Corticotropin-releasing hormone in the regulation of adaptive behavior

Recent findings on the role of corticotropin-releasing hormone (CRH) in the regulation of stress and its consequences are summarized and analyzed in the review. Being involved in stress-activating system this neurohormone is referred to as a neurochemical factor triggering and integrating both endocrine and behavioral functions. The CRH distribution in hypothalamus and extrahypothalamic brain regions relevant to its involvement in the controlling of endocrine processes and behavior is viewed in details. Distinct behavioral outcomes of stress and the contribution of amygdalar, hippocampal, and striatal CRH-structures, implicated in general organism response to external influences, are widely discussed. From this viewpoint the mechanisms involved in the development of post-stress psychopathology, as well as drug addiction and alcoholism are treated.     

Corticotropin-releasing hormone induces keratinocyte differentiation in the adult human epidermis

Previously we documented that human epidermis exclusively expresses corticotropin releasing hormone receptor 1 (CRH-R1). To define the role of CRH in the epidermis, we investigated its effects on differentiation of normal human adult epidermal keratinocytes. Thus, CRH inhibited proliferation in a dose dependent fashion and significantly decreased Ki-67 antigen expression. This effect was independent of either the presence or the absence of growth factors in the medium. Flow cytometry analysis demonstrated that CRH inhibited the transition from G0/1 to S phase of the cell cycle, which was accompanied by an increased expression of cdk inhibitor p16 (Ink4a) protein. The antiproliferative effect was attenuated by protein kinase C inhibitor (GF109203X) but not by H89 (protein kinase A inhibitor), PD98059, or SB203580 (MAP kinase inhibitors). The cell cycle withdrawal was associated with the induction of keratinocyte differentiation. Thus, CRH stimulated the expression of cytokeratin 1 and involucrin, and inhibited cytokeratin 14 on both mRNA and protein levels. It also increased cell granularity and cell size. Furthermore, CRH induced signal transduction cascade that included stimulation of inositol 1,4,5-triphosphate, which was time and dose dependent. CRH also increased activator protein-1 DNA binding activity with JunD identified as the most important element. Thus, activation of CRH-R1 induces a non-random and sequential signal transduction cascade governing both keratinocyte differentiation and the inhibition of cell proliferation through G0/1 arrest. We propose that this program, triggered by CRH interaction with CRH-R1, includes induction of a transduction pathway involving the sequential activation of phospholipase C, protein kinase C, activator protein-1 (including Jun D), and p16.     

Steroidal influences on pup-killing behavior in mice

Four experiments were conducted in order to examine the biochemical pathway through which testosterone (T) acts to produce pup-killing behavior in ovariectomized female mice. Estradiol benzoate (EB) and testosterone propionate (TP) were both effective in stimulating the pup-killing response (Experiment 1). The nonaromatizable androgen dihydrotestosterone (DHT) and the aromatizable androgen testosterone (T) were equipotent in eliciting the behavior while the nonaromatizable androgen androstanedione (AA) was ineffective (Experiment 2). Pup-killing behavior was activated by the aromatizable androgen androstenedione (AE) but only if it was administered chronically at very high doses (Experiment 3). The combination of subthreshold doses of EB and DHT synergized to produce the pup-killing response (Experiment 4). These findings suggest that both aromatization and reduction may be important for the stimulation of pup-killing behavior in mice.     

Corticotropin-releasing hormone receptors

Corticotropin-releasing hormone (CRH) and related peptides (urocortins, sauvagine, urotensin) play a central role in the co-ordination of autonomic, behavioural, cardiovascular, immune and endocrine responses to stressful stimuli. Their actions are mediated through activation of two types of G-protein-coupled receptors encoded by separate genes. In this review we focus on the diverse structural and functional characteristics of the family of CRH-like peptides and their receptors.     

Corticotropin-releasing hormone in the lateral parabrachial nucleus inhibits sodium appetite in rats

The present study investigated the role of corticotropin-releasing hormone (CRH) in the lateral parabrachial nucleus (LPBN) in the behavioral control of body fluid homeostasis by determining the effect of bilateral injections of the CRH receptor antagonist, alpha-helical corticotropin-releasing factor (CRF)(9-41), and the CRH receptor agonist, CRH, on sodium chloride (salt appetite) and water (thirst) intake. Groups of adult, male Sprague-Dawley rats had stainless-steel cannulas implanted bilaterally into the LPBN and were sodium depleted or water deprived. Bilateral injections of alpha-helical CRF(9-41) into the LPBN significantly potentiated water and salt intake in the sodium-depleted rats when access to fluids was restored. Bilateral injections of alpha-helical CRF(9-41) into the LPBN (1.0 microg) also increased sodium appetite in water-deprived rats. Conversely, in sodium-depleted animals, bilateral injections of CRH inhibited sodium chloride intake. These results suggest that there is an endogenous CRH inhibitory mechanism operating in the LPBN to modulate the intake of sodium (salt appetite). This mechanism may contribute to the behavioral control of restoration of body fluid homeostasis in sodium-deficient states.     

Corticotropin-releasing hormone induces proliferation and TNF-alpha release in cultured rat microglia via MAP kinase signalling pathways

We have previously demonstrated that corticotropin-releasing hormone (CRH) receptor 1 (CRH-R1) is functionally expressed in rat microglia. In the present study, we show that CRH, acting on CRH-R1, promoted cell proliferation and tumour necrosis factor-alpha (TNF-alpha) release in cultured rat microglia. Exogenous CRH resulted in an increase in BrdU incorporation compared with control cells, which was observed in a range of concentrations of CRH between 10 and 500 nm, with a maximal response at 50 nm. The effect of CRH on BrdU incorporation was inhibited by a CRH antagonist astressin but not by a cAMP-dependent protein kinase inhibitor H89. Exposure of microglial cells to CRH resulted in a transient and rapid increase in TNF-alpha release in a dose-dependent manner. In the presence of astressin, the effects of CRH on TNF-alpha release were attenuated. CRH effects on TNF-alpha release were also inhibited by specific inhibitors of MEK, the upstream kinase of the extracellular signal-regulated protein kinase (ERK) (PD98059) or p38 mitogen-activated protein kinase (SB203580), but not by H89. Furthermore, CRH induced rapid phosphorylation of ERK and p38 kinases. Astressin, PD98059, and SB230580 were able to inhibit CRH-induced kinase phosphorylation. These results suggest that CRH induces cell proliferation and TNF-alpha release in cultured microglia via MAP kinase signalling pathways, thereby providing insight into the interactions between CRH and inflammatory mediators.     

Corticotropin-releasing factor inhibits gastric emptying in dogs

The purpose of the present study was to evaluate the effect of ovine corticotropin-releasing factor (CRF) on the gastric emptying of a saline meal in conscious dogs. Intravenous infusion of CRF (220-880 pmol . kg-1 . h-1), induced a significant linear dose dependent inhibition of gastric emptying (16-71%). CRF action was not modified by naloxone and not associated with vomiting or other side effects. Intravenous infusion of sulfated cholecystokinin octapeptide (CCK-8, 50-200 pmol . kg-1 . h-1) inhibited gastric emptying by 29-52%. The relative potency of CRF with respect to CCK-8 is 4 times less. These studies demonstrated that CRF given intravenously in picomolar amount inhibits gastric emptying of a liquid meal in dogs through a mechanism unrelated to opiates. The role of endogenous CRF in stress-induced inhibition of gastric emptying needs to be investigated.     

Corticotropin-releasing hormone in depression and post-traumatic stress disorder

Corticotropin-releasing hormone (CRH) has been implicated in the regulation of a wide range of behaviors including arousal, motor function, feeding, and reproduction. Because depressed patients are often hypercortisolemic and intracerebroventricular administration of CRH to experimental animals produces a syndrome reminiscent of depression, dysregulation of this compound has been suggested to be involved in the pathogenesis of depressive and anxiety disorders. Studies of cerebrospinal fluid CRH levels and clinical neuroendocrine tests in patients with anxiety and affective disorders have supported this hypothesis. This review discusses these neuroendocrine findings in melancholic and atypical depression as well as post-traumatic stress disorder (PTSD). Overall, the data suggest that melancholic depression is characterized by hyperactive central CRH systems with overactivity of the pituitary-adrenal (HPA) axis. On the other hand, atypical depression is characterized by hypoactive central CRH systems and accompanying underactivity of the hypothalamic-pituitary-adrenal axis. Furthermore, the neuroendocrinology of PTSD appears to be unique, in that patients have hyperactive central CRH systems with underactivity of the pituitary-adrenal axis.     

Estradiol induces and progesterone inhibits the preovulatory surges of luteinizing hormone and follicle-stimulating hormone in heifers

Objectives were to determine: 1) whether estradiol, given via implants in amounts to stimulate a proestrus increase, induces preovulatory-like luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges; and 2) whether progesterone, given via infusion in amounts to simulate concentrations found in blood during the luteal phase of the estrous cycle, inhibits gonadotropin surges. All heifers were in the luteal phase of an estrous cycle when ovariectomized. Replacement therapy with estradiol and progesterone was started immediately after ovariectomy to mimic luteal phase concentrations of these steroids. Average estradiol (pg/ml) and progesterone (ng/ml) resulting from this replacement were 2.5 and 6.2 respectively; these values were similar (P greater than 0.05) to those on the day before ovariectomy (2.3 and 7.2, respectively). Nevertheless, basal concentrations of LH and FSH increased from 0.7 and 43 ng/ml before ovariectomy to 2.6 and 96 ng/ml, respectively, 24 h after ovariectomy. This may indicate that other ovarian factors are required to maintain low baselines of LH and FSH. Beginning 24 h after ovariectomy, replacement of steroids were adjusted as follows: 1) progesterone infusion was terminated and 2 additional estradiol implants were given every 12 h for 36 h (n = 5); 2) progesterone infusion was maintained and 2 additional estradiol implants were given every 12 h for 36 h (n = 3); or 3) progesterone infusion was terminated and 2 additional empty implants were given every 12 h for 36 h (n = 6). When estradiol implants were given every 12 h for 36 h, estradiol levels increased in plasma to 5 to 7 pg/ml, which resembles the increase in estradiol that occurs at proestrus. After ending progesterone infusion, levels of progesterone in plasma decreased to less than 1 ng/ml by 8 h. Preovulatory-like LH and FSH surges were induced only when progesterone infusion was stopped and additional estradiol implants were given. These surges were synchronous, occurring 61.8 +/- 0.4 h (mean +/- SE) after ending infusion of progesterone. We conclude that estradiol, at concentrations which simulate those found during proestrus, induces preovulatory-like LH and FSH surges in heifers and that progesterone, at concentrations found during the luteal phase of the estrous cycle, inhibits estradiol-induced gonadotropin surges. Furthermore, ovarian factors other than estradiol and progesterone may be required to maintain basal concentrations of LH and FSH in heifers.     

Corticotropin-releasing hormone: from endocrinology to psychobiology

Corticotropin-releasing hormone (CRH) is a brain neuropeptide which coordinates the endocrine, autonomic and behavioral responses to stress. We review the abnormal response to exogenous CRH in various psychiatric syndromes, including major depression and anorexia nervosa. We also contrast pituitary responses to CRH in patients with depression versus Cushing's disease. We hypothesize that CRH may play a role in the pathogenesis of various psychiatric syndromes which are characterized during their course by the symptom of depression.     

Corticotropin-releasing hormone and pituitary-adrenocortical responses in chronically stressed rats

Brain corticotropin-releasing hormone (CRH) concentration and pituitary adreno-cortical responses were examined in chronically stressed rats: body restraint stress (6 h/day) for 4 or 5 weeks. Stressed rats showed a reduction in weight gain. CRH concentration in the median eminence and the rest of the hypothalamus were not different between control and chronically immobilized rats. The anterior pituitary adenocorticotropic hormone (ACTH) concentration was elevated in chronically stressed rats, whereas plasma ACTH and corticosterone levels did not differ from the control values. The median eminence CRH concentration was reduced to the same extent at 5 min after onset of ether exposure (1 min) in chronically immobilized rats and controls. However, plasma ACTH and corticosterone showed greater responses to ether stress in chronically immobilized rats than in control rats. Plasma ACTH and corticosterone responses to exogenous CRH were not different between control and chronically immobilized rats, while the response to arginine vasopressin (AVP) was significantly greater in chronically immobilized rats. These results suggest that chronic stress caused an increase in the ACTH-secreting mechanism and that pituitary hypersensitivity to vasopressin might at least be partly responsible for this.     

Corticotropin-releasing hormone affects cytokine production in human HaCaT keratinocytes

CRH cutaneous expression is significantly enhanced after exposure to various stimuli (Physiol Rev 2000, 80;979-1020). We evaluated the effect of CRH on cytokine production in HaCaT keratinocytes, a cell line shown to express CRH receptors coupled to cAMP activation and calcium-dependent transmission pathways. It is demonstrated for the first time that exogenously added CRH stimulates production of IL-6 and IL-11. It also inhibits production of IL-1beta and does not affect TNF-alpha production. Our results indicate that CRH function(s) during cutaneous stress may be mediated by differential effects on cytokine production.     

Corticotropin-releasing hormone induces Fas ligand production and apoptosis in PC12 cells via activation of p38 mitogen-activated protein kinase.

Recent experimental findings involve corticotropin-releasing hormone (CRH) in the cellular response to noxious stimuli and possibly apoptosis. The aim of the present work was to examine the effect of CRH on apoptosis and the Fas/Fas ligand system in an in vitro model, the PC12 rat pheochromocytoma cell line, which is widely used in the study of apoptosis and at the same time expresses the CRH/CRH receptor system. We have found the following. CRH induced Fas ligand production and apoptosis. These effects were mediated by the CRH type 1 receptor because its antagonist antalarmin blocked CRH-induced apoptosis and Fas ligand expression. CRH activated p38 mitogen-activated protein kinase, which was found to be essential for CRH-induced apoptosis and Fas ligand production. CRH also promoted a rapid and transient activation of ERK1/2, which, however, was not necessary for either CRH-induced apoptosis or Fas ligand production. Thus, CRH promotes PC12 apoptosis via the CRH type 1 receptor, which induces Fas ligand production via activation of p38.     

Corticotropin-releasing hormone mediates alpha-melanocyte-stimulating hormone-induced anorexigenic action in goldfish

alpha-Melanocyte-stimulating hormone (alpha-MSH) and corticotropin-releasing hormone (CRH) both suppress food intake, and the alpha-MSH- or CRH-signaling pathway has possible potency to mediate anorexigenic actions induced by most other neuropeptides in goldfish. Therefore, using specific receptor antagonists, we examined whether the anorexigenic actions of alpha-MSH and CRH mutually interact. The inhibitory effect of ICV injection of the alpha-MSH agonist, melanotan II (MT II), on food intake was abolished by treatment with a CRH 1/2 receptor antagonist, alpha-helical CRH((9-41)), whereas the anorexigenic action of ICV-injected CRH was not affected by treatment with a melanocortin 4 receptor antagonist, HS024. This led us to investigate whether alpha-MSH-containing neurons in the goldfish brain have direct inputs to CRH-containing neurons, using confocal laser scanning microscopy. alpha-MSH- and CRH-like immunoreactivities were distributed throughout the brain, especially in the diencephalon. alpha-MSH-containing nerve fibers or endings lay in close apposition to CRH-containing neurons in a region of the hypothalamus, the nucleus posterioris periventricularis (NPPv). These results indicate that, in goldfish, alpha-MSH-induced anorexigenic action is mediated by the CRH-signaling pathway, and that CRH plays a crucial role in the regulation of feeding behavior as an integrated anorexigenic neuropeptide in this species.     

Growth hormone is secreted by ectopic pituitary grafts and stimulates maternal behavior in rats

The onset of maternal behavior at parturition in rats is hormonally regulated. Recently, we reported that treatment of behaviorally inexperienced, hypophysectomized (hypox), ovariectomized (ovx) rats with a sequential steroid treatment of progesterone (P) and estradiol (E2), and either ectopic anterior pituitary grafts or prolactin (PRL), stimulated maternal responsiveness toward foster young. That growth hormone (GH) has a number of PRL-like activities led us to ask whether the actions of PRL on maternal behavior were specific to PRL or might be shared by other PRL-like protein hormone, i.e., GH. In Experiment 1 we quantified plasma concentrations of GH and PRL by RIA in groups of hypox female rats that were ovariectomized and treated with a combination of ectopic pituitary grafts (Days 1-23) and Silastic capsules filled with P (Days 1-11) and E2 (Days 11-23). Blood samples were collected from Days 1 to 23 of treatment. Both plasma PRL and GH levels increased after grafting, initially rising 10- to 60-fold by Day 4 and gradually declining throughout the remainder of the 23-day sampling period. Throughout the 3-week period after grafting plasma GH levels were as high or higher than those of PRL. In Experiment 2 the behavioral effects of exogenously administered ovine (o)-GH were measured in groups of hypox, ovx rats that were treated with P and E2 as in Experiment 1. Experimental rats were injected twice daily with 0.25 mg oGH beginning on Day 1. Testing for maternal behavior toward foster young was conducted daily from Day 12 to Day 22. In steroid-treated rats, GH treatment stimulated a more rapid onset of maternal behavior (latencies of 3 vs greater than 10 days for vehicle-injected controls). These data indicate that GH, like PRL, is secreted by ectopic pituitary grafts and is capable of stimulating maternal behavior.     

Corticotropin-releasing hormone activates protein kinase C in an isoenzyme-specific manner

Protein kinase C (PKC) has recently emerged as mediator of corticotropin-releasing hormone (CRH) effects. Aim of the present study was to study the effects of CRH on each PKC isoenzyme. As a model we have used the PC12 rat pheochromocytoma cell line, expressing the CRH type 1 receptor (CRHR1). Our data were as follows: (a) CRH-induced rapid phosphorylation of conventional PKCalpha and PKCbeta, accompanied by parallel increase of their concentration within nucleus. (b) CRH suppressed the phosphorylation of novel PKCdelta and PKCtheta;, which remained in the cytosol. (c) CRH-induced transient phosphorylation of atypical PKClambda and had no effect on PKCmu. (d) The effect of CRH on each PKC isoenzyme was blocked by a CRHR1 antagonist. (e) Blockade of conventional PKC phosphorylation inhibited CRH-induced calcium ion mobilization from intracellular stores as well as the CRH-induced apoptosis and Fas ligand production. In conclusion, our findings suggest that CRH via its CRHR1 receptor differentially regulates PKC-isoenzyme phosphorylation, an apparently physiologically relevant effect since blockade of conventional PKC phosphorylation abolished the biological effect of CRH.     

Corticotropin-releasing hormone receptor 1 gene variants in irritable bowel syndrome

Background

Corticotropin-releasing hormone (CRH) acts mainly via the CRH receptor 1 (CRH-R1) and plays a crucial role in the stress-induced pathophysiology of irritable bowel syndrome (IBS). Several studies have demonstrated that variants of the CRH-R1 gene carry a potential risk for depression, but evidence for an association between CRH-R1 genotypes and IBS is lacking. We tested the hypothesis that genetic polymorphisms and haplotypes of CRH-R1 moderate the IBS phenotype and negative emotion in IBS patients.

Methods

A total of 103 patients with IBS and 142 healthy controls participated in the study. Three single-nucleotide polymorphisms of the CRH-R1 gene (rs7209436, rs242924, and rs110402) were genotyped. Subjects'' emotional states were evaluated using the Perceived-Stress Scale, the State-Trait Anxiety Inventory, and the Self-rating Depression Scale.

Results

The TT genotype of rs7209436 (P = 0.01) and rs242924 (P = 0.02) was significantly more common in patients with IBS than in controls. Total sample analysis showed significant association between bowel pattern (normal, diarrhea, constipation, or mixed symptoms) and the T allele of rs7209436 (P = 0.008), T allele of rs242924 (P = 0.019), A allele of rs110402 (P = 0.047), and TAT haplocopies (P = 0.048). Negative emotion was not associated with the examined CRH-R1 SNPs.

Conclusion

These findings suggest that genetic polymorphisms and the CRH-R1 haplotypes moderate IBS and related bowel patterns. There was no clear association between CRH-R1 genotypes and negative emotion accompanying IBS. Further studies on the CRH system are therefore warranted.     

Corticotropin-releasing hormone stimulates estrogen biosynthesis in cultured human placental trophoblasts

Estrogens and corticotrophin-releasing hormone (CRH) produced by the placenta play pivotal roles in the control of parturition in human and other primates. There is a strong correlation between maternal CRH and estrogen concentrations throughout gestation. To investigate whether CRH produced locally in the placenta could modulate estrogen production, we obtained human placental trophoblasts from uncomplicated term pregnancies and cultured them for 72 h. Cells were then treated with CRH and with a CRH receptor antagonist, alpha-helical CRH9-41. The results showed that CRH stimulated, but alpha-helical CRH9-41 inhibited, the production of estradiol in a time- and dose-dependent manner. Consistent with this thesis, CRH increased whereas alpha-helical CRH decreased the mRNA levels of STS, CYP19A1, and HSD17B1, the key enzymes for estrogen synthesis. These results suggest that, in the placenta, endogenously produced CRH exhibits a tonic stimulatory effect on estrogen production.     

Corticotropin-releasing hormone in the human hypothalamus. Free-floating immunostaining method

We have clearly demonstrated corticotropin-releasing hormone (CRH) immunoreactive cell bodies and nerve fibers in the human hypothalamus by immunocytochemistry using free-floating sections instead of paraffin-embedded sections. Human hypothalami were obtained at autopsy, fixed and cryostat-sectioned at 40 microns. Free-floating sections were immunostained with antibody to CRH using the Vector ABC system. Most of CRH immunoreactive nerve fibers from the paraventricular nucleus pass under the fornix, while some CRH immunoreactive nerve fibers pass beyond the fornix and some through the fornix. Then the CRH immunoreactive nerve fibers run downward, medially to the supraoptic nucleus and toward the pituitary stalk. This method of immunocytochemistry is a very sensitive and suitable means for immunocytochemical studies of neuropeptides in the human brain.