Prenatal exposure to dexamethasone alters hippocampal drive on hypothalamic-pituitary-adrenal axis activity in adult male rats

Glucocorticoids are essential for normal hypothalamic-pituitary-adrenal (HPA) axis activity; however, recent studies warn that exposure to excess endogenous or synthetic glucocorticoid during a specific period of prenatal development adversely affects HPA axis stability. We administered dexamethasone (DEX) to pregnant rats during the last week of gestation and investigated subsequent HPA axis regulation in adult male offspring in unrestrained and restraint-stressed conditions. With the use of real-time PCR and RIA, we examined the expression of regulatory genes in the hippocampus, hypothalamus, and pituitary, including corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), glucocorticoid receptors (GR), mineralcorticoid receptors (MR), and 11-beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1), as well as the main HPA axis hormones, adrenal corticotropic hormone (ACTH) and corticosterone (CORT). Our results demonstrate that the DEX-exposed group exhibited an overall change in the pattern of gene expression and hormone levels in the unrestrained animals. These changes included an upregulation of CRH in the hypothalamus, a downregulation of MR with a concomitant upregulation of 11beta-HSD-1 in the hippocampus, and an increase in circulating levels of both ACTH and CORT relative to unrestrained control animals. Interestingly, both DEX-exposed and control rats exhibited an increase in pituitary GR mRNA levels following a 1-h recovery from restraint stress; however, the increased expression in DEX-exposed rats was significantly less and was associated with a slower return to baseline CORT compared with controls. In addition, circulating levels of ACTH and CORT as well as hypothalamic CRH and hippocampal 11beta-HSD-1 expression levels were significantly higher in the DEX-exposed group compared with controls following restraint stress. Taken together, these data demonstrate that late-gestation DEX exposure in rats is associated with persistent changes in both the modulation of HPA axis activity and the HPA axis-mediated response to stress.     

Role of interleukin-1 in stress responses

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.     

Effect of cyclooxygenase inhibitors on the CRH-induced pituitary-adrenocortical activity during crowding stress.

The aim of the present study was to determine the effect of social stress and significance of prostaglandins (PG) generated by constitutive and inducible cyclooxygenase (COX-1 and COX-2) in the stimulation of hypothalamic-pituitary-adrenal (HPA) axis by corticotropin releasing hormone (CRH) under basal and social crowding stress conditions. The stressed rats were crowded in groups of 24 to a cage for 3 or 7 days, whereas the control animals were haused in groups of 7 to a cage of the same size. The activity of HPA axis was determined by measuring plasma ACTH and serum corticosterone levels 1 h after i.p. CRH administration. Inhibitors of COX-1, piroxicam (0.2, 2.0, and 5.0 mg/kg), and COX-2, compound NS-398 (0.2 and 2.0 mg/kg), were administered i.p. 15 min prior to CRH (0.1 microg/kg i.p.) to control or crowded rats. The obtained results indicate that social stress for 3 and 7 days markedly intensifies the stimulatory action of CRH on ACTH secretion. Neither piroxicam nor NS-398 induce any significant effect on the CRH-elicited ACTH and corticosterone secretion in non-stressed or crowded rats. Therefore, PG generated by COX-1 or COX-2 do not participate to a significant extent in the stimulation of HPA axis by CRH under either basal conditions or during crowding stress. These results also indicate that the stimulatory action of CRH on ACTH secretion is not only completely resistant to desensitization but is sensitized during social crowding stress. The results contrast with a significant involvement of PG in the vasopressin-induced stimulation of HPA response during crowding stress.     

Ovine corticotropin-releasing hormone stimulation test in patients with chronic renal failure: pharmacokinetic properties, and plasma adrenocorticotropic hormone and serum cortisol responses

The data on the status of the hypothalamic-pituitary-adrenal (HPA) axis in haemodialysis (HD) patients are conflicting. Moreover, a state reminiscent of Cushing's syndrome has been reported in this group of patients. Corticotropin-releasing hormone (CRH), that is produced by the hypothalamus and modulates the secretion of adrenocorticotropic hormone (ACTH), has been shown to be useful as a provocative test of the HPA axis. We investigated the effect of exogenous ovine CRH (oCRH) on plasma levels of ACTH and cortisol in 13 chronic HD patients. The plasma concentrations of immunoreactive CRH following oCRH administration were similar in patients and controls. In all patients, oCRH given intravenously as bolus injection caused a further increase in the already elevated levels of cortisol. The mean basal plasma levels of ACTH were within the normal range. There was, however, a blunted ACTH response to oCRH. We conclude that the HPA axis in chronic HD patients retains the ability to respond to exogenous oCRH. The patterns of the ACTH and cortisol response to this peptide resemble those observed in chronic stress (depression, anorexia nervosa). Besides, the kinetics of disappearance of oCRH indicate that the kidney may not be the major organ that metabolizes oCRH.     

Ghrelin is released from rat hypothalamic explants and stimulates corticotrophin-releasing hormone and arginine-vasopressin.

Ghrelin and synthetic growth hormone secretagogues have diverse effects on the hypothalamus including effects on appetite and the growth hormone axis as well as on the hypothalamus-pituitary-adrenal (HPA) axis. We previously studied the effect of synthetic growth hormone secretagogues on CRH and AVP release from rat hypothalami in vitro, and now report on the effects of ghrelin on CRH and AVP release. The ghrelin protein content and ghrelin output from rat hypothalamic explants was measured using a specific novel ghrelin enzyme immunoassay. The effect of 10(-8) M to 10(-6) M ghrelin on CRH and AVP release was studied in the rat hypothalamic explants, where stimulation with des-octanoyl ghrelin was used as control. The presence of both ghrelin mRNA and protein could be shown in the rat hypothalamus. Ghrelin output was detected in the incubation fluid of rat hypothalamic explants and could be stimulated with high potassium concentrations. Our data also demonstrated a dose-dependent effect of ghrelin on both CRH and AVP release, while des-octanoylated ghrelin showed no effect on either peptide. In summary, the current data suggest that ghrelin is expressed in the hypothalamus both at RNA and the protein levels. Ghrelin stimulates the HPA axis in the rat via stimulation of both CRH, and particularly, AVP release from the hypothalamus. The local autocrine/paracrine and endocrine effects of ghrelin in the hypothalamus could influence all the hormonal systems involved in ghrelin effects, including growth hormone release, the HPA axis and appetite.     

穹窿切断对大鼠下丘脑CRH表达的影响

目的观察穹窿切断对大鼠下丘脑促肾上腺皮质激素释放激素(CRH)表达的影响,探讨海马对HPA轴的抑制作用是否通过穹窿介导。方法成年健康雄性Wistar大鼠80只,随机分为穹窿切断组和假手术组,再分为0d、4d、7d、10d组,每组10只。建立大鼠穹窿切断模型,采用免疫组织化学和Westernblot技术检测穹窿切断组0d、4d、7d、10d时下丘脑CRH的表达变化和分布规律,并以假手术组相应时间段作为对照。结果穹窿切断组于7d时CRH表达升高,10d时升高显著。假手术组下丘脑仅有少量CRH表达。结论穹窿切断使CRH表达升高,HPA轴活动增强,海马对HPA轴的抑制作用减弱,揭示海马是通过穹窿纤维对HPA轴发挥抑制作用。     

Suppression of the HPA axis during extrahepatic biliary obstruction induces cholangiocyte proliferation in the rat

Cholestatic patients often present with clinical features suggestive of adrenal insufficiency. In the bile duct-ligated (BDL) model of cholestasis, the hypothalamic-pituitary-adrenal (HPA) axis is suppressed. The consequences of this suppression on cholangiocyte proliferation are unknown. We evaluated 1) HPA axis activity in various rat models of cholestasis and 2) effects of HPA axis modulation on cholangiocyte proliferation. Expression of regulatory molecules of the HPA axis was determined after BDL, partial BDL, and α-naphthylisothiocyanate (ANIT) intoxication. The HPA axis was suppressed by inhibition of hypothalamic corticotropin-releasing hormone (CRH) expression by central administration of CRH-specific Vivo-morpholinos or by adrenalectomy. After BDL, the HPA axis was reactivated by 1) central administration of CRH, 2) systemic ACTH treatment, or 3) treatment with cortisol or corticosterone for 7 days postsurgery. There was decreased expression of 1) hypothalamic CRH, 2) pituitary ACTH, and 3) key glucocorticoid synthesis enzymes in the adrenal glands. Serum corticosterone and cortisol remained low after BDL (but not partial BDL) compared with sham surgery and after 2 wk of ANIT feeding. Experimental suppression of the HPA axis increased cholangiocyte proliferation, shown by increased cytokeratin-19- and proliferating cell nuclear antigen-positive cholangiocytes. Conversely, restoration of HPA axis activity inhibited BDL-induced cholangiocyte proliferation. Suppression of the HPA axis is an early event following BDL and induces cholangiocyte proliferation. Knowledge of the role of the HPA axis during cholestasis may lead to development of innovative treatment paradigms for chronic liver disease.     

Effects of cortisol treatment on brain and adrenal corticotropin-releasing hormone (CRH) content and other parameters regulated by CRH

Corticotropin-releasing hormone (CRH) has been found in both hypothalamic and extrahypothalamic sites of the brain and also in the adrenal medulla. To study the timing and location of delayed glucocorticoid action in rats, we measured the effects of 2-day and 7-day cortisol treatment on immunoreactive CRH concentrations in hypothalamus, cerebral cortex, hippocampus, cerebellum, and adrenal gland. The activity of the hypothalamo-pituitary-adrenal (HPA) axis and the sympathoadrenal system were also measured. Studies were carried out both in the afternoon and/or in the morning, to get information about possible circadian changes. CRH contents were not changed in any brain areas studied, except there was a trend of decrease in the hypothalamus compared to vehicle in the afternoon due to the lack of circadian increase after 7-day cortisol treatment. Pituitary ACTH content decreased significantly after 7-day treatment, while beta-endorphin did not. Plasma levels of ACTH, corticosterone, norepinephrine and epinephrine and adrenal ACTH and beta-endorphin contents decreased after 2-day, adrenal CRH content after 7-day treatment with cortisol. Our findings suggest, that chronic cortisol treatment inhibits the circadian activation of the HPA axis at all levels but has variable effects on baseline measures because it causes different changes in release and synthesis at different sites.     

CRH stimulation of corticosteroids production in melanocytes is mediated by ACTH

The response to systemic stress is organized along the hypothalamic-pituitary-adrenal axis (HPA), whereas the response to a peripheral stress (solar radiation) is mediated by epidermal melanocytes (cells of neural crest origin) responsible for the pigmentary reaction. Melanocytes express proopiomelanocortin (POMC), corticotropin-releasing hormone (CRH), and CRH receptor-1 (CRH-R1) and can produce corticosterone. In the present study, incubation of normal epidermal melanocytes with CRH was found to trigger a functional cascade structured hierarchically and arranged along the same algorithm as in the HPA axis: CRH activation of CRH-R1 stimulated cAMP accumulation and increased POMC gene expression and production of ACTH. CRH and ACTH also enhanced production of cortisol and corticosterone, and cortisol production was also stimulated by progesterone. The chemical identity of the cortisol was confirmed by liquid chromatography-mass spectrometry (LC/MS2) with [corrected] mass spectrometry-mass spectrometry analyses. POMC gene silencing abolished the stimulatory effect of CRH on corticosteroid synthesis, indicating that this is indirect and mediated via production of ACTH. Thus the melanocyte response to CRH is highly organized along the same functional hierarchy as the HPA axis. This pattern demonstrates the fractal nature of the response to stress with similar activation sequence at the single-cell and whole body levels.     

HPA-axis responses during experimental colitis in the rat

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

睡眠中间断低氧对大鼠下丘脑-垂体-肾上腺轴和生长激素的影响

目的:探讨睡眠中间断低氧对大鼠下丘脑-垂体-肾上腺轴和生长激素水平的影响.方法:大鼠分别给予吸入空气,持续低氧和间断低氧气体,在1 d,3 d,7 d和30 d后测定下丘脑促肾上腺皮质激素释放激素(CRH)和生长激素释放激素(GHRH)mRNA水平,并测定30d后血浆CRH,GHRH,促肾上腺皮质激素(ACTH)和皮质酮水平,分析其间的变化关系.结果:与对照组比较,在低氧后1 d,3 d,7 d后大鼠下丘脑CRH mRNA升高,GHRH mRNA降低,在30 d后,间断低氧组下丘脑CRH mRNA升高,GHRH mRNA降低,而持续低氧组则接近正常.间断低氧30 d后,血浆CRH、ACTH,皮质酮均升高,GHRH降低,而生长激素没有明显变化.结论:大鼠睡眠中慢性间断低氧可以引起下丘脑-垂体-肾上腺轴激素水平升高,反馈调节紊乱,可引起GHRH分泌抑制.     

Regulation of Hypothalamo-Pituitary-Adrenocortical Responses to Stressors by the Nucleus of the Solitary Tract/Dorsal Vagal Complex

Hindbrain neurons in the nucleus of the solitary tract (NTS) are critical for regulation of hypothalamo-pituitary-adrenocortical (HPA) responses to stress. It is well known that noradrenergic (as well as adrenergic) neurons in the NTS send direct projections to hypophysiotropic corticotropin-releasing hormone (CRH) neurons and control activation of HPA axis responses to acute systemic (but not psychogenic) stressors. Norepinephrine (NE) signaling via alpha1 receptors is primarily excitatory, working either directly on CRH neurons or through presynaptic activation of glutamate release. However, there is also evidence for NE inhibition of CRH neurons (possibly via beta receptors), an effect that may occur at higher levels of stimulation, suggesting that NE effects on the HPA axis may be context-dependent. Lesions of ascending NE inputs to the paraventricular nucleus attenuate stress-induced ACTH but not corticosterone release after chronic stress, indicating reduction in central HPA drive and increased adrenal sensitivity. Non-catecholaminergic NTS glucagon-like peptide 1/glutamate neurons play a broader role in stress regulation, being important in HPA activation to both systemic and psychogenic stressors as well as HPA axis sensitization under conditions of chronic stress. Overall, the data highlight the importance of the NTS as a key regulatory node for coordination of acute and chronic stress.     

Upregulation of CRH gene expression and downregulation of arginine vasopressin gene expression in the hypothalamus of bilateral nephrectomized rats

The expression of the corticotropin-releasing hormone (CRH) gene and the arginine vasopressin (AVP) gene in the hypothalamus examined in bilateral nephrectomized rats by in situ hybridization histochemistry. The expression of the CRH gene was significantly increased in the parvocellular part of the paraventricular nucleus (PVN) 12 and 20 h after bilateral nephrectomy in comparison with that after sham operation. The plasma concentration of adrenocorticotropic hormone (ACTH) in nephrectomized rats was significantly higher than that in sham operated rats 20 h after surgery. In contrast, the expression of the AVP gene in both the parvocellular and magnocellular parts of the PVN and throughout the supraoptic nucleus (SON) was significantly decreased 20 h after bilateral nephrectomy in comparison with that after sham operation. These results suggest that nephrectomy-induced upregulation of the CRH gene with elevation of plasma ACTH may be due to the activation of the hypothalamo-pituitary adrenal (HPA) axis.     

Developmental expression of corticotropin releasing hormone messenger RNA and peptide in rat hypothalamus

We have examined corticotropin releasing hormone (CRH), arginine vasopressin (AVP) and somatostatin (SOM) mRNA expression and peptide content in the rat hypothalamus from day 20 of fetal life (F20) to the fifteenth day of postnatal life (P15). During this time, hypothalamic CRH mRNA levels did not change significantly, whereas there was a gradual six-fold rise in CRH peptide levels. AVP mRNA levels fell three-fold between F20 and P1 and increased six-fold between P1 and P15. AVP peptide levels increased three-fold, with most of the rise occurring between P1 and P15. From F20 to P15, SOM mRNA and peptide levels rose four- and eight-fold, respectively. The changes in the levels of these three hypothalamic gene products correlate with the previously described alterations in the responsiveness of the HPA axis observed in fetal and early postnatal rats, suggesting a role for these neuropeptides in the modulation of the HPA axis during this developmental period.     

17β-Estradiol is required for the sexually dimorphic effects of repeated binge-pattern alcohol exposure on the HPA axis during adolescence

Alcohol consumption during adolescence has long-term sexually dimorphic effects on anxiety behavior and mood disorders. We have previously shown that repeated binge-pattern alcohol exposure increased the expression of two critical central regulators of stress and anxiety, corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), in adolescent male rats. By contrast, there was no effect of alcohol on these same genes in adolescent females. Therefore, we tested the hypothesis that 17β-estradiol (E(2)), the predominant sex steroid hormone in females, prevents alcohol-induced changes in CRH and AVP gene expression in the paraventricular nucleus (PVN) of the hypothalamus. To test this hypothesis, postnatal day (PND) 26 females were ovariectomized and given E(2) replacement or cholesterol as a control. Next, they were given an alcohol exposure paradigm of 1) saline alone, 2) acute (single dose) or 3) a repeated binge-pattern. Our results showed that acute and repeated binge-pattern alcohol treatment increased plasma ACTH and CORT levels in both E(2)- and Ch-treated groups, however habituation to repeated binge-pattern alcohol exposure was evident only in E(2)-treated animals. Further, repeated binge-pattern alcohol exposure significantly decreased CRH and AVP mRNA in Ch-, but not E(2)-treated animals, which was consistent with our previous observations in gonad intact females. We further tested the effects of E(2) and alcohol treatment on the activity of the wild type CRH promoter in a PVN-derived neuronal cell line. Alcohol increased CRH promoter activity in these cells and concomitant treatment with E(2) completely abolished the effect. Together our data suggest that E(2) regulates the reactivity of the HPA axis to a repeated stressor through modulation of the habituation response and further serves to maintain normal steady state mRNA levels of CRH and AVP in the PVN in response to a repeated alcohol stressor.     

Repeated stress alters the ability of nicotine to activate the hypothalamic-pituitary-adrenal axis

Acute nicotine administration has been shown to activate the hypothalamic-pituitary-adrenal (HPA) axis and stimulate secretion of adrenocorticotrophic hormone (ACTH), corticosterone/cortisol and beta-endorphin (beta-END) in both rodents and humans, raising the possibility that activation of the HPA axis by nicotine may mediate some of the effects of nicotine. Since stress can increase the risk of drug use and abuse, we hypothesized that repeated stress would increase the ability of nicotine to stimulate the secretion of HPA hormones. To test our hypothesis, mice were exposed to repeated stress (swimming in 15 degrees C water for 3 min/day for 5 days) and killed 15 min after injection of saline or nicotine (0.1 mg/kg, s.c.). Repeated exposure to stress increased the ability of nicotine to stimulate plasma ACTH (p<0.05) and beta-END (p<0.05), but not corticosterone secretion. In contrast, repeated exposure to stress increased the post-saline injection levels of corticosterone (p<0.05), but not ACTH and beta-END. The present results suggest that chronic stress leads to an enhanced sensitivity of some components of the HPA axis to a subsequent nicotine challenge.     

Activity of the hypothalamic–pituitary–adrenal axis of prenatally stressed male rats in experimental model of depression

Changes in activity of the hypothalamic–pituitary–adrenal (HPA) axis were examined in adult, prenatally stressed male rats in the experimental depression model of ‘learned helplessness’. It was shown that in males descending from intact mothers a depressive-like state was accompanied by an increase in activity of the entire HPA axis. Namely, expression of corticotropin-releasing hormone (CRH) in the hypothalamic paraventricular nucleus (PVN) increased coupled to a rise in plasma levels of ACTH and corticosterone as well as in adrenal weight. At the same time, in males born to mothers who suffered stress during the last week of pregnancy a decrease was detected in activity both of the central (hypothalamus) and peripheral (adrenal cortex) parts of this regulatory hormonal axis, analogous to that we revealed previously in the ‘stress–restress’ experimental model. It is concluded that prenatal stress modifies the sensitivity of animals to inescapable intense stress impacts, as manifested in the specific pattern of HPA axis activity after stressing.