CRF receptor type 1 mediates continual hypoxia-induced CRF peptide and CRF mRNA expression increase in hypothalamic PVN of rats

We demonstrated previously that hypoxia activated CRF and CRF mRNA in PVN, and CRF receptor 1 (CRFR1) mRNA in rat pituitary. The aim of the study is to test whether the hypoxia-activated CRF and CRF mRNA is associated with triggering CRFR1. Rats were exposed to hypobaric hypoxia at altitude of 2 and 5 km. CRF and CRF mRNA were assayed by immunostaining and in situ hybridization. CRFR1 mRNA was assayed by RT-PCR. Results showed that 5 km continual hypoxia increased CRF and CRF mRNA in PVN, CRFR1 mRNA in pituitary, and plasma corticosterone. The hypoxia-increased CRF, CRF mRNA, CRFR1 mRNA, and corticosterone were blocked by CRFR1 antagonist (CP-154,526), suggesting that CRFR1 in PVN and pituitary are responsible for the hypoxia-increased CRF and CRF mRNA in PVN.     

Decreased expression of the mRNA for somatostatin in the periventricular nucleus of depression-model rats.

Expression of the mRNA for somatostatin (SRIF) in the periventricular nucleus (PeN), the level of SRIF in the stalk-median eminence (SME) and the concentration of growth hormone (GH) in the plasma were examined in depression-model rats in an attempt to confirm the hypothesis that SRIF neurons in the hypothalamus are hypofunctional in this model. We exposed male Wistar rats to intermittent walking stress for two weeks and then we measured their spontaneous running activity for 12 days. We divided the rats into a depression-model group and a partial-recovery group according to the spontaneous running activity of each rat after the termination of exposure to stress. Expression of SRIF mRNA in the PeN of the hypothalamus was monitored by in situ hybridization and relative levels were determined with an image analysis system. The relative level of expression of SRIF mRNA in the PeN was lower in rats in the depression-model group than in the control group and the partial-recovery group. The level of SRIF in the SME was lower and the plasma concentration of GH was higher in the depression-model group than in the other groups. Our findings suggest that reduced expression of mRNA for SRIF in the PeN might be associated with the pathophysiology of rats with this particular model of depression.     

The role of corticotropin-releasing factor receptors in stress and anxiety

Corticotropin releasing factor (CRF) is a critical integratorof the hypothalamic-pituitary-adrenal (HPA) axis in responseto stress. CRF and its related molecule urocortin (UCN) bindCRF receptor 1 (CRFR1) and CRFR2 with distinct affinities. Micedeficient for CRFR1 or CRFR2 were generated in order to determinethe physiological role of these receptors. While CRFR1-mutantmice show a depleted stress response and display anxiolytic-likebehavior, CRFR2-mutant mice are hypersensitive to stress anddisplay anxiogenic-like behavior. Both CRFR1- and CRFR2-mutantmice show normal basal feeding and weight gain, but CRFR2-mutantmice exhibit decreased food intake following a stress of fooddeprivation. While CRFR2-mutant mice display increased levelsof CRF mRNA in the central nucleus of the amygdala (cAmyg) butnot in the paraventricular nucleus of the hypothalamus (PVN),the CRFR1-mutant mice express high levels of CRF in the PVNbut normal levels in the cAmyg. CRFR2-mutant mice also displayincreased levels of Ucn mRNA and protein in the edinger westphalnucleus (EW) as well as an increased number of cells expressingUcn. The levels of these CRF-receptor ligands reflect the stateof the receptor-deficient mice. These results demonstrate apossible modulatory function of CRFR2 in response to CRFR1 stimulationof the HPA axis or anxiety.     

Adrenalectomy enhances endotoxemia-induced hypophagia: higher activation of corticotrophin-releasing-factor and proopiomelanocortin hypothalamic neurons

Inflammatory and infectious processes evoke neuroendocrine and behavioral changes known as acute-phase response that includes activation of the hypothalamo-pituitary-adrenal (HPA) axis and reduction of food intake. Besides its action as the most important ACTH secretagogue, corticotrophin-releasing factor (CRF), synthesized in the paraventricular nucleus (PVN), is also involved in the control of food intake. Alpha-melanocyte stimulating hormone (α-MSH) in the arcuate nucleus also plays a role in the energy homeostasis, possessing anorexigenic effects. To investigate the participation of neuropeptides involved in the regulation of food intake during endotoxemia, we administrated lipopolysaccharide (LPS) in sham-operated and adrenalectomized (ADX) male Wistar rats to evaluate food intake, hormone responses and Fos-CRF and Fos-α-MSH immunoreactivity in the PVN and arcuate nucleus, as well as CRF and POMC mRNA expression in these hypothalamic nuclei. In sham-operated rats, treatment with LPS (100 µg/kg) showed lower food intake, higher plasma ACTH and corticosterone levels, as well as an increase in Fos-CRF double labeled neurons and CRF mRNA expression in the PVN, with no changes in Fos-α-MSH immunoreactivity and POMC mRNA expression in the arcuate nucleus, compared to saline treated rats. After LPS treatment, ADX rats showed further increase in plasma ACTH levels, marked decrease of food intake, higher Fos-CRF immunoreactive neurons in the PVN and CRF mRNA expression, as well as an increase in Fos-α-MSH immunoreactivity and POMC mRNA expression in the arcuate nucleus, compared to sham-operated rats treated with LPS. In conclusion, the present data indicate that the marked hypophagia during endotoxemia following ADX is associated with an increased activation of CRF and POMC neurons in the hypothalamus and an increased mRNA expression of these neuropeptides.     

Effects of experimental hypothyroidism on the development of the hypothalamo-pituitary-adrenal axis in the rat

Hypothyroid pups were obtained by adding methimazole in the mother's drinking water from day 15 of gestation and sacrificed at 4, 8 or 15 days. Circulating corticosterone decreased at all ages, while CBG concentrations diminished at day 4, increased at day 8 and did not change at day 15 in hypothyroid rats. As opposed to controls, plasma ACTH concentrations decreased steadily with age while there was an accumulation of ACTH in the anterior pituitary of hypothyroid 15-day-old rats. Anterior pituitary POMC contents were unaffected by the treatment. In the hypothalamic PVN, CRF mRNA levels in the total population of CRF-synthesizing cells and in the CRF+/AVP+ subpopulation were below those of controls whatever the age considered while AVP mRNA in the CRF+/AVP+ subpopulation did not change at day 4 and decreased at day 8 and 15 in hypothyroid animals. Both the number of cell bodies expressing detectable levels of CRF mRNA and the percentage of CRF and AVP colocalization decreased at day 4 and were unchanged thereafter. CRF and AVP immunoreactivity in the zona externa of the median eminence increased with age but was not affected by methimazole treatment. The concentration of AVP mRNA in the magnocellular cell bodies of the PVN and the SON as well as AVP immunoreactivity in the zona interna of the median eminence were not changed by the treatment at days 4 and 8. In hypothyroid 15-day-old rats, SON AVP mRNA increased, AVP immunoreactivity decreased while plasma osmolality was enhanced. In conclusion, our data demonstrate that experimental hypothyroidism impairs specifically the maturation of hypothalamic parvocellular CRF and AVP gene expression during the stress hyporesponsive period. These observations suggest that the physiological peak in plasma thyroxine concentrations that occur between day 8-12 may participate in the maturation of hypothalamic CRF- and AVP-synthesizing cells.     

Regulation and role of p21-activated kinase 3 by corticotropin-releasing factor in mouse pituitary

Corticotropin-releasing factor (CRF) is a major regulatory peptide in the hypothalamic-pituitary-adrenal (HPA) axis under stress conditions. In response to stress, CRF, produced in the hypothalamic paraventricular nucleus, releases adrenocorticotropic hormone (ACTH) from the anterior pituitary (AP). ACTH in turn stimulates the release of glucocorticoid from the adrenal glands. Glucocorticoid then inhibits hypothalamic production of CRF and pituitary production of ACTH. Mice lacking a functional gene for CRF (CRF KO) showed severe impairment of the HPA axis, indicating that CRF is required for its regulation. We applied oligonucleotide microarray analysis to the AP of CRF KO to identify gene expression induced by CRF. Twenty-four genes showed less than 60% expression in CRF KO compared with normal mice. Real-time PCR analysis revealed that p21-activated kinase 3 (Pak3), prohormone convertase type 1 (PC1), and CRF-binding protein (BP) mRNA expression levels were increased by CRF in AP cells. Both Pak3 and PC1 were also increased by dexamethasone in AP cells, while CRF-BP mRNA levels were reduced. Therefore, both Pak3 and PC1 mRNA levels would be regulated by both CRF and glucocorticoids. Pak3 knockdown inhibited CRF-induced cell viability in AtT-20 cells, suggesting the important role of Pak3 in the proliferation of corticotrophs.     

The effects of ghrelin/GHSs on AVP mRNA expression and release in cultured hypothalamic cells in rats

Ghrelin, the endogenous ligand for growth hormone secretagogues (GHSs) receptor (GHS-R), increases adrenocorticotropin (ACTH) and cortisol (corticosterone) as well as GH secretion in humans and animals. However, the site of GHSs action to induce ACTH secretion is not fully understood. To clarify the mechanisms of the action of ghrelin/GHSs on ACTH secretion, we analyzed the effects of KP-102 and ghrelin on the mRNA expression and release of corticotropin releasing factor (CRF) and arginine vasopressin (AVP), ACTH secretagogues, in monolayer-cultured hypothalamic cells of rats. Incubation of cells with KP-102 for 4 h and 8 h and with ghrelin for 4 h significantly increased AVP mRNA expression and release without changing CRF mRNA expression. CRF levels in culture media were undetectable. Suppression of GHS-R expression by siRNA blocked ghrelin- and KP-102-induced AVP mRNA expression and release. NPY significantly increased AVP mRNA expression and release. Furthermore, treatment of cells with anti-NPY IgG blocked KP-102-induced AVP mRNA expression and release. We previously reported that KP-102 significantly increases NPY mRNA expression in cultured hypothalamic cells. Taken together, these results suggest that ACTH secretion by ghrelin/GHSs is induced mainly through hypothalamic AVP, and that NPY mediates the action of ghrelin/GHSs.     

The stress response neuropeptide CRF increases amyloid‐β production by regulating γ‐secretase activity

The biological underpinnings linking stress to Alzheimer's disease (AD) risk are poorly understood. We investigated how corticotrophin releasing factor (CRF), a critical stress response mediator, influences amyloid‐β (Aβ) production. In cells, CRF treatment increases Aβ production and triggers CRF receptor 1 (CRFR1) and γ‐secretase internalization. Co‐immunoprecipitation studies establish that γ‐secretase associates with CRFR1; this is mediated by β‐arrestin binding motifs. Additionally, CRFR1 and γ‐secretase co‐localize in lipid raft fractions, with increased γ‐secretase accumulation upon CRF treatment. CRF treatment also increases γ‐secretase activity in vitro, revealing a second, receptor‐independent mechanism of action. CRF is the first endogenous neuropeptide that can be shown to directly modulate γ‐secretase activity. Unexpectedly, CRFR1 antagonists also increased Aβ. These data collectively link CRF to increased Aβ through γ‐secretase and provide mechanistic insight into how stress may increase AD risk. They also suggest that direct targeting of CRF might be necessary to effectively modulate this pathway for therapeutic benefit in AD, as CRFR1 antagonists increase Aβ and in some cases preferentially increase Aβ42 via complex effects on γ‐secretase.     

Regulation of corticotropin-releasing factor receptor type 2beta mRNA by mitogen-activated protein kinases in aortic smooth muscle cells

The actions of the corticotropin-releasing factor (CRF) family of peptides are mediated by the seven transmembrane-domain G-protein-coupled receptors, the CRF receptors. CRF receptor type 2beta (CRFR2beta) messenger RNA (mRNA) is expressed primarily in the cardiovascular system, where its levels are decreased by urocortin 1 (Ucn1), a novel peptide in the CRF family. In a previous study, we reported that CRFR2beta mRNA levels were partially down-regulated via the cAMP-protein kinase A pathway. This study focused on the involvement of the intracellular mitogen-activated protein (MAP) kinase pathway in the modulation of CRFR2beta mRNA levels. Ribonuclease protection assays showed that decreases in CRFR2beta mRNA levels induced by Ucn1 and cAMP were attenuated by the p38 MAP kinase inhibitor SB202190 or SB203580. This finding suggested that the p38 MAP kinase pathway was involved in this regulation. Anisomycin, a classic p38 kinase activator, increased CRFR2beta mRNA levels in A7r5 cells. This effect of anisomycin was completely reversed by H7, a serine/threonine kinase inhibitor, while both p38 kinase and MAP kinase kinase inhibitors failed to block the increase in CRFR2beta mRNA levels caused by anisomycin. As anisomycin can activate Jun amino terminal kinases, as well as p38 MAP kinase, it is possible that other MAP kinases, such as Jun amino terminal kinases, also contribute to the increase in gene levels. Alternatively, anisomycin may increase CRFR2beta mRNA levels indirectly as a consequence of blocking protein synthesis.     

Transient gastric irritation in the neonatal rats leads to changes in hypothalamic CRF expression, depression- and anxiety-like behavior as adults

Aims

A disturbance of the brain-gut axis is a prominent feature in functional bowel disorders (such as irritable bowel syndrome and functional dyspepsia) and psychological abnormalities are often implicated in their pathogenesis. We hypothesized that psychological morbidity in these conditions may result from gastrointestinal problems, rather than causing them.

Methods

Functional dyspepsia was induced by neonatal gastric irritation in male rats. 10-day old male Sprague-Dawley rats received 0.1% iodoacetamide (IA) or vehicle by oral gavage for 6 days. At 8–10 weeks of age, rats were tested with sucrose preference and forced-swimming tests to examine depression-like behavior. Elevated plus maze, open field and light-dark box tests were used to test anxiety-like behaviors. ACTH and corticosterone responses to a minor stressor, saline injection, and hypothalamic CRF expression were also measured.

Results

Behavioral tests revealed changes of anxiety- and depression-like behaviors in IA-treated, but not control rats. As compared with controls, hypothalamic and amygdaloid CRF immunoreactivity, basal levels of plasma corticosterone and stress-induced ACTH were significantly higher in IA-treated rats. Gastric sensory ablation with resiniferatoxin had no effect on behaviors but treatment with CRF type 1 receptor antagonist, antalarmin, reversed the depression-like behavior in IA-treated rats

Conclusions

The present results suggest that transient gastric irritation in the neonatal period can induce a long lasting increase in depression- and anxiety-like behaviors, increased expression of CRF in the hypothalamus, and an increased sensitivity of HPA axis to stress. The depression-like behavior may be mediated by the CRF1 receptor. These findings have significant implications for the pathogenesis of psychological co-morbidity in patients with functional bowel disorders.     

Corticohypophysiotropic and corticotropic activity in adrenalectomized male and female rats after psychic stress

We show modifications in the hypothalamic CRF activity and plasma ACTH concentration in adult rats of both sexes, which were five day sham-operated or adrenalectomized and killed either under basal conditions or after a 3 min period or psychological stress. 1. Under basal conditions, the inhibition of the basal release of ACTH is suppressed in 5 day adrenalectomized rats and a sex difference appears: plasma ACTH concentration is twice as great in females than in males. 2. After a 3 min period of psychological stress, the usual increase in hypothalamic CRF activity observed in sham-operated rats, which seems to be sex-related, does not appear in adrenalectomized male or female rats. However, in adrenalectomized rats, the maximal increase in plasma ACTH concentration occurred more rapidly, with a rate 10 times as great in males and 4 times as great in females, than in sham-operated rats. Differences between the sexes in the maximal increase in plasma ACTH concentration remains 1,6 times as great in females than in males. 3. Our results confirm that corticosteroids exert: (1) a tonic feedback inhibition of the basal release of ACTH, (2) a fast feedback inhibition of the stress induced release of ACTH; the promote an increase in the hypothalamic CRF content. Relative intensity of these two inhibitory mechanisms seems to be sex-related.     

The effects of corticotropin-releasing factor and the urocortins on hypothalamic gamma-amino butyric acid release--the impacts on the hypothalamic-pituitary-adrenal axis

Corticotropin-releasing factor (CRF) and the urocortins (UCNs) are structurally and pharmacologically related neuropeptides which regulate the endocrine, autonomic, emotional and behavioral responses to stress. CRF and UCN1 activate both CRF receptors (CRFR1 and CRFR2) with CRF binding preferentially to CRFR1 and UCN1 binding equipotently to both receptors. UCN2 and UCN3 activate selectively CRFR2. Previously an in vitro study demonstrated that superfusion of both CRF and UCN1 elevated the GABA release elicited by electrical stimulation from rat amygdala, through activation of CRF1 receptors. In the present experiments, the same in vitro settings were used to study the actions of CRF and the urocortins on hypothalamic GABA release. CRF and UCN1 administered in equimolar doses increased significantly the GABA release induced by electrical stimulation from rat hypothalamus. The increasing effects of CRF and UCN1 were inhibited considerably by the selective CRFR1 antagonist antalarmin, but were not influenced by the selective CRFR2 antagonist astressin 2B. UCN2 and UCN3 were ineffective. We conclude that CRF1 receptor agonists induce the release of GABA in the hypothalamus as well as previously the amygdala. We speculate that CRF-induced GABA release may act as a double-edged sword: amygdalar GABA may disinhibit the hypothalamic CRF release, leading to activation of the hypothalamic-pituitary-adrenal axis, whereas hypothalamic GABA may inhibit the hypothalamic CRF release, terminating this activation.     

Possible involvement of orexin in the stress reaction in rats

We examined whether corticotropin-releasing factor (CRF) was involved in orexin-induced grooming and face-washing behaviors, and whether orexin was involved in the stress reaction. Administration of alpha-helical CRF, CRF antagonist, alone had no behavioral effect, but it blocked the orexin-induced grooming and face-washing behaviors in rats. The level of corticosterone increased in a dose-dependent manner 15 min after icv injection of orexin, and it remained high for at least 60 min. In 2-month-old rats, 1 h of immobilization stress increased orexin mRNA levels, but not the melanin-concentrating hormone (MCH) mRNA, in the lateral hypothalamic area (LHA). In 6-month-old rats, 30 min of cold stress increased the expression of orexin mRNA in the LHA. Unlike in the 2-month-old rats, immobilization stress did not change orexin mRNA expression in 6-month-old rats. These results suggest that CRF is involved in orexin-induced behaviors, and that orexin may play an important role in some stress reactions.     

Chronic leptin administration in developing rats reduces stress responsiveness partly through changes in maternal behavior

In adult rodents, leptin has been shown to significantly alter the activity of several neuroendocrine functions, including the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Leptin is generally believed to be inhibitory to HPA activity in adults. Developing rat pups have high circulating levels of leptin, which begs the question of leptin's physiological role in controlling basal and stress-induced adrenocortical activity in neonatal rats. In this study, we treated rat pups daily from days 2-9 (or 6-10) of life with either vehicle or leptin (1 or 3 mg/kg body wt, ip) and determined the effects on body weight gain, fat pad deposits, and HPA activity in 10-day-old pups. We measured hypothalamic CRF mRNA levels in vehicle- and leptin-treated pups by in situ hybridization and determined plasma ACTH, corticosterone, and leptin concentrations under basal conditions or following exposure to a 3-min ether stress. Because leptin activates sympathetic activity and energy expenditure in adults and possibly also in rat pups, and because litter temperature is an important determinant of maternal behavior, we also investigated whether chronic leptin administration would modify aspects of maternal care that are important for the maintenance of HPA function. Chronic leptin treatment increased circulating levels of leptin and had significant dose-related metabolic effects, including reduced body weight gain and fat pad weight in 10-day-old pups. Basal expression of CRF mRNA in the PVN or secretion of ACTH and corticosterone was not modified by leptin treatment. In contrast, chronically elevated leptin concentrations during the neonatal period significantly lowered CRF expression in the PVN 60 min after stress and reduced the duration of the ACTH response to stress in pups, suggesting that glucocorticoid feedback on the HPA axis might be altered by this treatment. In addition, mothers caring for pups injected with leptin displayed longer bouts of anogenital licking of pups than mothers of vehicle-treated rats. Given that this particular type of pup stimulation has been shown to influence stress responsiveness, it is possible that the maternal response modulates the effects of exogenous leptin treatment. In conclusion, our results demonstrate that the leptin signal is functional during the early developmental period and that leptin can modulate the hormonal response to stress in young rats either by a direct effect on the HPA axis or indirectly through changing some aspects of maternal behavior.     

Separate locations of urocortin and its receptors in mouse testis: function in male reproduction and the relevant mechanisms.

Urocortin (UCN), a newly identified corticotrophin-releasing-factor (CRF) related peptide, has been demonstrated to play important roles in female reproductive system. However, few studies were reported about its effects on male reproduction. This study aimed to investigate the expression profile of UCN and CRF receptors (CRFR) in mouse testis and functions of UCN in male reproduction. Expression of UCN and CRFR mRNA was detected by RT-PCR. Localization of UCN peptide was determined by immunohistochemistry and double-immunostaining. We found that both UCN mRNA and peptide were obviously expressed in mature spermatozoa, whereas CRFR1 and CRFR2 were expressed respectively in spermatocytes and spermatogonia. Double-immunostaining results showed that UCN expression decreased with acrosome reaction (AR) proceeding. UCN significantly inhibited AR initiated by progesterone with chlortetracycline staining and decreased spermatozoa motility concentration-dependently. Pre-incubation of spermatozoa with astressin, a CRFR antagonist, did not affect these inhibitions. In addition, flow cytometry showed that UCN concentration-dependently decreased intracellular Ca(2+) [Ca(2+)](i) in spermatozoa. In summary, UCN located in mouse spermatozoa and exerted inhibitory effects on male reproductive functions including motility and AR. UCN's inhibition on [Ca(2+)](i) via T-type calcium channels might be responsible for these effects.     

Sex differences in the effects of chronic stress and food restriction on body weight gain and brain expression of CRF and relaxin‐3 in rats

This study investigated sex‐specific effects of repeated stress and food restriction on food intake, body weight, corticosterone plasma levels and expression of corticotropin‐releasing factor (CRF) in the hypothalamus and relaxin‐3 in the nucleus incertus (NI). The CRF and relaxin‐3 expression is affected by stress, and these neuropeptides produce opposite effects on feeding (anorexigenic and orexigenic, respectively), but sex‐specific regulation of CRF and relaxin‐3 by chronic stress is not fully understood. Male and female rats were fed ad libitum chow (AC) or ad libitum chow and intermittent palatable liquid Ensure without food restriction (ACE), or combined with repeated food restriction (60% chow, 2 days per week; RCE). Half of the rats were submitted to 1‐h restraint stress once a week. In total, seven weekly cycles were applied. The body weight of the RCE stressed male rats significantly decreased, whereas the body weight of the RCE stressed female rats significantly increased compared with the respective control groups. The stressed female RCE rats considerably overate chow during recovery from stress and food restriction. The RCE female rats showed elevated plasma corticosterone levels and low expression of CRF mRNA in the paraventricular hypothalamic nucleus but not in the medial preoptic area. The NI expression of relaxin‐3 mRNA was significantly higher in the stressed RCE female rats compared with other groups. An increase in the expression of orexigenic relaxin‐3 and misbalanced hypothalamic‐pituitary‐adrenal axis activity may contribute to the overeating and increased body weight seen in chronically stressed and repeatedly food‐restricted female rats .     

Differences in response to corticotropin-releasing factor after short- and long-term consumption of a high-fat diet

We previously reported an exaggerated endocrine and weight loss response to stress in rats fed a high-fat (HF) diet for 5 days. Others report blunted stress-induced anxiety in rats made obese on a HF diet. Experiments described here tested whether sensitivity to stress-related peptides was changed in obese and nonobese HF-fed rats. Third ventricle infusion of corticotropin-releasing factor (CRF) in rats made obese on HF diet (40% kcal fat) produced an exaggerated hypophagia, which is thought to be mediated by CRF(2) receptors. Obese rats responded to a lower dose of CRF for a longer time than rats fed a low-fat (LF) diet (12% kcal fat). CRF-induced release of corticosterone, which is thought to be mediated by CRF(1) receptors, was not exaggerated in obese HF-fed rats. In contrast, rats fed HF diet for 5 days showed the same food intake and corticosterone response to CRF as LF-fed rats. CRF mRNA expression in the paraventricular nucleus of the hypothalamus was stimulated by mild stress (ip saline injection and placement in a novel cage) in LF-fed rats but not in rats fed HF diet for 5 days because of a nonsignificant increase in expression in nonstressed HF-fed rats. In addition, nonstressed levels of urocortin (UCN) I mRNA expression in the Edinger-Westphal nucleus were significantly inhibited in HF-fed rats. These data suggest that rats that have become obese on a HF diet show a change in responsiveness to stress peptides, whereas the increased stress response in nonobese HF-fed rats may be associated with changes in basal CRF and UCN I mRNA expression.     

Type 1 corticotropin-releasing factor receptors in the ventromedial hypothalamus promote hypoglycemia-induced hormonal counterregulation

Type 2 corticotropin-releasing factor (CRF) receptors (CRFR2) within the ventromedial hypothalamus (VMH), a key glucose-sensing region, play a major role in regulating the hormonal counterregulatory responses (CRRs) to acute hypoglycemia. The VMH expresses both subtypes of CRF receptors, CRFR1 and CRFR2. The objective of this study was to examine the role of the CRFR1 receptor in the VMH in the regulation of the CRR to acute hypoglycemia. To compare the hormonal CRR to hypoglycemia, awake and unrestrained Sprague-Dawley rats were bilaterally microinjected to the VMH with either 1) aECF, 2) CRF (1 pmol/side), 3) CRFR1 antagonist Antalarmin (500 pmol/side), or 4) CRF + Antalarmin prior to undergoing a hyperinsulinemic hypoglycemic (2.8 mM) clamp. A second series of studies also incorporated an infusion of [(3)H]glucose to allow the calculation of glucose dynamics. In addition the effect of CRFR1 antagonism in the paraventricular nucleus (PVN) was studied. Activation of VMH CRFR1 increased, whereas inhibition of CRFR1 suppressed hypoglycemia-induced CRRs. Inhibition of VMH CRFR1 also increased peripheral glucose utilization and reduced endogenous glucose production during hypoglycemia, whereas VMH CRF reduced peripheral glucose utilization. In contrast CRFR1 inhibition in the PVN blunted corticosterone but not epinephrine or glucagon CRR to hypoglycemia. In contrast to CRFR2 activation, CRFR1 activation within the VMH amplifies CRRs to acute hypoglycemia. The balance between these two opposing CRFRs in this key glucose-sensing region may play an important role in determining the magnitude of CRRs to acute hypoglycemia.     

Effects of antalarmin,a CRF receptor 1 antagonist,on fright reaction and endocrine stress response in crucian carp (<Emphasis Type="Italic">Carassius carassius</Emphasis>)

The corticotrophin-releasing factor (CRF) receptors show striking homogeneity throughout the vertebrate subphylum. In mammals, the CRF(1) receptor (CRFR(1)) plays an important role in mediating behavioral and endocrine responses to fear and stress. The specific roles of this receptor subtype in fear and stress reactions in non-mammalian vertebrates are largely unknown. Crucian carp displays the olfactory-mediated fright reaction, a stereotypic behavioral response to waterborne cues from damaged skin of conspecifics. This reaction shows several similarities to basic components of avoidance behavior in mammals. In the present study, we applied the non-peptide CRFR(1) antagonist, antalarmin, to crucian carp 1 h before exposure to conspecific skin extract. This treatment resulted in a suppression of the fright reaction. After skin extract exposure, antalarmin treatment also lead to lower plasma cortisol values, as compared to vehicle treatment. This suppression of the behavioral fright reaction and the stress induced rise in plasma cortisol in crucian carp suggests that the functions of the CRFR(1) are conserved by evolution.