Effects of acute and chronic restraint and estrus cycle on pituitary-adrenal function in the rat

Female Long-Evans hooded rats with 5-day estrus cycles were subjected to 4 hr of continuous restraint for either 1 or 20 days. On the last day of the stress regimen, plasma and adrenal corticosterone concentrations were determined and classified according to the stage of the estrous cycle. The results indicated that acute stress produced greater plasma corticosterone concentrations than controls only during estrus, whereas in response to chronic stress significant stress-induced increments were observed during estrus and proestrus. The results suggest that the estrous cycle influences the magnitude of the stress-induced increments for both acute and chronic stress. In addition, the pituitary-adrenal system did not show habituation to repeated administration of this stress, but sensitization was observed during proestrus.     

Energetic response to repeated restraint stress in rapidly growing mice

There is a cost of stress that may result in the loss of normal biological function (e.g., growth). Repeated, and even single, applications of stressors have been shown to induce negative energy balance in rodents. However, here we addressed whether this energetic response changes during multiple stress exposure and whether there is complete recovery subsequent to the cessation of stress exposure. These questions were addressed in growing C57Bl/6 mice (31 day) by determining at different times the energetic and endocrine responses after the exposure to restraint (R) stress for 4 h applied once (R1), repeatedly over 3 days (R3), or repeatedly over 7 days (R7). Compared with control values, R elevated (P<0.05) plasma corticosterone and reduced plasma insulin-like growth factor I on all days of exposure to the stressor. Seven days, but not 1 or 3 days of R, decreased the net growth (126%, P<0.05) and deposition of fat (71%, P<0.05) and lean (60%, P<0.05) energy over the 7 days. Only R7 depressed the 7-day metabolizable energy intake (P<0.05), and R7, but not R1 or R3, increased the overall energy expenditure (10%, P<0.05). Our results demonstrate that repeated episodes of stress are energetically costly to the rapidly growing animal, but compensatory mechanisms mitigate this cost of repeated stress exposure and permit complete recovery of energy balance after the cessation of stress application.     

Expression of hypothalamic neuropeptides and the desensitization of pituitary-adrenal axis and hypophagia in the endotoxin tolerance

Repeated exposure to lipopolysaccharide (LPS) induces desensitization of hypothalamus-pituitary-adrenal axis (HPA) responses and hypophagia. We investigated the interplay between the neural circuitries involved in the control of food intake and HPA axis activity following single or repeated LPS injections. Male Wistar rats received a single or repeated i.p. injection of LPS (100 microg/kg) for 6 days and were subdivided into four groups: 6 saline, 5 saline+1 LPS, 5 LPS+1 saline and 6 LPS. Animals with a single exposure to LPS showed increased plasma levels of ACTH, CORT, PRL, TNF-alpha and also CRF mRNA in the paraventricular nucleus of the hypothalamus. These animals exhibited a reduced food intake and body weight associated with an increase of CART expression in the arcuate nucleus (ARC). Leptin plasma levels were not altered. On the other hand, repeated LPS administration did not alter ACTH, CORT, PRL and TNF-alpha, but it reduced leptin level, compared to single LPS or saline treatment. Furthermore, repeated LPS administration did not increase CRF or CART mRNA expression. Food intake and weight gain after repeated LPS injections were not different from saline-treated animals. There was no change in NPY and POMC mRNA expression in the ARC after single or repeated injections of LPS. In conclusion, desensitization induced by repeated exposure to LPS involves the blockade of HPA axis activation and anorexigenic response, which are both associated with an unresponsiveness of TNF-alpha production and CRF and CART expression in the hypothalamus.     

Role of hypothalamic neuropeptide Y (NPY) in the change of feeding behavior induced by repeated treatment of amphetamine

Neuropeptide Y (NPY), an orexigenic peptide, is involved in the control of food intake. Repeated administration of amphetamine (AMPH), an anorectic agent, results in an anorectic effect on day 1 and a tolerant anorectic effect on the followings. In an attempt to know the role of hypothalamic NPY in these effects of AMPH, contents of hypothalamic NPY were determined by radioimmunoassay at first. In AMPH-treated groups, the contents of hypothalamic NPY decreased rapidly on day 1 but restored gradually to the normal level on the following days as observed in repeated AMPH. An involvement of hypothalamic NPY in the feeding change of repeated AMPH can thus be considered. Moreover, daily injection of NPY antisense oligonucleotide into brain (10 microg/10 microl/day, i.c.v.) to inhibit the gene expression of hypothalamic NPY were performed at 1 hour before daily 2 mg/kg AMPH. The reversion of food intake from the anorectic level to the normal level (tolerant anorexia) was abolished by this antisense pretreatment. It is suggested that hypothalamic NPY may play a role in the change of feeding behavior induced by repeated AMPH administration.     

下丘脑食欲素在药物成瘾中的作用

下丘脑是调控自然奖赏的重要脑区,它能特异性地表达一种神经肽——食欲素(orexin),这种神经肽在药物奖赏中的作用受到广泛关注。在成瘾研究中,发现不同脑区中的食欲素神经元对奖赏和动机行为的调节作用是不相同的:围穹窿区(PFA)和背内侧下丘脑区(DMH)的食欲素神经元主要参与激活应激系统,而外侧下丘脑(LH)的食欲素神经元主要通过激活与奖赏学习相关的大脑环路参与奖赏行为的调控。提示食欲素系统可在延长戒断防止复吸发生中成为新的研究目标,食欲素受体可以作为治疗药物成瘾的一种新的治疗靶标。     

Changes in rat adipocyte and liver glucose metabolism following repeated restraint stress

Rats exposed to repeated restraint weigh less than controls even 8 weeks after stress. Stress-induced weight loss is lean tissue, but the post-stress difference in weight between control and restrained rats is lean and fat mass. Whole-body glucose clearance is enhanced 1 day after stress, but adipocyte glucose utilization is inhibited and muscle glucose transport is unchanged. The studies described here demonstrated that glucose transport was increased in both restrained and pair-fed rats, but that glycogen synthesis was increased only in restrained rats, which may account for the improved whole-body glucose clearance. Adipocyte glucose transport was inhibited and adipose plasma membrane beta-adrenergic receptor number was increased 1 day post-stress in restrained rats when weight loss was lean tissue, but were not different from control rats 5 days post-stress, when both fat and lean tissue were reduced. Thus, repeated restraint induces reversible changes in adipocyte metabolism that may represent a transition from the catabolic state of stress to a new energetic equilibrium in rats that maintain a reduced body weight for an extended period of time.     

Prior hypoglycemia enhances glucose responsiveness in some ventromedial hypothalamic glucosensing neurons

Antecedent insulin-induced hypoglycemia (IIH) reduces adrenomedullary responses (AMR) to subsequent bouts of hypoglycemia. The ventromedial hypothalamus [VMH: arcuate (ARC) + ventromedial nuclei] contains glucosensing neurons, which are thought to be mediators of these AMR. Since type 1 diabetes mellitus often begins in childhood, we used juvenile (4- to 5-wk-old) rats to demonstrate that a single bout of IIH (5 U/kg sc) reduced plasma glucose by 24% and peak epinephrine by 59% 1 day later. This dampened AMR was associated with 46% higher mRNA for VMH glucokinase, a key mediator of neuronal glucosensing. Compared with neurons from saline-injected rats, ventromedial nucleus glucose-excited neurons from insulin-injected rats demonstrated a leftward shift in their glucose responsiveness (EC50 = 0.45 and 0.10 mmol/l for saline and insulin, respectively, P = 0.05) and a 31% higher maximal activation by glucose (P = 0.05), although this maximum occurred at a higher glucose concentration (saline, 0.7 vs. insulin, 1.5 mmol/l). Although EC50 values did not differ, ARC glucose-excited neurons had 19% higher maximal activation, which occurred at a lower glucose concentration in insulin- than saline-injected rats (saline, 2.5 vs. insulin, 1.5 mmol/l). In addition, ARC glucose-inhibited neurons from insulin-injected rats were maximally inhibited at a fivefold lower glucose concentration (saline, 2.5 vs. insulin, 0.5 mmol/l), although this inhibition declined at >0.5 mmol/l glucose. These data suggest that the increased VMH glucokinase after IIH may contribute to the increased responsiveness of VMH glucosensing neurons to glucose and the associated blunting of the AMR.     

Acute and repeated restraint differentially activate orexigenic pathways in the rat hypothalamus

Stress and obesity are highly prevalent conditions, and the mechanisms through which stress affects food intake are complex. In the present study, stress-induced activation in neuropeptide systems controlling ingestive behavior was determined. Adult male rats were exposed to acute (30 min/d × 1 d) or repeated (30 min/d × 14 d) restraint stress, followed by transcardial perfusion 2 h after the termination of the stress exposure. Brain tissues were harvested, and 30 μm sections through the hypothalamus were immunohistochemically stained for Fos protein, which was then co-localized within neurons staining positively for the type 4 melanocortin receptor (MC4R), the glucagon-like peptide-1 receptor (GLP1R), or agouti-related peptide (AgRP). Cell counts were performed in the paraventricular (PVH), arcuate (ARC) and ventromedial (VMH) hypothalamic nuclei and in the lateral hypothalamic area (LHA). Fos was significantly increased in all regions except the VMH in acutely stressed rats, and habituated with repeated stress exposure, consistent with previous studies. In the ARC, repeated stress reduced MC4R cell activation while acute restraint decreased activation in GLP1R neurons. Both patterns of stress exposure reduced the number of AgRP-expressing cells that also expressed Fos in the ARC. Acute stress decreased Fos-GLP1R expression in the LHA, while repeated restraint increased the number of Fos-AgRP neurons in this region. The overall profile of orexigenic signaling in the brain is thus enhanced by acute and repeated restraint stress, with repeated stress leading to further increases in signaling, in a region-specific manner. Stress-induced modifications to feeding behavior appear to depend on both the duration of stress exposure and regional activation in the brain. These results suggest that food intake may be increased as a consequence of stress, and may play a role in obesity and other stress-associated metabolic disorders.     

Role of the pituitary-adrenal system in mechanism regulating vascular permeability during stress

Disturbances of the microvascular permeability were studied by the "vascular labelling" technique during the immobilization stress of hypophysectomized and adrenalectomized rats. Animals with sham operations served as controls. As revealed, hypophysectomy and adrenalectomy caused disturbances of vascular permeability in the mesentery. Vascular permeability disturbances in the hypophysectomized and adrenalectomized rats under conditions of immobilization were more expressed than in the sham-operated animals. Removal of the pituitary and adrenal glands produced mast cell degranulation at the earlier immobilization period.     

Role of B cells in maintaining helper T-cell memory

The cellular interactions involved in maintaining CD4+ T-cell memory have hitherto not been identified. In this report, we have investigated the role played by B cells in this process. We show that that long-lasting helper T-cell memory depends on the presence of B cells, but that direct antigen presentation by B cells is not required. These findings provide new insights into the mechanisms which underlie helper T-cell memory. They also suggest that the efficacy of future vaccines will depend critically on the inclusion of B- as well as T-cell epitopes.     

Gender differences in oxidative stress in spinal cord of rats submitted to repeated restraint stress

Behavioral and neurochemical gender-specific effects have been observed following repeated stress. The aim of this study is to verify the effects of repeated restraint stress on free radical production (evaluated by DCF test), lipoperoxidation (evaluated by TBARS levels), and total antioxidant reactivity (TAR) in the spinal cord of male and female rats. Results demonstrate no effect on lipoperoxidation; chronic stress decreased TAR both in male and female spinal cord. In addition, gender differences were observed both in TAR and in the production of free radicals, both being increased in females. These results may be relevant to the gender-specific differences observed after exposure to repeated stress.     

Role of estrogen and androgen in maintaining the preovulatory follicle

Summary The effects of Nitromifene citrate (CI 628), an antiestrogen, and Flutamide, an antiandrogen, on the ultrastructure and viability of the preovulatory follicle and granulosa cells were examined both in vivo and in vitro. In vivo administration of either antihormone induced degeneration within the granulosa cells. In some of the affected granulosa cells, the nuclear material was condensed while the cytoplasm and associated organelles were unaltered. In others, the density of the cytoplasm was reduced, the smooth endoplasmic reticulum was dilated but the nucleus remained unaltered. In vitro, either antihormone reduced granulosa-cell viability but the granulosa cells were twenty times more sensitive to CI 628 than to Flutamide. In addition, exposure to CI 628 induced nuclear condensation without affecting the cytoplasm, while Flutamide induced the deterioration of the cytoplasm without altering the nucleus. These observations suggest that: (1) both estrogen and androgens control the viability of the granulosa cells and thereby the follicle, (2) the action of estrogen and androgen is mediated through receptors within the granulosa cells since these antihormones prevent the nuclear uptake of their respective hormone, (3) the granulosa cells of preovulatory follicles appear to be more dependent on estrogen than on androgen, and (4) each steroid appears to have a specific role in maintaining the granulosa cell; estrogens control the integrity of the nucleus while androgens preserve the cytoplasmic organization of the granulosa cell.The authors are indebted to Dr. Neri of Schering AG for donating the Flutamide and to Dr. Westland of Warner-Lambert/Parke-Davis for providing CI-628     

Increased anxiety-like behavior during the post-stress period in mice exposed to repeated restraint stress

Mice exposed to repeated restraint (RR: 2 h of restraint on each of 3 consecutive days) lose weight and do not return to the weight of non-stressed controls after restraint ends. These mice also exhibit an exaggerated endocrine response to mild stressors in the post-stress period. To determine if other aspects of the stress response are altered, NIH Swiss mice were repeatedly restrained then evaluated for anxiety-like behavior in various behavioral tests. Twelve days after the end of RR half of the control and RR mice were subjected to the mild stress of an intraperitoneal injection of saline before placement in an elevated plus maze. RR mice not subjected to mild stress showed the same level of anxiety as the control and RR mice exposed to mild stress. Placement in a light-dark box 20 days after restraint also indicated an increase in anxiety-like behavior in RR mice that had not been exposed to mild stress. In contrast, RR mice displayed no increase in anxiety-like behavior in the defensive withdrawal apparatus and the marble burying test 6 and 17 days, respectively, after restraint. RR mice released more corticosterone than non-restrained controls exposed to defensive withdrawal or EPM apparatus although baseline corticosterone remained at control levels. These results suggest that RR induces an exaggeration of both endocrine and behavioral responses to subsequent mild stressors. This post-stress hypersensitivity to mild stress may contribute to the sustained reduction in the body weight of RR animals.     

Bupleurum falcatum prevents depression and anxiety-like behaviors in rats exposed to repeated restraint stress

Previous studies have demonstrated that repeated restraint stress in rodents produces increases in depression and anxietylike behaviors and alters the expression of corticotrophinreleasing factor (CRF) in the hypothalamus. The current study focused on the impact of Bupleurum falcatum (BF) extract administration on repeated restraint stress-induced behavioral responses using the forced swimming test (FST) and elevated plus maze (EPM) test. Immunohistochemical examinations of tyrosine hydroxylase (TH) expression in rat brain were also conducted. Male rats received daily doses of 20, 50, or 100 mg/kg (i.p.) BF extract for 15 days, 30 min prior to restraint stress (4 h/day). Hypothalamicpituitary- adrenal axis activation in response to repeated restraint stress was confirmed base on serum corticosterone levels and CRF expression in the hypothalamus. Animals that were pre-treated with BF extract displayed significantly reduced immobility in the FST and increased open-arm exploration in the EPM test in comparison with controls. BF also blocked the increase in TH expression in the locus coeruleus of treated rats that experienced restraint stress. Together, these results demonstrate that BF extract administration prior to restraint stress significantly reduces depression and anxiety-like behaviors, possibly through central adrenergic mechanisms, and they suggest a role for BF extract in the treatment of depression and anxiety disorders.     

Effect of repeated stress on the function of pituitary-adrenal and immune systems in gray rats selected for behavior

Reaction of pituitary-adrenal axis to a 10-day immobilisation stress and a humoral immune response to subsequent injection of sheep red blood cells were investigated in gray rats selected for enhancement of decrease of aggressive behavior towards humans. It was show that pituitary-adrenal axis reaction of aggressive animals to repeated stress did not change during the experiment, while a decrease of stress-induced corticosterone level was observed already on day 5 of stress. Repeated stress led to enhancement of humoral immune response in aggressive rats, whereas it did not bring about any change in tame animals. based on the obtained data, it could be supposed that breeding of gray rats for domesticated behavior led a faster adaptation to repeated stress and the absence of stimulating influence on humoral immune response in tame rats.