Effects of rearing condition on activity-induced weight loss.

This study evaluated the effects of differential rearing conditions on a rat protocol for various human syndromes. Subjects were 26 male Sprague-Dawley rats, 24 days old at the start of the experiment, matched according to weight, and randomly assigned to an isolation- or group-reared (4 rats/cage) condition. At 60 days of age (273 +/- 13 g), subjects were individually housed in cages allowing access to running wheels. Weight loss was produced through voluntary exercise and restricted food access. Animals in the isolation-reared condition lost weight at a faster rate and had heavier relative thymus weights than those in the group-reared condition. Animals in both conditions ran equivalent distances and ate equivalent amounts of food. The data show that postweaning rearing conditions impact the interpretation of behavioral and physiological outcomes of animal models. The results implicate a shift from maternal regulation of pup physiological and behavioral systems to the broader social niche.

Exercise in food-restricted rats produces 2DG feeding and metabolic abnormalities similar to anorexia nervosa.

Anorexia nervosa (AN) is associated with a paradoxical reduction in hunger ratings following 2-deoxy-D-glucose (2DG) induced glucose insufficiency. Because of the relationship between exercise and AN, there is interest in the weight-loss phenomenon produced by exercise in food restricted rats. This investigation determined if the weight-loss phenomenon is associated with a paradoxical suppression of food intake following 2DG and if the effect is related to reductions in prevailing glucose and insulin levels. Weight-matched, normal-weight exercised and normal-weight unexercised rats served as controls. As predicted, 2DG reduced food intake in animals subjected to the phenomenon (1.5 h/day food access and 22.5 h/day running wheel access). This effect was related to reductions in plasma glucose and insulin under the conditions that prevailed at the time of injection. Since these changes also occurred in weight-matched controls, they were attributed to the general effects of weight loss. A situational specificity for the "anorexia" of the weight-loss syndrome was also demonstrated. Finally, the strengths and weaknesses of the phenomenon as a model of AN were considered.

Weight cycling alters the effects of D-fenfluramine on susceptibility to activity-based anorexia.

It has been proposed that anorexia nervosa (AN) is treatable with serotonergic (5-HT) agonists. It seems paradoxical to treat a disorder characterized by reduced food intake with appetite suppressants. The effects of the indirect-acting 5-HT agonist D-fenfluramine on activity-based anorexia (ABA) were investigated, coincident with ABA (experiment 1), and after tolerance and weight cycling (experiment 2). Rats were chronically infused with D-fenfluramine by using subcutaneous mini-pumps and then tested for susceptibility to ABA (22.5 h free running wheel access, 1.5 h access to food). Concurrent D-fenfluramine increased the risk of ABA by decreasing food consumption. Conversely, D-fenfluramine reduced the incidence of ABA in tolerant rats with a history of weight cycling. Therefore, the effects of D-fenfluramine depend on whether drug administration coincides with ABA or whether tolerance and weight cycling precede ABA onset. The results were related to the metabolic effects of weight cycling and the treatment of anorexia nervosa.

Systemic clonidine increases feeding and wheel running but does not affect rate of weight loss in rats subjected to activity-based anorexia.

Activity-based anorexia (ABA) is an animal model of anorexia nervosa with two characteristics of the disorder, decreased food intake and increased activity. We have shown that chronic noradrenergic stimulation of the paraventricular hypothalamus exacerbates ABA rather than ameliorates it. This study determined if peripheral chronic administration of clonidine affects ABA. Rats were implanted SC with osmotic minipumps infusion 0, 30, or 300 micrograms/kg/day of clonidine and exposed to ABA (1.5 h/day ad lib food, 22.5 h/day ad lib wheel access). Results showed that clonidine did not affect the rate of weight loss during ABA, but increased food intake at the lower dose and wheel activity at the higher dose. It is proposed that increased energy expenditure due to wheel running is counteracted by an inhibition of sympathetically mediated diet-induced thermogenesis, and that the elevation in running by the higher dose potentially increases the risk of developing ABA.

Effects of insulin and 2-deoxy-D-glucose administration on CNS IGF-II content.

In order to determine whether effects of insulin on central nervous system (CNS) insulin-like growth factor II (IGF-II) content are direct or whether they are due to insulin-induced glucoprivation, short-term (2 h) time course studies were conducted utilizing the glucoprivic agent 2-deoxy-D-glucose (2-DG). Insulin (2 U/kg b.wt.), 2-DG (500 mg/kg b.wt.) or vehicle were administered to Sprague-Dawley rats (350-450 kg) and groups of animals were killed at time 0 and 15, 30, 45, 60, and 120 min following injection. Specific hypothalamic and hindbrain regions obtained by microdissection, were analyzed for IGF-II content by RIA. Insulin and 2-DG exerted similar effects on IGF-II content in the dorsomedial hypothalamus and the paraventricular nucleus. These data suggest that IGF-II was primarily regulated by glucoprivation in these regions. Only 2-DG altered ventromedial hypothalamic IGF-II content, and opposite responses to the two agents were observed in the arcuate nucleus. This uncoupling of IGF-II response suggests that differences in peripheral vs. central signals for IGF-II secretion may be involved. The vagal complex was responsive only to insulin injection indicating a specific response that may be tied to sensory vagal function.

Fluoxetine induced insulin-like growth factor II (IGF-II) changes in hypothalami of normal, exercised and food restricted rats.

Hypothalamic and pituitary insulin-like growth factor II (IGF-II) peptide concentrations are differentially regulated by factors associated with metabolism such as insulin and glucoprivation. However, the effects of other metabolic stressors such as food restriction or exercise on hypothalamic IGF-II concentrations remain largely to be explored. In order to assess whether metabolic stress alters central nervous system IGF-II secretion, peptide analysis was conducted in rats exhibiting activity-based anorexia (ABA) compared to exercised-matched, body weight-matched or ad libitum fed controls. Further, the possibility of serotonergic control of IGF-II secretion was examined by determining IGF-II response to fluoxetine (FLX) injections (15 mg/kg body wt., i.p.). While ABA and body weight loss altered peripheral IGF-II concentrations compared to ad libitum fed or exercised controls, these treatments had no effect on hypothalamic or posterior pituitary IGF-II content. However, FLX administration increased IGF-II concentrations in the ventromedial hypothalamus and decreased IGF-II content in the lateral hypothalamus compared to vehicle injected. Anterior pituitary levels of IGF-II were also decreased by FLX. These data suggest that a serotonergic influence on CNS IGF-II exists and that IGF-II secretion may be altered by factors affecting serotonin metabolism or efficacy.

Beta-endorphin and dynorphin abnormalities in rats subjected to exercise and restricted feeding: relationship to anorexia nervosa?

Exercise and the endogenous opioids have been linked to anorexia nervosa. This investigation determined the effects of the weight-loss syndrome induced by voluntary exercise (22.5 h/day) in food-restricted rats (1.5 h/day food access) on the endogenous opioids. The animals were tested under resting-fed and 2-deoxy-D-glucose (2DG) stimulated conditions. Weight-matched, freely fed exercised and ad libitum fed unexercised groups served as controls. Specific opioid abnormalities were found in the syndrome. These included a basal elevation in plasma beta-endorphin, which was abnormally suppressed by 2DG, and 2DG-induced elevations in arcuate hypothalamic beta-endorphin content and supraoptic hypothalamic dynorphin-A content. None of these changes occurred in controls. Finally, it was found that short-term moderate exercise itself chronically reduced adenohypophysial beta-endorphin content and elevated supraoptic dynorphin-A content. The relationship of the syndrome's hyperendorphinism to the hypothalamo-pituitary-adrenal axis and the auto-addiction hypothesis of anorexia nervosa was considered, as was the significance of the supraoptic dynorphin-A abnormality to the hypothalamo-neurohypophysial system. The differential sensitivity of the supraoptic dynorphin-A system compared to the arcuate hypothalamic beta-endorphin system to moderate exercise was also discussed.

Fluoxetine induces vasopressin and oxytocin abnormalities in food-restricted rats given voluntary exercise: relationship to anorexia nervosa.

Anorexia nervosa is associated with vasopressin, oxytocin and serotonin abnormalities. Because of the relationship between exercise and anorexia nervosa, we explored the weight-loss syndrome produced by wheel running in food-deprived rats. Its effects on regional vasopressin and oxytocin concentrations were determined under basal conditions and following systemic fluoxetine. Weight-matched, exercised and unexercised rats served as controls. Fluoxetine caused abnormalities in suprachiasmatic vasopressin and dynorphin A content and in thymus oxytocin content that did not occur in weight-matched or exercised controls. No syndrome-specific anomalies occurred in the hypothalamo-neurohypophysial system or dorsal vagal complex (DVC). However, weight reduction and fluoxetine increased circulating vasopressin; moderate exercise caused fluoxetine-induced elevations in posterior pituitary vasopressin and oxytocin; and, unlike the other groups, fluoxetine increased DVC oxytocin in freely fed unexercised rats. It was concluded that syndrome-specific vasopressin and oxytocin abnormalities occur that are not secondary to weight loss or moderate exercise; that weight loss or fluoxetine increases circulating vasopressin; that moderate exercise alters neurohypophysial vasopressin and oxytocin content; and that weight loss or exercise inhibits a fluoxetine-stimulated increase in DVC oxytocin. Finally, it was argued that the fluoxetine abnormalities indicate possible serotonin dysfunction in the syndrome.

Water deprivation produces an exercise-induced weight loss phenomenon in the rat.

Rats given restricted feeding and allowed free access to activity wheels increase activity, decrease food intake, and lose body weight compared to nonexercised controls. The phenomenon is of interest because of the relationship between exercise and anorexia nervosa. This study determined if another factor that energizes behavior in rats, water deprivation, produces similar exercise-induced weight loss. Rats were maintained on a restricted water schedule (10 min/day) combined with free access to running wheels and food; controls had no wheel access or were food deprived only. Both water-deprived groups consumed similar amounts of food and water, with the exercised group losing more body weight. Plasma osmolality, hematocrit, and posterior pituitary vasopressin content were equivalent in the two water-deprived groups, indicating similar hydrational status. It is concluded that the weight loss effect in water-deprived rats is due to excessive voluntary exercise, and that other factors that energize behavior should produce a similar effect.

Paraventricular hypothalamic clonidine increases rather than decreases susceptibility to activity-based anorexia in the rat.

Anorexia has been related to reduced activity of the paraventricular hypothalamic (PVN) noradrenergic-feeding system. In this study we determined whether clonidine (an alpha 2-adrenergic agonist) infused into the PVN reduced susceptibility to activity-based anorexia (ABA) in the rat. In Experiment 1, clonidine (6 doses) was chronically infused into the PVN of male Sprague-Dawley rats. All animals were exposed to ABA (1.5 hr/day food access; 22.5 hr/day running wheel access) until a 25% body weight loss was reached. Dose-related increases in susceptibility to ABA and decreases in food intake were observed. In Experiment 2, for which heavier animals and 3 doses of clonidine were used, we found no difference in food intake and wheel activity but increased susceptibility to ABA. Chronic clonidine infused into the PVN does not produce hyperphagia and exacerbates rather than attenuates susceptibility to ABA.

Prolactin response to anesthetic stress and beta-endorphin is altered in female rats treated neonatally with monosodium glutamate.

MSG (4 mg/g, sc) or saline was administered to neonatal female rats on days 1, 3, 5, 7 and 9. Study 1) Prl levels were assessed at 30, 60 and 75 days after birth to monitor possible development of hyperprolactinemia. No hyperprolactinemia was observed at any time studied. Study 2) MSG and control rats were administered pentobarbital anesthesia at 2 months of age. At 20, 60 and 90 min following anesthesia, plasma was collected for assay of Prl. 20 min prior to the 90 min bleeding, BE (5 micrograms/5 ul) was stereotaxically administered, into the third ventricle. MSG-treated rats had an attenuated Prl response to the stress of anesthesia (bleeding 1). Prl levels in control and MSG-treated rats were similar at 60 min post-anesthesia (bleeding 2) which represented a return of Prl levels to baseline after stress-induced elevation of Prl. Control and MSG-treated rats exhibited an increase in plasma Prl following intracerebroventricular BE; however, the amplitude of this response was markedly attenuated in the MSG-treated animals (bleeding 3). Thus, an observed loss of TH-positive neurons in the arcuate nucleus of the hypothalamus following MSG treatment and the attenuated response of Prl to anesthesia-stress and BE administration suggests that Prl secretion in response to these agents is operative through inhibition of the TIDA system. Furthermore, these studies show that the Prl response to these agents (anesthetic and BE) is intact but sub-operational in MSG-treated rats.

Activity-based anorexia: relationship to gender and activity-stress ulcers.

The phenomena of activity-based anorexia (ABA) and the activity-stress ulcer (ASU) both involve paradigms in which the food intake of rats is restricted and the animals are allowed voluntary exercise in a running wheel. This study determined the susceptibility of male and female rats to ABA and ASU following 25- and 30-percent losses of their original body weights. Male rats reached both weight loss criteria in a fewer number of days than did female rats. None of the male and female rats sacrificed at the 25% weight loss criterion evidenced gastric lesions; 52% of the animals sacrificed at the 30% weight loss criterion had one or more lesions. No gender differences with respect to gastric lesions were observed at the 30% weight loss criterion; however, at both weight loss criteria, females ate and ran more than males. It is concluded that ASUs are a consequence rather than a cause of ABA, and that there is a sexually "dimorphic" susceptibility to ABA but not ASUs. The utility of using a 25% weight loss criterion for defining ABA is also discussed.

Divergent effects of insulin on insulin-like growth factor-II gene expression in the rat hypothalamus.

The effect of peripheral insulin treatment on brain content and synthesis of insulin-like growth factor-II (IGF-II) was studied in acute and chronic conditions. After a 3-h hyperinsulinemic/euglycemic clamp, rats were killed, and brains were removed for IGF-II analysis. Insulin infusion elevated IGF-II concentrations in the dorsomedial hypothalamus (DMH) and suprachiasmatic nucleus, but decreased IGF-II in the paraventricular nucleus, lateral hypothalamus (LtH), and supraoptic nucleus compared to values in control animals. In separate parallel studies, the effects of 4 days of insulin injection (1 U insulin/rat, sc, twice daily) on brain IGF-II mRNA and peptide were determined. For RNA analysis the hypothalamus was divided into three regions (lateral, ventral, and dorsal). IGF-II mRNA content was shown to vary by an order of magnitude within the adult rat hypothalamus under control conditions, and there appeared to be a differential region-dependent response to insulin treatment. Relative abundance of IGF-II mRNA in control hypothalami was VH much greater than cortex greater than or equal to LtH greater than DMH. IGF-II mRNA content declined after insulin treatment in the VH, but rose in all other regions. Insulin increased IGF-II peptide content in the paraventricular nucleus, LtH, and VMH but decreased IGF-II in the DMH and suprachiasmatic nucleus. These results indicate that peripheral insulin status may be an important factor in the synthesis and secretion of IGF-II in the brain.

Abnormalities in hypothalamic and neurohypophysial vasopressin content are not a consequence of hypertension in the spontaneously hypertensive rat.

In order to determine if the decreased hypothalamic and increased posterior pituitary content of vasopressin (VP) observed previously in spontaneously hypertensive rats (SHR) were a secondary consequence of the hypertension, the effect of preventing the development of hypertension on VP content of the hypothalamoneurohypophyseal system was evaluated. Two methods for preventing the hypertension were used: (1) chronic angiotensin-converting enzyme inhibition (oral captopril, 100 mg/kg/day at 4-12 weeks of age); and (2) intraventricular 6-hydroxydopamine (6-OHDA, 200 micrograms at 4 and 5 weeks of age). Both of these treatments markedly attenuated the increase in systolic blood pressure in SHRs at 5-11 weeks of age. The captopril-treated rats had a significant elevation in serum renin activity at 12 weeks of age indicating the presence of chronic converting enzyme inhibition, and the 6-OHDA-treatment resulted in a depletion of hypothalamic (86%) and brainstem (76%) norepinephrine content. Hypothalamic VP content was reduced in untreated SHRs compared to normotensive Wistar-Kyoto rats (WKYs, P = 0.0015). It was not significantly altered in either strain by the 6-OHDA treatment. Captopril caused a reduction in hypothalamic VP content in both SHRs and WKYs (P less than 0.01). Posterior pituitary VP content was elevated in untreated SHRs compared to WKYs (P less than 0.001), and remained elevated with captopril and 6-OHDA treatments. These data indicate that the abnormalities in VP content in the hypothalamus and posterior pituitary of SHRs are not a response to the hypertension. Therefore, they may represent primary abnormalities in the SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Osmotic regulation of vasopressin and renin in spontaneously hypertensive rats.

Abnormalities in the vasopressin and renin systems have been reported in spontaneously hypertensive rats (SHR). Therefore, studies were performed to evaluate the responsiveness of these systems to changes in plasma osmolality and sodium concentration. These variables were manipulated in vivo by intraperitoneal administration of distilled water, isotonic saline, or hypertonic saline to 8- and 18-week-old SHR and normotensive Wistar-Kyoto rats (WKY). Animals were decapitated 30 minutes later, and trunk blood was collected. The hypertonic saline injections resulted in an increase in plasma osmolality and serum sodium at both ages (p less than 0.001). Serum vasopressin was higher in all groups of animals receiving hypertonic saline (1200 mosm/kg H2O; p less than 0.05), but the magnitude of increase was not significantly different in the SHR and WKY at either age. Serum renin activity was lower in SHR than in WKY following acute decreases in serum sodium at 8 weeks, but it was the same for both strains at 18 weeks. Both kidney renin content and concentration were lower in SHR than in WKY at 18 weeks but not at 8 weeks. Therefore, the suppressed renin response to acute osmotic challenge in 8-week-old SHR is not the consequence of reduced kidney renin content. The vasopressin response to osmotic stimulation also was evaluated in vitro using hypothalamoneurohypophyseal explants obtained from 5-, 8-, and 18-week-old SHR and WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

Reinnervation of transplanted hypothalamic neurons by host aminergic fibers in rats.

Fetal mediobasal hypothalamic tissue which receives an extensive noradrenergic innervation in the adult brain, was implanted into the vicinity of the medial forebrain bundle of adult rats to determine whether host noradrenergic fibers would innervate the ectopically placed tissue in an organotypic manner. Tissue from the site of implantation was prepared for light and ultrastructural immunocytochemistry at 6, 12, or 20 weeks postsurgery. Putative host catecholamine fibers formed dense plexuses in localized portions of the grafts and made synaptic contacts with dendrites and somata of transplanted neurons. This suggests that a mature host central nervous system is capable of a region-specific integration of transplanted neurons.