Inhibitory Effect Of Corticotropin-releasing Factor Research Articles

CRF-5-HT interactions in the dorsal raphe nucleus and motivation for stress-induced opioid reinstatement.

The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our previous data show that stressors can inhibit 5-HT neuronal activity and release by stimulating the release of the stress neurohormone corticotropin-releasing factor (CRF) within the serotonergic dorsal raphe nucleus (DRN). The inhibitory effects of CRF on 5-HT DRN neurons are indirect, mediated by CRF-R1 receptors located on GABAergic afferents. We tested the hypothesis that DRN CRF-R1 receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP). We also examined the role of this circuitry in stress-induced negative affective state with 22-kHz distress ultrasonic vocalizations (USVs), which are naturally emitted by rats in response to environmental challenges such as pain, stress, and drug withdrawal. First, we tested if activation of CRF-R1 receptors in the DRN with the CRF-R1-preferring agonist ovine CRF (oCRF) would reinstate morphine CPP and then if blockade of CRF-R1 receptors in the DRN with the CRF-R1 antagonist NBI 35965 would attenuate swim stress-induced reinstatement of morphine CPP. Second, we tested if intra-DRN pretreatment with NBI 35965 would attenuate foot shock stress-induced 22-kHz USVs. Intra-DRN injection of oCRF reinstated morphine CPP, while intra-DRN injection of NBI 35965 attenuated swim stress-induced reinstatement. Moreover, intra-DRN pretreatment with NBI 35965 significantly reduced 22-kHz distress calls induced by foot shock. These data provide evidence that stress-induced negative affective state is mediated by DRN CRF-R1 receptors and may contribute to reinstatement of morphine CPP.

Inhibitory effect of corticotropin-releasing factor on food intake in the bullfrog, Aquarana catesbeiana

Corticotropin-releasing factor (CRF) and CRF-related peptides exert hypophysiotropic and anorexigenic effects in mammals and teleost fish. In anuran amphibians, CRF acts as a potent stimulator of thyrotropin release from the pituitary. According to our recent study, CRF also acts as an anorexigenic factor for the cessation of food intake in the metamorphosing bullfrog larvae. However, the anorexigenic action of CRF has not been confirmed in adult bullfrogs. In this context, we examined the effect of feeding status on the expression level of the CRF transcript in the hypothalamus of the adult bullfrog. Levels of CRF mRNA in the hypothalami from bullfrogs fasted for 7 days were lower than in those from the bullfrogs that had been fed normally. Subsequently, we developed a method for measuring food intake in adult bullfrogs, and then investigated the effect of CRF on their food consumption in these animals. Intracerebroventricular (ICV) administration of CRF at 1 and 10pmol/g body weight (BW) induced a significant decrease of food intake during 60min. The CRF-induced anorexigenic action was blocked by treatment with a CRF receptor 1/CRF receptor 2 antagonist, α-helical CRF(9–41), at 100pmol/g BW. These results provide direct evidence for the inhibitory effect of CRF on food intake, and suggest the involvement of CRF in the regulation of feeding through a CRF receptor-signaling pathway in the adult bullfrog.

Pro- and Anti-Nociceptive Effects of Corticotropin-Releasing Factor (CRF) in Central Amygdala Neurons Are Mediated Through Different Receptors

Corticotropin-releasing factor (CRF) is not only a stress hormone but also acts as a neuromodulator outside the hypothalamic-pituitary-adrenocortical axis, playing an important role in anxiety, depression, and pain modulation. The underlying mechanisms remain to be determined. A major site of extra-hypothalamic expression of CRF and its receptors is the amygdala, a key player in affect-related disorders such as anxiety. The latero-capsular division of the central nucleus of the amygdala (CeLC) is also important for pain modulation and pain affect. This study analyzed the effects of CRF on nociceptive processing in CeLC neurons and the contribution of CRF1 and CRF2 receptors and protein kinases A and C. Extracellular single-unit recordings were made from CeLC neurons in anesthetized adult rats. All neurons responded more strongly to noxious than innocuous mechanical stimulation of the knee. Evoked responses and background activity were measured before and during administration of CRF into the CeLC by microdialysis. CRF was administered alone or together with receptor antagonists or protein kinase inhibitors. CRF (0.01-1 microM; concentrations in microdialysis probe; 15 min) facilitated the evoked responses more strongly than background activity; a higher concentration (10 microM) had inhibitory effects. Facilitation by CRF (0.1 microM) was reversed by a selective CRF1 receptor antagonist (NBI27914, 10 microM) but not a CRF2 receptor antagonist (astressin-2B, 100 microM) and by a protein kinase A (PKA) inhibitor (KT5720, 100 microM) but not a protein kinase C inhibitor (GF109203X, 100 microM). Inhibitory effects of CRF (10 microM) were reversed by astressin-2B. These data suggest that CRF has dual effects on amygdala neurons: CRF1 receptor-mediated PKA-dependent facilitation and CRF2 receptor-mediated inhibition.

Psychological Stress can Trigger Atopic Dermatitis in NC/Nga Mice: An Inhibitory Effect of Corticotropin-Releasing Factor

Atopic dermatitis (AD) is one of the most common inflammatory diseases of the skin and is usually associated with a family history of atopic diathesis. It has been well established that many environmental or psychological factors aggravate AD. However, it is not clear whether psychological stress by itself can trigger AD. We examined the effect of psychological stress on the onset of AD, using an animal model, the NC/Nga mouse. The animals were exposed to the water avoidance stress (WAS) test to induce psychological stress. Additionally, we examined how corticotropin-releasing factor (CRF) affected the development of AD induced by psychological stress. Under specific pathogen-free (SPF) conditions, NC/Nga mice did not develop AD-like skin lesions. In contrast, NC/Nga mice exposed to psychological stress developed AD-like skin lesions along with elevated levels of serum immunoglobulin E even when kept under SPF conditions. The AD-like skin lesions induced by WAS were completely blocked by pretreating the animals with CRF. Our data indicate that a psychological factor is capable of eliciting AD-like skin lesions in NC/Nga mice. It is possible that the inhibitory effect of CRF may be mediated by the functional modification of various cells that have CRF receptors.

Novel effects of CRF on visuomotor behavior and autonomic function in anuran amphibians

Administration of corticotropin-releasing factor (CRF) or exposure to stressors inhibits feeding in anuran amphibians. Since most amphibians rely on visual cues for feeding, these findings have led to the hypothesis that CRF may modulate visuomotor pathways involved in prey detection and predator avoidance. The inhibitory effects of CRF on feeding and prey capture are rapid, and do not appear to require the pituitary-adrenal axis in the short term. CRF neurons are located in key visuomotor processing areas of the anuran brain. Corticotropin-releasing factor also has potent stimulatory effects on sympathetic nervous system activity, a key regulatory system involved in both prey capture and predator avoidance. In this review I will discuss the unique model that amphibian species provide for investigating CRF effects on visual perception and visuomotor processing, and will summarize the data suggesting a role for CRF in visuomotor behavior and autonomic function in amphibians.

Corticotropin-releasing factor inhibits luteinizing hormone-stimulated P450c17 gene expression and androgen production by isolated thecal cells of human ovarian follicles.

Recently, we reported that the thecal compartment of the human ovary contains a CRF system replete with gene expression and protein for corticotropin-releasing factor (CRF), CRF-Receptor 1 (CRF-R1), and the blood-derived high affinity CRF binding protein (CRF-BP). Granulosa cells are devoid of the CRF system. The parallel increases in intensity of CRF, CRF-R1, and 17 alpha-hydroxylase messenger ribonucleic acid (mRNA) and proteins in thecal cells with follicular maturation suggest that the intraovarian CRF system may play an autocrine role regulating androgen biosynthesis, with a downstream effect on estrogen production by granulosa cells. The functionality of the ovarian CRF system may be conditioned by the relative presence of plasma-derived CRF-BP by virtue of its localization of protein, but not transcript in thecal cells and its ability to compete with CRF for the CRF receptor. To further these findings, in the present study we have examined the effect of CRF on LH-stimulated 17 alpha-hydroxylase (P450c17) gene expression and androgen production by isolated thecal cells from human ovarian follicles (11-13 mm). During the 48-h culture, addition of LH (10 ng/mL) to the medium increased by 5- and 6-fold dehydroepiandrosterone and androstenedione production by thecal cells. Remarkably, the LH-stimulated, but not basal, androgen production was inhibited by CRF in a time- and dose-dependent manner. The half-maximal (ID50) effect dose of CRF occurred at 5 x 10(-8) mol/L, and at a maximal concentration of 10(-6) mol/L, CRF completely inhibited LH-stimulated androgen production. This inhibitory effect of CRF became evident at 12 h (45%), and by 24 h the effect was more pronounced, with a 70% reduction from baseline. As determined by Northern analyses, CRF dose dependently decreased LH-stimulated P450c17 mRNA levels, with a maximal inhibition of 85% P450c17 gene expression at a CRF concentration of 10(-6) mol/L. With the addition of 10(-6) mol/L of the antagonist alpha-helical CRF-(9-41), the inhibitory effect of CRF was partially reversed for both P450c17 mRNA (75%) and androgen production (50%), indicating the CRF-R1-mediated event. In conclusion, the present study demonstrated a potent inhibitory effect of CRF on LH-stimulated dehydroepiandrosterone and androstenedione production that appears to be mediated through the reduction of P450c17 gene expression. Thus, the ovarian CRF system may function as autocrine regulators for androgen biosynthesis in the thecal cell compartment to maintain optimal substrate for estrogen biosynthesis by granulosa cells. Further studies to define the role of CRF-BP in the endocrine modulation of the intraovarian CRF system are needed.

Effect of corticotropin releasing factor (CRF) injected into the median eminence on LH secretion in male rats.

We determined the dose-response relationship and examined the time-related effect of CRF (corticotropin releasing factor) injected directly into the Median Eminence (ME) on LH secretion in conscious intact and castrated male rats. Doses of 0.25, 0.75, 1, and 1.5 nmol CRF dissolved in 1 microl of saline (or saline only in the controls) were injected into the ME and blood samples collected 30, 60, 90, and 120 min postinjection to determine by RIA serum LH. CRF at doses of 0.75, 1 and 1.5 nmol significantly decreased serum LH in castrated and intact animals. The lower dose of CRF did not decrease LH in the two groups studied. The results suggest that in males as in females, CRF inhibits by itself LH secretion, at least in part, by a central action in the ME; the inhibitory effect of CRF on LH is similar in castrated and intact males; the dose of 0.25 nmoles of CRF was ineffective in decreasing LH and finally that CRF at ME levels may participate in a variety of stress-related responses, including reproduction inhibition, through LH suppression.

Effect of CRF injected into the median eminence on GH secretion in female rats under different steroid status.

To evaluate whether the median eminence (ME) is a site of action of CRF (corticotropin releasing factor) on GH secretion and to determine the possible role of estradiol and progesterone in modifying theses secretion, we injected CRF (0.25, 0.75, 1, and 1.5 nmol of peptide dissolved in 1 microliter of water) directly into the ME in three experimental groups of rats: Long-term ovariectomized (OVX); OVX primed by estradiol (OVX +/- E) and OVX primed by estradiol plus progesterone (OVX +/- EP). Blood was collected to determine GH (30, 60, 90, and 120 min postinjection). Serum T3, T4, and glucose levels were measured in OVX +/- E rats 30 min postinjection. CRF at all doses studied significantly decreased serum GH levels in the three experimental groups. Serum T3, T4, and glucose levels were unchanged after CRF administration. The results suggest that: CRF inhibits "per se" GH secretion, at least in part, by a central action in the ME. The inhibitory effect of CRF on GH is independent of the estrogen/progesterone status of the animal. CRF at ME levels may participate in a variety of stress-related responses, including growth inhibition, through GH suppression.

Microinfusion of corticotropin-releasing factor into the locus coeruleus/subcoeruleus nuclei inhibits gastric acid secretion via spinal pathways in the rat

Brain corticotropin-releasing factor (CRF) is involved in stress-related alterations of gastric acid secretion. CRF in the locus coeruleus has been shown to induce anxiogenic behavioral responses and to mimic stress-induced alterations of colonic motor function. Whether the locus coeruleus/subcoeruleus nucleus (LC/SC) is a site of action for CRF to alter gastric acid secretion was investigated in urethane-anesthetized gastric fistula rats. In sham-operated animals, CRF (126–420 pmol) microinfused bilaterally into the LC/SC induced a dose-dependent inhibition of pentagastrin (PG)-stimulated gastric acid secretion of 60–81%, within the first hour after microinjection. At the 420 pmol dose, this inhibitory effect of CRF into the LC/SC lasted throughout the whole observation period of 120 min. After bilateral vagotomy, basal and PG-stimulated gastric acid secretion at microinjection of vehicle was reduced. Nevertheless, microinfusion of 420 pmol CRF into the LC/SC still inhibited significantly gastric acid secretion by 62.1%. In contrast, in spinal cord transected animals bilateral microinfusion of 420 pmol CRF into the LC/SC did not reduce PG-stimulated gastric acid secretion. These data indicate that CRF acts in the LC/SC to induce a long lasting inhibition of peripherally stimulated gastric acid secretion via spinal pathways. These findings suggest a possible role of the LC/SC in the regulation of gastric secretion and of endogenous CRF at these sites in the stress-related inhibition of gastric acid secretion by affecting autonomic nervous system activity.

Inhibition of Gastric Motor Function by Circulating Corticotropin‐Releasing Factor in Anesthetized Rats

We have investigated the influence of intravenous corticotropin‐releasing factor (CRF) on intraluminal pressure of the body of the stomach and the neurohumoral pathways through which CRF inhibits gastric motor function in rats. CRF (0.21–210 pmol) injected intravenously produced a dose‐dependent, long‐lasting decrease in baseline tone and inhibited phasic gastric contractions measured manometrically in urethane‐anesthetized rats. The inhibitory effect of CRF was abolished by administration of hexamethonium or by subdiaphragmatic vagotomy but was unaffected by perineural treatment of the vagus nerves with capsaicin, adrenalectomy, or celiac/superior mesenteric ganglionectomy. Intravenous administration of CRF (126 pmol) inhibited by 69% the emptying of a noncaloric liquid meal as measured by the phenol red technique in conscious rats. Hexamethonium pretreatment significantly attenuated the CRF ‐induced delay in gastric emptying; bretylium, naloxone, adrenalectomy, and celiac I superior mesenteric ganglionectomy had no such effect. In an isolated tissue preparation, CRF (10−11 to 10−6 M) inhibited spontaneous, but not carbachol‐induced, contractions of rat antral longitudinal muscle. The effect of CRF was dose‐dependent and abolished in the presence of tetrodotoxin. These results suggest that peripheral CRF‐induced inhibition of corpus and antral motor contractility may mediate delayed gastric emptying via an action involving a nicotinic synapse, presumably in the enteric nervous system, that requires a vagal input. The in vitro studies support the concept that the action of CRF is not direct on smooth muscle but involves neural transmission within the enteric nervous system.

Influence of corticotropin-releasing factor on reproductive functions in the rat.

The acute administration of 0.015-1.5 nmol ovine corticotropin-releasing factor (CRF) into the lateral ventricle of gonadectomized (or gonadectomized/adrenalectomized) female rats caused a rapid and prolonged dose-related inhibition of LH (but not FSH) secretion. By contrast, the acute peripheral injection of up to 15 nmol CRF was without effect in the same animal preparations. In cycling intact female rats, injection of 1.5 nmol CRF into the brain or of 75 nmol CRF sc inhibited ovulation and blocked the proestrous LH surge in about 50% of the animals. Lower doses of peripherally administered CRF were ineffective. Finally, CRF injected daily sc (15 nmol/day) to female rats during the first 12 days after mating caused a 40% disruption of pregnancy. These results indicate that CRF will lower plasma LH levels and can exert this effect in the absence of circulating steroids of either adrenal or gonadal origin. CRF inhibition of LH secretion, which we have previously reported to be absent in vitro, was unaltered by the opiate receptor antagonist naltrexone or by the ganglionic blocker chlorisondamine. Furthermore, blockade of CRF-induced beta-endorphin or ACTH release into the general circulation by dexamethasone did not interfere with the inhibitory effect of CRF on LH secretion. Such observations suggest that CRF exerts deleterious actions on reproductive functions through brain sites of action which, at least under the experimental mental design used, do not appear to directly involve opiate or peripheral catecholaminergic pathways.

Inhibition of gastric acid secretion in rats and in dogs by corticotropin-releasing factor

Intravenously injected synthetic ovine corticotropin-releasing factor inhibited gastric secretion by reducing gastric secretory volume, acid concentration, and acid output, but elevated plasma gastrin levels in conscious 2-h pylorus-ligated rats. Corticotropin-releasing factor suppressed pentagastrinstimulaled gastric acid output at intravenous doses of 4–17 nmol · kg−1 · h−1 in urethane-anesthetized, gastric fistula rats and at 0.1–1-nmol · kg−1 · h−1 doses in conscious, gastric-fistula dogs. The inhibitory effect of corticotropin-releasing factor was dosedependent, long-lasting, and reversible. The other newly characterized hypothalamic-hypophysiotropic peptide, growth hormone-releasing factor, hpGRF (1–40), infused at a dose of 18 nmol · kg−1 · h−1, did not modify gastric acid secretion stimulated by pentogastrin in rats. Gastric response to corticotropin-releasing factor in rats was altered neither by naloxone (5 mg/kg i.p.) or indomethacin (10 mg/kg i.p.) pretreatment, nor by hypophysectomy or adrenalectomy, but was partly reversed by vagotomy. These results demonstrate that corticotropin-releasing factor inhibits gastric acid secretion in both rats and dogs. The inhibitory effect of corticotropinreleasing factor on gastric secretion does not require the presence of the pituitary or the adrenal glands. or a functional prostaglandin biosynthetic pathway, and is not mediated through changes in gastrin secretion. It appears to be partially dependent on a degree of vagal tone as well as other mechanisms that await further elucidation.

Inhibition of gastric acid secretion in rats by intracerebral injection of corticotropin-releasing factor.

Intracisternal injection of ovine corticotropin-releasing factor (CRF) into the pylorus-ligated rat or the rat with gastric fistula resulted in a dose-dependent inhibition of gastric secretion stimulated with pentagastrin or thyrotropin-releasing hormone. When injected into the lateral hypothalamus--but not when injected into the cerebral cortex--CRF suppressed pentagastrin-stimulated acid secretion. The inhibitory effect of CRF was blocked by vagotomy and adrenalectomy but not by hypophysectomy or naloxone treatment. These results indicate that CRF acts within the brain to inhibit gastric acid secretion through vagal and adrenal mechanisms and not through hypophysiotropic effects.

Adrenal modulation of the inhibitory effect of corticotropin releasing factor on feeding

Corticotropin releasing factor (CRF) reduces food intake in rats after central administration. In these studies we examined whether the adrenal gland and the vagus were involved in CRF suppression of intake. One hour intake was reduced by a 5 μg (ICV) injection of CRF in sham but not adrenalectomized rats maintained on 0.9% NaCl. In a separate experiment on rats maintained on tap water, the inhibitory effect of CRF (5 μg) lasted at least 4 hours in sham rats whereas adrenalectomized rats did not significantly differ from controls. These experiments suggest that the adrenal gland modulates the feeding response to CRF. As replacement with corticosterone (0.75 mg/kg) in total adrenalectomized rats did not restore responsiveness to 5 or 10 μg of CRF, we next studied whether the adrenal medulla was responsible for the decreased responsiveness to CRF. In rats lacking the adrenal medulla only, food intake was reduced by a 5 μg injection of CRF; in sham rats, intake was significantly reduced by doses as low as 0.1 μg of CRF. An additional experiment examined the effect of gastric vagotomy on the CRF feeding response. Vagotomized rats were as responsive to 5 and 10 μg injections of CRF as sham rats, which suggests that the effect is not dependent on the vagus nerve. These findings indicate that the adrenal gland, primarily the medulla, plays an intermediate role in the reduction of food intake caused by central injections of CRF. This conclusion is consistent with the known effect of CRF on adrenomedullary discharge.