Brain corticotropin-releasing factor acts as inhibitor of stress-induced gastric erosion in rats

The Realization of the Brain-Gut Interactions with Corticotropin-Releasing Factor and Glucocorticoids

BACKGROUND

The brain and the gut interact bi-directionally through the brain-gut axis. The interaction is mediated by the autonomic nervous system and the hypothalamic-pituitary-adrenocortical (HPA) system. The first brilliant demonstration of the brain-gut interactions was the cephalic phase of gastric and pancreatic secretion discovered by Ivan Pavlov, the first physiologist who was awarded the Nobel Prize for Physiology or Medicine in 1904. This review aims to identify the HPA system as a key hormonal branch of the brain-gut axis in stress.

METHODS

We first outlined main components of the brain-gut axis and then focused on the HPA system as a key hormonal branch of the brain-gut axis in stress. We undertook a structured search of bibliographic databases for peer-reviewed research literature using a focused review question.

RESULTS

Seventy-one articles were included in the review, the eleventh of them were articles of Filaretova L. and co-authors. We will discuss in our articles how an endocrinological approach to gastroenterological field can advance our understanding of the HPA axis role in regulation of gastric mucosal integrity and uncover new findings. According to these findings activation of the HPA system is gastroprotective component of the brain-gut axis in stress but not ulcerogenic one as it was generally accepted. Corticotropin-releasing factor (CRF) and glucocorticoids are important natural players provided gastroprotection. The results suggest that an initial action of endogenous glucocorticoids, including stress- and CRF-produced ones, as well as exogenous glucocorticoids, even used at pharmacological doses, is physiological gastroprotective. Prolongation of the hormonal action may lead to the transformation of gastroprotective hormonal effect to proulcerogenic one.

CONCLUSION

The findings of this review demonstrate that corticotropin-releasing factor and glucocorticoids contribute to the realization of the brain-gut interactions and that activation of the HPA system is gastroprotective component of this interaction in stress.

Role of urocortin 2 secreted by the pituitary in the stress-induced suppression of luteinizing hormone secretion in rats

We have previously shown that urocortin 2 (Ucn 2), a member of the corticotropin-releasing factor (CRF) peptide family that binds to CRF type 2 receptor, is expressed in proopiomelanocortin (POMC) cells of rat pituitary and that its secretion and expression are increased by CRF in both the anterior and intermediate lobes and suppressed by glucocorticoids in the anterior lobe. We have also shown that Ucn 2 secreted by POMC cells acts on gonadotrophs expressing CRF type 2 receptors and inhibits the expression and secretion of gonadotropins. In the present study, we examined whether pituitary Ucn 2 is involved in stress-induced inhibition of gonadotropin secretion. A 90-min period of immobilization stress increased POMC mRNA expression without influencing Ucn 2 mRNA expression and suppressed luteinizing hormone (LH) β-subunit mRNA expression in the anterior lobe and plasma LH levels, while it increased both POMC and Ucn 2 mRNA expression in the intermediate lobe of the pituitary. Pretreatment with anti-CRF IgG blocked immobilization-induced increases in plasma ACTH and corticosterone and in POMC mRNA expression in both pituitary lobes and Ucn 2 mRNA expression in the intermediate pituitary. It also blocked immobilization-induced suppression of plasma LH and LH β-subunit mRNA expression. Pretreatment with anti-Ucn 2 IgG blocked immobilization-induced suppression of plasma LH and LH β-subunit expression without affecting immobilization-induced ACTH and corticosterone release and POMC or Ucn 2 mRNA expression. These results suggest that CRF suppresses the secretion and expression of LH probably through pituitary Ucn 2 in stress.

The hypothalamus-pituitary-adrenal axis does not influence the protective effects of nociceptin/orphanin FQ on the rat gastric mucosa

The participation of hypothalamus-pituitary-adrenal axis in the gastroprotective effects of nociceptin/orphanin FQ (N/OFQ) has been investigated. Gastric mucosal lesions were induced by intragastric administration of 50% ethanol, 1 ml/rat. Rats received N/OFQ either by the intracerebroventricular (icv) route, at 3 microg/rat, or by the intraperitoneal (ip) route, at 10 microg/kg, 30 min before ethanol administration. The protective effect of icv and ip administered N/OFQ was assessed in adrenalectomized rats and in rats pretreated with the glucocorticoid receptor antagonist, mifepristone, or with the CRF receptor antagonist, alpha-helical CRF(9-41). The damaging effect of ethanol was apparently not influenced by adrenalectomy. N/OFQ markedly reduced macroscopically and histologically assessed gastric mucosal damage. The extent of reduction by N/OFQ was comparable in adrenalectomized and in sham-operated rats, with either icv or ip route of administration. Pretreatment with mifepristone, both icv (80 microg/rat) and ip (10 mg/kg) injected, did not modify the response to icv and ip N/OFQ. Pretreatment with alpha-helical CRF(9-41) (25 microg/rat icv or 250 microg/kg ip), had no effect on the reduction of gastric damage produced by icv or ip N/OFQ. Present findings suggest that the gastroprotective effects of N/OFQ on ethanol-induced damage do not involve the endocrine pathway through the HPA axis.

Gastric ulceration and expression of prolactin receptor in the brain in Hatano high- and low-avoidance rats

Recently, prolactin was shown to inhibit the development of stress-induced ulcers. However, the mechanism for suppression of gastric ulcers by prolactin has not been clarified. Hatano high-avoidance (HAA) and low-avoidance (LAA) strains of rats were originally selected and bred from Sprague-Dawley rats based on shuttle-box tasks. The present study focused on the relationships among gastric ulceration and endocrine response with special reference to prolactin secretion and restraint stress in water of HAA and LAA rats. The restraint stress induced an elevation of plasma concentrations of ACTH, corticosterone, and prolactin. Peak levels of plasma ACTH during stressful condition were significantly higher in HAA rats than in LAA rats, while peak levels of prolactin were significantly lower in HAA rats than in LAA rats. The gastric erosion index was significantly higher in HAA rats than in LAA rats 7 h after restraint stress in water. The numbers of prolactin- receptor-positive cells determined by immunohistochemistry in the paraventricular nucleus was significantly increased in LAA rats than in HAA rats 7 h after restraint stress in water. These results indicate that HAA rats were more sensitive than LAA rats to restraint stress in water. The strain differences in gastric ulceration under stress may be involved in peripheral prolactin secretion and central prolactin receptor expression. The expression of prolactin receptor in the paraventricular nucleus may be important in suppressing gastric ulceration.

Anti-inflammatory effect of acute stress on experimental colitis is mediated by cholecystokinin-B receptors

We aimed to investigate the effects of electric shock (ES) on the course of experimental colitis and the involvement of possible central and peripheral mechanisms. In Sprague-Dawley rats (n = 190) colitis was induced by intracolonic administration 2,4,6-trinitrobenzenesulfonic acid (TNBS). The effects of ES (0.3-0.5 mA) or the central administration of corticotropin-releasing factor (CRF; astressin, 10 microg/kg) or cholecystokinin (CCKB; 20 microg/kg) receptor antagonists and peripheral glucocorticoid receptor (RU-486; 10 mg/kg) or ganglion (hexamethonium; 15 mg/kg) blockers on TNBS-induced colitis were studied by the assessment of macroscopic score, histological analysis and tissue myeloperoxidase activity. ES reduced all colonic damage scores (p < 0.05-0.01), while central CRF (p < 0.05-0.001) and CCKB receptor (p < 0.05-0.01) blockers or peripheral hexamethonium (p < 0.05-0.01) and RU-486 (p < 0.05) reversed stress-induced improvement. ES demonstrated an anti-inflammatory effect on colitis, which appears to be mediated by central CRF and CCK receptors with the participation of hypothalamo-pituitary-adrenal axis and the sympathetic nervous system.

Prolactin prevents acute stress-induced hypocalcemia and ulcerogenesis by acting in the brain of rat

Stress causes hypocalcemia and ulcerogenesis in rats. In rats under stressful conditions, a rapid and transient increase in circulating prolactin (PRL) is observed, and this enhanced PRL induces PRL receptors (PRLR) in the choroid plexus of rat brain. In this study we used restraint stress in water to elucidate the mechanism by which PRLR in the rat brain mediate the protective effect of PRL against stress-induced hypocalcemia and ulcerogenesis. We show that rat PRL acts through the long form of PRLR in the hypothalamus. This is followed by an increase in the long form of PRLR mRNA expression in the choroid plexus of the brain, which provides protection against restraint stress in water-induced hypocalcemia and gastric erosions. We also show that PRL induces the expression of PRLR protein and corticotropin-releasing factor mRNA in the paraventricular nucleus. These results suggest that the PRL levels increase in response to stress, and it moves from the circulation to the cerebrospinal fluid to act on the central nervous system and thereby plays an important role in helping to protect against acute stress-induced hypocalcemia and gastric erosions.

Intermittent foot shock stress prolongs the telogen stage in the hair cycle of mice

Stress significantly influences skin diseases and cutaneous functions. Recently, interactions between stress and skin conditions have been studied in animal models using various systemic stressors. Here, we studied the effect of intermittent foot shock stress on the hair cycle of C57BL/6 mice. After a 2-week period of intermittent foot shock stress, we examined the changes in the depilation-synchronized hair cycle macroscopically and histologically and we also measured the plasma levels of corticosterone. We found that foot shock stress prolonged the telogen stage and delayed the subsequent anagen induction in the hair cycle. The distribution patterns of corticotrophin releasing factor or corticotrophin releasing factor receptor positive cells in the skin of stressed or of control mice were identical with those in the ordinal hair cycle. It is noteworthy that corticotrophin releasing factor positive keratinocytes were observed in the telogen follicles of the stressed mice but were negative in the telogen follicles of the non-stressed mice in this study. Plasma corticosterone levels were significantly higher in the stressed group than in the control group. These results suggest that increased levels of plasma corticosterone may be involved in the mechanism underlying the stress-induced delay of the hair cycle.

Corticotropin-releasing factor receptor type 1 is involved in the stress-induced exacerbation of chronic contact dermatitis in rats

Cutaneous diseases such as psoriasis and atopic dermatitis are worsened by psychic stress. We attempted to clarify the involvement of the corticotropin-releasing factor (CRF) receptor (CRFR) in stress-induced exacerbation of chronic contact dermatitis in rats. Male Wistar rats, in which chronic contact dermatitis had been induced by 2,4,6-trinitro-1-chlorobenzene (TNCB), were exposed to a 1-h period of electric foot-shock following intraperitoneal administration of CRA1000, a selective CRFR type 1 (CRFR1) antagonist, or vehicle everyday for 9 days. Histological examination of the skin showed that the epidermis significantly thickened and the number of mast cells in the dermis significantly increased by repeated exposure to stress, and that these changes were blocked by CRA1000. These results suggest that CRFR1 is involved in the stress-induced exacerbation of chronic contact dermatitis.

The role of the interaction between endogenous opioids and nitric oxide in the pathophysiology of ethanol-induced gastric damage in cholestatic rats

Interaction between endogenous opioids and nitric oxide (NO) has been shown in different biological models and pharmacological evidence suggest that opioids can induce NO release in endothelium as well as in neural cells. Cholestasis is associated with NO overproduction. The reason for increased NO synthesis is not clearly known but it can potentiate development of gastric mucosal damage in cholestatic subjects. Based on increased plasma levels of endogenous opioids and existence of NO overproduction in cholestasis, the present experiments were performed to investigate the role of interaction between endogenous opioids and NO in generation of ethanol-induced gastric damage in cholestatic rats. Cholestasis was induced by surgical ligation of bile duct and sham-operated rats served as controls. The animals received either 20 mg/kg of naltrexone or saline for 6 days and then were fasted and received L-arginine (200 mg/kg), NG-nitro-L-arginine methylester (L-NAME; 2, 5 and 10 mg/kg) or saline. The ethanol-induced gastric mucosal damage was significantly more severe in cholestatic rats than in sham-operated animals (115 +/- 12 mm2 vs. 72 +/- 11 mm2, P < 0.05). L-NAME significantly enhanced the development of gastric mucosal lesions in sham-operated rats. But in cholestatic animals, L-NAME decreased and L-arginine enhanced the severity of gastric damage. Pretreatment of animals with naltrexone decreased severity of gastric mucosal damage in cholestatic rats. Concurrent administration of naltrexone with L-arginine was protective against ethanol-induced gastric damage in both normal and cholestatic groups. Administration of naltrexone with L-NAME had the same effect in cholestatic and control rats and increased severity of gastric damage. Plasma levels of NO2- + NO3- were significantly higher in cholestatic rats than control animals (72 +/- 6 microM vs. 39 +/- 3 microM, P < 0.05). Pretreatment of animals with naltrexone significantly reduced plasma levels of NO2- + NO3- in cholestatic animals, but not in control rats (33 +/- 6 microM vs. 32 +/- 4 microM). The protective effect of L-NAME against gastric damage in cholestatic rats can be explained by inhibition of NO overproduction and it seems that interaction between opioids and NO may have an important role in generation of NO overproduction and gastric complications in cholestatic rats.

Effect of psychogenic stress on gastrointestinal function

This review summarizes the studies published over the last twenty years on the effects of psychogenic stress on gastrointestinal function, using animal models. The effects of stress on gastric ulceration have received wide attention and the central and local mechanisms of mucosal damage have been, for the most part, clearly delineated. In comparison, relatively few studies have focused on the impact of stress on intestinal and colonic physiology, even though its influence on intestinal motility, mucosal permeability and inflammation has been established. More work is necessary in this field, especially considering the importance of irritable bowel syndrome in modern society.

N(G)-nitro-L-arginine methylester is protective against ethanol-induced gastric damage in cholestatic rats

In this study the effect of nitric oxide (NO) synthesis inhibition on ethanol-induced gastric damage was evaluated in bile duct-ligated, sham-operated and unoperated rats. The animals were injected intraperitoneally with saline, L-arginine (200 mg/kg) or N(G)-nitro-L-arginine methylester (L-NAME) in doses of 5, 15 and 30 mg/kg, 30 min before ethanol administration. The animals were killed 1 h after ethanol administration and their stomachs were removed for measurement of gastric mucosal damage. The results showed that L-NAME significantly enhanced the development of gastric mucosal lesions in sham-operated and unoperated rats, while in bile duct-ligated animals, L-NAME decreased and L-arginine enhanced the potentiation of ethanol-induced gastric mucosal damage. The plasma level of nitrite and nitrate was also measured and was significantly higher in bile duct-ligated rats than in control groups. The results suggest that inhibition of NO synthase with L-NAME has different effects on ethanol-induced gastric damage in cholestatic groups and in normal rats and that these effects can be explained by overproduction of NO in bile duct-ligated animals.

Susceptibility of Lewis and Fischer rats to stress-induced worsening of TNB-colitis: protective role of brain CRF

We assessed the role of central corticotropin-releasing factor (CRF) in stress-induced worsening of colitis in inbred rat strains with hypo (Lewis/N) and hyper (Fischer344/N) CRF responses to stress. Intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (TNB) induced colitis of similar severity in both strains as assessed on day 7 by macroscopic scoring, histological evaluation, tissue myeloperoxidase (MPO) activity, and decrease in food intake and body weight. Colitis was inhibited by daily intracerebroventricular injections of CRF in both strains. Chronic stress (3 h/day, water avoidance or wrap restraint on alternate days for 6 days) aggravated colitis more in Lewis than Fischer rats (71 and 22% further increase in MPO activity, respectively). The CRF antagonist astressin injected intracerebroventricularly enhanced the colitis response to stress and caused mortality in both strains. Fischer rats had higher plasma corticosterone levels 20 min after stress alone on day 1 and after TNB plus stress on days 1 and 3 compared with Lewis. These data show that central CRF restrains the proinflammatory action of stress in experimental colitis.

Non-peptidic corticotropin-releasing hormone receptor type 1 antagonist reverses restraint stress-induced shortening of sodium pentobarbital-induced sleeping time of rats: evidence that an increase in arousal induced by stress is mediated through CRH receptor type 1

Stress shortens sodium pentobarbital (PbNa)-induced sleeping time through corticotropin-releasing hormone (CRH) in rats. We investigated whether this effect of brain CRH is mediated by CRH receptor type 1 (CRHR1) using a non-peptidic CRHR1 antagonist in rats. A 60 min period of restraint significantly shortened PbNa-induced sleeping time. This shortening was completely reversed by peripheral administration of CRHR1 antagonist. These results suggest that the stress-induced increase in arousal is mediated by CRHR1.

Brain vasopressin is involved in stress-induced suppression of immune function in the rat

The possibility that vasopressin (VP) is involved in stress-induced suppression of immune function was examined in rats. Intermittent electrical footshock for 60 min suppressed the proliferative response of splenic T cells to the mitogen concanavalin A as well as natural killer (NK) cytotoxicity, and the former change was partially, and the latter was completely, blocked by intracerebroventricular (i.c.v.) preadministration of a V1 receptor antagonist. The footshock-induced suppression of the T cell proliferative response was completely abolished by coadministration of a corticotropin-releasing hormone (CRH) receptor antagonist and the V1 receptor antagonist. The i.c.v. administration of VP suppressed the proliferative response of splenic T cells and NK cytotoxicity in an adrenal-independent manner. These effects were completely reversed by i.c.v. preadministration of the V1 receptor antagonist. These results suggest that brain VP, in conjunction with CRH, suppresses immune function through the V1 receptor in rats under stress.

Immobilization-induced and crowded environment-induced stress delay barrier recovery in murine skin

To examine the effect of stress on skin homeostasis, cutaneous barrier recovery was measured in rate exposed to immobilization stress after tape stripping or sodium dodecyl sulphate treatment. The barrier function was evaluated by measuring transepidermal water loss. Barrier recovery was delayed in rats exposed to stress in comparison with untreated controls. This tendency was observed in both male and female animals. The delay in barrier recovery was blocked by application of the sedative drugs diazepam and chlorpromazine. The barrier recovery rate in mice which were kept at a high population density (10 animals per cage) for 2 weeks was slower than that in mice kept at lower population densities (five animals or one animal per cage). These animal models could be useful for objectively quantifying the influence of stress on the cutaneous function.

Expression of aggression attenuates both stress-induced gastric ulcer formation and increases in noradrenaline release in the rat amygdala assessed by intracerebral microdialysis

The effects of an aggressive biting response on stress-induced noradrenaline (NA) release in the rat amygdala and gastric ulcer formation were studied with an intracerebral microdialysis technique. Rats were exposed to a 60-min period of cold restraint stress with or without being allowed to bite a wooden stick. They were sacrificed 100 min after release from stress to investigate gastric ulcer formation. Cold-restraint stress increased NA release to 304 +/- 22.3 and 206 +/- 23.8% of basal levels (mean +/- SEM) in the nonbiting and biting groups, respectively. The stress-induced increases in NA release in the nonbiting group were significantly higher than those in the biting group. In the nonbiting group, significant increases in NA release continued for 80 min after release from stress; however, NA levels in the biting group recovered to basal levels immediately after the cessation of stress. Although many severe gastric lesions with bleeding were found in the nonbiting group, fewer gastric lesions without bleeding were found in the biting group. The cumulative length of gastric lesions in the nonbiting group and in the biting group was 26.2 +/- 7.4 and 6.8 +/- 3.9 mm (mean +/- SEM), respectively. The mean number of ulcers in the nonbiting group and the biting group was 11.8 +/- 1.3 and 1.8 +/- 0.7 (mean +/- SEM), respectively. Both the cumulative length of ulcers and the number of ulcers were significantly lower than those seen in the nonbiting group. These findings strongly suggest that expression of aggression during stress exposure attenuates not only stress-induced increases in NA release in the rat amygdala but also gastric ulcer formation consequent to stress.

Cold restraint-induced gastric lesions in individual- and group-stressed rats

The aim of the present study was to 1) determine the intensity of cold restraint-induced gastric lesions and core body temperature in single- and group-stressed rats, and establish a correlation between them; and 2) determine the influence of visual contact among animals during cold restraint on development of gastric stress ulcer. Therefore, adult male Wistar rats were put into individual or group restraint boxes (composed of two, three, six or nine single boxes) with or without possibility of visual contact and then exposed 2 hr to the cold (4 degrees C). Core body temperature was measured just before and after cold restraint using a digital rectal thermometer. The results showed that: 1) single stressed animals expressed significantly higher ulcer index than those stressed in group of three, six and nine rats; 2) there was no significant difference in degree of hypothermia among rats exposed to various group paradigms; and 3) there was no significant difference in ulcer index among animals stressed in conditions with or without visual contact. An absence of significant difference in ulcer index between single and paired stressed rats implies that three is the lowest number of animals per group at which an influence of group size on behavioral and adaptive mechanisms in rats exposed to cold restraint becomes manifest.

Intracerebroventricular CRF inhibits cold restraint-induced c-fos expression in the dorsal motor nucleus of the vagus and gastric erosions in rats

Acute exposure to cold-restraint induces vagal-dependent gastric erosions associated with activation of neurons in the dorsal motor nucleus of the vagus (DMN) in rats. The influence of intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF) (10 micrograms) on c-fos expression in the brain and gastric erosions induced by 3 h cold-restraint was investigated in conscious rats. In cold-restraint exposed rats, CRF injected i.c.v. inhibited gastric erosions and the number of Fos positive neurons in the DMN by 93 and 72%, respectively, while Fos labelling in the nucleus tractus solitarius (NTS) was increased by 5-fold compared with vehicle group. c-fos expression was also induced in the central amygdala by i.c.v. CRF, unlike the vehicle-injected group exposed to cold-restraint. c-fos expression induced by cold-restraint in the raphe pallidus (Rpa) and paraventricular nucleus of the hypothalamus was not altered by i.c.v. CRF. These data indicate that central CRF-induced gastric protection results from the inhibition of DMN neuronal activity enhanced by cold-restraint. CRF action on DMN neurons may be related to the increase in the NTS and central amygdala inputs leading to inhibition of DMN neurons rather than to the decrease in the excitatory input from the caudal raphe projections to the DMN.

Beta 1-adrenergic mechanism is involved in stress-induced increase in arousal

It has been shown that 1 h restraint shortens pentobarbital (PbNa)-induced sleeping time and that brain corticotropin-releasing hormone (CRH) is involved in the mechanism by which restraint shortens. PbNa-induced sleeping time. The present study was designed to further examine the mechanism of the antagonistic effect of 1 h restraint on PbNa in rats. Intracerebroventricular (i.c.v.) administration of propranolol and metoprolol, but not butoxamine reversed the shortening of PbNa-induced sleeping time by 1 h restraint. The i.c.v. administration of phentolamine blocked the shortening of PbNa-induced sleeping time by restraint, while the same dose of phentolamine prolonged the sleeping time in unrestrained rats. Atropine did not affect the PbNa-induced sleeping time in restrained rats. These results suggest that in addition to CRH, the brain beta 1-adrenergic system is involved in the restraint stress-induced increase in arousal.

Restraint stress in biomedical research: an update

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.

Restraint changes pentobarbital-induced sleeping time in rats: evidence that arousal is modulated by brain corticotropin-releasing hormone and opioid in stress

The effect of restraint of different duration on sodium pentobarbital (PbNa)-induced sleeping time was examined in rats. 1 h-restraint significantly shortened PbNa (50 mg/kg b.wt., administered i.p. immediately after restraint)-induced sleeping time as reported previously, whereas 2 h-restraint significantly prolonged the sleeping time. Naloxone (1 mg/kg b.wt.) administered i.p. 15 min before the start of restraint further exaggerated the 1 h-restraint-caused shortening of PbNa-induced sleeping time, and it blocked the 2 h-restraint-caused prolongation of the sleeping time. SDZ202-250 (0.1 pmol and 0.5 pmol), a selective mu agonist, but not [D-Pen2-D-Pen5]enkephalin (0.1 pmol-1.0 nmol), a selective delta agonist, or U50488H (0.1 pmol-1.0 nmol), a selective kappa agonist, administered i.c.v. 15 min before the i.p. injection of PbNa significantly prolonged PbNa-induced sleeping time; its prolongation was blocked by naloxone. These results suggest that a mu receptor-binding opioid prolongs PbNa-induced sleeping time in stress. The 2 h-restraint-caused prolongation of PbNa-induced sleeping time was also blocked by alpha-helical CRH(9-41) (26 nmol), a corticotropin-releasing hormone (CRH) receptor antagonist, administered i.c.v. 15 min before the start of restraint. In conjunction with our previous findings that the i.c.v. administration of CRH shortens PbNa-induced sleeping time and the 1 h restraint-caused shortening of PbNa-induced sleeping time is blocked by the CRH receptor antagonist, the present results suggest that CRH may stimulate an opioid-specific sedative mechanism, thus causing the prolongation of PbNa-induced sleeping time in 2 h-restraint.(ABSTRACT TRUNCATED AT 250 WORDS)

The amygdaloid complex, corticotropin releasing factor and stress-induced gastric ulcerogenesis in rats

The amygdaloid complex and corticotropin releasing factor (CRF) are both important in stress reactions and we thus evaluated the effects of intra-amygdalar CRF on stress ulceration in rats. Bilateral micro-applications of CRF (0.05, 0.5 or 5.0 micrograms) into the central amygdala (CEA) attenuated cold restraint-induced gastric mucosal lesions in a dose-related manner. Similar gastric cytoprotective effects were seen with intra-CEA noradrenaline (NA; 3.0 micrograms), whereas the NA neurotoxin, DSP-4 (25 micrograms), or the beta-adrenoceptor antagonist, propranolol (1 microgram), aggravated stress ulcer pathology. Intra-CEA pretreatment with DSP-4 or propranolol clearly reversed the ulceroprotective effects of CRF during stress. These results indicate that the CEA is a neural substrate for CRF effects, and CRF-NA interactions in this limbic area are crucial for the regulation of stress ulcerogenesis.

Psychological stress increases arousal through brain corticotropin-releasing hormone without significant increase in adrenocorticotropin and catecholamine secretion

The effect of psychological and psychophysical stress on pentobarbital (PbNa)-induced sleeping time was examined in rats to clarify the influence of psychological stress on arousal. Psychological stress and electric footshock of 5-60 min duration significantly shortened PbNa-induced sleeping time, and the shortening was reversed by intracerebroventricular administration of a corticotropin-releasing hormone (CRH)-receptor antagonist. Electrical footshock and restraint significantly raised plasma adrenocorticotropin (ACTH) and catecholamine levels, whereas psychological stress did not significantly affect the plasma hormones levels. These results suggest that both psychological and psychophysical stress increase arousal through brain CRH. It is also concluded that expression of the central nervous system action of CRH, such as increasing arousal, is not necessarily accompanied by a significant increase in the secretion of ACTH and catecholamine in psychological stress.

CNS effects on gastric functions: from clinical observations to peptidergic brain-gut interactions

Clinical observations as early as the last century pointed to the stomach's link to the brain. Animal studies in this century have given us detailed information about the neuroanatomical and neurophysiological basis of brain-gut interactions. Psychological stress models and stereotaxic brain procedures have been important tools in gaining this information. During the last 10 years, there has been much focus on the effects of neuropeptides on gastric functions. Several CNS-peptides have indeed been shown to influence multiple gastric functions such as: acid secretion, bicarbonate secretion, mucus secretion, motility, blood flow and prostaglandin synthesis. Accordingly, direct CNS-application of these peptides also influences the development of gastric erosions during experimental stress procedures.

The neurobiology of stress ulcers

We have reviewed the neurobiology of stress ulcers from animal models to potential pharmacotherapeutic mechanisms. The evidence strongly supports the hypothesis that certain stress-related gastric lesions are 'brain-driven' events which may be more effectively managed through central manipulations than by altering local, gastric factors. Recent advances in the use of anxiolytic and antidepressant drugs in the management of stress-related gastric mucosal injury further supports the contention that a brain-gut axis, which may have nervous, peptidergic and classic monoaminergic components, modulates the intricate and complicated pattern of communication between the brain and the stomach. Delineation of the precise pathways which make up this communication as well as their manipulation by various pharmacological agents will be the focus of future research endeavour.

Brain corticotropin-releasing hormone increases arousal in stress

The effect of restraint stress on pentobarbital-induced sleeping time was examined in rats. Restraint for 60 and 75 min significantly shortened pentobarbital-induced sleeping time. The shortening of sleeping time by restraint was completely reversed by intracerebroventricular (i.c.v.) administration of alpha-helical CRH(9-41), a corticotropin-releasing hormone (CRH) receptor antagonist. In conjunction with our previous finding that i.c.v. administration of CRH shortens pentobarbital-induced sleeping time, the results suggest that restraint stress increases arousal through brain CRH.

Interleukin-1 inhibits stress-induced gastric erosion in rats

The effect of interleukin (IL)-1 on the occurrence of stress-induced gastric erosions was examined in rats. The intracerebroventricular (icv) administration of IL-1 beta significantly inhibited the occurrence of water-immersion restraint stress-induced gastric erosion at doses of 200 ng, 500 ng and 1 microgram, whereas the intravenous (iv) administration of IL-1 beta altered the occurrence of gastric erosion only at a dose of 1 microgram. The inhibitory effect of IL-1 alpha icv administered on the occurrence of gastric erosion was found only at a dose of 1 microgram. The inhibitory effect of IL-1 beta icv administered on the occurrence of stress-induced gastric erosion was not influenced by icv administration of alpha-helical CRF(9-41), a corticotropin-releasing factor (CRF) receptor antagonist. Indomethacin completely blocked the inhibitory action of IL-1 beta icv administered on stress-induced gastric erosion. It is concluded from these results that IL-1 acts mainly in the central nervous system to inhibit the occurrence of stress-induced gastric erosion and that the IL-1 beta-induced inhibition of gastric erosion is mediated by prostaglandin in a manner that is independent of brain CRF.