting in plasma Cort levels twofold higher (medium) than normal, or greater than twofold higher (high) in Adx-Cort-EtOH animals increased neurodegeneration. In separate experiments, pharmacological blockade of the Type II glucocorticoid (GC) receptor was initiated with mifepristone (RU38486; 0, 5, 15 mg/kg/day, i.p.). At the higher dose, mifepristone decreased the number of degenerating hippocampal DG cells in binge-EtOH-treated intact animals, whereas, only a trend for reduction was observed in 15 mg/kg/day mifepristone-treated animals in the EC, as determined by fluoro-jade B staining. These results suggest that elevated circulating Cort in part mediates EtOH-induced neurotoxicity in the brain through activation of Type II GC receptors.

Glucocorticoid excess induces long-lasting changes in body composition in male C57Bl/6J mice only with high-fat diet

Glucocorticoid (GC) overexposure period as observed in Cushing's syndrome (CS) is associated with the metabolic syndrome and cardiovascular disease, which persist after long-term correction of GC excess. We performed a mouse study to identify factors that modulate metabolic recovery from a GC overexposure period. Male C57Bl/6J mice, fed a low-fat diet (LFD) or a high-fat diet (HFD), received corticosterone (CORT) (50 μg/mL) or vehicle in the drinking water for 4 weeks, followed by an 8-week washout period. Plasma circadian CORT, lipids, insulin, and glucose levels were assessed regularly. Hyperinsulinemic-euglycemic clamp and body composition were analyzed at week 12 under anesthesia. CORT treatment increased plasma CORT levels, food intake, and plasma insulin and lipid levels on both diets. CORT treatment abrogation normalized CORT levels, food intake, and body weight, whereas plasma insulin levels remained significantly higher in CORT-treated mice on both diets. Only on a HFD, CORT-treated mice had decreased lean body mass and higher fat mass. In conclusion, CORT excess period induces long-lasting metabolic changes and some are present only on a HFD. These observations indicate that diet-dependent CORT effects might contribute to the adverse cardiovascular risk profile observed in CS patients, and possibly also in subjects exposed to chronic stress.

Intact catecholamine inputs to the forebrain are required for appropriate regulation of corticotrophin-releasing hormone and vasopressin gene expression by corticosterone in the rat paraventricular nucleus

Corticotrophin-releasing hormone (CRH) neuroendocrine neurones in the paraventricular nucleus of the hypothalamus (PVH) drive adrenocorticotrophic hormone (ACTH) and thereby glucocorticoid release from pituitary corticotrophs and the adrenal cortex, respectively. Glucocorticoids suppress the ability of neuroendocrine corticotrophin-releasing hormone (CRH) neurones to synthesise and release ACTH secretogogues. Despite the importance of glucocorticoids as regulatory signals to CRH neurones in the extended time domain, how and where they act in this capacity is still not fully understood. Ascending catecholamine projections encode important cardiovascular, metabolic and other visceral information to the rat PVH and surrounding hypothalamus. These afferents have previously been implicated as targets for glucocorticoid action, including a role in the feedback regulation of PVH neuroendocrine neurones. To determine the contribution of these neurones to the long-term actions of corticosterone on CRH and vasopressin (AVP) gene expression in the PVH, we used an immunocytotoxin (a conjugate of the cytotoxin saporin and an antibody against dopamine-β-hydroxylase) that specifically ablates adrenergic and noradrenergic neurones. Lesions were administered to intact animals and to adrenalectomised animals with either no corticosterone or corticosterone replacement that provided levels above those required to normalise Crh expression. The ability of elevated levels of corticosterone to suppress Crh expression was abolished in animals lacking catecholaminergic innervation of the PVH. No effect was seen in the absence of corticosterone or in animals with intact adrenals. Furthermore, Avp expression, which is increased in CRH neurones following adrenalectomy, was suppressed in adrenalectomised catecholaminergic-lesioned animals. Interactions between corticosterone and catecholaminergic projections to the hypothalamus therefore make significant contributions to the regulation of Crh and Avp expression. However, the importance of catecholamine inputs is only apparent when circulating corticosterone concentrations are maintained either below or above those required to maintain the activity of the hypothalamic-pituitary-adrenal axis that is seen in intact animals.

Effect of global and regional sympathetic blockade on arterial pressure during water deprivation in conscious rats

Forty-eight hours of water deprivation (WD) in conscious rats results in a paradoxical increase in mean arterial pressure (MAP). Previous studies suggest this may be due to increased sympathetic nerve activity (SNA). However, this remains to be investigated in conscious, freely behaving animals. The purpose of this study was to determine, in conscious rats, the role of the sympathetic nervous system (SNS) in mediating WD-induced increases in MAP and to identify which vascular beds are targeted by increased SNA. Each rat was chronically instrumented with a radiotelemetry transmitter to measure MAP and heart rate (HR) and an indwelling venous catheter for plasma sampling and/or drug delivery. MAP and HR were continuously measured during a 2-day baseline period followed by 48 h of WD and then a recovery period. By the end of the WD period, MAP increased by ∼15 mmHg in control groups, whereas HR did not change significantly. Chronic blockade of α(1)/β(1)-adrenergic receptors significantly attenuated the WD-induced increase in MAP, suggesting a role for global activation of the SNS. However, the MAP response to WD was unaffected by selective denervations of the hindlimb, renal, or splanchnic vascular beds, or by adrenal demedullation. In contrast, complete adrenalectomy (with corticosterone and aldosterone replaced) significantly attenuated the MAP response to WD in the same time frame as α(1)/β(1)-adrenergic receptor blockade. These results suggest that, in conscious water-deprived rats, the SNS contributes to the MAP response and may be linked to release of adrenocortical hormones. Finally, this sympathetically mediated response is not dependent on increased SNA to one specific vascular bed.

Role of glucocorticoids in tuning hindbrain stress integration

The nucleus of the solitary tract (NTS) is a critical integrative site for coordination of autonomic and endocrine stress responses. Stress-excitatory signals from the NTS are communicated by both catecholaminergic [norepinephrine (NE), epinephrine (E)] and noncatecholaminergic [e.g., glucagon-like peptide-1 (GLP-1)] neurons. Recent studies suggest that outputs of the NE/E and GLP-1 neurons of the NTS are selectively engaged during acute stress. This study was designed to test mechanisms of chronic stress integration in the paraventricular nucleus, focusing on the role of glucocorticoids. Our data indicate that chronic variable stress (CVS) causes downregulation of preproglucagon (GLP-1 precursor) mRNA in the NTS and reduction of GLP-1 innervation to the paraventricular nucleus of the hypothalamus. Glucocorticoids were necessary for preproglucagon (PPG) reduction in CVS animals and were sufficient to lower PPG mRNA in otherwise unstressed animals. The data are consistent with a glucocorticoid-mediated withdrawal of GLP-1 in key stress circuits. In contrast, expression of tyrosine hydroxylase mRNA, the rate-limiting enzyme in catecholamine synthesis, was increased by stress in a glucocorticoid-independent manner. These suggest differential roles of ascending catecholamine and GLP-1 systems in chronic stress, with withdrawal of GLP-1 involved in stress adaptation and enhanced NE/E capacity responsible for facilitation of responses to novel stress experiences.

Recovery from disrupted ultradian glucocorticoid rhythmicity reveals a dissociation between hormonal and behavioural stress responsiveness

Ultradian release of glucocorticoids is thought to be essential for homeostasis and health. Furthermore, deviation from this pulsatile release pattern is considered to compromise resilience to stress-related disease, even after hormone levels have normalised. In the present study, we investigate how constant exposure to different concentrations of corticosterone affects diurnal and ultradian pulsatility. The rate of recovery in pulsatile hypothalamic-pituitary-adrenal (HPA) activity after withdrawal of exogenous corticosterone is also examined. Finally, the behavioural and neuroendocrine responsiveness to an audiogenic stressor is studied. Adrenally intact male rats were subcutaneously implanted with vehicle, 40% or 100% corticosterone pellets for 7 days. The continuous release of corticosterone from these implants abolished diurnal and ultradian corticosterone variation, as measured with high-frequency automated blood sampling. Pellet removal on post-surgery day 8 allowed rapid recovery of endogenous rhythms in animals previously exposed to daily average concentrations (40%) but not after exposure to high concentrations (100%) of corticosterone. Behavioural and neuroendocrine responsiveness to stress was distinctly different between the treatment groups. Audiogenic stimulation 1 day after pellet removal resulted in a similar corticosterone response in animals previously exposed to 40% corticosterone or vehicle. The 40% pellet group, however, showed less and shorter behavioural activity (i.e. locomotion, risk assessment) to noise stress compared to 100% corticosterone and vehicle-treated animals. In conclusion, unlike the animals impanted with 100% corticosterone, we find that basal HPA axis activity in the 40% group, which had mean daily levels of circulating corticosterone in the physiological range, rapidly reverts to the characteristic pulsatile pattern of corticosterone secretion. Upon reinstatement of the ultradian rhythm, and despite the fact that these animals did not differ from controls in their response to noise stress, they did show substantial changes in their behavioural response to stress.

Glucocorticoid treatment--effect on adrenal medullary catecholamine production

Glucocorticoid and epinephrine are important stress hormones secreted from the adrenal gland during critical illness. Adrenal glucocorticoid stimulates phenylethanolamine N-methyltransferase (PNMT) to convert norepinephrine to epinephrine in the adrenal medulla. Glucocorticoid is sometimes used in catecholamine-resistant septic shock in critically ill patients. By suppressing adrenal glucocorticoid production, glucocorticoid therapy might also reduce the secretion of epinephrine during stress. To investigate this, we used a mouse model subjected to glucocorticoid therapy under basal conditions (experiment 1) and during stress (experiment 2). In experiment 1, pellets containing 0% to 8% dexamethasone were implanted subcutaneously in mice for 4 weeks. In experiment 2, animals received 14 days of intraperitoneal injections of normal saline, low- or high-dose dexamethasone, followed by 2 h of restraint. We found that in experiment 1, adrenal corticosterone did not differ with dexamethasone treatment. Phenylethanolamine N-methyltransferase messenger RNA levels and adrenal catecholamines were highest in the 8% dexamethasone group. Compared with experiment 1, restrained control mice in experiment 2 had high adrenal corticosterone, which decreased with dexamethasone. Phenylethanolamine N-methyltransferase messenger RNA content doubled with restraint but decreased with dexamethasone treatment. As in experiment 1, adrenal catecholamine content increased significantly with dexamethasone treatment. We conclude that without stress, when adrenocorticotropic hormone is low, high doses of exogenous dexamethasone stimulate PNMT and catecholamine synthesis, likely independently of adrenal corticosterone concentration. After stress, adrenocorticotropic hormone levels are elevated, and exogenous dexamethasone suppresses endogenous corticosterone and PNMT production. Nonetheless, catecholamines increase, possibly due to direct neural stimulation, which may override the hormonal regulation of epinephrine synthesis during stress.

Disengaging insulin from corticosterone: roles of each on energy intake and disposition

Corticosterone and insulin play complex roles in the amount and composition of calories ingested, and the utilization and deposition of this energy. Understanding the interplay of these two hormones is complicated because increasing concentrations of corticosterone dose-dependently increase circulating insulin levels. We addressed individual contributions of each hormone by controlling, at steady-state levels, corticosterone (by adrenalectomy and exogenous replacement) and insulin (by streptozotocin-induced destruction of pancreatic beta-cells and exogenous replacement) across a spectrum of concentrations in rats, creating 8 hormonal combinations. For 5 days after surgery, all rats received chow. At day 5, they were subdivided into those that continued to receive chow and those that had a choice between chow, lard, and 32% sucrose for a further 5 days. During the choice/chow period, total calories ingested were stimulated by corticosterone and choice diet, and subject to a corticosterone-insulin interaction. Sucrose, but not lard, intake was stimulated by insulin. Body weight was increased by insulin, decreased by high corticosterone, and unaffected by diet. White adipose tissue depot weights were stimulated by insulin, corticosterone, and diet. Plasma triglycerides, free fatty acids, total ketone bodies, glucose, and glycerol were all significantly increased by corticosterone and the choice diet but inhibited by insulin. In contrast, plasma leptin was only increased by insulin and diet, plasma glucagon and liver glycogen was only affected by insulin and liver triglycerides, and arcuate nucleus proopiomelanocortin mRNA was only influenced by diet. Collectively, these data show that corticosterone and insulin determine the intake, form, and compartmentalization of energy both independently and interactively.

Non-intromissive mating stimuli are sufficient to enhance sexual behaviors in ovariectomized female rats

When ovariectomized/adrenalectomized female rats, injected with subthreshold doses of estradiol are given copulatory stimulation by a male rat at half hour intervals, the level of lordosis gradually increases over the course of a few hours. We tested the hypothesis that paracopulatory behaviors (behaviors that occur repetitively prior to and between mounts), also generally considered to be heavily dependent on progesterone, are enhanced by this stimulation as well. We have reported previously that the enhancement of copulatory behavior is dependent to a large extent on intromissive stimulation by the male. In the present study, mating stimulation induced high levels of paracopulatory behaviors, as well as lordosis. Surprisingly, though, and in contrast to previous findings, this increase was seen not only in rats receiving intromissive stimulation, but in those receiving non-intromissive stimulation as well. Furthermore, intromissive stimulation induced high levels of rejection behavior. In a subsequent experiment, experimenter-induced, mechanical stimulation increased only rejection behaviors, not copulatory behavior. The results collectively demonstrate that, under the conditions used in these experiments, non-intromissive stimulation is sufficient for inducing both copulatory and paracopulatory behaviors in estradiol-primed rats. However, under the conditions used in these studies, intromissive stimulation increases rejection behaviors.

Stress induces a switch of intracellular signaling in sensory neurons in a model of generalized pain

Stress dramatically exacerbates pain in diseases such as fibromyalgia and rheumatoid arthritis, but the underlying mechanisms are unknown. We tested the hypothesis that stress causes generalized hyperalgesia by enhancing pronociceptive effects of immune mediators. Rats exposed to nonhabituating sound stress exhibited no change in mechanical nociceptive threshold, but showed a marked increase in hyperalgesia evoked by local injections of prostaglandin E(2) or epinephrine. This enhancement, which developed more than a week after exposure to stress, required concerted action of glucocorticoids and catecholamines at receptors located in the periphery on sensory afferents. The altered response to pronociceptive mediators involved a switch in coupling of their receptors from predominantly stimulatory to inhibitory G-proteins (G(s) to G(i)), and for prostaglandin E(2), emergence of novel dependence on protein kinase C epsilon. Thus, an important mechanism in generalized pain syndromes may be stress-induced coactivation of the hypothalamo-pituitary-adrenal and sympathoadrenal axes, causing a long-lasting alteration in intracellular signaling pathways, enabling normally innocuous levels of immune mediators to produce chronic hyperalgesia.

The gastroduodenal branch of the common hepatic vagus regulates voluntary lard intake, fat deposition, and plasma metabolites in streptozotocin-diabetic rats

The common hepatic branch of the vagus nerve negatively regulates lard intake in rats with streptozotocin (STZ)-induced, insulin-dependent diabetes. However, this branch consists of two subbranches: the hepatic branch proper, which serves the liver, and the gastroduodenal branch, which serves the distal stomach, pancreas, and duodenum. The aim of this study was to determine whether the gastroduodenal branch specifically regulates voluntary lard intake. We performed a gastroduodenal branch vagotomy (GV) on nondiabetic, STZ-diabetic, and STZ-diabetic insulin-treated groups of rats and compared them with sham-operated counterparts. All rats had high steady-state corticosterone levels to maximize lard intake. Five days after surgery, all rats were provided with the choice of chow or lard to eat for another 5 days. STZ-diabetes resulted in a reduction in lard intake that was partially rescued by either GV or insulin treatment. Patterns of white adipose tissue (WAT) deposition differed after GV- and insulin-induced lard intake, with subcutaneous WAT increasing exclusively after the former and mesenteric WAT increasing exclusively in the latter. GV also prevented the insulin-induced reduction in the STZ-elevated plasma glucagon, triglycerides, free fatty acids, and total ketone bodies but did not alter the effect of insulin-induced reduction of plasma glucose levels. These data suggest that the gastroduodenal branch of the vagus inhibits lard intake and regulates WAT deposition and plasma metabolite levels in STZ-diabetic rats.

A noninvasive measure of negative-feedback strength, approximate entropy, unmasks strong diurnal variations in the regularity of LH secretion

The secretion of anterior-pituitary hormones is subject to negative feedback. Whether negative feedback evolves dynamically over 24 h is not known. Conventional experimental paradigms to test this concept may induce artifacts due to nonphysiological feedback. These limitations might be overcome by a noninvasive methodology to quantify negative feedback continuously over 24 h without disrupting the axis. The present study exploits a recently validated model-free regularity statistic, approximate entropy (ApEn), which monitors feedback changes with high sensitivity and specificity (both >90%; Pincus SM, Hartman ML, Roelfsema F, Thorner MO, Veldhuis JD. Am J Physiol Endocrinol Metab 273: E948-E957, 1999). A time-incremented moving window of ApEn was applied to LH time series obtained by intensive (10-min) blood sampling for four consecutive days (577 successive measurements) in each of eight healthy men. Analyses unveiled marked 24-h variations in ApEn with daily maxima (lowest feedback) at 1100 +/- 1.7 h (mean +/- SE) and minima (highest feedback) at 0430 +/- 1.9 h. The mean difference between maximal and minimal 24-h LH ApEn was 0.348 +/- 0.018, which differed by P < 0.001 from all three of randomly shuffled versions of the same LH time series, simulated pulsatile data and assay noise. Analyses artificially limited to 24-h rather than 96-h data yielded reproducibility coefficients of 3.7-9.0% for ApEn maxima and minima. In conclusion, a feedback-sensitive regularity statistic unmasks strong and consistent 24-h rhythmicity of the orderliness of unperturbed pituitary-hormone secretion. These outcomes suggest that ApEn may have general utility in probing dynamic mechanisms mediating feedback in other endocrine systems.

Daily cocaine self-administration under long-access conditions augments restraint-induced increases in plasma corticosterone and impairs glucocorticoid receptor-mediated negative feedback in rats

Cocaine addiction appears to be associated with a drug-induced dysregulation of stressor responsiveness that may contribute to further cocaine use. The present study examined alterations in stressor-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis in rats provided daily access to cocaine for self-administration (SA) under long-access conditions (1.0 mg/kg/infusion; 6 hx14 days). Cocaine self-administering rats displayed reduced basal plasma corticosterone (CORT) levels but showed an augmented restraint-induced percent increase response from baseline compared to saline self-administering controls when measured 24 days after SA testing. This augmented CORT response may have been attributable to impaired glucocorticoid receptor (GR)-mediated feedback regulation of HPA function, since cocaine self-administering rats were also less susceptible to dexamethasone (0.01 mg/kg, i.p.) suppression of plasma CORT levels. GR protein expression measured using Western blot analysis was significantly reduced in the dorsomedial hypothalamus (including the paraventricular nucleus [PVN]) but not in the pituitary gland, ventromedial hypothalamus, dorsal hippocampus, ventral subiculum, medial prefrontal cortex or amygdala in cocaine self-administering rats. Surprisingly, basal corticotropin-releasing hormone (CRH) mRNA or post-restraint increases in CRH mRNA measured at a single (90 min) time-point in the PVN using in situ hybridization did not differ between groups. The findings suggest that cocaine use produces persistent changes in individual responsiveness to stressors that may contribute to the addiction process.

Afferent signalling through the common hepatic branch of the vagus inhibits voluntary lard intake and modifies plasma metabolite levels in rats

The common hepatic branch of the vagus nerve is a two-way highway of communication between the brain and the liver, duodenum, stomach and pancreas that regulates many aspects of food intake and metabolism. In this study, we utilized the afferent-specific neurotoxin capsaicin to examine if common hepatic vagal sensory afferents regulate lard intake. Rats implanted with a corticosterone pellet were made diabetic using streptozotocin (STZ) and a subset received steady-state exogenous insulin replacement into the superior mesenteric vein. These were compared with non-diabetic counterparts. Each group was then subdivided into those whose common hepatic branch of the vagus was treated with vehicle or capsaicin. Five days after surgery, the rats were offered the choice of chow and lard to consume for a further 5 days. The STZ-diabetic rats ate significantly less lard than the non-diabetic rats. Capsaicin treatment restored lard intake to that of the insulin-replaced, STZ-diabetic rats, but modified neither chow nor total caloric intake. This increased lard intake led to selective fat deposition into the mesenteric white adipose tissue depot, as opposed to an increase in all visceral fat pad depots evident after insulin replacement-induced lard intake. Capsaicin treatment also increased the levels of circulating glucose and triglycerides and negated the actions of insulin on these and free fatty acids and ketone bodies. Collectively, these data suggest that afferent signalling through the common hepatic branch of the vagus inhibits lard, but not chow, intake, directs fat deposition and regulates plasma metabolite levels.

Glucocorticoids and insulin both modulate caloric intake through actions on the brain

Glucocorticoids act primarily in a feed-forward fashion on brain to activate CNS pathways that implement wanting appropriate to physiological needs. Thus, depending on the available conditions, elevated glucocorticoids may augment the behavioural want to run, fight or feed. Although glucocorticoids stimulate intake of chow, fat and sucrose, insulin appears to sculpt calorie-associated desires toward foods high in fat, acting through hepatic branch afferents of the vagus nerve. Both conditions of reduced food allowance and chronic stress excite glucocorticoid-augmented central neural networks that may lead toward ultimate abdominal obesity.

Effects of spontaneous and forced running on activation of hypothalamic corticotropin-releasing hormone neurons in rats

Corticotropin-releasing hormone (CRH)-containing neurons in the hypothalamic paraventricular nucleus (PVN) are known to be activated during physical or psychological stress, and play an important role as one of the central activators of integrated stress response. Physical exercise has also been suggested as one of the stressors activating CRH neurons in the PVN. Spontaneous wheel running (SWR) has recently been reported to result in improved mental health or mood, unlike treadmill running that commonly forces the animal to run. Thus, forced running may strongly induce an activation of CRH neurons compared with spontaneous running, and spontaneous running may not represent a strong stressor. However, whether the effects of spontaneous running on activation of CRH neurons in the PVN differ from those of forced running is unknown. The present study examined the activity of CRH neurons in 1-h forced wheel running (FWR) and SWR using c-Fos/CRH immunohistochemistry in male Wistar rats. No significant differences in 1-h running distance were observed between FWR and SWR, indicating that amount of work was almost equal between exercises. Number of double-labeled neurons for c-Fos and CRH in the PVN was markedly higher in FWR than in SWR. In addition, no significant differences in Fos expression in the LC, which is related to various stress responses, were found between FWR and SWR. These results indicate that FWR strongly activates CRH neurons in the PVN compared with SWR, suggesting that spontaneous running is not an intense stressor even though running distance does not differ significantly from forced running.

Chronic corticosterone-induced deterioration in rat behaviour is not paralleled by changes in hippocampal NF-kappaB-activation

We investigated whether long-lasting stress induced by chronic glucocorticoid (GC) exposure affects activation of brain NF-kappaB and whether these changes are related to functional deterioration and structural changes in the rat hippocampus. Psychometric investigations were conducted using a holeboard test system in 28 one-year-old male Wistar rats. Thereafter, rats were divided into three groups for daily administration of 10 mg corticosterone (treatment) or sesame oil (placebo = sham control for effects of the vehicle) for 60 days. Additional control rats did not receive any treatment or handling until the end of the experiment. Behavioural and cognitive changes were tested again in the holeboard system. Rat body weights and corticosterone concentrations in plasma, hippocampus and urine were determined and adrenal glands were investigated histopathologically. Hippocampal concentrations of corticosterone, NF-kappaB and I-kappaBalpha were determined using RIA, EMSA and Western blotting techniques, respectively. Structural changes in rat hippocampus were measured using magnetic resonance imaging techniques. High peripheral corticosterone concentrations after chronic treatment led to significant reductions in rat body weight. Significant atrophy of both adrenal glands with marked histological deterioration was detected. Furthermore, an increase in hippocampal corticosterone concentrations was observed after chronic administration. Chronic corticosterone treatment also significantly altered behaviour and working and reference memory capacity without changing hippocampal structure. Daily injections of sesame oil in the placebo group, however, were also sufficient to reduce the pellet-finding time. However, neither in the corticosterone group nor in the placebo group were behavioural changes paralleled by significant changes in brain NF-kappaB activation and I-kappaBalpha expression. Thus, cognitive alterations in rats seen after chronic corticosterone exposure are not paralleled by hippocampal NF-kappaB modulation.

Aldosterone target neurons in the nucleus tractus solitarius drive sodium appetite

Sodium appetite can be enhanced by the adrenal steroid aldosterone via an unknown brain mechanism. A novel group of neurons in the nucleus tractus solitarius expresses the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which makes them selectively responsive to aldosterone. Their activation parallels sodium appetite in different paradigms of salt loss even in the absence of aldosterone. These unique aldosterone target neurons may represent a previously unrecognized central convergence point at which hormonal and neural signals can be integrated to drive sodium appetite.

Time-dependent alterations in mRNA expression of brain neuropeptides regulating energy balance and hypothalamo-pituitary-adrenal activity after withdrawal from intermittent morphine treatment

Chronic stressors alter brain function and may leave traces after their relief. We used intermittent morphine treatment to examine the relationships between stress-induced changes in energy balance and hypothalamo-pituitary-adrenal (HPA) activity and the recovery thereafter. We studied the effects of morphine injections on energy balance, hormones and fat stores, brain neuropeptide expression, and the ACTH and corticosterone responses to restraint 12 hr after the final injection and 8 d later during recovery. Weight gain, food intake, and caloric efficiency decreased at morphine onset, and these were maintained throughout the morphine injections. At 12 hr, fat stores, leptin, insulin, and testosterone concentrations were reduced. Subsequently, body weight gain and food intake increased and caloric efficiency was above control during the final days. By the eighth recovery day, fat stores and peripheral hormones were no longer depressed. At 12 hr, an over-response of CRF mRNA to restraint occurred in the hypothalamus, similar to the facilitated ACTH and corticosterone responses. On day 8, the hypothalamic CRF mRNA response to restraint was still facilitated, opposite to inhibited ACTH responses. Hypothalamic CRF mRNA correlated highly with mesenteric fat weight in morphine-treated rats. We conclude that there is a prolonged recovery from chronic stressors involving interrelated changes in energy balance and HPA activity. Nonetheless, 8 d after withdrawal from morphine, rats still display facilitated central stress responses, similar to the HPA symptoms described in posttraumatic stress disorder patients. Repeated partial withdrawal associated with intermittent morphine treatment, compounded by complete withdrawal associated with termination of the treatment, is likely required for these metabolic and HPA derangements.

Adrenal cortex: scalpels, syringes, and separatory funnels

This essay looks at the historical significance of three APS classic papers that are freely available online:

Houssay BA and Lewis JT. The relative importance to life of cortex and medulla of the adrenal glands. Am J Physiol 64: 512—521, 1923 ( http://ajplegacy.physiology.org/cgi/reprint/64/3/512 ).

Marine D and Baumann EJ. Duration of life after suprarenalectomy in cats and attempts to prolong it by injections of solutions containing sodium salts, glucose and glycerol. Am J Physiol 81: 86—100, 1927 ( http://ajplegacy.physiology.org/cgi/reprint/81/1/86 ).

Swingle WW and Pfiffner JJ. Studies on the adrenal cortex. I. The effect of a lipid fraction upon the life-span of adrenalectomized cats. Am J Physiol 96: 153—163, 1931 ( http://ajplegacy.physiology.org/cgi/reprint/96/1/153 ).

17Beta-oestradiol modulates glucocorticoid, neural and behavioural adaptations to repeated restraint stress in female rats

Sex steroids have a role in modulating responses that extends beyond reproduction. The current study investigated the influence of the sex steroid 17beta-oestradiol on hypothalamic-pituitary-adrenal (HPA) and behavioural responses to acute or repeated restraint stress. Ovariectomized rats treated with 17beta-oestradiol or peanut oil via a subcutaneous silastic capsule were subjected to daily handling (non stressed), acute (single, 1 h) or daily (10 days, 1 h/day) restraint stress. Blood collected at the end of stress revealed that 17beta-oestradiol treatment augmented the corticosterone response to acute restraint. After daily exposure to restraint, the corticosterone response was noticeably diminished in untreated females but 17beta-oestradiol-treated rats still showed an exaggerated response compared to castrated, untreated females. Brain tissue collected 3 h after the end of restraint was probed using isotopic in situ hybridization for corticotropin-releasing factor (CRF) and vasopressin gene expression in the paraventricular nucleus (PVN) of the hypothalamus. 17beta-oestradiol treatment at the higher dose (120 microg/ml) decreased basal CRF mRNA. Stress caused an increase in CRF mRNA expression in 17beta-oestradiol-treated rats but not in the vehicle group. Repeated restraint stress caused an increase in PVN parvocellular vasopressin gene expression, which was more pronounced in 17beta-oestradiol-replaced rats. Animals were exposed to the elevated plus maze for 5 min as a test for anxiety. Non-stressed control rats with or without 17beta-oestradiol replacement spent the same percentage amount of time exploring the open arms of the maze. Previous exposure to acute restraint stress caused a marked reduction in the time spent exploring the open arms, indicating an increase in anxiety levels in these rats; this effect was observed in both vehicle and 17beta-oestradiol-treated rats. After repeated restraint stress, 17beta-oestradiol-replaced rats spent as much time exploring the open arms of the maze as controls, indicating adaptation. By contrast, nonreplaced rats were still showing a significant reduction in open arm exploration after repeated restraint. The present study presents novel data showing that the HPA axis remains reactive to repeated stress in 17beta-oestradiol-treated ovariectomized rats, but stress-induced anxiety behaviour is reduced.

Characterization of blood pressure and morphological traits in cardiovascular-related organs in 13 different inbred mouse strains

To better understand the contributions of various genetic backgrounds to complex quantitative phenotypes, we have measured several quantitative traits of cardiovascular interest [i.e., systolic blood pressure, weight (corrected by body weight) of several cardiac compartments and adrenals and kidneys, and histological correlates for kidneys and adrenals] in male and female mice from 13 different inbred strains. We selected strains so that each major genealogical group would be represented and to conform to priorities set by the Mouse Phenome Database project. Interstrain comparisons of phenotypes made it possible to identify strains that displayed values that belonged to either the low or the high end of the interstrain variance for quantitative traits, such as systolic blood pressure, body weight, left ventricular weight, and/or adrenocortical structure. For instance, both male and female C3H/HeJ and A/J mice displayed either low systolic blood pressure or low cardiac ventricular mass, respectively, and male C57BL6/J displayed low adrenal weight. Likewise, intersex comparisons made it possible to identify phenotypic values that were sexually dimorphic for some of the same traits. For instance, female AKR/J mice had relatively higher body weight and systolic blood pressure values than their male counterparts, perhaps constituting an animal model of the metabolic X syndrome. These strain- and sex-specific features will be of value both for future genetic and/or developmental studies and for the development of new animal models that will help in the generation of mechanistic hypotheses. All data have been deposited to the Mouse Phenome Database for future integration with the Mouse Genome Database and can be further analyzed and compared with tools available on the site.

Glucocorticoids reduce responses to AMPA receptor activation and blockade in nucleus tractus solitarius

We tested the hypothesis that glucocorticoids attenuate changes in arterial pressure and renal sympathetic nerve activity (RSNA) in response to activation and blockade of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors within the nucleus of the solitary tract (NTS). Experiments were performed in Inactin-anesthetized male Sprague-Dawley rats treated for 7 +/- 1 days with a subcutaneous corticosterone (Cort) pellet or in control rats. Baseline mean arterial pressure (MAP) was significantly higher in Cort-treated rats (109 +/- 2 mmHg, n = 39) than in control rats (101 +/- 1 mmHg, n = 48, P < 0.05). In control rats, microinjection of AMPA (0.03, 0.1, and 0.3 pmol/100 nl) into the NTS significantly decreased MAP at all doses and decreased RSNA at 0.1 and 0.3 pmol/100 nl. Responses to AMPA in Cort-treated rats were attenuated at all doses of AMPA (P < 0.05). Responses to the AMPA-kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were also significantly reduced in Cort-treated rats relative to control rats. Blockade of glucocorticoid type II receptors with mifepristone significantly enhanced responses to CNQX in both control and Cort rats. We conclude that glucocorticoids attenuate MAP and RSNA responses to activation and blockade of AMPA receptors in the NTS.

Differential regulation of adrenal corticosteroids after restriction-induced drinking in rats

Water-restricted rats exhibit a rapid decrease in plasma corticosterone after drinking. The present study examined the effect of restriction-induced drinking on plasma aldosterone and plasma clearance of corticosterone. Rats were water restricted for 6-7 days and then killed before or 15 min after water administration; plasma and adrenal hormones were assayed. Plasma and adrenal corticosterone decreased after drinking without a change in plasma corticosteroid-binding globulin; plasma ACTH decreased or did not change. In contrast, plasma aldosterone did not change or increased after drinking; plasma renin activity was elevated by water restriction and increased further after drinking. In another experiment, rats were adrenalectomized, and corticosterone and aldosterone were replaced with pellets and osmotic minipumps, respectively. Rats were water restricted and killed. There was a small decrease in plasma corticosterone but no change in aldosterone after drinking in adrenalectomized animals. These data suggest that changes in plasma steroids after restriction-induced drinking result from zone-specific responses of the adrenal to known secretagogues, with minimal contribution from increased plasma clearance.

HPA-axis responses during experimental colitis in the rat

We investigated the responses of the hypothalamic-pituitary-adrenal (HPA) axis during experimental colitis induced by intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid in the rat. On days 3 and 7 after induction of colitis, the corticotropin-releasing hormone (CRH) mRNA level in the parvocellular paraventricular nucleus (pPVN) of the hypothalamus was reduced, the plasma ACTH level remained at the basal level, and the plasma corticosterone (Cort) level was high. Induction of colitis on day 3 after adrenalectomy with Cort pellet replacement (ADX + Cort) resulted in a marked increase in CRH mRNA on day 7 after induction of colitis compared with noncolitic ADX + Cort animals. Pair feeding to match the food intake of the colitic animals resulted in no significant change in CRH mRNA in the pPVN, plasma ACTH, and Cort compared with healthy control animals. These findings indicated that CRH mRNA expression in the pPVN was inhibited by glucocorticoid feedback during this experimental colitis, and the decrease in food intake during colitis was not simply responsible for the expression of CRH mRNA. It is inferred that the HPA axis including the CRH level in the pPVN is altered in patients with inflammatory bowel disease.

Endogenous corticosteroids modulate Clostridium difficile toxin A-induced enteritis in rats

We examined the role of glucocorticoids in acute inflammatory diarrhea mediated by Clostridium difficile toxin A. Toxin A (5 microg) or buffer was injected in rat ileal loops, and intestinal responses were measured after 30 min to 4 h. Ileal toxin A administration increased plasma glucocorticoids after 1 h, at which time the toxin-stimulated secretion was not significant. Administration of the glucocorticoid analog dexamethasone inhibited toxin A-induced intestinal secretion and inflammation and downregulated toxin A-mediated increase of macrophage inflammatory protein-2. Adrenalectomy followed by replacement with glucocorticoids at various doses suggested that intestinal responses to toxin A were related to circulating levels of glucocorticoids. Administration of the glucocorticoid receptor antagonist RU-486 enhanced toxin A-mediated intestinal secretion and inflammation. We conclude that C. difficile toxin A causes increased secretion of endogenous glucocorticoids, which diminish the intestinal secretory and inflammatory effects of toxin A.

Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Exercise training produces a vast array of physiological adaptations, ranging from changes in metabolism to muscle mitochondrial biogenesis. Researchers studying the physiological effects of exercise often use animal models that employ forced exercise regimens that include aversive motivation, which could activate the stress response. This study examined the effect of forced treadmill running (8 wk) on several physiological systems that are sensitive to training and stress. Forced treadmill running produced both positive and negative physiological adaptations. Indicative of positive training adaptations, exercised male Sprague-Dawley rats had a decrease in body weight gain and an increase in muscle citrate synthase activity compared with sedentary controls. In contrast, treadmill running also resulted in the potentially negative adaptations of adrenal hypertrophy, thymic involution, decreased serum corticosteroid binding globulin, elevated lymphocyte nitrite concentrations, suppressed lymphocyte proliferation, and suppressed antigen-specific IgM. Such alterations in neuroendocrine tissues and immune responses are commonly associated with chronic stress. Thus treadmill running produces both positive training adaptations and potentially negative adaptations that are indicative of chronic stress. Researchers employing forced activity need to be aware that this type of exercise procedure also produces physiological adaptations indicative of chronic stress and that these changes could potentially impact other measures of interest.

Glucocorticoid negative feedback selectively targets vasopressin transcription in parvocellular neurosecretory neurons

To identify molecular targets of corticosteroid negative feedback effects on neurosecretory neurons comprising the central limb of the hypothalamo-pituitary-adrenal (HPA) axis, we monitored ether stress effects on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) heteronuclear RNA (hnRNA) expression in rats that were intact or adrenalectomized (ADX) and replaced with corticosterone (B) at constant levels ranging from nil to peak stress concentrations. Under basal conditions, relative levels of both primary transcripts varied inversely as a function of plasma B titers. In response to stress, the kinetics of CRF hnRNA responses of intact and ADX rats replaced with low B were similar, peaking at 5 min after stress. By contrast, intact rats showed a delayed AVP hnRNA response (peak at 2 hr), the timing of which was markedly advanced in ADX/low B-replaced animals (peak at 5-30 min). Transcription factors implicated in these responses responded similarly. Manipulation of B status did not affect the early (5-15 min) phosphorylation of transcription factor cAMP-response element-binding protein (CREB) but accelerated maximal Fos induction from 2 hr after stress (intact) to 1 hr (ADX). Assays of binding by proteins in hypothalamic extracts of similarly manipulated rats toward consensus CRE and AP-1 response elements supported a role for the stress-induced plasma B increment in antagonizing AP-1, but not CRE, binding. These findings suggest that glucocorticoid negative feedback at the transcriptional levels is exerted selectively on AVP gene expression through a mechanism that likely involves glucocorticoid receptor interactions with immediate-early gene products.

Corticotropin-releasing hormone links pituitary adrenocorticotropin gene expression and release during adrenal insufficiency

Corticotropin-releasing hormone (CRH)-deficient (KO) mice provide a unique system to define the role of CRH in regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Despite several manifestations of chronic glucocorticoid insufficiency, basal pituitary proopiomelanocortin (POMC) mRNA, adrenocorticotrophic hormone (ACTH) peptide content within the pituitary, and plasma ACTH concentrations are not elevated in CRH KO mice. The normal POMC mRNA content in KO mice is dependent upon residual glucocorticoid secretion, as it increases in both KO and WT mice after adrenalectomy; this increase is reversed by glucocorticoid, but not aldosterone, replacement. However, the normal plasma levels of ACTH in CRH KO mice are not dependent upon residual glucocorticoid secretion, because, after adrenalectomy, these levels do not undergo the normal increase seen in KO mice despite the increase in POMC mRNA content. Administration of CRH restores ACTH secretion to its expected high level in adrenalectomized CRH KO mice. Thus, in adrenal insufficiency, loss of glucocorticoid feedback by itself can increase POMC gene expression in the pituitary; but CRH action is essential for this to result in increased secretion of ACTH. This may explain why, after withdrawal of chronic glucocorticoid treatment, reactivation of CRH secretion is a necessary prerequisite for recovery from suppression of the HPA axis.

The effect on opioid peptides in the rat brain, after chronic treatment with the anabolic androgenic steroid, nandrolone decanoate

In recent years, an increase in abuse of anabolic androgenic steroids (AAS) has been seen among individuals not directly connected to sports. Clinical evidence suggests that abuse of these steroids may result in profound changes in personality, expressed by depressive symptoms, irritability and increased aggression. It is still unknown whether these alterations are related to changes in any particular transmitter system or whether they are persistent or reversible. In this study we focused on AAS effect on the endogenous dynorphin and enkephalin system in the brain. Male rats were given intramuscular injections of the AAS nandrolone decanoate (15 mg/kg), once daily for 2 weeks. The levels of the opioid peptide immunoreactivities (ir) were assessed by radioimmunoassay in two groups immediately after the treatment and in two other groups after additional 3 weeks without any drug treatment (recovery period). The result indicates that chronic AAS treatment increased the activity in the dynorphin B- and Met-enkephalin-Arg(6)Phe(7)-ir in the hypothalamus, striatum and periaqueductal gray (PAG) compared to controls. In addition, the steroid induced an imbalance between the dynorphin and the enkephalin opioid system in the nucleus accumbens, hypothalamus and PAG. This imbalance remained after the recovery period. Since increased peptide activity was found in brain regions regulating emotions, dependence, defensive reactions and aggression, it was suggested that the actual endogenous opioid systems are involved in previously reported AAS-induced changes in these behaviours.

Repeated, but not acute, stress suppresses inflammatory plasma extravasation

Clinical findings suggest that inflammatory disease symptoms are aggravated by ongoing, repeated stress, but not by acute stress. We hypothesized that, compared with single acute stressors, chronic repeated stress may engage different physiological mechanisms that exert qualitatively different effects on the inflammatory response. Because inhibition of plasma extravasation, a critical component of the inflammatory response, has been associated with increased disease severity in experimental arthritis, we tested for a potential repeated stress-induced inhibition of plasma extravasation. Repeated, but not single, exposures to restraint stress produced a profound inhibition of bradykinin-induced synovial plasma extravasation in the rat. Experiments examining the mechanism of inhibition showed that the effect of repeated stress was blocked by adrenalectomy, but not by adrenal medullae denervation, suggesting that the adrenal cortex mediates this effect. Consistent with known effects of stress and with mediation by the adrenal cortex, restraint stress evoked repeated transient elevations of plasma corticosterone levels. This elevated corticosterone was necessary and sufficient to produce inhibition of plasma extravasation because the stress-induced inhibition was blocked by preventing corticosterone synthesis and, conversely, induction of repeated transient elevations in plasma corticosterone levels mimicked the effects of repeated stress. These data suggest that repetition of a mild stressor can induce changes in the physiological state of the animal that enable a previously innocuous stressor to inhibit the inflammatory response. These findings provide a potential explanation for the clinical association between repeated stress and aggravation of inflammatory disease symptoms and provide a model for study of the biological mechanisms underlying the stress-induced aggravation of chronic inflammatory diseases.

Sex steroid regulation of the inflammatory response: sympathoadrenal dependence in the female rat

To investigate the role of sex steroids in sex differences in the response of rats to the potent inflammatory mediator bradykinin (BK), we evaluated the effect of sex steroid manipulation on the magnitude of BK-induced synovial plasma extravasation (PE). The magnitude of BK-induced PE is markedly less in females. Ovariectomy of female rats increased BK-induced PE, and administration of 17beta-estradiol to ovariectomized female rats reconstituted the female phenotype. Castration in male rats decreased BK-induced PE, and administration of testosterone or its nonmetabolizable analog dihydrotestosterone reconstituted the male phenotype. The results of these experiments strongly support the role of both male and female sex steroids in sex differences in the inflammatory response. Because the stress axes are sexually dimorphic and are important in the regulation of the inflammatory response, we evaluated the contribution of the hypothalamic-pituitary-adrenal and the sympathoadrenal axes to sex differences in BK-induced PE. Neither hypophysectomy nor inhibition of corticosteroid synthesis affected BK-induced PE in female or male rats. Adrenal denervation in females produced the same magnitude increase in BK-induced PE as adrenalectomy or ovariectomy, suggesting that the adrenal medullary factor(s) in females may account for the female sex steroid effect on BK-induced PE. Furthermore, we have demonstrated that in female but not male rats, estrogen receptor alpha immunoreactivity is present on medullary but not cortical cells in the adrenal gland. These data suggest that regulation of the inflammatory response by female sex steroids is strongly dependent on the sympathoadrenal axis, possibly by its action on estrogen receptors on adrenal medullary cells.

CRH and the immune system

Inflammatory cytokines released during immune system activation can stimulate the hypothalamic-pituitary-adrenal axis and cause increased secretion of corticotropin-releasing hormone (CRH), adrenocorticotropin and glucocorticoids. Identification of CRH peptide and mRNA, as well as its receptors in immune tissues, suggested a role for this peptide as a mediator of the neuroendocrine-immune interactions. Experimental evidence suggests that CRH may modulate the immune and inflammatory responses via two pathways: an antiinflammatory one operated by centrally released CRH, most likely through stimulation of glucocorticoid and catecholamine release, and one proinflammatory, through direct action of peripherally released CRH. This review highlights these concepts. In addition preliminary data on immune activation and inflammatory response in CRH-deficient mice created in our laboratory are discussed.

Increase in vascular permeability produced in rat airways by PAF: potentiation by adrenalectomy

1. The effect of bilateral adrenalectomy on the sensitivity of blood vessels in rat airways to mediators that increase vascular permeability was examined. 2. An increase in vascular permeability was induced by intravenous platelet activating factor (PAF, 50, 100, 500, 1000 ng kg-1) and measured by quantifying the extravasation of Evans blue dye. 3. PAF consistently increased the amount of Evans blue extravasation in the larynx, trachea, main bronchi and intrapulmonary airways in sham-operated rats. 4. The magnitude of this extravasation was significantly greater in the larynx (P less than 0.05), trachea (P less than 0.05) and main bronchi (P less than 0.05) of the adrenalectomized rats than it was in these tissues of the sham-operated rats. 5. When adrenalectomized rats were given subcutaneous dexamethasone (0.2 mg kg-1 4 h before PAF) the amount of plasma extravasation produced by PAF was decreased to the level of the sham-operated rats. 6. We conclude that adrenalectomy potentiates the increase in airway vascular permeability induced by PAF in rats and that this effect may be due to the depletion of endogenous corticosteroids.