Hypothalamic-pituitary-adrenocortical Axis Hyperactivity Research Articles

Paeoniflorin Alleviates Anxiety and Visceral Hypersensitivity via HPA Axis and BDNF/TrkB/PLCγ1 Pathway in Maternal Separation-induced IBS-like Rats.

Irritable Bowel Syndrome (IBS) is a prevalent gastrointestinal disorder that significantly diminishes the quality of life for affected individuals. The pathophysiology of IBS remains poorly understood, and available therapeutic options for IBS are limited. The crucial roles of brain-gut interaction, which is mediated by the Hypothalamic-Pituitary-Adrenocortical (HPA) axis and the autonomic nervous system in IBS, have attracted increasing attention. The objective of this study was to examine the impact of paeoniflorin (PF) on anxiety and visceral hypersensitivity in maternal separation-induced IBS-like rats. The IBS-like rat model was established through the implementation of Maternal Separation (MS) and subsequently subjected to various doses of PF administered via oral gavage for 14 days. Anxiety-like behavior was evaluated using the Open Field Test (OFT) and Elevated Plus Maze (EPM) test. The assessment of visceral sensitivity involved the utilization of the Abdominal Withdrawal Reflex (AWR) score and electromyographic (EMG) responses of the external oblique muscle in response to colorectal distention. The levels of adrenocorticotropic hormone (ACTH), corticosterone (CORT), and corticotrophin-releasing hormone (CRH) were examined by ELISA. Quantitative real-time PCR (qRT-PCR) and immunofluorescence were employed to detect the expressions of CRH receptors 1 (CRHR1) and 2 (CRHR2). Glucocorticoid receptors (GR), mineralocorticoid receptor (MR), brain-derived neurotrophic factor (BDNF), tyrosine receptor kinase B (TrkB), and phospholipase C γ1 (PLCγ1) were examined by Western blot. The results showed that MS induced anxiety-like behavior and visceral hypersensitivity, while PF treatment attenuated these changes. Furthermore, the HPA axis hyperactivity in MS rats was attenuated by PF treatment, indicated by reduced serum ACTH, CORT, and CRH levels and recovered hippocampal CRHR1 and GR expressions. In addition, PF inhibited BDNF/TrkB signaling by downregulating the protein levels of BDNF, TrkB, and phospho-PLCγ1 in the colon. These findings suggest that PF alleviated anxiety and visceral hypersensitivity in MS-induced IBS-like rats, which may be the modulation of HPA axis activity and BDNF/TrkB/PLCγ1 signaling pathway.

Ablation of NPFFR2 in Mice Reduces Response to Single Prolonged Stress Model

Mental stress is highly related to many clinical symptoms and disorders, as it activates the hypothalamic-pituitary-adrenocortical (HPA) axis to affect a wide variety of physiological functions. Furthermore, stress leads to the aberrations in HPA axis activity and disruptions of body homeostasis. It was previously shown that neuropeptide FF (NPFF) regulates the HPA axis through the activation of hypothalamus paraventricular nucleus (PVN), and genetic overexpression or pharmacological stimulation of NPFF receptor 2 (NPFFR2) triggers hyperactivity of HPA axis and suppresses behavioral correlates of emotion in mice. In this study, we further examined the role of NPFFR2 in stress response in mice by utilizing a single prolonged stress (SPS). SPS is considered a model of post-traumatic stress disorder (PTSD), and mice undergo physical restraint, forced swimming, and ether anesthesia within a day followed by social isolation for one week. NPFFR2 knockout B6 mice were generated by CRISPR/Cas9 technology and exposed to SPS. The NPFFR2 knockouts showed resistance to stress exposure-induced anxiety-like behaviors and HPA axis hyperactivity. Additionally, the hippocampal mRNA levels of glucocorticoid receptor and mineralocorticoid receptor were reduced in wild-type (WT) mice but not in NPFFR2 knockouts after stress exposure. Our data also suggested that NPFFR2 knockout mice have stronger negative feedback on the HPA axis after exposure to SPS. Mice with intra-PVN Npffr2 shRNA injection displayed trends toward resistance to SPS exposure in both behavioral and molecular assays. Together, our findings suggest that NPFFR2 may be a potential therapeutic target for disorders relating to stress/anxiety and HPA dysregulation.

Hyperactivity of Hypothalamic-Pituitary-Adrenal Axis Due to Dysfunction of the Hypothalamic Glucocorticoid Receptor in Sigma-1 Receptor Knockout Mice.

Sigma-1 receptor knockout (σ1R-KO) mice exhibit a depressive-like phenotype. Because σ1R is highly expressed in the neuronal cells of hypothalamic paraventricular nuclei (PVN), this study investigated the influence of σ1R deficiency on the regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Here, we show that the levels of basal serum corticosterone (CORT), adrenocorticotropic hormone (ACTH) and corticotrophin releasing factor (CRF) as well as the level of CRF mRNA in PVN did not significantly differ between adult male σ1R-KO mice and wild-type (WT) mice. Acute mild restraint stress (AMRS) induced a higher and more sustainable increase in activity of HPA axis and CRF expression in σ1R-KO mice. Percentage of dexamethasone (Dex)-induced reduction in level of CORT was markedly attenuated in σ1R−/− mice. The levels of glucocorticoid receptor (GR) and protein kinase C (PKC) phosphorylation were reduced in the PVN of σ1R-KO mice and σ1R antagonist NE100-treated WT mice. The exposure to AMRS in σ1R-KO mice induced a stronger phosphorylation of cAMP-response element binding protein (CREB) in PVN than that in WT mice. Intracerebroventricular (i.c.v.) injection of PKC activator PMA for 3 days in σ1R-KO mice not only recovered the GR phosphorylation and the percentage of Dex-reduced CORT but also corrected the AMRS-induced hyperactivity of HPA axis and enhancement of CRF mRNA and CREB phosphorylation. Furthermore, the injection (i.c.v.) of PMA in σ1R-KO mice corrected the prolongation of immobility time in forced swim test (FST) and tail suspension test (TST). These results indicate that σ1R deficiency causes down-regulation of GR by reducing PKC phosphorylation, which attenuates GR-mediated feedback inhibition of HPA axis and facilitates the stress response of HPA axis leading to the production of depressive-like behaviors.

Protein kinase C phosphorylates the cAMP response element binding protein in the hypothalamic paraventricular nucleus during morphine withdrawal

Exposure to drugs of abuse or stress results in adaptation in the brain involving changes in gene expression and transcription factors. Morphine withdrawal modulates gene expression through various second-messenger signal transduction systems. Here, we investigated changes in activation of the transcription factor, cAMP-response element binding protein (CREB), in the hypothalamic paraventricular nucleus (PVN) and the kinases that may mediate the morphine withdrawal-triggered activation of CREB and the response of the hypothalamic-pituitary-adrenocortical (HPA) axis after naloxone-induced morphine withdrawal. The effects of morphine dependence and withdrawal, phosphorylated CREB (pCREB), corticotrophin-releasing factor (CRF) expression in the PVN and HPA axis activity were measured using immunoblotting, immunohistochemistry and radioimmunoassay in controls and in morphine-dependent rats, withdrawn with naloxone and pretreated with vehicle, calphostin C, chelerythrine (inhibitors of protein kinase C (PKC) or SL-327 [inhibitor of extracellular signal regulated kinase (ERK) kinase]. In addition, changes in PKCα and PKCγ immunoreactivity were measured after 60 min of withdrawal. In morphine-withdrawn rats, pCREB immunoreactivity was increased within CRF immunoreactive neurons in the PVN and plasma corticosterone levels were raised. SL-327, at doses that reduced the augmented pERK levels in the PVN, did not attenuate the rise in pCREB immunoreactivity or plasma corticosterone secretion. In contrast, PKC inhibition reduced the withdrawal-triggered rise in pCREB, pERK1/2 and corticosterone secretion. PKC mediated, in part, both CREB activation and the HPA response to morphine withdrawal. The ERK kinase/ERK pathway might not be necessary for either activation of CREB or HPA axis hyperactivity.

The Role of the Forebrain Glucocorticoid Receptor in Acute and Chronic Stress

Previous work has implicated the forebrain glucocorticoid receptor (GR) in feedback regulation of the hypothalamic-pituitary-adrenocortical (HPA) axis. The present series of experiments used male mice with a targeted forebrain-specific GR knockout (in which forebrain includes the prefrontal cortex, hippocampus, and basolateral amygdala) to determine the role of forebrain GR in HPA axis regulation after stress. The data indicate that the forebrain GR is necessary for maintaining basal regulation of corticosterone secretion in the morning, confirming its role in HPA axis regulation. Our data further indicate that the forebrain GR is necessary for negative feedback after both mild and robust acute psychogenic stressors but not hypoxia, a systemic stressor. In contrast, forebrain-specific GR knockout and control mice exhibit equivalent HPA axis hyperactivity and facilitation after chronic variable stress, suggesting that changes in forebrain GR are not essential for chronic stress-induced pathology. These studies provide novel and definitive evidence that the forebrain GR selectively contributes negative feedback regulation of HPA axis responses to psychogenic stressors. Moreover, the data indicate that chronic stress-induced alterations in HPA axis function are mediated by mechanisms independent of the forebrain GR. Overall, the data are consistent with an essential role of the forebrain GR in coordinating endocrine responses to stimuli of a psychological origin.

Strain differences in hypothalamic–pituitary–adrenocortical axis function and adipogenic effects of corticosterone in rats

Our aim was to explore the nutritional consequences of functional variations in the hypothalamic-pituitary-adrenocortical (HPA) axis in rats. We first aimed to compare the HPA axis activity and reactivity to stress between Fischer 344 (F344) and LOU/C (LOU) strains that differ in food behavior and metabolism. When compared with F344 rats, LOU rats showed lower corticosterone (Cort) levels across the circadian cycle and after restraint stress. Then, we compared the effects of adrenalectomized (ADX) and Cort substitution after ADX on food intake, body weight gain, body composition, and biochemical parameters related to metabolism and HPA axis function between 1) the F344 rat strain, a model of HPA axis hyperactivity and hyperreactivity to stress, and characterized by a large fat mass; 2) the LOU strain, shown to exhibit hypoactive/hyporeactive HPA axis, reduced fat mass, and resistance to diet-induced obesity; and 3) the Lewis (LEW) strain, a third condition of fat deposition (high) related to HPA axis function (low activity/reactivity). The F344 and LEW strains exhibited classical responses to ADX and Cort. On the contrary, LOU rats showed an apparent insensitivity to ADX. Despite the highest effects of Cort related to glucocorticoid receptor (on thymus weight, corticotropin-releasing factor, or corticosteroid-binding globulin), the LOU strain was insensitive to Cort effects on body weight, liver, and abdominal fat mass. These characteristics could be involved in the leanness, insensitivity to diet-induced obesity, and healthy aging in LOU. Our study shows the relevance of comparing the F344, LOU, and LEW strains to cover the complexity of interactions between metabolism and HPA axis function.

Neuroendocrinological Mechanisms of Actions of Antidepressant Drugs

Noradrenaline or serotonin (5-HT) reuptake-inhibiting antidepressants such as reboxetine or citalopram acutely stimulate cortisol and adrenocorticotrophic hormone (ACTH) secretion in healthy volunteers, whereas mirtazapine acutely inhibits the ACTH and cortisol release, probably due to its antagonism at central 5-HT(2) and/or H(1) receptors. These differential effects of antidepressants on cortisol and ACTH secretion in healthy subjects after single administration are also reflected by their different time course in the down-regulation of hypothalamic-pituitary-adrenocortical (HPA) axis hyperactivity in depressed patients as assessed by serial dexamethasone (DEX)/corticotrophin-releasing hormone (CRH) tests: Reuptake-inhibiting antidepressants such as reboxetine gradually normalise HPA axis hyperactivity in depressed patients during several weeks of treatment via up-regulation of mineralocorticoid and glucocorticoid receptor function and by step-by-step restoration of the disturbed feedback control. By contrast, mirtazapine markedly reduces HPA axis activity in depressed patients within 1 week, but there is a partial re-enhancement of HPA hormone secretion after several weeks of therapy. In all studies performed to date, the short-term effects of daily treatment with antidepressants on the DEX/CRH test results are comparable in responders and nonresponders. Moreover, a reduction in HPA axis activity is not necessarily followed by a favourable clinical response and some depressed patients keep on showing nonsuppression in the DEX/CRH test despite clinical improvement. Therefore, the importance of HPA axis dysregulation for the short-term efficacy of antidepressants continues to be a matter of debate. However, there are convincing data suggesting that persisting nonsuppression in the DEX/CRH test despite clinical remission predicts an enhanced risk for relapse of depressive symptomatology with respect to the medium- and long-term outcome.

Molecular mechanisms of glucocorticoid receptor sensitivity and relevance to affective disorders.

Changes in the hypothalamic-pituitary-adrenocortical (HPA) system are characteristic of depression, and in the majority of these patients these result in HPA axis hyperactivity. This is further supported by the reduced sensitivity to the inhibitory effects of the glucocorticoid, dexamethasone (DEX), on the production of adrenocorticotropic hormone (ACTH) and cortisol, during the DEX suppression test and the DEX-corticotropin-releasing hormone (DEX/CRH) test. Because the effects of glucocorticoids are mediated by intracellular receptors including, most notably, the glucocorticoid receptor (GR), several studies have examined the number and/or function of GRs in depressed patients. These studies have consistently demonstrated that GR function is impaired in major depression, resulting in reduced GR-mediated negative feedback on the HPA axis and increased production and secretion of CRH in various brain regions postulated to be involved in the causality of depression. This article summarizes the literature on GR in depression and on the impact of antidepressants on the GR in clinical and preclinical studies, and supports the concept that impaired GR signaling is a key mechanism in the pathogenesis of depression, in the absence of clear evidence of decreased GR expression. The data also indicate that antidepressants have direct effects on the GR, leading to enhanced GR function and increased GR expression. Hypotheses regarding the mechanism of these receptor changes involve non-steroid compounds that regulate GR function via second messenger pathways, such as cytokines and neurotransmitters. Moreover, we present recent evidence suggesting that membrane steroid transporters such as the multidrug resistance (MDR) p-glycoprotein, which regulate access of glucocorticoids to the brain, could be a fundamental target of antidepressant treatment. Research in this field will lead to new insights into the pathophysiology and treatment of affective disorders.

Cortisol and ACTH Response to Oral Dexamethasone in Obesity and Effects of Sex, Body Fat Distribution, and Dexamethasone Concentrations: A Dose-Response Study

There is increasing evidence that the abdominal obesity phenotype may be associated with multiple alterations of the hypothalamic-pituitary-adrenocortical (HPA) axis activity in both sexes. Our hypothesis is that the lack of adequate cortisol suppression after the dexamethasone test may constitute an indirect marker of HPA axis hyperactivity in the presence of the abdominal obesity phenotype. A total of 34 normal-weight (13 men and 21 women) and 87 obese (36 men and 51 women), healthy, nondepressed subjects therefore underwent four different dexamethasone suppression tests randomly performed at varying intervals of at least 1 wk between each test. After a standard overnight 1-mg dexamethasone test, which served as a reference, three other tests were randomly performed at 1-wk intervals by administering 0.0035, 0.0070, and 0.015 mg oral dexamethasone per kilogram of body weight overnight. Blood samples were obtained for cortisol, ACTH, and dexamethasone. Results were analyzed separately in men and women as well as in normal-weight [body mass index (BMI) < or = 25 kg/m(2)] and overweight or obese (BMI > 25 kg/m(2)) subjects. The waist circumference and the waist to hip ratio (WHR) were used as markers of body fat distribution. After the standard 1-mg test, cortisol suppression was greater than 90% in all subjects. However, after each test, obese women had significantly higher values of percent cortisol and percent ACTH suppression than normal-weight women without any difference between obese and normal-weight men. Considering the response to the three variable-dose tests, a clear dose- response pattern (P < 0.001 for trend analysis) in percent cortisol and percent ACTH suppression was found in all subjects. After each test men had significantly higher dexamethasone levels than women, regardless of BMI. However, obese women, but not men, had significantly higher dexamethasone levels after each test than their normal-weight counterpart. Plasma dexamethasone concentrations were dose related (P < 0.001 for trend analysis) in all subjects, but the dose-related increase was significantly higher in normal-weight men than normal-weight women, whereas it was similar in obese subjects of both sexes. Stepwise multiple regression analysis revealed that both percent cortisol and percent ACTH variations were significantly and negatively influenced by dexamethasone levels, as well as by waist circumference values in men, and independently by BMI and waist circumference in women. However, in contrast to what has been found in men, a divergent contribution of BMI and waist circumference was found in women indicating that, with increasing waist values, a smaller suppression of the HPA axis was found with respect to that expected on the basis of BMI values. In conclusion, this study provides data of both physiological and physiopathological relevance. Overall, our data indicated that adjustment of the dexamethasone dose to body weight does not seem to substantially improve the sensitivity of the test, even in obese individuals, particularly when near-maximal doses are administered. However, this study demonstrated a highly significant effect of dexamethasone blood level concentrations on cortisol and ACTH suppression to low-dose dexamethasone tests. In addition, a significant effect of gender on postdexamethasone cortisol concentrations, suppression of the HPA axis, and dexamethasone levels were found, which may be dependent on related differences in both cortisol and dexamethasone metabolism. We showed that pituitary sensitivity to feedback inhibition by dexamethasone is preserved in obesity in both sexes even at low dosages. On the other hand, our data suggest that, at least in women, abdominal fat distribution may partially counteract the progressively greater suppressibility of the HPA axis that would be expected according to increasing BMI.

Excitatory influence of the locus coeruleus in hypothalamic-pituitary-adrenocortical axis responses to stress.

The locus coeruleus (LC) is a key brainstem region involved in arousal and is highly responsive to alerting/stressful stimuli, including those that activate the hypothalamic-pituitary-adrenocortical (HPA) axis. It is currently unclear whether the LC exerts any regulatory influence on the HPA axis and, consequently, on neuroendocrine responses to stress. The present studies were designed to test the hypothesis that the LC promotes HPA axis responses to acute and chronic stress. Adult male rats received bilateral (6-hydroxydopamine) lesions of the LC that produced severe cell loss in the LC and 80% depletion of noradrenaline in medial prefrontal cortex. Notably, lesions did not affect dopamine-beta-hydroxylase protein content in the parvocellular paraventricular nucleus (PVN), indicating a lack of collateral damage to other ascending noradrenergic pathways. LC lesions significantly reduced peak adrenocorticotropic hormone (ACTH) and corticosterone responses to 30 min acute restraint stress. However, LC lesions did not significantly attenuate neuroendocrine or other physiological responses to a 4-week chronic variable stress regimen. LC lesions did not substantially affect basal concentrations of plasma corticosterone or corticotropin-releasing hormone mRNA expression in the hypothalamic paraventricular nucleus following chronic stress. We conclude that the LC is a HPA-excitatory brain region, promoting neuroendocrine and physiological responses primarily to acute stress. However, a potential role for the LC in the induction of HPA axis hyperactivity following chronic stress can not be ruled out.