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.

Serum glucose, glucose tolerance, corticosterone and free fatty acids during aging in energy restricted mice.

Energy restriction, the only method known to increase maximum life span in laboratory animals, was used as a tool to test hypotheses regarding possible mechanisms of aging. Serum glucose and corticosterone (CS) concentrations in mice of a long-lived hybrid mouse strain, aged 7, 17, and 29 months, and on 50%, 80%, and 100% of ad libitum intake, were measured. Serum glucose and CS concentrations were also measured in response to intraperitoneal (i.p.) glucose challenge in mice at ages 7 and 29 months. Serum glucose and CS concentrations were also measured at several time points over 36 h, to assess their diurnal variation. There were no differences in single fasting glucose concentrations in 7- and 29-month-old mice at the same degree of energy restriction, but energy restriction decreased glucose concentrations. Serum CS concentrations were generally increased restricted animals with respect to fully fed ones. Average serum glucose concentrations were found to be significantly decreased by dietary restriction. Glucose tolerance curves were unchanged by age in ad libitum fed or 50% restricted animals, but in 80% ad libitum groups, older animals showed evidence of decreased glucose tolerance with respect to young animals. For each age, peak serum glucose concentrations after i.p. glucose loading varied with degree of energy restriction, with more severely restricted animals showing less glucose tolerance. Average serum CS concentrations were elevated at 7 months by restriction, especially at night and long after feeding, but we found no differences with age or diet in average CS concentrations. Our serum glucose results support the hypothesis that nonenzymatic glycation is mechanistically involved in normal aging. Our serum CS results do not support the hypothesis that CS contributes significantly to the pathophysiology of normal aging in mice.

Ingestive responses to homeostatic challenges in rats with ablations of the anterolateral neocortex.

Because rats with either anterolateral neocortical or lateral hypothalamic (LH) damage initially display similar feeding and drinking deficits and recovery patterns, the possibility that anterolateral neocortical ablations would also produce similar chronic ingestive impairments to glucoprivic and hydrational challenges was examined. In general, rats with anterolateral neocortical ablations exhibited normal feeding responses to food deprivation and glucoprivation induced by insulin or moderate doses of 2-deoxy-D-glucose (2-DG), but their response to a high dose (500 mg/kg) of 2-DG was impaired. These animals also drank normally in response to hypertonic saline injections and following water deprivation, but only if food was available during the test session, results indicating that they drank prandially. Results indicate that although the anterolateral neocortex and LH are anatomically related, these brain regions appear to be functionally dissimilar in terms of the regulation of ingestion.

Bombesin microinfusion into the paraventricular nucleus suppresses gastric acid secretion in the rat.

Bombesin is a particularly potent inhibitor of gastric acid secretion when injected intracisternally in the rat. Because bombesin-like immunoreactivity is found in several forebrain regions implicated in gut regulation, the ability of bombesin to affect gastric secretion was tested in these areas by direct microinfusion. Bombesin significantly and dose-relatedly suppressed gastric acid secretion when it was infused into the hypothalamic paraventricular nucleus. Bombesin microinfusion into the ventromedial or lateral hypothalamic areas, or the caudate-putamen, had no significant effect. A further experiment using glass micropipets showed that back-diffusion of bombesin along the cannula track to a distant site of action was unlikely to account for the results obtained, and provided further evidence that the active site is limited to the paraventricular nucleus and possibly the ventralmost nucleus reuniens. The results suggest that the bombesin receptors and immunoreactive terminals previously identified in this region may be involved in the central regulation of gastric secretion.

Intrahypothalamic microinfusion of corticotropin-releasing factor inhibits gastric acid secretion but increases secretion volume in rats.

Bilateral microinfusion of synthetic ovine corticotropin releasing factor (oCRF; 0-4.0 microgram/rat [0-856 pmol/rat]) into the paraventricular nucleus or the ventromedial nucleus of the rat hypothalamus inhibited gastric acid secretion in a dose-related manner. Unexpectedly, these microinfusions both decreased acid concentration and increased secretion volume; total acid output (acid concentration multiplied by secretion volume) was strongly inhibited. In the lateral hypothalamus. CRF microinfusion also both decreased acid concentration and increased secretion volume, but total acid output did not change. oCRF microinfusion into the caudate-putamen did not significantly affect any measure of gastric acid secretion even at the highest dose used. The increased secretion volume seen after oCRF microinfusion is unique; all other centrally acting inhibitors of gastric acid secretion decrease secretion volume. It is possible that hypothalamic CRF may influence gastric secretory function.

Destruction of different fiber tracts underlies development of lateral hypothalamic lesion-induced hyperthermia and loss of bombesin-induced hypothermia.

The relative roles of lateral hypothalamic cell bodies and fibers of passage were assessed in the development of lesion-induced hyperthermia and bombesin-induced hypothermia. Electrolytic lesions or discrete fiber transections were combined with intracisternal bombesin injection to show that each of these two thermoregulatory effects involves fibers crossing the borders of the lateral hypothalamus; however, the two effects primarily involve fibers crossing different borders. Thus, the hyperthermia and the abolition of bombesin-induced hypothermia which follow lateral hypothalamic damage appear to result from disruption of separate thermoregulatory pathways.

Intracranial microinfusion of pancreastatin elevates blood glucose, free fatty acids, and corticosterone in rats.

Pancreastatin, a novel peptide recently isolated from porcine pancreas, significantly inhibits insulin and somatostatin release and augments glucagon release from the isolated perfused rat pancreas. This implies a role for endogenous pancreatic pancreastatin in the regulation of blood glucose and free fatty acids, the two major metabolic fuels. Since many peptides have similar biological effects when administered centrally and peripherally, the effects of centrally administered pancreastatin on blood glucose and free fatty acids were examined in 3 studies. Corticosterone was also measured in two of these studies. Intraventricular microinfusion of pancreastatin significantly elevated blood glucose, free fatty acid, and corticosterone concentrations in a dose-related manner. None of these effects was seen after subcutaneous injection of the same doses. Centrally administered pancreastatin appears to produce its effects on glucose and free fatty acids through actions in the brain, and either the brain, the median eminence, and/or pituitary for corticosterone.

Lateral hypothalamic lesions or transections block bombesin hyperglycemia in rats.

The peptide bombesin-14 causes hyperglycemia when injected into the cisterna magna of rats. We report that acute lateral hypothalamic lesions block bombesin hyperglycemia. Lateral thalamic lesions do not have this effect. We further report that transections on the lateral or posterior borders of the lateral hypothalamus also block bombesin hyperglycemia. Cuts on the medial border also somewhat diminish this hyperglycemia, while cuts on the anterior border are not reliably effective. These results suggest that fibers traversing the lateral hypothalamus are involved in the hyperglycemic response to intracisternal bombesin-14.

Role of hypothalamic paraventricular nucleus alpha- and beta-adrenergic receptors in regulation of blood glucose, free fatty acids and corticosterone.

The potential roles of adrenergic and noradrenergic terminals in the hypothalamic paraventricular nucleus in the regulation of blood glucose and free fatty acids, the two major metabolic fuels, were examined. Corticosterone was also measured, both to assess the specificity of any effects for metabolic fuels, and because endogenous catecholamines in this site have previously been implicated in corticosterone regulation. In the first experiment adult male albino rats having chronically implanted guide cannulae aimed at the hypothalamic paraventricular nucleus or the caudate nucleus received microinjections of the agonists methoxamine (alpha 1), clonidine (alpha 2), and isoproterenol (beta) (0, 10, 30, 100 nmol/500 nl), and blood samples were taken from the tail tip. In the second experiment a different set of rats received 30 nmol clonidine or vehicle subcutaneously instead of brain microinjections. Intracranial clonidine and isoproterenol produced marked and moderate hyperglycemia, respectively; methoxamine did not alter glucose. For neither clonidine nor isoproterenol was there any difference in hyperglycemia as a function of microinjection site; also, subcutaneous clonidine injections produced the same peak glucose response as was found after both paraventricular and caudate nucleus microinjections of the same dose. Free fatty acid levels were increased by clonidine and isoproterenol, but slightly suppressed by methoxamine; the alpha agonist effects, but not the beta agonist effect, were greater after paraventricular microinjections than after caudate microinjections. Corticosterone was increased by both alpha agonists after paraventricular but not after caudate nucleus microinjections; beta agonist microinjections into the paraventricular and caudate nuclei produced equivalent corticosterone elevations. These results suggest that most, if not all, of the hyperglycemic effects of alpha and beta adrenergic agonist microinjection into the paraventricular nucleus can be ascribed to leakage of the material into the vasculature, with subsequent action at a distant site. In contrast, all 3 agonists seem capable of acting within the brain to alter free fatty acid levels. The effects on corticosterone of both the alpha 1 and alpha 2 agonists, but not the beta agonist, also appear due, at least in part, to actions within the brain. Previous suggestions that catecholamine terminals in the hypothalamic paraventricular nucleus are directly and strongly involved in metabolic fuel regulation may require reconsideration.

Bombesin microinfusion into the rat hypothalamic paraventricular nucleus increases blood glucose, free fatty acids and corticosterone.

Bombesin is a particularly potent hyperglycemic agent when administered intraventricularly or intracisternally in the rat. Because bombesin-like immunoreactivity is found in several forebrain regions implicated in glucoregulation, the ability of direct hypothalamic microinfusions of this peptide to affect serum metabolic fuel levels was tested. Three experiments, using anesthetized, acutely infused rats, or unanesthetized rats with chronic intracranial implants, showed that microinfusion of bombesin into the hypothalamic paraventricular nucleus caused significant, dose-related increases in serum glucose; infusions into the lateral hypothalamus or the caudate nucleus were ineffective. Infusions into the ventromedial nucleus significantly elevated glucose only in acutely anesthetized rats. In unanesthetized rats with chronic intracranial cannulae, bombesin infusions into all 3 hypothalamic sites, but not the caudate-putamen, significantly elevated blood free fatty acids, while only infusions into the paraventricular nucleus caused significant dose-related increases in blood corticosterone. The results demonstrate that the paraventricular nucleus is a sensitive site for bombesin-induced elevation of blood glucose, free fatty acids, and corticosterone. They also imply that the bombesin binding sites and immunoreactive terminals previously identified in these regions may be involved in the central regulation of circulating metabolic fuel levels and the pituitary-adrenal axis, and that the effects of acute surgery may augment the hyperglycemic response to intrahypothalamic bombesin administration.

Amygdaloid lesions attenuate neurogenic gastric mucosal erosions but do not alter gastric secretory changes induced by intracisternal bombesin.

Bilateral lesions of the lateral hypothalamus in rats produce glandular gastric mucosal damage. The results of the first experiment demonstrated that the severity of the neurogenic gastric erosions is attenuated by prior lesions of the centromedial amygdala. In a second experiment it was shown that fasting gastric acidity is significantly reduced following chronic amygdaloid lesions and this may be the mechanism involved in the protective nature of the amygdaloid lesions against gastric mucosal damage. In addition, it was found that gastric secretory changes induced by intracisternal injection of bombesin are unaffected by amygdaloid damage. The present results are consistent with the view that the centromedial amygdaloid region may influence gastric functions by modulating the activity of the preoptic-anterolateral hypothalamic areas or by directly influencing lower brain stem autonomic control areas.

Suppression of gastric acid secretion by intracisternal bombesin does not require the ventromedial hypothalamus.

Intracisternal administration of the tetradecapeptide peptide bombesin suppresses gastric acid release. Other studies have shown that the ventromedial hypothalamus (VMH) may have an inhibitory role in gastric regulation. To determine if the inhibition of gastric acid secretion by intracisternally administered bombesin is mediated by the ventromedial hypothalamus, bombesin was injected intracisternally in rats with ventromedial hypothalamic lesions. Neither anterior nor posterior VMH lesions altered the effects of bombesin on gastric acid, concentration, volume, total output, or on serum gastrin. The bombesin-induced rise in gastric pH was very mildly attenuated by both lesions. The previous finding of enhanced gastric acid secretion after anterior VMH lesions was confirmed. The results suggest that the VMH is not crucial in the bombesin-induced inhibition of acid secretion.

Stimulation of gastric secretion by acute lateral hypothalamic lesions and its reversal by intracisternal injection of bombesin.

Lateral hypothalamic (LH) but not lateral thalamic (LT) electrolytic lesions markedly increased gastric secretion (volume and acidity) in rats within 2 h of production of the lesions and pylorus ligation. Intracisternal injection of bombesin inhibited gastric secretion (volume and acidity) and reduced to control levels the enhanced acid output produced by the LH lesions. These data demonstrate that acute LH lesions stimulate gastric secretion, and that bombesin exerts a potent gastric antisecretory influence, probably through interaction with LH-related stimulatory pathways.

Bombesin-induced hypothermia and hypophagia are associated with plasma metabolic fuel alterations in the rat.

Microinfusion of bombesin into the preoptic area (POA) has previously been shown to reduce core body temperature and feeding in rats that are food-deprived or made hypoglycemic with insulin. The present study determined the metabolic fuel state of rats under these experimental conditions. In addition, changes in plasma metabolic fuels following the microinfusion of bombesin (50 ng/0.25 microliters) into the POA were evaluated. Rats (n = 8) were tested under conditions of food satiation, food deprivation (20 h), and insulin pretreatment (10 U/kg). Prior to peptide infusion, food-deprived rats exhibited the expected elevation in free fatty acids coupled with a small decline in plasma glucose. Insulin treatment resulted in hypoglycemia which persisted for at least 120 min. Following bombesin infusion, free fatty acids and corticosterone levels were elevated in food-sated rats. Food-deprived rats exhibited elevation in plasma glucose, free fatty acids, and corticosterone following peptide infusion. In insulin-treated rats, bombesin attenuated the hypoglycemia observed in controls and increased corticosterone levels. These findings suggest that bombesin-like peptides localized within the POA may participate in the regulation of metabolic fuels.

Dietary quinine has a nongustatory effect on food intake in rats.

Recent data suggests that quinine adulteration of rats' maintenance diets may suppress food intake by postingestional (i.e., pharmacological or toxicological) mechanisms. This possibility was tested by increasing rats' rates of drug excretion prior to presentation of quinine maintenance diets. This treatment increased consumption of 3 concentrations (0.1, 0.2, 0.4%) of quinine diet in 2 separate experiments. In a third experiment, the same treatment did not alter consumption of quinine water in a 2 bottle test, suggesting that the increased consumption of quinine adulterated food was not due to a generalized decrease in the gustatory aversiveness of quinine. The data directly support the idea that quinine has postingestional effects which account for at least part of the suppression of food intake seen with quinine adulterated diets. The data further suggest that at least some of these effects occur postabsorptively.

Forebrain and hindbrain involvement of neuropeptide Y in ingestive behaviors of rats.

Neuropeptide Y (NPY) is an extremely potent orexigenic agent. These studies demonstrate that the effect of NPY on food and water intake are seen after infusion into either the third (3V) or fourth (4V) ventricle and that this is a specific effect, as it was not seen with the deaminated form. There was a nonsignificant tendency for lateral midbrain knife cuts to food intake. Both 3V and 4V NPY infusions showed an attenuated increases in food intake at 1 but not 2 h following NPY infusion in the lateral knife cut rats compared to the sham controls. Medical knife cuts resulted in significantly greater food intake in the basal state and a lesser increase in food intake in response to NPY infused into the 3V. These midbrain data suggest a role for both medical and lateral fibers in mediating the effects of NPY on food intake. Lateral fibers appear to be more important, but their transection only delays the time of onset of the stimulating effect of NPY to the second hour. Lateral knife cuts virtually abolish the effect of 4V NPY on stimulating water intake. 3V NPY in the presence of NPY has a less clear effect at 1 h, but mildly attenuated the NPY effect on water intake at 2 h in lateral knife cut rats. Medial knife cuts slightly attenuate the effect of 3V NPY on water intake. However, medial knife cuts markedly increased basal water ingestion. These studies demonstrate the importance of neuronal communications between third and fourth ventricle associated structures in the modulation of ingestive behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Unimpaired quinine metabolism in rats with ventromedial hypothalamic lesions.

Rats with lesions of the ventromedial hypothalamus (VMH) show a greater decrease in food intake than normal rats if fed diets adulterated with quinine. To determine if this hyperresponsivity is due to impaired quinine metabolism, in vitro rates of drug metabolism of female hooded rats with VMH lesions were measured. Determinations were made both under basal conditions and under conditions known to cause induction of drug metabolizing enzymes. VMH rats showed rates of drug metabolism virtually identical to controls under all conditions tested. These data suggest that VMH lesioned rats are not more sensitive to quinine dietary adulteration because of impaired quinine metabolism.