Effects of chronic stress on anterior pituitary and brain corticotropin-releasing factor receptors

Diurnal Range and Intra-patient Variability of ACTH Is Restored With Remission in Cushing's Disease

CONTEXT

Single ACTH measurements have limited ability to distinguish patients with Cushing's disease (CD) from those in remission or with other conditions.

OBJECTIVE

To investigate the changes in ACTH levels before and after transsphenoidal surgery (TSS) to identify trends that could confirm remission from CD and help establish ACTH cutoffs for targeted clinical trials in CD.

DESIGN

Retrospective analysis of CD patients who underwent TSS from 2005 to -2019.

SETTING

Referral center.

PATIENTS

CD patients (n = 253) with ACTH measurements before and after TSS.

INTERVENTIONS

TSS for CD.

MAIN OUTCOME MEASURES

Remission after TSS.

RESULTS

Remission was observed in 223 patients after TSS. Those in remission had higher ACTH variability at AM (P = .02) and PM (P < .001) time points compared to nonremission. The nonremission group had a significantly narrower diurnal range compared to the remission group (P = <.0001). A decrease in plasma ACTH of ≥50% from mean preoperative levels predicted CD remission after TSS, especially when using PM values. The absolute plasma ACTH concentration and ratio of preoperative to postoperative values were significantly associated with nonremission after multivariable logistic regression (adj P < .001 and .001, respectively).

CONCLUSIONS

Our findings suggest that ACTH variability is suppressed in CD, and remission from CD is associated with the restoration of this variability. Furthermore, a decrease in plasma ACTH by 50% or more may serve as a predictor of remission post-TSS. These insights could guide clinicians in developing rational outcome measures for interventions targeting CD adenomas.

Earlier post-operative hypocortisolemia may predict durable remission from Cushing's disease

CONTEXT

Achievement of hypocortisolemia following transsphenoidal surgery (TSS) for Cushing's disease (CD) is associated with successful adenoma resection. However, up to one-third of these patients recur.

OBJECTIVE

We assessed whether delay in reaching post-operative cortisol nadir may delineate patients at risk of recurrence for CD following TSS.

METHODS

A retrospective review of 257 patients who received 291 TSS procedures for CD at NIH, between 2003 and 2016. Early biochemical remission (serum cortisol nadir <5 μg/dL) was confirmed with endocrinological and clinical follow-up. Recurrence was detected by laboratory testing, clinical stigmata or medication dependence during a median follow-up of 11 months.

RESULTS

Of the 268 unique admissions, remission was recorded in 241 instances. Recurrence was observed in 9% of these cases with cortisol nadir ≤5 μg/dL and 6% of cases with cortisol nadir ≤2 μg/dL. The timing of hypocortisolemia was critical in detecting late recurrences. Morning POD-1 cortisol <3.3 μg/dL was 100% sensitive in predicting durable remission and morning POD-3 cortisol ≥18.5 μg/dL was 98.6% specific in predicting remote recurrence. AUROC analysis revealed that hypocortisolemia ≤5 µg/dL before 15 h (post-operative) had 95% sensitivity and an NPV of 0.98 for durable remission. Serum cortisol level ≤2 µg/dL, when achieved before 21 h, improved sensitivity to 100%.

CONCLUSIONS

In our cohort, early, profound hypocortisolemia could be used as a clinical prediction tool for durable remission. Achievement of hypocortisolemia ≤2 µg/dL before 21 post-operative hours appeared to accurately predict durable remission in the intermediate term.

Normalized Early Postoperative Cortisol and ACTH Values Predict Nonremission After Surgery for Cushing Disease

CONTEXT

Perioperative increases in adrenocorticotropic hormone (ACTH) and cortisol mimic results of corticotropin-releasing hormone (CRH) stimulation testing. This phenomenon may help identify patients with residual adenoma after transsphenoidal surgery (TSS) for Cushing disease (CD).

OBJECTIVE

To predict nonremission after TSS for CD.

DESIGN

Retrospective case-control study of patients treated at a single center from December 2003 until July 2016. Early and medium-term remission were assessed at 10 days and 11 months.

PATIENTS AND SETTING

Two hundred and ninety-one consecutive TSS cases from 257 patients with biochemical evidence of CD seen at a clinical center.

INTERVENTIONS

Normalized early postoperative values (NEPVs) for cortisol and ACTH were calculated as immediate postoperative cortisol or ACTH levels minus preoperative post-CRH-stimulation test levels.

MAIN OUTCOME MEASURES

Prediction of early nonremission was evaluated using logistic regression. Prediction of medium-term remission was assessed using Cox regression. Predictive ability was quantified by area under the receiver operating characteristic curve (AUROC).

RESULTS

NEPVs for cortisol and ACTH predicted early nonremission [adjusted odds ratio (OR): 1.1; 95% confidence interval (CI): 1.0, 1.1; P = 0.016 and adjusted OR: 1.0; 95% CI: 1.0, 1.0; P = 0.048, respectively]. AUROC for NEPV of cortisol was 0.78 (95% CI: 0.61, 0.95); for NEPV of ACTH, it was 0.80 (95% CI: 0.61, 0.98). NEPVs for cortisol and ACTH predicted medium-term nonremission [hazard ratio (HR): 1.1; 95% CI: 1.0, 1.1; P = 0.023 and HR: 1.0; 95% CI: 1.0, 1.0; P = 0.025, respectively].

CONCLUSIONS

NEPVs for cortisol and ACTH predicted nonremission after TSS for CD.

Effects of Valerianae Radix et Rhizoma extract on psychological stress in mice

Background:

The aim of this study was to identify the effects of Valerianae Radix et Rhizoma water extract (VRe) originated from Valeriana fauriei Briquet on reducing psychological stress (PS) on mice.

Objective:

Mice were put under PS with communication box method: Restraining mice and forcing to see other mice underfoot shock stress.

Materials and Methods:

Measurements on plasma corticosterone, noradrenaline and lipid peroxidation, and elevated plus-maze (EPM) tests were carried out to determine the effect of VRe administration on physiological and behavioral responses of mice.

Results:

VRe showed anxiolytic effects in plasma corticosterone, noradrenaline, and EPM transfer latency levels, but it did not show any significant effects on the other indicators.

Conclusion:

V. fauriei, which has been used as a natural anxiolytic drug, exerts positive effects in the communication box induced PS in mice.

Hypothalamo-pituitary-adrenocortical axis, glucocorticoids, and neurologic disease

Neurologic diseases are often accompanied by significant life stress and consequent increases in stress hormone levels. Glucocorticoid stress hormones are known to have deleterious interactions with neurodegenerative processes, and are hypersecreted in neurologic disorders as well as in comorbid psychiatric conditions, such as depression. This article highlights the state of our knowledge on mechanisms controlling activation and inhibition of glucocorticoid secretion, outlines signaling mechanisms used by these hormones in neural tissue, and describes how endogenous glucocorticoids can mediate neuronal damage in various models of neurologic disease. The article highlights the importance of controlling stress and consequent stress hormone secretion in the context of neurologic disease states.

A single episode of restraint stress regulates central corticotrophin- releasing hormone receptor expression and binding in specific areas of the mouse brain

The importance of restraining stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) system within tolerable limits requires efficient mechanisms for feedback inhibition. Recently, central corticotrophin-releasing hormone (CRH) receptor type 1 (CRHR1) has been shown to mediate HPA system feedback inhibition. To date, most of the data regarding stress-associated expression changes of CRHR1 and CRHR2 mRNA and their ligand CRH have been generated in rats. Taken considerable species differences into consideration, and with the growing importance of transgenic mice, a systematic analysis of the time course of expression changes of CRH and its two receptors in the mouse brain is needed to provide more insight into the regulation of the HPA system, both under physiological and pathophysiological conditions in this species. We analysed in detail the time course of expression changes of CRH, CRHR1 and CRHR2 mRNA after of restraint stress in mice in stress-relevant brain regions (paraventricular nucleus, hippocampus, neocortex). We could show a rapid, strong and long-lasting decrease in cortical and hippocampal CRHR1 mRNA expression after stress, whereas CRHR2 mRNA increased in the same neuroanatomical areas. In situ hybridisation analyses could be further confirmed at the protein level by CRH receptor autoradiography with changes in CRH binding that persisted even 7 days after a single episode of restraint stress. Our observation that stress has opposing effects on CRHR1 and CRHR2 neuronal systems supports the idea that regulation of the relative contribution of the two CRH receptors to brain CRH pathways may be essential in coordinating physiological responses to stress. We further hypothesise that the sustained alteration of CRH receptor expression and binding after a single episode of stress could mediate the long-term effects of stress on neuroendocrine function and emotional regulation.

The central corticotropin releasing factor system during development and adulthood

Corticotropin releasing factor (CRH) has been shown to contribute critically to molecular and neuroendocrine responses to stress during both adulthood and development. This peptide and its receptors are expressed in the hypothalamus, as well as in limbic brain areas including amygdala and hippocampus. This is consistent with roles for CRH in mediating the influence of stress on emotional behavior and cognitive function. The expression of CRH and of its receptors in hypothalamus, amygdala and hippocampus is age-dependent, and is modulated by stress throughout life (including the first postnatal weeks). Uniquely during development, the cardinal influence of maternal care on the central stress response governs the levels of central CRH expression, and may alter the 'set-point' of CRH-gene sensitivity to stress in a lasting manner.

Chronic administration of fluoxetine alters locomotor behavior, but does not potentiate the locomotor stimulating effects of CRH in juvenile Chinook salmon (Oncorhynchus tshawytscha)

The present study investigated: 1) the behavioral effects of chronic administration of a serotonin uptake inhibitor (fluoxetine) in juvenile Chinook salmon, Oncorhynchus tshawytscha and, 2) whether chronic administration of fluoxetine alters the behavioral effects of corticotropin-releasing hormone (CRH). Chronic (20 day) treatment with fluoxetine decreased locomotor activity when compared to fish given long-term injections of saline. An intracerebroventricular (i.c.v.) injection of CRH had no effect on locomotor activity following a 20 day intraperitoneal treatment with either saline or fluoxetine. Chronic treatment with fluoxetine also increased the amount of time fish spent near the center of the tank. A similar increase was seen in fish given a chronic intraperitoneal (i.p.) series of saline followed by an acute i.c.v. injection of CRH. However, the effect was not additive when fish were given chronic i.p. injections of fluoxetine followed by an acute i.c.v. injection of CRH. These results provide evidence to support the hypothesis that the serotonergic system is involved in mediating locomotor activity and habitat choice in teleosts.

Glucocorticoids, chronic stress, and obesity

Glucocorticoids either inhibit or sensitize stress-induced activity in the hypothalamo-pituitary-adrenal (HPA) axis, depending on time after their administration, the concentration of the steroids, and whether there is a concurrent stressor input. When there are high glucocorticoids together with a chronic stressor, the steroids act in brain in a feed-forward fashion to recruit a stress-response network that biases ongoing autonomic, neuroendocrine, and behavioral outflow as well as responses to novel stressors. We review evidence for the role of glucocorticoids in activating the central stress-response network, and for mediation of this network by corticotropin-releasing factor (CRF). We briefly review the effects of CRF and its receptor antagonists on motor outflows in rodents, and examine the effects of glucocorticoids and CRF on monoaminergic neurons in brain. Corticosteroids stimulate behaviors that are mediated by dopaminergic mesolimbic "reward" pathways, and increase palatable feeding in rats. Moreover, in the absence of corticosteroids, the typical deficits in adrenalectomized rats are normalized by providing sucrose solutions to drink, suggesting that there is, in addition to the feed-forward action of glucocorticoids on brain, also a feedback action that is based on metabolic well being. Finally, we briefly discuss the problems with this network that normally serves to aid in responses to chronic stress, in our current overindulged, and underexercised society.

Paraventricular-coerulear interactions: role in hypertension induced by prenatal undernutrition in the rat

Rats submitted to fetal growth retardation by in utero malnutrition develop hypertension when adult, showing increased hypothalamic mRNA expression for corticotropin-releasing hormone (CRH) and increased central noradrenergic activity. As hypothalamic CRH serves as an excitatory neurotransmitter within the locus coeruleus (LC) and coerulear norepinephrine plays a similar role within the paraventricular nucleus (PVN) of the hypothalamus, we studied, in both normal and prenatally undernourished 40-day-old anesthetized rats, the effects of intra-LC microinjection of CRH and intra-PVN microinjection of the alpha(1)-adrenoceptor antagonist prazosin on multiunit neuronal activity recorded simultaneously from the two nuclei, as well as the effects on systolic pressure. Undernutrition was induced during fetal life by restricting the diet of pregnant mothers to 10 g daily, whereas mothers of control rats received the same diet ad libitum. At day 40 of postnatal life: (i) undernourished rats showed increased neuronal activity in the PVN and LC, as well as increased systolic pressure; (ii) intra-LC CRH stimulated LC and PVN neurons and increased systolic pressure only in normal rats; (iii) intra-PVN prazosin decreased LC and PVN neuronal activity and systolic pressure only in undernourished rats; and (iv) in normal rats, prazosin prevented the stimulatory effect of CRH only in PVN activity; in undernourished rats, prazosin allowed CRH to regain its stimulatory effects. The results point to the existence of an excitatory PVN-LC closed loop, which seems to be hyperactive in prenatally undernourished rats as a consequence of fetal programming; this loop could be responsible, in part, for the hypertension developed by these animals.

Hypothalamic-Pituitary-Adrenal Axis, Glucocorticoids, and Neurologic Disease

Neurologic diseases often are accompanied by significant life stress and consequent increases in stress hormone levels. Glucocorticoid stress hormones are known to have deleterious interactions with neurodegenerative processes and are hypersecreted in neurologic disorders and comorbid psychiatric conditions. This review highlights the current state of knowledge of mechanisms controlling activation and inhibition of glucocorticoid secretion, outlines signalling mechanisms used by these hormones in neural tissue, and describes how endogenous glucocorticoids can mitigate neuronal damage in models of neurologic disease. This review highlights the importance of controlling stress and consequent stress hormone secretion in the context of neurologic disease states.

A centrally acting, anxiolytic angiotensin II AT1 receptor antagonist prevents the isolation stress-induced decrease in cortical CRF1 receptor and benzodiazepine binding

Long-term pretreatment with an angiotensin II AT1 antagonist blocks angiotensin II effects in brain and peripheral organs and abolishes the sympathoadrenal and hypothalamic-pituitary-adrenal responses to isolation stress. We determined whether AT1 receptors were also important for the stress response of higher regulatory centers. We studied angiotensin II and corticotropin-releasing factor (CRF) receptors and benzodiazepine binding sites in brains of Wistar Hannover rats. Animals were pretreated for 13 days with vehicle or a central and peripheral AT1 antagonist (candesartan, 0.5 mg/kg/day) via osmotic minipumps followed by 24 h of isolation in metabolic cages, or kept grouped throughout the study (grouped controls). In another study, we determined the influence of a similar treatment with candesartan on performance in an elevated plus-maze. AT1 receptor blockade prevented the isolation-induced increase in brain AT1 receptors and decrease in AT2 binding in the locus coeruleus. AT1 receptor antagonism also prevented the increase in tyrosine hydroxylase mRNA in the locus coeruleus. Pretreatment with the AT1 receptor antagonist completely prevented the decrease in cortical CRF1 receptor and benzodiazepine binding produced by isolation stress. In addition, pretreatment with candesartan increased the time spent in and the number of entries to open arms of the elevated plus-maze, measure of decreased anxiety. Our results implicate a modulation of upstream neurotransmission processes regulating cortical CRF1 receptors and the GABA(A) complex as molecular mechanisms responsible for the anti-anxiety effect of centrally acting AT1 receptor antagonists. We propose that AT1 receptor antagonists can be considered as compounds with possible therapeutic anti-stress and anti-anxiety properties.

Inhibiting cortisol response accelerates recovery from a photic phase shift

Jetlag results when a temporary loss of circadian entrainment alters phase relationships among internal rhythms and between an organism and the outside world. After a large shift in the light-dark (LD) cycle, rapid recovery of entrainment minimizes the negative effects of internal circadian disorganization. There is evidence in the existing literature for an activation of the hypothalamic-pituitary-adrenal (HPA) axis after a photic phase shift, and it is possible that the degree of HPA-axis response is a determining factor of reentrainment time. This study utilized a diurnal rodent, Octodon degus, to test the prediction that the alteration of cortisol levels would affect the reentrainment rate of circadian locomotor rhythms. In experiment 1, we examined the effects of decreased cortisol (using metyrapone, an 11beta-hydroxylase inhibitor) on the rate of running-wheel rhythm recovery after a 6-h photic phase advance. Metyrapone treatment significantly shortened the length of time it took animals to entrain to the new LD cycle (11.5% acceleration). In experiment 2, we examined the effects of increased cortisol on the rate of reentrainment after a 6-h photic phase advance. Increasing plasma cortisol levels increased the number of days (8%) animals took to reentrain running-wheel activity rhythms, but this effect did not reach significance. A third experiment replicated the results of experiment 1 and also demonstrated that suppression of HPA activity via dexamethasone injection is capable of accelerating reentrainment rates by approximately 33%. These studies provide support for an interaction between the stress axis and circadian rhythms in determining the rate of recovery from a phase shift of the LD cycle.

Anxiogenic-like effect of corticotropin-releasing factor receptor 2 antisense oligonucleotides infused into rat brain

Corticotropin-releasing factor (CRF) is widely distributed in the brain and coordinates behavioural responses to stress. Its receptor subtypes, CRF-R1 and CRF-R2, are expressed in the brain. For this study, we tested the effect of a continuous infusion of CRF-R2 antisense oligonucleotides into the lateral ventricle on anxiety-related behaviours in rats. Our results indicate that CRF-R2 antisense oligonucleotides produced an anxiogenic-like effect in elevated plus maze, black and white box and conditioned fear stress in rats. No significant effect on general locomotor activity was seen. These results indicate that inhibition of CRF-R2 induces an increase in anxiety-related behaviours suggesting an anxiogenic-like effect.

Chronic social stress: effects on limbic brain structures

Different types of stressors are known to activate distinct neuronal circuits in the brain. Acute physiological stimuli that are life threatening and require immediate reactions lead to a rapid stimulation of brainstem and hypothalamus to activate efferent visceral pathways. In contrast, psychological stressors activate higher-order brain structures for further interpretations of the perceived endangerment. Common to the later multimodal stressors is that they need cortical processing and, depending on previous experience or ongoing activation, the information is assembled within limbic circuits connecting, e.g., the hippocampus, amygdala and prefrontal cortex to induce neuroendocrine and behavioral responses. In view of the fact that stressful life events often contribute to the etiology of psychopathologies such as depressive episodes, several animal models have been developed to study central nervous mechanisms that are induced by stress. The present review summarizes observations made in the tree shrew chronic psychosocial stress paradigm with particular focus on neurotransmitter systems and structural changes in limbic brain regions.

Molecular targets in the treatment of anxiety

Although the cathecholamine systems have long been the focus of drug therapy in anxiety and depression, the development of novel drugs specifically aimed at new targets within these traditional neurotransmitter systems and at targets outside of these systems is now propelling the field of drug development in anxiety. A greater understanding of regional brain networks implicated in stress, anxiety, and anxious behaviors has provided localized targets for anxiolytics. Within the serotonin and norepinephrine systems, increased understanding of postsynaptic receptor regulation with chronic treatment and cross-system effects of drug therapy have been critical in furthering our understanding of effective pharmacological interventions. Receptors within the glutamate, gamma-aminobutyric acid, and neuropeptide systems provide a rich diversity of drug targets, both in localization and function. While acknowledging significant clinical and biological differences between the various anxiety disorders, an important aspect of modern neurobiological research is to look for similarities among these disorders, given that they are highly comorbid with each other and often respond to the same spectrum of treatments. Here we review current views on both traditional and new molecular targets in the treatment of anxiety, realizing that the ultimate challenge in effective anxiolytic drug development may be achieving specificity in brain regions important in generating and sustaining anxiety.

The combined effects of pyridostigmine and chronic stress on brain cortical and blood acetylcholinesterase, corticosterone, prolactin and alternation performance in rats

Thousands of soldiers who served in the Gulf War have symptoms that have been collectively termed Gulf War Illness (GWI). It has been suggested that a combination of operational stress and pyridostigmine, a drug given as a pretreatment to protect soldiers against the effects of exposure to nerve agents, might have had unexpected adverse health effects causing these symptoms. Our laboratory has previously modeled operational stress in rats using a paradigm of around-the-clock intermittent signalled footshock. In the present studies, this model was used to investigate the potential synergistic effects of chronic stress and pyridostigmine on physiology and behavior. Seventy-two rats were trained to perform an alternation lever pressing task to earn their entire daily food intake. The rats were then implanted with osmotic minipumps containing vehicle, pyridostigmine (25 mg/ml pyridostigmine bromide) or physostigmine (20 mg/ml eserine hemisulfate). The pumps delivered 1 microl/h, which resulted in a cumulative dosing of approximately 1.5 mg/kg/day of pyridostigmine or 1.2 mg/kg/day of physostigmine, equimolar doses of the two drugs. The rats were then returned to their home cages where performance continued to be measured 24 h/day. After 4 days, 24 of the 72 rats were trained to escape signalled footshock (avoidance-escape group) and 24 other rats (yoked-stressed group) were each paired to a rat in the avoidance-escape group. The remaining 24 rats were not subjected to footshock (unstressed group). Shock trials were intermittently presented in the home cage 24 h/day for 3 days, while alternation performance continued to be measured. Since only 12 test cages were available, each condition was repeated to achieve a final n of six rats per group. Pyridostigmine and physostigmine each decreased blood acetylcholinesterase levels by approximately 50%. Physostigmine also decreased brain cortical acetylcholinesterase levels by approximately 50%, while pyridostigmine had no effect on cortical acetylcholinesterase activity. Alternation performance was impaired on the first day of stress and then recovered. Neither pyridostigmine nor physostigmine affected performance in the absence of stress or increased the effects of stress alone. Corticosterone was significantly increased in the yoked stress group compared to unstressed controls. These data suggest that pyridostigmine does not exacerbate the effects of stress on performance or levels of stress hormones. Furthermore, these data do not suggest that stress enables pyridostigmine to cross the blood brain barrier.

Differential responsivity of the hypothalamic-pituitary-adrenal axis to glucocorticoid negative-feedback and corticotropin releasing hormone in rats undergoing morphine withdrawal: possible mechanisms involved in facilitated and attenuated stress responses

Chronic morphine treatment produces profound and long-lasting changes in the pituitary-adrenal responses to stressful stimuli. The purpose of the present study was to explore the mechanisms involved in these altered stress responses. Chronic morphine administration increased basal plasma concentrations of corticosterone and adrenocorticotropic hormone (ACTH), which peaked at 36 h after the final morphine injection and returned to normal levels within 84-h. Whole brain glucocorticoid receptor protein expression was reduced (approximately 70%) in morphine-treated rats 4-h after the final morphine injection and these levels recovered within 16-h. Twelve hours following morphine withdrawal, rats displayed normal ACTH, but potentiated and prolonged corticosterone responses to restraint stress. Both the ACTH and corticosterone responses to restraint in acutely withdrawn rats were insensitive to dexamethasone. Furthermore, acutely withdrawn rats displayed reduced ACTH but prolonged corticosterone responses to peripheral corticotropin releasing hormone (CRH) administration. These findings suggest that the normal ACTH and enhanced corticosterone responses to stress in acutely withdrawn rats involved decreased sensitivity of negative-feedback systems to glucocorticoids, reduced pituitary responsivity to CRH, and enhanced sensitivity of the adrenals to ACTH. Eight days following morphine withdrawal, rats displayed dramatically reduced ACTH, but normal corticosterone responses to restraint stress. These rats displayed enhanced sensitivity to dexamethasone and normal pituitary-adrenal responses to CRH. These data suggest that the reduced ACTH responses to stress in 8-day withdrawal rats involved increased sensitivity of negative-feedback systems to glucocorticoids as well as reduced CRH and/or AVP function in response to stress. Taken together, the results of this study illustrate some of the mechanisms mediating altered stress responsivity in rats that have received chronic morphine treatment.

Altered regulation of gene and protein expression of hypothalamic-pituitary-adrenal axis components in an immature rat model of chronic stress

Chronic stress early in postnatal life influences hormonal and behavioural responses to stress persistently, but the mechanisms and molecular cascades that are involved in this process have not been clarified. To approach these issues, a chronic stress paradigm for the neonatal rat, using limited bedding material to alter the cage environment, was devised. In 9-day-old rats subjected to this chronic stress for 1 week, significant and striking changes in the expression and release patterns of key molecules that govern the neuroendocrine stress responses were observed. The presence of sustained stress was evident from enhanced activation of peripheral elements of the neuroendocrine stress response, i.e. increased basal plasma corticosterone concentrations, high adrenal weight and decreased body weight. Central regulatory elements of the neuroendocrine stress response were perturbed, including reduced expression of hypothalamic corticotropin-releasing hormone that, surprisingly, was accompanied by reduced glucocorticoid receptor expression. Thus, the effects of chronic sustained stress in the neonatal rat on the hypothalamic-pituitary-adrenal axis included substantial changes in the expression and activity of major regulators of this axis. Importantly, the changes induced by this chronic stress differed substantially from those related to acute or recurrent stress, providing a novel model for studying the long-term effects of chronic, early life stress on neuroendocrine functions throughout life.

Persistent corticotropin-releasing factor(1) receptor desensitization and downregulation in the human neuroblastoma cell line IMR-32

Brain corticotropin-releasing factor (CRF) systems integrate various responses to stress. Pathological responses to stress may result from errors in CRF receptor regulation in response to changes in synaptic CRF levels. To establish an in vitro model to study brain CRF receptors, we characterized the CRF-induced modulation of CRF(1) receptors in the human neuroblastoma cell line, IMR-32. Treatment with CRF decreased CRF(1) receptor binding and desensitized CRF-induced increases in cAMP. The decrease in binding had an EC(50) of approximately 10 nM, was maximal by 30 min, and was blocked by the CRF receptor antagonist [D-Phe(12), Nle(21,38), C(alpha)-MeLeu(37)]CRF(12-41). The desensitization was homologous as vasoactive intestinal polypeptide-induced increases in cAMP were unchanged, and elevation of cAMP did not alter CRF(1) receptor binding. Treatment with CRF for up to 24 h did not alter CRF(1) receptor mRNA levels, suggesting that a posttranscriptional mechanism maintains the decrease in receptor binding. Interestingly, recovery of CRF receptor binding and CRF-stimulated cAMP production was only partial following exposure to 100 nM CRF. In contrast, receptor binding recovered to control levels following exposure to 10 nM CRF. These data suggest that exposure to high doses of CRF result in permanent changes characterized by only partial recovery. Identifying the mechanisms underlying this partial recovery may provide insights into mechanisms underlying the acute and chronic effects of stress on CRF receptor regulation.

Vasopressin pressor receptor-mediated activation of HPA axis by acute ethanol stress in rats

The plasma arginine vasopressin (AVP), ACTH, and corticosterone levels and the hypothalamic corticotropin-releasing hormone (CRH) content were measured after oral administration of 1 ml of 75% ethanol to rats, a model known to induce acute gastric erosions and stress. Elevated plasma AVP, ACTH, and corticosterone levels were detected 1 h after ethanol administration. Treatment with the vasopressin pressor (V(1)) receptor antagonist [d(CH(2))(5)Tyr(Me)-AVP] before ethanol administration significantly reduced the ACTH and corticosterone level increases. A higher hypothalamic CRH content was measured at 30 or 60 min after ethanol administration. V(1) receptor antagonist injection, 5 min before ethanol administration, inhibited the rise in hypothalamic CRH content. The protein synthesis blocker cycloheximide prevented the hypothalamic CRH content elevation after stress. The AVP-, CRH-, and AVP + CRH-induced in vitro ACTH release in normal anterior pituitary tissue cultures was also prevented by pretreatment with the V(1) receptor antagonist. The results support the hypothesis that stress-induced AVP may not only act directly on the ACTH producing anterior pituitary cells but also indirectly at the hypothalamic level via the synthesis and release of CRH.

Behavior and body temperature in rats following chronic foot shock or psychological stress exposure

In an attempt to examine stress-induced behavioral disorders, including circadian rhythm disturbances, we measured motor activity, feeding, drinking, and body temperature over a 14-day period following a long-term stress exposure in rats. Male Wistar rats were exposed to foot shock (physical) or non-foot shock stress (psychological) induced by the communication box for 1 h daily over 12 weeks. Two to three months after the termination of the stress sessions, motor activity, food intake, water intake, and body temperature were measured by means of an automatic behavioral measurement system under a 12:12-h light:dark cycle. Motor activity, feeding, and drinking patterns were not influenced by either of the previous stress exposures. Daily rhythm of body temperature was also unchanged in either stress group, however, a significant elevation in body temperature (by 0.20 degrees C, p<0.05) was observed only in non-foot-shocked rats. The present study suggests that only psychological stress induces an elevation of body temperature following the stress exposures; however, long-term stress exposures in the present experiment do not disturb behavioral activities and daily rhythms of behaviors.

Chronic sustained stress increases levels of anterior pituitary prolactin mRNA

Our laboratory is investigating the effects of chronic stress on physiological, endocrine and behavioral measures, in order to elucidate the neuronal substrates for the pathophysiological consequences of stress in humans. In these studies, we have employed a rodent model of sustained stress in which rats are exposed to around-the-clock intermittent footshock that can be avoided or escaped by rats in the controllable stress group, but not by rats in the uncontrollable stress group. Each rat in the uncontrollable stress group is paired (yoked) to a rat in the controllable stress group such that the controllable stress group rat avoids or escapes shock for both rats. A third group of rats receives no shock (controls). We have previously reported that in male rats, plasma prolactin levels were elevated after 3 days of stress in both stress groups. In the present experiments we determined whether the increases in plasma prolactin were correlated with increases in anterior pituitary prolactin mRNA. In addition, we measured hormones and mRNA at three time points and we examined these responses in female as well as male rats. Adult male and female Sprague-Dawley rats were exposed to chronic stress for 1, 3 or 14 days. In unstressed control rats, levels of anterior pituitary prolactin mRNA were fivefold higher in female as compared to male rats. However, stress increased levels of anterior pituitary prolactin mRNA over baseline in both genders. After 1 day of stress, anterior pituitary prolactin mRNA levels increased in male and female rats belonging to both stress groups, with no significant difference seen between the uncontrollable vs. controllable stress groups. After 3 days of stress, anterior pituitary prolactin mRNA levels were even more elevated, and rats in the uncontrollable stress group had higher anterior pituitary prolactin mRNA levels than those in the controllable stress group. After 14 days of stress, there were no significant differences in control and stressed groups with respect to anterior pituitary prolactin mRNA. These data suggest that chronic sustained stress increases the synthesis of anterior pituitary prolactin mRNA during the first days of stress, and that levels return to prestress values sometime between 3 and 14 days of stress.

Increased corticotropin-releasing factor concentrations in the bed nucleus of the stria terminalis of anhedonic rats

Chronic mild stress in rats is an antidepressant-responsive model for anhedonic symptoms of major depression. Many patients with depression exhibit alterations in hypothalamic-pituitary-adrenal axis activity, and corticotropin-releasing factor (CRF) neuronal function. This study investigated the potential involvement of CRF and CRF receptors in the development of chronic mild stress-induced anhedonia in rats. Rats were subjected to 19 days of chronic mild stress, during which time anhedonia was periodically assessed by determining the threshold for self-stimulation of the ventral tegmental area. Anhedonic rats exhibited a 50% increase in CRF concentrations in the bed nucleus of the stria terminalis compared to control rats. There were no significant changes in hypothalamic-pituitary-adrenal axis activity, CRF or CRF(1) receptor mRNA expression, or CRF receptor binding in the brain regions analyzed. Though preliminary, these results are consistent with the hypothesis that chronic stress-induced modulation of CRF function in specific brain structures such as the bed nucleus of the stria terminalis may contribute to the pathophysiology of depression.

Effect of corticotropin releasing factor receptor 1 antagonist on extracellular norepinephrine, dopamine and serotonin in hippocampus and prefrontal cortex of rats in vivo

Corticotropin releasing factor (CRF) is a major mediator of adaptive responsiveness to stress. We measured changes in extracellular concentrations of catecholamine and indoleamines in freely moving rats in response to administration of CRF1 antagonist CP-154,526 by using in vivo microdialysis. Dialysis probes were placed stereotaxically in either the hippocampus or the prefrontal cortex. We examined the response in the hippocampus or the prefrontal cortex to 32.0 mg/kg i.p. administration of CP-154,526. CP-154,526 reduced the extracellular concentration of norepinephrine (NE) from 30 min to 180 min and 5-hydroxytryptamine (5-HT) from 30 min to 60 min after injection in the hippocampus. CP-154,526 did not remarkably change dopamine (DA). There were no significant differences between CP-154,526 and vehicle in NE, 5-HT and DA in the prefrontal cortex. The present results indicate that CRF1 receptor antagonist produced a decrease in dialysate concentration of NE and 5-HT, but not DA, in the hippocampus. These results suggest that the CRH-1 receptor antagonist suppresses the release of NE and 5-HT in the hippocampus.

Behavioral effects Of 8-OH-DPAT in chronically stressed male and female rats

The present study tested the hypothesis that chronic stress desensitizes serotonergic 5-HT(1A) receptors and alters behavioral changes following 5-HT(1A) agonist administration. Eating, acoustic startle response (ASR), and locomotor activity were measured in stressed and nonstressed male and female rats after 8-OH-DPAT administration. Stressed rats were paired and stressed by around-the-clock intermittent foot shock. Controllable stress (CS) rats could avoid/terminate shock for themselves and their yoked partners by pulling a ceiling chain, whereas their partners, the uncontrollable stress (UCS) rats, could not. Rats earned their entire daily ration of food by pressing a lever. In previous experiments, this paradigm was stressful, but not debilitating and rats continued to eat, groom, sleep, and avoid/escape greater than 99% of shock trials. Locomotor activity and ASR were measured in the present study after saline and 8-OH-DPAT administration (0.25 mg/kg, IP) before, 24 h, and 72 h after shock onset. 8-OH-DPAT only decreased food intake significantly in male and female rats after the first administration. Stress decreased food intake in both the CS and UCS rats, with UCS rats eating the least. However, the effects of stress and 8-OH-DPAT were not additive. 8-OH-DPAT significantly increased peak startle amplitude at 100 and 120 dB, and decreased latency to peak startle amplitude at 100 dB in male and female rats. In contrast, 8-OH-DPAT did not alter percent prepulse inhibition (%PPI) at 100 dB, but significantly decreased %PPI in males but not females at 120 dB. Stress did not have a consistent effect on ASR, but reduced %PPI in males, but not females. Neither stress nor 8-OH-DPAT significantly altered locomotor activity. Although the results do not show an increased sensitivity to 8-OH-DPAT in stressed rats, the unexpectedly weak effects of 8-OH-DPAT alone on the behavioral measures chosen limits the conclusions that can be drawn.

Increased adrenocorticotropin responses to acute stress in Otsuka Long-Evans Tokushima Fatty (type 2 diabetic) rats

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is a new diabetic strain of rats whose disease closely resembles human type 2 diabetes. We measured plasma adrenocorticotropic hormone (ACTH) and corticostrone levels, and iodine-125-labeled ovine corticotropin-releasing factor ([125I]oCRF) binding in the anterior pituitary after ether-laparotomy stress in OLETF rats to examine the alteration of the hypothalamic-pituitary-adrenal (HPA) axis. In addition, we examined ACTH secretion following CRF administration in vivo and in vitro to characterize the mechanisms regulating the HPA axis in OLETF rats. Body weight, plasma glucose and insulin levels in OLETF rats were significantly higher than that in Long-Evans Tokushima Otsuka (LETO) rats. Basal plasma ACTH levels tended to be higher in OLETF rats than in LETO but it did not reach statistical significance. Ether-laparotomy stress dramatically increased plasma ACTH levels at 2 h after the stress both in either OLETF and LETO rats; the peak plasma ACTH level in OLETF rats following the stress was significantly greater than in LETO rats. Plasma ACTH levels following CRF (2 microg/kg, i.v.) in OLETF and LETO rats showed statistically significant increases at 10 and 30 min after CRF administration compared to ACTH levels at 0 min, however, the peak plasma ACTH level in OLETF rats at 10 min after CRF administration was significantly greater than in LETO rats. In contrast to ACTH levels, no significant differences in corticosterone levels between OLETF and LETO were observed at any of the time points. CRF (10 ng/ml) significantly increased ACTH secretion in pituitary cultures from OLETF compared to LETO rats. These data reveal a complex regulation of the endocrine system in this diabetic condition and suggest that HPA axis may be more stimulated during acute stress in diabetes mellitus than in unaffected subjects.

Biologic rhythms in the immune system

In all of its components, the immune system shows regularly recurring, rhythmic variations in numerous frequencies; the circadian (about 24 h) rhythms are the best explored. The circadian variations in immunocompetent cells circulating in the peripheral blood are of a magnitude to require attention in medical diagnostics. Both the humoral arm and the delayed (cellular) arm of the immune system function in a rhythmic manner. The response of the immune system to introduction of an antigen and to challenge of the sensitized organism varies in extent in the circadian frequency range and also in lower frequencies, for example, of about a week (circaseptan) or seasonally (circannual). The medical application of the biologic rhythms of the immune system extends to diagnostic measures, as well as treatment.

Effect of a chronic stress on CRF neuronal activity and expression of its type 1 receptor in the rat brain

The purpose of this study was to compare the effect of an acute versus a chronic immobilization stress on the genetic expression of c-fos and corticotropin-releasing factor type 1 receptor (CRF1 receptor) in the paraventricular nucleus (PVN) of the rat hypothalamus. Male Sprague-Dawley rats were exposed to either a single 90-min immobilization stress or the same session for 11 consecutive days. Animals were deeply anesthetized before (control); immediately, 1.5, 3, 6, or 12 h after the acute stress; or after the last session of the repeated exposures to immobilization. Coronal frozen sections (30 micrometers) of the brains were cut and mRNAs encoding the rat c-fos and CRF1 receptor were assayed by in situ hybridization histochemistry using 35S-labeled riboprobes. Localization of these transcripts within PVN CRF-immunoreactive (ir) neurons was also determined. The expression of the mRNA encoding either c-fos or CRF1 receptor was barely detectable to low in the PVN of control animals, but the acute stress session induced a robust signal for both transcripts in this endocrine nucleus. Numerous CRF-ir neurons were positive for the gene encoding either c-fos or CRF1 receptor in the PVN of acutely stressed animals. In contrast, the PVN of chronically stressed animals displayed a significantly lower CRF1 receptor mRNA signal after the last stress session. In these animals, stress-induced transcription of c-fos mRNA occurred in the magnocellular PVN 90 min after the end of the last stress session but only a low signal was detected in the parvocellular division. Moreover, very few CRF-ir neurons of the PVN expressed either the CRF1 receptor or c-fos transcript in chronically stressed rats. These data provide evidence for an adaptive cellular mechanism involving an attenuated action of CRF within the PVN in response to repeated homotypic stress exposures.

Structure and function of the ovine type 1 corticotropin releasing factor receptor (CRF1) and a carboxyl-terminal variant

Corticotropin releasing factor (CRF) is the major neuropeptide regulating the hypothalamo-pituitary-adrenocortical axis in most species. A pituitary receptor for CRF (designated CRF1) belonging to the seven-transmembrane helix, G-protein-coupled receptor superfamily has been cloned for human, rat, mouse and xenopus. Since ovine CRF shares only 84% identity to human/rat CRF (h/rCRF) we postulated that the sheep pituitary CRF1 receptor may have similarly diverged from the rodent and human CRF1. We report the molecular cloning of an ovine pituitary cDNA containing a 1245 bp open reading frame encoding a 415 amino acid sheep CRF1 receptor 78, 86, 94, and 95% homologous to xenopus, chicken, rat, mouse, and human CRF1, respectively. The divergence in primary structure between the sheep CRF1 and the other mammalian CRF1s is primarily localized to the extracellular amino terminal domain of the receptor (18 of 22 divergent residues, ovine vs human CRF1). A variant of the oCRF1 was also isolated (oCRF1var) with 133 bp deleted from nucleotide (nt) 1080 to nt 1213 of the open reading frame (ORF) resulting in a new ORF of 1176 nt predicting a 392 residue CRF1 variant receptor. The 133 bp deletion would cause a frame-shift at residue 358 within the carboxyl-third of the seventh transmembrane domain (TM7) resulting in a shortened cytoplasmic tail with a new amino acid sequence from residue 358 to 392. Scatchard analysis of saturation curves using membrane prepared from Cos 7 cells transfected with oCRF1 or oCRF1var indicated that both wild-type and variant receptors were expressed similarly (number of CRF binding sites) and both bound oCRF with high affinity [oCRF1 (Kd): 2.5 + 1.6 nM; oCRF1var: 5.1 + 2.3 nM]. The non-hydrolyzable GTP analogue (GTPgammaS) lowered the affinity of both wild-type and variant oCRF1 receptors to a similar extent (oCRF1: 18.2 nM; oCRF1var: 22.4 nM). Both wild-type and variant oCRF1 receptors exhibited approximately 10-fold greater selectivity for oCRF and sauvagine compared to h/rCRF or alpha-helical [9-41]oCRF. CRF effectively stimulated the accumulation of cAMP (EC50 = 51 pM) in Cos 7 cells transiently transfected with wild-type but not variant oCRF1 receptor. In Cos 7 cells transfected with oCRF1var, cAMP accumulation was only observed at the highest concentration of oCRF utilized (100 nM). Basal (unstimulated) levels of cAMP in Cos 7 cells transfected with oCRF1var (in the presence of 2 mM IBMX) were approximately 50% lower than for the wild-type oCRF1. Differences in cAMP accumulation could not be attributed to differences in receptor number since total binding sites in the transfected cells were not different between wild-type or variant oCRF1 receptors. Agonist-induced receptor internalization, determined as the percent of total [125I] Tyr0-oCRF bound located in the acid-resistant fraction of transfected Cos 7 cells, increased with time (0-60 min at 37 degrees C) for both wild-type and variant oCRF1. Wild-type CRF1 internalized approximately 2-fold greater percent of total [125I] Tyr0-oCRF bound compared to the variant receptor. In summary, an ovine CRF1 and a CRF1 cytoplasmic tail receptor variant displaying high affinity binding to oCRF as well as selectivity for oCRF vs h/rCRF, were cloned from an adult sheep pituitary cDNA library. GTPgammaS studies indicate that both variant and wild-type receptors couple efficiently to Galphas however, only the wild-type oCRF1 is capable of stimulating cAMP production at physiological levels of CRF. Agonist-induced internalization of the ovine CRF1var is also reduced compared to the wild-type CRF1 receptor. We suggest that the oCRF1var interacts efficiently with Galphas but is unable (post-hormonal binding) to effectively stimulate G-protein activation of adenylate cyclase, indicating that the cytoplasmic tail of the CRF1 can modulate receptor function related to signal transduction. (ABSTRACT TRUNCATED)

Physiological and neurochemical aspects of corticotropin-releasing factor actions in the brain: the role of the locus coeruleus

Corticotropin-releasing factor (CRF) is both a major regulator of the hypothalamo-pituitary-adrenal (HPA) axis and the activity of the autonomic nervous system. Besides, it exerts numerous effects on other physiological functions such as appetite control, motor and cognitive behavior and immune function. The basis for these effects is constituted by its distribution in hypothalamic and extra-hypothalamic brain areas, the latter being represented by limbic structures such as the central nucleus of the amygdala or by brain stem neurons such as the locus coeruleus (LC) or nucleus of the solitary tract (NTS). The effects of CRF are mediated through recently described CRF-receptor subtypes, whose molecular biology, biochemistry and pharmacological regulation are discussed in detail. In the second part of this review, we will focus on the physiology of CRF-systems in the brain, with a particular emphasis on cardiovascular regulation, respiration, appetite control and stress-related behavior. Finally, the role of the locus coeruleus in the control of CRF-mediated behavioral activities is discussed. The interaction of noradrenergic and CRF-neurons clearly implies that CRF appears to directly activate LC neurons in a stressful situation, thus ultimately coordinating the bodily response to a stressful stimulus.

Reduced activity of hypothalamic corticotropin-releasing hormone neurons in transgenic mice with impaired glucocorticoid receptor function

Loss of central glucocorticoid receptor (GR) function is thought to be involved in the development of neuroendocrine and psychiatric disorders associated with corticotropin-releasing hormone (CRH) hyperactivity. The possible causal relationship between defective GR function and altered activity of CRH neurons was studied in transgenic mice (TG) expressing antisense RNA against GR. Immunocytochemical studies showed significant reductions in CRH immunoreactive neurons in the paraventricular nucleus (PVN) and in CRH and vasopressin (AVP) stores in the external zone of the median eminence. Concomitantly, stimulus-evoked CRH secretion from mediobasal hypothalami of TG mice in vitro was reduced significantly. However, CRH mRNA levels in the PVN of TG mice were marginally lower than those in wild-type (WT) mice. 125I-CRH binding autoradiography revealed no differences between WT and TG animals in any of the brain regions that were studied. Basal plasma corticosterone (cort) levels and 125I-CRH binding, CRH-R1 mRNA, POMC mRNA, and POMC hnRNA levels in the anterior pituitary gland were similar in WT and TG mice. Intraperitoneal injection of interleukin-1beta (IL-1beta) increased plasma cort levels, CRH mRNA in the PVN, and anterior pituitary POMC hnRNA similarly in WT and TG mice. The injection of saline significantly reduced anterior pituitary CRH-R1 mRNA levels in WT mice, but not in TG mice, whereas IL-1beta produced a decrease in these mRNA levels in both strains. The data show that long-term GR dysfunction can be associated with reduced activity of CRH neurons in the PVN and decreased sensitivity of pituitary CRH-R1 mRNA to stimulus-induced downregulation. Moreover, the hypothalamic changes observed in this model suggest that impaired GR function, at least if present since early embryonic life, does not necessarily result in CRH hyperexpression characteristics of disorders such as major depression.

Principles of psychoneuroendocrinology

The goal of this article is to describe some of the central nervous system circuits involved in the regulation of the hypothalamopituitary-adrenocortical (HPA) axis, with an emphasis on animal models believed to mimic the human experience of emotional stress. First, the basic constitutive elements of the HPA axis that control glucocorticoid secretion are reviewed. A description of the neural systems assumed to regulate the activity of the HPA axis, both anatomically and functionally, follows. It is argued that hypothalamic, septal and bed nucleus of the stria terminalis neurons are involved in the regulation of the HPA axis by situations eliciting emotional responses.

Long-term intracerebroventricular infusion of corticotropin-releasing hormone alters neuroendocrine, neurochemical, autonomic, behavioral, and cytokine responses to a systemic inflammatory challenge

Corticotropin-releasing hormone (CRH) was infused intracerebroventricularly into rats for 7 d via a miniosmotic pump (1 microg . microl-1 . hr-1). Body temperature and locomotor activity were recorded during the treatment using biotelemetry, whereas hippocampal serotonergic neurotransmission and free corticosterone levels were monitored using in vivo microdialysis on day 7 of CRH treatment. During the microdialysis experiment, behavioral activity was scored by assessing the time during which rats were active (locomotion, grooming, eating, drinking). Continuous intracerebroventricular infusion of CRH produced a transient increase in body temperature and locomotion. Moreover, intracerebroventricularly CRH-treated rats showed elevated free corticosterone levels with no apparent diurnal rhythm. Intraperitoneal administration of bacterial endotoxin -lipopolysaccharide (LPS); 100 microg/kg body weight- on day 7 of CRH/vehicle treatment produced a marked fever response in control animals, which was significantly blunted in intracerebroventricularly CRH-treated rats. Although free corticosterone levels reached similar peak concentrations in both intracerebroventricularly vehicle- and CRH-infused groups after LPS, this response was delayed significantly by approximately 1 hr in the intracerebroventricularly CRH-treated animals. Microdialysis experiments showed no changes in basal extracellular levels of serotonin and 5-hydroxyindoleacetic acid in intracerebroventricularly CRH-infused animals. Injection of LPS in intracerebroventricularly CRH-treated rats produced a blunted 5-HT response and a delayed onset of behavioral inhibition and other signs of sickness behavior. Assessment of the endotoxin-induced cytokine responses showed significantly enhanced plasma interleukin-1 (IL-1) and IL-6 bioactivities in the intracerebroventricularly CRH-infused animals 3 hr after injection of LPS, whereas tumor necrosis factor bioactivity responses were not different. Our data demonstrate that chronically elevated brain CRH levels produce marked changes in basal (largely CRH regulated) physiological and behavioral processes accompanied by aberrant responses to an acute challenge. The present study provides evidence that chronic CRH hypersecretion is an important factor in the etiology of stress-related disorders.

Functional corticotropin-releasing factor receptors in human neuroblastoma cells

The present study examined the presence of functional corticotropin-releasing factor (CRF) receptors in IMR-32 neuroblastoma cells. [125I]Tyro-ovine CRF binding was linear with increasing protein concentrations, saturable, reversible and of high affinity. Scatchard analysis indicated a Kd of approximately 0.8 nM and a Bmax of approximately 32 fmol/mg protein. Competition studies with CRF and related peptides revealed a pharmacological profile characteristic of the CRF1 receptor subtype. CRF stimulated cAMP production in a dose-dependent manner with an apparent EC50 of approximately 4 nM. In addition, the putative CRF receptor antagonist alpha-helical CRF9-41 dose-dependently inhibited CRF stimulated (10 nM) cAMP production with an IC50 of approximately 60 nM. CRF treatment down regulated its own receptor while treatment with the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA), increased CRF binding in neuroblastoma cells. Taken together, these data demonstrate the utility of the human neuroblastoma cell line for functional studies on CRF receptors and suggest that CRF may play a regulatory role in the pathophysiology of human neuroblastoma.

Effects of chronic stress on food acquisition, plasma hormones, and the estrous cycle of female rats

Our laboratory has previously conducted a number of studies to determine the effects of chronic stress on the physiology and behavior of male rats. The present study was performed to extend these investigations to female rats. Female rats were chronically stressed using a behavioral paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock (stress) while another group of rats is yoked to the first group (yoked-stress) and does not have control over shock termination. Control rats were never shocked but all groups lever pressed for food pellets on an FR1 schedule (one pellet per lever press). Daily vaginal samples were obtained for several weeks prior to stress onset and throughout the chronic stress period. After 14 days of stress, the experiment was terminated and morning blood samples were collected for hormonal assays. Stress transiently decreased lever pressing for food pellets and body weights, but both measures returned to prestress levels by day 14 of stress. Plasma adrenocorticotropic hormone (ACTH) concentrations were significantly elevated in the yoked-stress group compared to the other two groups, but there were no significant effects of 14 days of stress treatment on plasma corticosterone, prolactin, estradiol, or progesterone concentrations. There were no significant differences in estrous cycle length among experimental groups.

Reciprocal cross-desensitization of locus coeruleus electrophysiological responsivity to corticotropin-releasing factor and stress

While acutely administered corticotropin-releasing factor (CRF) and acute stress each activate neurons of the locus coeruleus (LC), desensitization to both develops with repeated treatment. The present experiments were designed to investigate whether cross-desensitization develops between CRF and stress. Because acute hemodynamic stress caused by intravenous infusion of sodium nitroprusside increases LC electrophysiological discharge rate via a CRF-dependent mechanism, it was hypothesized that repeated CRF administration would cause desensitization to the effect of this stressor on LC. For a complementary experiment, it was hypothesized that repeated stress, which presumably results in the repeated release of endogenous CRF, would result in desensitization to subsequent exogenous CRF. The results of the first experiment showed that repeated intracerebroventricular (i.c.v.) administration of CRF caused a significant attenuation of the sodium nitroprusside-induced increase in LC discharge rate seen in naive rats, although this pretreatment actually potentiated the decrease in blood pressure produced by sodium nitroprusside. In the second experiment, either one or eight sessions of white-noise stress attenuated the effect of CRF on LC activity 24 h after the last stress exposure, and this attenuation was more pronounced following eight sessions of stress than following one session. In a test of the specificity of this effect, stress-induced desensitization did not generalize to the LC electrophysiological response to clonidine (i.c.v.). One week following the last of eight sessions of stress, LC responsivity to CRF had recovered to control levels. These experiments demonstrate reciprocal cross-desensitization between CRF and stress using LC electrophysiological responsivity as an assay. This modifiability of the interaction between CRF and the LC may represent the operation of mechanisms mediating adaptive responding to stress.

Homologous desensitization of human corticotropin-releasing factor1 receptor in stable transfected mouse fibroblast cells

Previous radioligand binding and second messenger studies have shown that corticotropin-releasing factor (CRF) modulates its receptor following both in vivo and in vitro treatment. In the present study, we determined the sequence of events leading to CRF-induced downregulation and desensitization of cloned CRF receptors in murine fibroblast cells (Ltk-) stably transfected with CRF1 DNA (from human pituitary). Treatment of cells with rat/human CRF produced a dose- and time-dependent decrease in [125I]Tyr degrees-ovine CRF ([125I]oCRF) binding and a concomitant decrease in CRF-stimulated adenylate cyclase activity. Significant decreases in [125I]oCRF binding and agonist-stimulated cAMP production were evident minutes after CRF treatment with maximal (60-80%) reductions seen following 1 h of CRF treatment. Scatchard analysis revealed that the decrease in [125I]oCRF binding was due to the downregulation of the receptor with no significant alteration seen in the affinity of the ligand. Since the transfected cell line is engineered using an artificial promoter, we did not detect any significant changes in CRF1 receptor mRNA levels following CRF treatment for up to 24 h.

Interleukin-1 receptors in the brain-endocrine-immune axis. Modulation by stress and infection

In the present study, we examined the in vitro and in vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 h with neuroendocrine mediators of stress such as CRF and catecholamines produced dose-dependent increases in cAMP production and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increases in [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to up-regulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis, and spleen) at 2-6 h after a single LPS injection (30 micrograms LPS/mouse); however, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen, and testis was significantly decreased at 2 h following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 h by low dose of LPS and was significantly decreased by high-dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 h), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen, and testis were observed at 2 h after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in coordinating brain-endocrine-immune responses to stress and infection.

Effects of pretreatment with corticotropin-releasing factor on the electrophysiological responsivity of the locus coeruleus to subsequent corticotropin-releasing factor challenge

Both acute central administration of exogenous, and stress-induced release of endogenous corticotropin-releasing factor result in electrophysiological activation of the noradrenergic neurons constituting the locus coeruleus. The present experiments were designed to examine whether single (1) or repeated (8) intracerebroventricular pretreatment with exogenous corticotropin-releasing factor would alter locus coeruleus electrophysiological responsivity to subsequent corticotropin-releasing factor challenge in rats. A single corticotropin-releasing factor (3 microg) pretreatment significantly attenuated challenge-induced locus coeruleus activation 24 and 72, but no 96 h later, while a single vehicle pretreatment had no significant effect on the response to subsequent challenge at any pretreatment-to-test interval. Repeated pretreatment with either corticotropin-releasing factor or vehicle completely attenuated locus coeruleus response to challenge 24 h after the final pretreatment. Seventy-two hours after the last vehicle pretreatment, challenge resulted in a significant increase in locus coeruleus activity, though the response was less than in naive controls. Challenge continued to produce no effect on locus coeruleus activity in repeated corticotropin-releasing factor-pretreated rats at this (72 h) time point. One week (168 h) after the cessation of repeated pretreatment, challenge resulted in a significant increase in locus coeruleus activity which was equal to that of naive controls in vehicle-pretreated rats, but reduced by comparison to controls in corticotropin-releasing factor-pretreated rats. Basal discharge rates of locus coeruleus neurons 24 h after the last repeated corticotropin-releasing factor pretreatment were significantly less than in naive controls. Thus, the failure of challenge to increase neuronal activity in these rats was not due to a "ceiling" effect caused by elevated tonic discharge rate. Repeated vehicle pretreatment produced a functional change similar to that produced by exogenous corticotropin-releasing factor administration. One hypothesis is that repeated vehicle pretreatment was stressful and caused the repeated release of endogenous corticotropin-releasing factor. This hypothesis was tested by determining whether locus coeruleus neurons remained responsive to challenge following repeated administration of a corticotropin-releasing factor antagonist. Thus, the effect if repeated pretreatment with the antagonist, [D-Phe, Nle, Calpha MeLeu]CRF was also examined. Challenge resulted ina significant increase in discharge rate 24 h after the final antagonist pretreatment, providing support for the hypothesis. Additionally, in rats repeatedly pretreated with vehicle, carbachol challenge induced an increase in locus coeruleus activity equal to that induced in naive controls. These results indicate that prior exposure to corticotropin-releasing factor, or the repeated mild stress of vehicle infusions, reduces locus coeruleus responsiveness to corticotropin-releasing factor, and reveal that the relationship between these two neurotransmitter systems is modifiable. This altered relationship may contribute to stress-related affective disorders in which both systems have been implicated.

Modulation of interleukin-1 receptors in the neuro-endocrine-immune axis

Interleukin-1 (IL-1) receptors with kinetics, pharmacological and biochemical characteristics of type I IL-1 receptors have been identified in the mouse neuro-endocrine-immune axis. In the present study, we examined the in-vitro and in-vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 hr with neuro-endocrine mediators of stress such as corticotropin releasing factor (CRF) and catecholamine (beta 2 adrenergic) receptor agonists produced a dose-dependent increase in cAMP and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increase of [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to upregulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin lipopolysaccharide (LPS) treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis and spleen) at 2-6 hr after a single LPS injection (30 micrograms LPS/mouse). However, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen and testis was significantly decreased at 2 hr following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 hr by a low dose of LPS and was significantly decreased by high dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 hr), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen and testis were observed at 2 hr after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in co-ordinating neuro-endocrine-immune responses to stress and infection.

Effects of chronic stress on sleep in rats

The present study was conducted to determine the effects of chronic stress on sleep using a rodent paradigm of around-the-clock signalled intermittent foot shock in which some rats can pull a chain to avoid/escape shock while another group of rats is yoked to the first group. We measured sleep using telemetry; four-channel EEG was collected 24 h/day in rats during 2 prestress days; days 1, 2, 3, 7, and 14 during chronic stress; and 3 poststress days. States of REM sleep, non-REM (NREM) sleep, and waking were scored for each 15-s period of the EEG recordings. During the prestress period, rats slept (REM plus NREM) 55% of available time during the light hours and 34% of the dark hours with the remainder represented by waking. On the first day of stress, total sleep and, especially REM sleep, decreased markedly. By the second day of stress, only REM sleep in the controllable stress group (but not the uncontrollable stress group) was still significantly decreased compared to prestress levels, and REM sleep returned to baseline levels by day 7 of stress. The recovery of sleep quantity was accomplished by increased sleep during the dark hours, resulting in a long-lasting disruption of normal circadian sleep patterning.

Corticotropin-releasing factor receptors: physiology, pharmacology, biochemistry and role in central nervous system and immune disorders

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioral and immune responses to stress through actions in the brain and the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between the brain (58,000 Da) and the pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. The recently cloned CRF receptor in the pituitary and the brain (designated as CRF1) encodes a 415 amino acid protein comprising seven putative membrane-spanning domains and is structurally related to the calcitonin/vasoactive intestinal peptide/growth hormone-releasing hormone subfamily of G-protein-coupled receptors. A second member of the CRF receptor family encoding a 411 amino acid rat brain protein with approximately 70% homology to CRF1 has recently been identified (designated as CRF2); there exists an additional splice variant of the CRF2 receptor with a different N-terminal domain encoding a protein of 431 amino acids. In autoradiographic studies, CRF receptors were localized in highest densities in the anterior and intermediate lobes of the pituitary gland, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-enriched zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in a reciprocal manner. For example, stress and adrenalectomy increase hypothalamic CRF secretion which, in turn, down-regulates CRF receptors in the anterior pituitary. CRF receptors in the brain and pituitary are also altered as a consequence of the development and aging processes. In addition to a physiological role for CRF in integrating the responses of the brain, endocrine and immune systems to physiological, psychological and immunological stimuli, recent clinical data implicate CRF in the etiology and pathophysiology of various endocrine, psychiatric, neurologic and inflammatory illnesses. Hypersecretion of CRF in the brain may contribute to the symptomatology seen in neuropsychiatric disorders, such as depression, anxiety-related disorders and anorexia nervosa. Furthermore, overproduction of CRF at peripheral inflammatory sites, such as synovial joints may contribute to autoimmune diseases such as rheumatoid arthritis. In contrast, deficits in brain CRF are apparent in neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, as they relate to dysfunction of CRF neurons in the brain areas affected in the particular disorder. Strategies directed at developing CRF-related agents may hold promise for novel therapies for the treatment of these various disorders.

Modulation of binding sites for corticotropin-releasing hormone by chronic psychosocial stress

This study was conducted to determine whether long lasting psychosocial stress would affect corticotropin-releasing hormone (CRH) binding sites in the brain, the pituitary, and the adrenal gland. As a model for sustained emotional stress we used chronic psychosocial conflict in male tree shrews. In subordinate tree shrews, repeated confrontation with a dominant conspecific results in constant hyperactivity of the HPA-axis and an elevated neurosympathetic tone. After 24 days of psychosocial conflict, CRH binding sites were quantified by in vitro-autoradiography with 125I-ovine CRH in 23 discrete brain regions, the pituitaries, and the adrenal glands of subordinate and control animals. Chronic stress significantly reduced the number of binding sites (Bmax) in the anterior lobe of the pituitary, the dentate gyrus, the CA1-CA3 areas of the hippocampus, and in both the stratum griseum superficiale and the stratum opticum of the superior colliculus. In cortical area 17, the reduction of Bmax was counterbalanced by an increase in the affinity (Kd) of the radioligand for the binding sites. A significant stress-induced enhancement of Bmax was observed in the frontal cortex, cingulate cortex, claustrocortex, the central and lateral nucleus of the amygdala, and in the choroid plexus. This increase was accompanied by a significant decrease of Kd-values in the frontal and cingulate cortex, the lateral nucleus of the amygdala, and the choroid plexus. These findings represent the first in vivo demonstration of a modulation of extrahypothalamic CRH receptors by a naturally occurring form of stress. The different response patterns of the central CRH binding sites reflect distinct neuroendocrine processes which are presumed to coordinate behavioral, autonomic, endocrine, and immune responses to long-lasting psychosocial conflict.

Reciprocal modulation of corticotropin-releasing factor and interleukin-1 receptors following ether-laparotomy stress in the mouse

Ether-laparotomy stress resulted in a dramatic decrease in specific iodine-125-labeled ovine CRF binding ([125I]oCRF) in the pituitary at 6 h after the onset of the stress although it did not affect [125I]oCRF binding in the pituitary at 2 h after the stress. [125I]oCRF binding was unchanged in the frontal cortex after the stress. In contrast, [125I]interleukin-1 (IL-1)alpha binding was significantly increased in the pituitary at 2 h after the stress and tended to be higher than non-stressed levels at 6 h after the stress but was not statistically significant. Ether-laparotomy stress did not affect [125I]IL-1 alpha binding in hippocampus, spleen and testis at any time after the stress. Plasma adrenocorticotropic hormone (ACTH) and corticosterone were increased at 2 h after the stress. These data demonstrate complex interactions between CRF and IL-1 receptors on HPA axis during stress.