Expression of corticotropin-releasing factor mRNA in response to stress

Effect of heat exposure on gene expression of feed intake regulatory peptides in laying hens

The aim of this paper was to investigate the effect of heat stress on the regulation of appetite-associated genes in laying hens. Forty eight laying hens were randomly divided into two circumstances: high (31 ± 1.5°C; relative humidity, 82.0 ± 2.2%) or normal (20 ± 2°C, control; relative humidity, 60.1 ± 4.5%) ambient environment. Heat stress decreased body weight gain (P < 0.01), feed intake (P < 0.01), laying rate (P < 0.05), average egg mass (P < 0.01), egg production (P < 0.01), shell thickness (P < 0.01), and feed efficiency (P < 0.05). High ambient temperature decreased plasma uric acid (P < 0.05). Heat stress significantly increased mRNA levels of ghrelin and cocaine- and amphetamine-regulated transcript (P < 0.05) and decreased mRNA levels of cholecystokinin (P < 0.05) in the hypothalamus. Heat stress significantly increased (P < 0.05) mRNA levels of ghrelin in the glandular stomach and jejunum but significantly decreased (P < 0.05) mRNA levels of cholecystokinin in the duodenum and jejunum. In conclusion, heat stress plays a unique role in some special neuropeptides (e.g., ghrelin, cocaine- and amphetamine-regulated transcript, and cholecystokinin), which might participate in the regulation of feed intake in laying hens under high ambient temperature.

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.

Housing in pyramid counteracts neuroendocrine and oxidative stress caused by chronic restraint in rats

The space within the great pyramid and its smaller replicas is believed to have an antistress effect. Research has shown that the energy field within the pyramid can protect the hippocampal neurons of mice from stress-induced atrophy and also reduce neuroendocrine stress, oxidative stress and increase antioxidant defence in rats. In this study, we have, for the first time, attempted to study the antistress effects of pyramid exposure on the status of cortisol level, oxidative damage and antioxidant status in rats during chronic restraint stress. Adult female Wistar rats were divided into four groups as follows: normal controls (NC) housed in home cage and left in the laboratory; restrained rats (with three subgroups) subject to chronic restraint stress by placing in a wire mesh restrainer for 6 h per day for 14 days, the restrained controls (RC) having their restrainers kept in the laboratory; restrained pyramid rats (RP) being kept in the pyramid; and restrained square box rats (RS) in the square box during the period of restraint stress everyday. Erythrocyte malondialdehyde (MDA) and plasma cortisol levels were significantly increased and erythrocyte-reduced glutathione (GSH) levels, erythrocyte glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities were significantly decreased in RC and RS rats as compared to NC. However, these parameters were maintained to near normal levels in RP rats which showed significantly decreased erythrocyte MDA and plasma cortisol and significantly increased erythrocyte GSH levels, erythrocyte GSH-Px and SOD activities when compared with RS rats. The results showed that housing in pyramid counteracts neuroendocrine and oxidative stress caused by chronic restraint in rats.

Corticosterone influences on Mammalian neonatal sensitive-period learning

Infant rats exhibit sensitive-period odor learning characterized by olfactory bulb neural changes and odor preference acquisitions critical for survival. This sensitive period is coincident with low endogenous corticosterone (CORT) levels and stress hyporesponsivity. The authors hypothesized that low corticosterone levels modulate sensitive-period learning. They assessed the effects of manipulating CORT levels by increasing and removing CORT during (Postnatal Day 8) and after (Postnatal Day 12) the sensitive period. Results show that (a) exogenous CORT prematurely ends sensitive-period odor-shock-induced preferences; (b) adrenalectomy developmentally extends the sensitive period as indicated by odor-shock-induced odor-preference learning in older pups, whereas CORT replacement can reinstate fear learning; and (c) CORT manipulation modulates olfactory bulb correlates of sensitive-period odor learning in a manner consistent with behavior.

Role of hypothalamic inputs in maintaining pituitary-adrenal responsiveness in repeated restraint

The role of hypothalamic structures in the regulation of chronic stress responses was studied by lesioning the mediobasal hypothalamus or the paraventricular nucleus of hypothalamus (PVH). Rats were acutely (60 min) and/or repeatedly (for 7 days) restrained. In controls, a single restraint elevated the plasma adrenocorticotropin (ACTH), corticosterone, and prolactin levels. Repeated restraint produced all signs of chronic stress, including decreased body and thymus weights, increased adrenal weight, basal corticosterone levels, and proopiomelanocortin (POMC) mRNA expression in the anterior pituitary. Some adaptation to repeated restraint of the ACTH response, but not of other hormonal responses, was seen. Lesioning of the mediobasal hypothalamus abolished the hormonal response and POMC mRNA activation to acute and/or repeated restraint, suggesting that the hypothalamo-pituitary-adrenal axis activation during repeated restraint is centrally driven. PVH lesion inhibited the ACTH and corticosterone rise to the first restraint by approximately 50%. In repeatedly restrained rats with PVH lesion, the ACTH response to the last restraint was reduced almost to basal control levels, and the elevation of POMC mRNA level was prevented. PVH seems to be important for the repeated restraint-induced ACTH and POMC mRNA stimulation, but it appears to partially mediate other restraint-induced hormonal changes.

Corticosterone differentially modulates expression of corticotropin releasing factor and arginine vasopressin mRNA in the hypothalamic paraventricular nucleus following either acute or repeated restraint stress

Exposing rats to repeated restraint stress induces well-characterized adaptations in the expression of either corticotropin-releasing factor (CRF) or arginine-vasopressin (AVP) mRNA in the parvocellular neurons of the hypothalamic paraventricular nucleus (PVN). The effects of regulating corticosterone levels on this adaptation was studied in male rats. In intact rats, acute restraint stress increased the expression of CRF mRNA whilst AVP mRNA expression was no different to control. Repeated exposure resulted in habituation of CRF expression, whereas AVP mRNA increased above that seen in either non stressed or acutely stressed animals. In adrenalectomised rats with replacement pellets of corticosterone that replicated blood levels approximating to the daily trough (mean levels 37--65 ng/mL), basal CRF expression levels were raised, but the response to acute stress was still observed. However, the habituation seen in normal animals that had been repeatedly stressed was prevented, so that CRF mRNA levels continued to be raised after repeated stress. By contrast, the AVP response to both acute and repeated stress was unaltered in these low-dose corticosterone-treated rats compared with controls. Higher dose pellets, which resulted in blood levels around those of the daily maximum (mean 118--141 ng/mL) had the opposite effects. There was no change compared to intact rats in the expression of CRF mRNA following either acute or repeated stress, but the expected increase in AVP following repeated restraint was prevented. These experiments show that corticosterone has important modulating effects on the adaptive pattern of both CRF and AVP mRNA expression in the parvocellular PVN. The 'set-point' of corticosterone differs; for CRF, experiencing higher levels is necessary for subsequent adaptation to repeated restraint to occur, whereas for AVP a return to lower levels is necessary to allow this peptide to respond to repeated stress.

Neuronal activity and stress differentially regulate hippocampal and hypothalamic corticotropin-releasing hormone expression in the immature rat

Corticotropin-releasing hormone, a major neuromodulator of the neuroendocrine stress response, is expressed in the immature hippocampus, where it enhances glutamate receptor-mediated excitation of principal cells. Since the peptide influences hippocampal synaptic efficacy, its secretion from peptidergic interneuronal terminals may augment hippocampal-mediated functions such as learning and memory. However, whereas information regarding the regulation of corticotropin-releasing hormone's abundance in CNS regions involved with the neuroendocrine responses to stress has been forthcoming, the mechanisms regulating the peptide's levels in the hippocampus have not yet been determined. Here we tested the hypothesis that, in the immature rat hippocampus, neuronal stimulation, rather than neuroendocrine challenge, influences the peptide's expression. Messenger RNA levels of corticotropin-releasing hormone in hippocampal CA1, CA3 and the dentate gyrus, as well as in the hypothalamic paraventricular nucleus, were determined after cold, a physiological challenge that activates the hypothalamic pituitary adrenal system in immature rats, and after activation of hippocampal neurons by hyperthermia. These studies demonstrated that, while cold challenge enhanced corticotropin-releasing hormone messenger RNA levels in the hypothalamus, hippocampal expression of this neuropeptide was unchanged. Secondly, hyperthermia stimulated expression of hippocampal immediate-early genes, as well as of corticotropin-releasing hormone. Finally, the mechanism of hippocampal corticotropin-releasing hormone induction required neuronal stimulation and was abolished by barbiturate administration. Taken together, these results indicate that neuronal stimulation may regulate hippocampal corticotropin-releasing hormone expression in the immature rat, whereas the peptide's expression in the hypothalamus is influenced by neuroendocrine challenges.

Infantile spasms: hypothesis-driven therapy and pilot human infant experiments using corticotropin-releasing hormone receptor antagonists

BACKGROUND AND RATIONALE

Infantile spasms (IS) are an age-specific seizure disorder occurring in 1:2,000 infants and associated with mental retardation in approximately 90% of affected individuals. The costs of IS in terms of loss of lifetime productivity and emotional and financial burdens on families are enormous. It is generally agreed that the seizures associated with IS respond poorly to most conventional anticonvulsants. In addition, in the majority of patients, a treatment course with high-dose corticotropin (ACTH) arrests the seizures completely within days, often without recurrence on discontinuation of the hormone. However, the severe side effects of ACTH require development of better treatments for IS. Based on the rapid, all-or-none and irreversible effects of ACTH and on the established physiological actions of this hormone, it was hypothesized that ACTH eliminated IS via an established neuroendocrine feedback mechanism involving suppression of the age-specific endogenous convulsant neuropeptide corticotropin-releasing hormone (CRH). Indeed, IS typically occur in the setting of injury or insult that activate the CNS stress system, of which CRH is a major component. CRH levels may be elevated in the IS brain, and the neuropeptide is known to cause seizures in infant rats, as well as neuronal death in brain regions involved in learning and memory. If 'excess' CRH is involved in the pathogenesis of IS, then blocking CRH receptors should eliminate both seizures and the excitotoxicity of CRH-receptor-rich neurons subserving learning and memory.

PATIENTS AND METHODS

With FDA approval, alpha-helical CRH, a competitive antagonist of the peptide, was given as a phase I trial to 6 infants with IS who have either failed conventional treatment or who have suffered a recurrence. The study was performed at the Clinical Research Center of the Childrens Hospital, Los Angeles. The effects of alpha-helical CRH on autonomic parameters (blood pressure, pulse, temperature, respiration) were determined. In addition, immediate and short-term effects on ACTH and cortisol and on electrolytes and glucose were examined. The potential efficacy of alpha-helical CRH for IS was studied, using clinical diaries and video EEG.

RESULTS

alpha-Helical CRH, a peptide, did not alter autonomic or biochemical parameters. Blocking peripheral CRH receptors was evident from a transient reduction in plasma ACTH and cortisol. No evidence for the compound's penetration of the blood-brain barrier was found, since no central effects on arousal, activity or seizures and EEG patterns were observed. In addition, a striking resistance of the patients' plasma ACTH to the second infusion of alpha-helical CRH was noted.

CONCLUSIONS

Peptide analogs of CRH do not cross the blood-brain barrier, and their effects on peripheral stress hormones are transient and benign. Nonpeptide compouds that reach CNS receptors are required to test the hypothesis that blocking CRH receptors may ameliorate IS and its cognitive consequences.

Expression of preprogalanin mRNA following acute and chronic restraint stress in brains of normotensive and hypertensive rats

Exposure to stress is known to induce widespread changes in the central nervous system (CNS) involving multiple neuropeptides. The neuropeptide galanin has been implicated in the central response to different stressors; however, the role of galanin in the response to restraint stress has not been reported. Therefore, this study utilised in situ hybridisation histochemistry to observe the effects of acute and chronic restraint stress on preprogalanin (preproGAL) mRNA expression in the CNS of normotensive (Wistar Kyoto; WKY) and Spontaneously Hypertensive (SHR) rats. Rats were exposed to 1 h of restraint for 0 (control), 1, 3, 5, or 10 consecutive days, and central preproGAL mRNA expression following these restraint periods was compared between strains. Significant differences in the basal expression of preproGAL mRNA were detected, with expression decreased by approximately 50% in the supraoptic nucleus (SON; P<0. 01) and increased by approximately 100% in the rostral ventrolateral medulla (RVLM; P<0.05) of SHR when compared to WKY. Following acute restraint (1 session), preproGAL mRNA expression was significantly increased by approximately 135% in the central nucleus of the amygdala (CeA; P<0.05) in WKY. In SHR, significant increases of up to 300% were observed in the CeA (P<0.01) and SON (P<0.05) following chronic restraint (up to 10 days). In addition, expression of preproGAL mRNA was significantly decreased in the locus coeruleus (LC) of SHR following acute restraint (1 session) (P<0.05). These results provide the first evidence that both acute (LC) and chronic (CeA, SON) restraint stress is associated with alterations in preproGAL mRNA expression. As such, the present study provides further evidence linking neurons containing galanin with the central response to restraint stress.

Transcriptional responses of the vasopressin and corticotropin-releasing hormone genes to acute and repeated intraperitoneal hypertonic saline injection in rats

The contribution of corticotropin releasing hormone (CRH) and vasopressin (VP) to the adaptation of ACTH responses to chronic stress was studied by analysis of CRH and VP expression in the hypothalamic paraventricular nucleus (PVN) of rats receiving acute or chronic i.p. hypertonic saline injection (ipHS), a stress model in which the HPA axis is not desensitized after repeated stimulation. Repeated ipHS for 14 days had no effect on CRH hnRNA levels but increased CRH mRNA levels by 42.2%. Parallel with preserved plasma corticosterone responses to repeated ipHS, CRH hnRNA responses and CRH mRNA response to the last injection in repeatedly stressed rats were identical to those in naive rats (8.6-fold increase by 15 min, returning to basal level by 1 h). Parvocellular VP hnRNA responses to a single ipHS were slower and more prolonged than for CRH (7.1-, 11.5-, 9.8- and 4.6-fold by 1, 2, 4 and 6 h), and VP mRNA levels increased by 4 h and remained elevated 12 h later. Parvocellular VP hnRNA was at basal levels after 14 days ipHS, but VP mRNA levels remained elevated as during acute stimulation. Despite high basal mRNA levels, VP hnRNA responses to the last repeated ipHS were minor, suggesting increases in mRNA stability. This study shows that conserved pituitary ACTH responsiveness to a homotypical repeated stress is associated with the ability of parvocellular PVN neurons to increase CRH transcription after repeated stimulation.

Maternal deprivation effect on the infant's neural stress markers is reversed by tactile stimulation and feeding but not by suppressing corticosterone

After 24 hr of maternal deprivation, significant elevations in ACTH and the naturally occurring glucocorticoid corticosterone (CORT) are observed during the stress-hyporesponsive period. The deprived pups also showed in the paraventricular nucleus (PVN) a marked increase of stress-induced c-fos mRNA and a reduction of corticotropin-releasing hormone (CRH) and glucocorticoid receptor (GR) mRNA; in hippocampal CA1, a reduction of the mineralocorticoid receptor (MR) and GR was observed. Here, we examined whether these changes are reversed by (1) preventing the elevations of CORT characteristic for the 11-d-old deprived pups by administering the synthetic glucocorticoid dexamethasone (DEX); or (2) reinstating some aspects of maternal behavior. The pups were either (1) left undisturbed, (2) stroked, or (3) stroked and episodically fed by cheek cannulation. At postnatal day 12, peripheral and neural stress markers were measured. Nondeprived animals served as controls. Experiment 1 demonstrates that although CORT was kept low by DEX, the central effects on CORT receptors, CRH, and c-fos mRNA were still present, except for MR in hippocampal CA1. Experiment 2 shows that stroking alone prevented the stress-induced rise in ACTH and c-fos mRNA and in the reduction in CRH and MR mRNA. In pups that were fed and stroked, CORT and GR mRNA resembled nondeprived controls. In conclusion, the changes in peripheral endocrine responses and in the brain cannot be attributed to the effect of elevated CORT concentrations, which are characteristic of the maternally deprived neonate. However, reinstating some components of the dams' nurturing behavior can reverse the effects evoked by maternal deprivation.

Early vs. late maternal deprivation differentially alters the endocrine and hypothalamic responses to stress

Twenty-four hours of maternal deprivation results in persistent changes in the ACTH response to mild stress. These effects are dependent on the age of the neonate at the time of deprivation. Pups that were separated from the dam at postnatal days (pnd) 3-4 showed an enhanced stress-induced ACTH response at age 20, while pups deprived at pnd 11-12 displayed an attenuated ACTH response to stress at that time. The present study was designed to test the hypothesis that the immediate effects of deprivation at pnd 3 vs. pnd 11 would provide an explanation for these paradoxical effects observed at day 20. For this purpose, we measured the basal and the stress-induced ACTH and corticosterone (CORT) response at days 4 and 12, following 24 h of maternal deprivation. Furthermore, we examined whether similar differences in c-fos and CRH mRNA expression in the paraventricular nucleus (PVN) accompanied the differences in response characteristics of ACTH at pnd 20. The results indicate that changes in the ACTH and CORT responses were minimal after 24 h of maternal deprivation at day 4, whereas these hormones were markedly elevated following deprivation at day 12. The persistent effects also showed age-dependency: pups deprived early showed at pnd 20 an exaggerated ACTH response. Late deprived juveniles exhibited an attenuated ACTH response to stress at pnd 20 while in both conditions the CORT response was not different from the non-deprived litter mates. These persistent endocrine changes were accompanied by the changes in the neural stress markers. The expressions of c-fos and CRH mRNA in the PVN were at pnd 20 significantly greater in their controls in early-deprived animals. The late deprived juveniles showed a reduced response in these neural markers. In conclusion, the persistent alterations in ACTH are reflected by changes in c-fos and CRH mRNA, but these changes in endocrine and in neural stress markers do not appear to be related to any of the hormonal changes that occur at the time of maternal deprivation.

Co-localization of corticotropin-releasing hormone with glutamate decarboxylase and calcium-binding proteins in infant rat neocortical interneurons

Corticotropin releasing hormone (CRH) has been localized to interneurons of the mammalian cerebral cortex, but these neurons have not been fully characterized. The present study determined the extent of co-localization of CRH with glutamate decarboxylase (GAD) and calcium-binding proteins in the infant rat neocortex using immunocytochemistry. CRH-immunoreactive (ir) neurons were classified into two major groups. The first group was larger and consisted of densely CRH-immunostained small bipolar cells, predominantly localized to layers II and III. The second group of CRH-ir cells was lightly labeled and included multipolar neurons mainly found in deep cortical layers. Co-localization studies indicated that the vast majority of CRH-ir neurons, including both bipolar and multipolar types, was co-immunolabeled for GAD-65 and GAD-67. Most multipolar, but only some bipolar, CRH-ir neurons also contained parvalbumin, while CRH-ir neurons rarely contained calbindin or calretinin. These results indicate that virtually all CRH-ir neurons in the rat cerebral cortex are GABAergic. Furthermore, since parvalbumin is expressed by cortical basket and chandelier cells, the co-localization of CRH and parvalbumin suggests that some cortical CRH-ir neurons may belong to these two cell types.

Corticotropin releasing factor mRNA expression in the hypothalamic paraventricular nucleus and the central nucleus of the amygdala is modulated by repeated acute stress in the immature rat

Age-appropriate acute stress, such as cold exposure, provokes the secretion of corticotropin releasing factor (CRF) from the hypothalamus, leading to a robust increase of plasma corticosterone in the immature rat. This activation of the hypothalamic-pituitary-adrenal system is accompanied by a stress-induced increase of steady-state CRF-mRNA expression in the hypothalamic paraventricular nucleus (PVN). In the current study, we analysed changes in CRF-mRNA expression in the PVN and the central nucleus of the amygdala (ACe) in the immature rat in response to a single episode of cold stress and three repeated exposures to this same stressor. CRF-mRNA expression in the PVN increased after a single, but not repeated exposures to cold stress, while repeated acute stress increased the content of the CRF peptide in the anterior hypothalamus. In the ACe, repeated episodes of cold stress resulted in increased expression of CRF-mRNA. These findings indicate a differential regulation of CRF gene expression in the PVN and ACe of the immature rat by single and repeated acute stress.

Stress-induced changes of gene expression in the paraventricular nucleus are enhanced in spontaneously hypertensive rats

Heightened hypothalamic-pituitary-adrenal (HPA) axis responses have been implicated in hypertension in the spontaneously hypertensive rat (SHR), but the exact mechanisms involved are poorly understood. To determine changes in gene expression in SHR in the paraventricular nucleus (PVN), stress-induced accumulation of CRF, CRF type 1 receptor (CRFR-1) genes, and immediate-early genes were examined using in situ hybridization in young (5 weeks old) and adult (12 weeks old) stroke-prone SHR (SHRSP), compared with normotensive Wistar Kyoto (WKY) rats. Restraint stress-induced accumulation of c-fos, jun B, and NGFI-B mRNA, and CRF hnRNA in the PVN was significantly higher in young and adult SHRSP than in WKY rats at 30 min, except for c-fos in young rats. CRFR-1 mRNA expression in the PVN was also significantly higher in adult SHRSP than in WKY rats at 120 min after stress onset. CRF mRNA was increased in response to stress in young SHRSP. The basal CRF mRNA level in the PVN was significantly lower in adult SHRSP than in WKY rats. Young SHRSP exhibit greater ACTH responses to stress without significant changes in plasma corticosterone concentrations. The adult SHRSP exhibited lower baseline concentrations of corticosterone and similar corticosterone response to stress with enhanced secretion of ACTH. Overall, these results demonstrated that stress-induced activation of immediate early genes and CRF gene transcription in the PVN, and ACTH secretion is enhanced in early hypertensive, young, and adult SHRSP, suggesting that they are probably not the result of chronic alterations in blood pressure. The abnormal hypothalamic-pituitary response to stress thus appears to be related to the development of hypertension.

Development neurobiology of the stress response: multilevel regulation of corticotropin-releasing hormone function

The ability to respond to adverse environmental cues is present in the neonatal and infant rat, although in an immature form: A number of laboratories have demonstrated stress-induced elevations of plasma glucocorticoids during the first two postnatal weeks. The limbic and hypothalamic mechanisms controlling the hormonal stress-response during this period are not fully understood and are, therefore, the focus of this report. Both hypothalamic corticotropin-releasing hormone (CRH) and vasopressin contribute to the release of ACTH from the pituitary in the adult. The relative roles of these two peptides during the neonatal (first week) and infant (second week) developmental period, are controversial. Evidence is presented that argues strongly for a major role for CRH. Up-regulation of hypothalamic CRH synthesis is a major component in the mature stress response. CRH-mRNA levels in the hypothalamic PVN are increased with cold stress by ninth postnatal day, but not during the first postnatal week. Further, down-regulation of CRH gene expression by glucocorticoids (GC) constitutes a critical "shut-down" mechanism for the hormonal stress response. In vivo and in vitro experiments supporting the "immaturity" of GC feedback on CRH synthesis during the first postnatal week are described. CRH-mediated neurotransmission, in both the endocrine and neuronal effector arms of the response to stress may be modulated via alteration of receptor number. The first member of the CRH receptor family, CRF1, probably mediates the neuroendocrine effects of CRH. The developmental profile of CRF1-mRNA reveals several distinctive spatial and temporal patterns. In the hippocampal CA1, CA2, and CA3a peak (300-600% adult values) CRF1-mRNA is found on postnatal day 6. In the amygdala, CRH receptor mRNA levels are maximal on the ninth postnatal day (at 180% of adult values). In cortex, a steady decline from high postnatal day 2 levels results in adult levels by 12. These findings demonstrate distinct, regional, age-specific control of the synthesis of CRF1. Receptor expression profile may provide important information regarding modulation of the age-specific roles of CRH in different regions. For example, a high ratio of hippocampus/amygdala receptors may preferentially activate negative hippocampal input to the hypothalamus during the neonatal period. Additionally, increased CRH receptor mRNA in the infant compared with the adult provides a mechanism for enhanced excitatory effect of the peptide at this age. In conclusion, increasing evidence exists for multiple control points of the early postnatal response and adaptation to stress. CRH synthesis in hypothalamus and amygdala, its sensitivity to GC feedback, and the abundance and distribution of at least two distinct CRH receptors in the limbic central nervous system and the pituitary are developmentally regulated. All serve as control points permitting an effective endocrine, autonomic, and behavioral response to stressful environmental cues.

Evidence for arginine vasopressin as the primary activator of the HPA axis during adjuvant-induced arthritis

1. Adjuvant-induced arthritis (AA) is an experimental inflammation of the joints that results in chronic activation of the hypothalamo-pituitary-adrenal (HPA) axis. 2. In this study the role of hypothalamic corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP) in the regulation of the HPA axis in this condition both in Sprague-Dawley (SD), and Piebald-Viral-Glaxo (PVG) rats has been further characterized. 3. The increase in AVP peptide content of portal blood (as early as day 11), just prior to the onset of arthritis is confirmed and further increases, peaking at day 16 are shown, coincident with the progression of inflammation in the PVG rats. 4. The increase in AVP is associated with a significant increase in the expression of AVP but not CRF mRNAs in the medial parvocellular division of the hypothalamic paraventricular nucleus (PVN) of arthritic SD rats. 5. In the presence of maximal inflammation of SD rats there was a significant decrease in the maximum binding of [125I]-Tyr-oCRF to anterior pituitary membranes, whereas AVP receptor concentration in anterior pituitary membranes from both PVG and SD rats showed a significant increase with respect to controls. 6. The basal adrenocorticotrophin (ACTH) secretion in vitro was similar in both control and arthritic SD rats but that from arthritic PVG rat pituitaries was significantly greater than the respective controls (436 +/- 91 v 167 +/- 23 pg/tube). The ACTH response of pituitaries of arthritic PVG rats to CRF or the combination of CRF and AVP was significantly higher compared with the controls, although the ACTH response of arthritic SD rat pituitaries was unchanged. 7. The results are consistent with the view that activation of the parvocellular vasopressin system has an important role in the adaptation of the HPA axis to experimentally-induced chronic stress of arthritis.

Effects of maternal and sibling deprivation on basal and stress induced hypothalamic-pituitary-adrenal components in the infant rat

Prolonged maternal deprivation during early infancy increases basal- and stress-induced corticosterone (CORT) levels, but the underlying mechanism is not clear. In general, stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, with secretion and compensatory synthesis of hypothalamic cortcotropin-releasing hormone (CRH). In the infant rat, we have demonstrated that maximally tolerated acute cold stress induced a robust elevation of plasma CORT throughout the first 2 postnatal weeks. However CRH messenger RNA (CRH-mRNA) abundance 4 h subsequent to cold stress was enhanced only in rats aged 9 days or older. This suggests a developmental regulation of the CRH component of the HPA-response to this stressor. The present study examined whether increased basal and cold stress-induced CORT levels after 24 h of maternal deprivation were due to enhanced CRH-mRNA abundance in the hypothalamic paraventricular nucleus (PVN). CRH-mRNA abundance, and basal- and cold-induced plasma CORT levels were measured in maternally deprived 6 and 9-day-old pups compared to non-deprived controls. Maternal deprivation increased basal and cold-induced CORT levels on both 6 and 9-day-old rats. CRH-mRNA abundance in the PVN of deprived rats did not differ from that in non-deprived rats. Our results indicate that the enhanced basal and stress-induced plasma CORT observed after 24 h maternal deprivation is not due to increased CRH-mRNA abundance in the PVN.

Peptide-induced infant status epilepticus causes neuronal death and synaptic reorganization

Status epilepticus (SE) produced by excitatory amino acids is a well established model in adult rodents. Limbic neuronal degeneration and synaptic reorganization observed after, for example, kainic acid-induced SE are considered relevant to human epilepsy. Kainic acid also produces severe seizures in infant rats, but neuronal injury and sprouting have not been demonstrated. The results of the present study show that corticotropin releasing hormone (CRH)-induced SE causes limbic neuronal death and reorganization in infant rats. In adults, CRH produced seizures at much higher doses, and no neuronal degeneration. As a modulator of the CNS stress response, CRH is activated in various 'stressful' circumstances. Its age-dependent ability to kill neurons represents a unique form of cell death potentially important in human medicine.

Corticotropin-releasing hormone mediates the response to cold stress in the neonatal rat without compensatory enhancement of the peptide's gene expression

A variety of stressors activate the hypothalamic-pituitary-adrenal axis, with secretion and compensatory enhanced synthesis of hypothalamic corticotropin-releasing hormone (CRH). Whether CRH is a major effector in the stress response of the neonatal rat and whether the peptide's gene expression is subsequently up-regulated are not fully understood. We studied the effect of cold-separation stress on plasma corticosterone (CORT) levels and CRH messenger RNA (CRH-mRNA) abundance in the paraventricular nucleus. Rats (4-16 days old) were subjected to maximal tolerated cold-separation. CORT and CRH-mRNA abundance were measured before and at several time points after stress. Cold-separation stress resulted in a significant plasma CORT increase in all age groups studied. This was abolished by the administration of an antiserum to CRH on both postnatal days 6 and 9. CRH-mRNA increased in rats aged 9 days or older, but not in 6-day-old rats, by 4 h after stress. These results suggest the presence of robust CRH-mediated adrenal responses to cold-separation stress in neonatal rats. Before postnatal day 9, however, the compensatory increase in CRH-mRNA abundance is minimal.