Hypothalamic corticotrophin releasing hormone neurons in stress-induced psychopathology: Revaluation of synaptic contributions

Stress has a strong influence on mental health around the world. Decades of research has sought to identify mechanisms through which stress contributes to psychiatric disorders such as depression, to potentially guide the development of therapeutics targeting stress systems. The hypothalamic pituitary adrenal (HPA) axis is the key endocrine system that is responsible for coordinating body-wide changes that are necessary for survival under stress, and much of the research aimed at understanding the mechanisms by which stress contributes to depression has focussed on HPA axis dysfunction. Corticotrophin releasing hormone (CRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) sit at the apex of the HPA axis, integrating signals relevant to stress and external threats, to ensure HPA axis activity is appropriate for the given context. In addition to this, emerging research has demonstrated that neural activity in PVN^CRH neurons regulates stress related behaviours via modulation of downstream synaptic targets. This review will summarize convergent evidence from preclinical studies on chronic stress and clinical research in mood disorders demonstrating changes in PVN^CRH neural function, consider how this may influence synaptic targets of PVN^CRH neurons, and discuss the potential role of these PVN^CRH synaptic pathways in the development of maladaptive behaviours following chronic stress that are relevant to depression. We will also highlight important questions for future research aimed at precisely dissecting endocrine and synaptic roles of PVN^CRH neurons in chronic stress, their potential interactions, and therapeutic opportunities for the treatment of stress related disorders.

Downregulated Dopamine Receptor 2 and Upregulated Corticotrophin Releasing Hormone in the Paraventricular Nucleus Are Correlated With Decreased Glucose Tolerance in Rats With Bilateral Substantia Nigra Lesions

Patients with Parkinson’s disease (PD) have a high prevalence of glucose metabolism abnormalities. However, the mechanism underlying these symptoms remains unclear. The hypothalamic-pituitary-adrenal (HPA) axis is the major neuroendocrine axis that regulates homeostasis in mammals, including glucose metabolism. Corticotrophin releasing hormone (CRH), which is synthesized in the paraventricular nucleus (PVN) of the hypothalamus, plays an important role in the regulation of blood glucose levels via the HPA axis. Our previous studies have reported that PVN neurons express numerous dopamine receptors (DRs) and accept direct projections from the substantia nigra (SN). We hypothesize that damage to dopaminergic neurons in the SN might influence the blood glucose level through the HPA system. Rats with bilateral SN lesions induced by 6-hydroxydopamine (6-OHDA) (referred to as 6-OHDA rats) were used to investigate alterations in the levels of blood glucose, CRH, and factors related to the HPA axis and to explore possible mechanisms. Blood glucose levels were detected at different time points after the glucose solution was intraperitoneally administered. CRH and DRs in the PVN were evaluated by immunofluorescence and western blot analysis. Adrenocorticotropic hormone (ACTH) in the pituitary and plasma corticosterone (CORT) was evaluated by radioimmunoassay (RIA). The results showed that 6-OHDA rats exhibited significantly decreased tyrosine hydroxylase (TH) in the SN and decreased glucose tolerance at 6 weeks, but not at 4 weeks. In the PVN, dopamine receptor 2 (D2) was expressed on CRH-positive neurons, and D2-positive neurons were surrounded by TH-positive fibers. Additionally, the expression of CRH was upregulated, whereas the expression of D2 and TH were downregulated in 6-OHDA rats compared with control rats. In D2 knock-out mice, the significantly enhanced expression of CRH and reduced expression of D2 were detected in the PVN. Furthermore, RIA revealed increased ACTH in the pituitary and elevated CORT in the blood. In summary, the present study suggests that the dopaminergic neurons in the SN are involved in the regulation of body glucose metabolism through CRH neurons that express D2 in the hypothalamic PVN. SN lesions decrease glucose tolerance mainly by downregulating D2 and upregulating CRH in the PVN through the HPA neuroendocrine system.

Electroacupuncture Alleviates Surgical Trauma-Induced Hypothalamus Pituitary Adrenal Axis Hyperactivity Via microRNA-142

Electroacupuncture (EA) could improve the hyperactivity of the hypothalamus pituitary adrenal (HPA) axis induced by hepatectomy. However, its underlying mechanism still remains largely unclear. Here, we found that hypothalamic corticotrophin releasing hormone (CRH) modulates the function of the HPA axis, while hepatectomy induced an HPA axis disorder and EA application could regulate the hypothalamic CRH. We first demonstrated that microRNAs (miRNAs) target on CRH via bioinformatics analysis and screened them in the primary hypothalamic neurons. MicroR-142 (miR-142) and miR-376c were identified to inhibit CRH at the mRNA and protein levels, and a dual luciferase reporter assay confirmed their binding to the 3'-untranslated regions (3'-UTR) of CRH. Further analyses revealed a decrease in hypothalamic miR-142 expression in the hepatectomy rats and an increase in miR-142 and miR-376c after EA intervention. Importantly, the improvement effect of EA on the HPA axis regulatory function in hepatectomy rats was blocked by miR-142 antagomir. Our findings illustrated that EA could up-regulate hypothalamic miR-142 expression and decrease the CRH level to alleviate the hyperactivity of the HPA axis induced by hepatectomy.

Peripheral chemerin administration modulates hypothalamic control of feeding

Chemerin is a recently identified adipokine that is involved in the regulation of adipogenesis, energy metabolism, and inflammation. The aim of the present study was to investigate the role of chemerin on food intake, body weight and hypothalamic peptidergic and aminergic modulators which play a pivotal role in feeding regulation in rats. Male adult Wistar rats were intraperitoneally injected, daily for 17 days at 9.00am, with either vehicle (saline; N=12) or chemerin (8μg/kg; N=12) and (16μg/kg; N=12). Food intake was recorded 24h after each administration. Animals were sacrificed 24h after the last injection. Total RNA was extracted from hypothalami and reverse transcribed to evaluate gene expression of agouti-related peptide (AgRP), neuropeptide Y (NPY), orexin-A, corticotrophin releasing hormone (CRH), pro-opiomelanocortin (POMC) and cocaine and amphetamine-regulated transcript (CART). Furthermore, we evaluated the effect of chemerin on dopamine, norepinephrine and serotonin steady state concentrations in rat hypothalamus homogenate, and monoamine release from rat hypothalamic synaptosomes. Chemerin administration (8 and 16μg/kg) decreased both food intake and body weight compared to vehicle, possibly associated with a significant increase in serotonin synthesis and release, in the hypothalamus. On the other hand, the pattern of gene expression following chemerin administration indicates a minor role played by chemerin as a peripheral appetite-regulating signal.

Obesity in the ageing man

As the population is ageing globally, both ageing and obesity are recognized as major public health challenges. The aim of this narrative review is to present and discuss the current evidence on the changes in body composition, energy balance and endocrine environment that occur in the ageing man. Obesity in the ageing man is related to changes in both body weight and composition due to alterations in energy intake and total energy expenditure. In addition, somatopenia (decreased GH secretion), late-onset hypogonadism (LOH), changes in thyroid and adrenal function, as well as changes in appetite-related peptides (leptin, ghrelin) and, most importantly, insulin action are related to obesity, abnormal energy balance, redistribution of the adipose tissue and sarcopenia (decreased muscle mass). A better understanding of the complex relationship of ageing-related endocrine changes and obesity could lead to more effective interventions for elderly men.

Orexigenic effects of endomorphin-2 (EM-2) related to decreased CRH gene expression and increased dopamine and norepinephrine activity in the hypothalamus

Endomorphin-1 (EM-1) and endomorphin-2 (EM-2) are opioid peptides which are selective partial agonists of μ-opioid receptor. We studied the effects of EM-2 injected into the arcuate nucleus (ARC) of the hypothalamus on feeding behavior and gene expression of orexigenic [agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A] and anorexigenic [cocaine and amphetamine-regulated transcript (CART), corticotrophin releasing hormone (CRH) and proopiomelanocortin (POMC)] peptides in male Wistar rats fed a standard laboratory diet. Furthermore, we evaluated the effects of EM-2 on dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) steady state concentrations, in the hypothalamus. 64 rats (16 for each group of treatment) were injected into the ARC, at 9.00 am, with either vehicle or EM-2 (0.50-0.75 μmol/kg) or EM-2 (0.50 μmol/kg) plus β-funaltrexamine (0.20 μmol/kg). Food intake was recorded through 24h following injection, and hypothalamic DA, NE, 5-HT levels and neuropeptide gene expression were evaluated 24h after EM-2 administration. Compared to vehicle, EM-2 significantly increased food intake, throughout 24h post-injection. Furthermore, EM-2 treatment led to a significant increase of DA and NE concentrations and a decrease of CRH mRNA levels. On the other hand, β-funaltrexamine administration reverted both feeding stimulatory and neuromodulatory effects induced by EM-2. We can conclude that the orexigenic effect of μ-opioid receptor activation by EM-2 could be related to both inhibition of CRH and stimulation of dopamine and norepinephrine levels, in the hypothalamus.

Steroidogenesis in the skin: implications for local immune functions

The skin has developed a hierarchy of systems that encompasses the skin immune and local steroidogenic activities in order to protect the body against the external environment and biological factors and to maintain local homeostasis. Most recently it has been established that skin cells contain the entire biochemical apparatus necessary for production of glucocorticoids, androgens and estrogens either from precursors of systemic origin or, alternatively, through the conversion of cholesterol to pregnenolone and its subsequent transformation to biologically active steroids. Examples of these products are corticosterone, cortisol, testosterone, dihydrotesterone and estradiol. Their local production can be regulated by locally produced corticotropin releasing hormone (CRH), adrenocorticotropic hormone (ACTH) or cytokines. Furthermore the production of glucocorticoids is affected by ultraviolet B radiation. The level of production and nature of the final steroid products are dependent on the cell type or cutaneous compartment, e.g., epidermis, dermis, adnexal structures or adipose tissue. Locally produced glucocorticoids, androgens and estrogens affect functions of the epidermis and adnexal structures as well as local immune activity. Malfunction of these steroidogenic activities can lead to inflammatory disorders or autoimmune diseases. The cutaneous steroidogenic system can also have systemic effects, which are emphasized by significant skin contribution to circulating androgens and/or estrogens. Furthermore, local activity of CYP11A1 can produce novel 7Δ-steroids and secosteroids that are biologically active. Therefore, modulation of local steroidogenic activity may serve as a new therapeutic approach for treatment of inflammatory disorders, autoimmune processes or other skin disorders. In conclusion, the skin can be defined as an independent steroidogenic organ, whose activity can affect its functions and the development of local or systemic inflammatory or autoimmune diseases. This article is part of a Special Issue entitled 'CSR 2013'.

Interleukin-1β (IL-1β) increases pain behavior and the blood glucose level: possible involvement of glucocorticoid system

The possible involvement of glucocorticoid system in interleukin-1β (IL-1β)-induced nociception and the blood glucose level was studied in ICR mice. In the first experiment, mice were treated intrathecally (i.t.) with IL-1β (100 pg). Corticotrophin releasing hormone (CRH) mRNA (hypothalamus) and c-Fos mRNA (pituitary gland, spinal cord, and the adrenal gland) levels were measured at 30, 60 and 120 min after IL-1β administration. We found that i.t. injection with IL-1β increased CRH mRNA level in the hypothalamus. The IL-1β administered i.t. elevated c-Fos mRNA levels in the spinal cord, pituitary and adrenal glands. Furthermore, i.t. administration of IL-1β significantly increased the plasma corticosterone level up to 60 min. In addition, the adrenalectomy caused the reductions of the blood glucose level and pain behavior induced by IL-1β injected i.t. in normal and D-glucose-fed groups. Furthermore, intraperitoneal (i.p.) pretreatment with RU486 (100mg/kg) attenuated the blood glucose level and pain behavior induced by IL-1β administered i.t. in normal and D-glucose-fed groups. Our results suggest that IL-1β administered i.t. increases the blood glucose level and pain behavior via an activation of the glucocorticoid system.

Paraventricular nucleus corticotrophin releasing hormone contributes to sympathoexcitation via interaction with neurotransmitters in heart failure

Recent studies indicate that systemic administration of tumor necrosis factor (TNF)-α induces increases in corticotrophin releasing hormone (CRH) and CRH type 1 receptors in the hypothalamic paraventricular nucleus (PVN). In this study, we explored the hypothesis that CRH in the PVN contributes to sympathoexcitation via interaction with neurotransmitters in heart failure (HF). Sprague-Dawley rats with HF or sham-operated controls (SHAM) were treated for 4 weeks with a continuous bilateral PVN infusion of the selective CRH-R1 antagonist NBI-27914 or vehicle. Rats with HF had higher levels of glutamate, norepinephrine (NE) and tyrosine hydroxylase (TH), and lower levels of gamma-aminobutyric acid (GABA) and the 67-kDa isoform of glutamate decarboxylase (GAD67) in the PVN when compared to SHAM rats. Plasma levels of cytokines, NE, ACTH and renal sympathetic nerve activity (RSNA) were increased in HF rats. Bilateral PVN infusions of NBI-27914 attenuated the decreases in PVN GABA and GAD67, and the increases in RSNA, ACTH and PVN glutamate, NE and TH observed in HF rats. These findings suggest that CRH in the PVN modulates neurotransmitters and contributes to sympathoexcitation in rats with ischemia-induced HF.

Adrenergic stimulation mediates visceral hypersensitivity to colorectal distension following heterotypic chronic stress

BACKGROUND & AIMS

Chronic stress exacerbates or causes relapse of symptoms such as abdominal pain and cramping in patients with irritable bowel syndrome. We investigated whether chronic stress increases plasma norepinephrine and sensitizes colon-specific dorsal root ganglion (DRG) neurons by increasing expression of nerve growth factor (NGF) in the colon wall.

METHODS

Heterotypic chronic stress (HeCS) was applied to male Wistar rats and neurologic and molecular responses were analyzed. Tissues were analyzed for NGF expression.

RESULTS

HeCS significantly increased visceromoter response to colorectal distension; expression of NGF increased in colonic muscularis externa and mucosa/submucosa. Rheobase decreased, resting membrane potential was depolarized, and electrogenesis of action potentials increased in colon-specific thoracolumbar DRG neurons. Luminal administration of resiniferatoxin in distal colon, systemic administration of anti-NGF antibody, or inhibition of the NGF receptor trkA by k252a or antisense oligonucleotides in thoracolumbar DRG blocked the chronic stress-induced visceral hypersensitivity to colorectal distension. Blockade of alpha1/alpha2- and beta1/beta2-adrenergic receptors prevented the stress-induced visceral hypersensitivity and increased expression of NGF in the colon wall. HeCS did not induce any inflammatory response in the colon wall.

CONCLUSIONS

The peripheral stress mediator norepinephrine induces visceral hypersensitivity to colorectal distension in response to HeCS by increasing the expression of NGF in the colon wall, which sensitizes primary afferents in the absence of an inflammatory response.

Stress-induced differences in primary and secondary resistance against bacterial sepsis corresponds with diverse corticotropin releasing hormone receptor expression by pulmonary CD11c+ MHC II+ and CD11c- MHC II+ APCs

Stress responses have been associated with altered immunity and depending upon the type of stressor, can have diverse effects on disease outcomes. As the first line of defense against potential pathogens, alterations in cellular immune responses along the respiratory tract can have a significant impact on the manifestation of local and systemic disease. Utilizing a murine model of respiratory pneumonia, the current study investigated the effects of restraint stress on the induction of primary and secondary immunity along the respiratory tract, influencing host susceptibility. Female CD-1 mice were subjected to three hours of restraint stress over a period of four days followed by primary and secondary Streptococcus pneumoniae infection via intranasal route. Stress exposure led to increased retention of bacterial carriage in the lungs, enhanced polymorphonuclear cells and a preferential decrease in pulmonary CD11c(+) MHC II(+) cells resulting in delayed lethality during primary infection but significant impairment of acquired immune protection after secondary infection. We also provide evidence to support a role for lung-associated corticotropin releasing hormone regulation through peripheral CRH and diverse CRH receptor expression by MHC II(+) antigen presenting cells (APCs). We conclude that repeated restraint stress has distinct influences on immune cell populations that appear to be important in the generation of innate and adaptive immune responses along the respiratory tract with the potential to influence local and systemic protection against disease pathogenesis.

Nramp1 is expressed in neurons and is associated with behavioural and immune responses to stress

The gene Nramp1 encoding the natural resistance-associated macrophage protein (Nramp1) influences susceptibility to intracellular infections and autoimmune diseases, and the humoral response to stress. Nramp1 functions as a proton/divalent cation antiporter in the membranes of late endosomes/lysosomes, regulating cytoplasmic iron levels in macrophages. The Drosophila homologue of Nramp1 is expressed in sensory neurons and macrophages, and influences taste behaviour directly through divalent cation transport. Here we demonstrate that murine Nramp1 is also expressed on neurons as well as microglial cells in the brain and influences the behavioural response to stress, hypothalamus-pituitary-adrenal (HPA) axis activation and mortality following Toxoplasma gondii infection in control and prestressed mice. We hypothesise that, although differences in HPA activation translate into differences in adrenal enlargement and basal circulating corticosterone levels, the primary influence of Nramp1 is at the level of the neuronal response to stress. These results provide new insight into the possible roles of divalent cation transporters of the Nramp gene family in regulating metal ion homeostasis in the brain and its pathological implications.