Insulin and the constituent branches of the hepatic vagus interact to modulate hypothalamic and limbic neuropeptide mRNA expression differentially

Insulin and signalling through the vagus nerve act in concert to regulate metabolic homeostasis and ingestive behaviour. Our previous studies using streptozotocin (STZ)-diabetic rats have shown that hepatic branch vagotomy (HV), gastroduodenal branch vagotomy (GV) and capsaicin treatment of the common hepatic branch that selectively destroys afferent fibres (CapV), all promote lard, but not total, caloric intake to levels similar to those achieved with insulin treatment. Because hypothalamic and limbic mRNA expression of neuropeptides linked to energy balance is altered by STZ-diabetes and HV, we examined the role(s) of insulin and the common hepatic and gastroduodenal branches of the vagus nerve and hepatic afferent fibres in the regulation of these neuropeptides in rats with high, steady-state corticosterone levels. STZ-diabetic rats were prepared with osmotic minipumps containing either saline or insulin and were compared with nondiabetic counterparts: half of each group received a vagal manipulation, the other half were sham operated. Five days after surgery, rats were offered the choice of lard and chow to consume for another 5 days, when brains were collected and processed for in situ hybridisation. Paraventricular nucleus corticotrophin-releasing factor (CRF) mRNA was elevated by STZ treatment, an effect prevented by either insulin treatment or GV. By contrast, CRF mRNA expression in the central nucleus of the amygdala and bed nuclei of the stria terminalis was unaffected by STZ treatment, but HV and CapV manipulations elevated expression in the nondiabetic, but not STZ-diabetic groups. Arcuate nucleus neuropeptide Y, but not pro-opiomelanocortin, mRNA expression was elevated by STZ treatment and all vagal manipulations; however, exogenous insulin treatment failed to prevent this, in keeping with their previously documented elevated caloric intake. These results strongly suggest that the gastroduodenal branch and hepatic branch proper, which merge to form the common hepatic branch, differentially interact with prevailing insulin levels to regulate hypothalamic and limbic neuropeptide mRNA expression.

Mapping brain c-Fos immunoreactivity after insulin-induced voluntary lard intake: insulin- and lard-associated patterns

In addition to the inhibitory role of central insulin on food intake, insulin also acts to promote lard intake. We investigated the neural pathways involved in this facet of insulin action. Insulin or saline was infused into either the superior mesenteric or right external jugular veins of streptozotocin-diabetic rodents with elevated steady-state circulating corticosterone concentrations. After postsurgical recovery, rats were offered the choice of chow or lard to eat. Irrespective of the site of venous infusion, insulin increased lard and decreased chow intake. After 4 days, lard was removed for 8 h. On return for 1 h, only insulin infused into the superior mesenteric vein resulted in lard intake. This facilitated distinction between the effects of circulating insulin concentrations (similar in the two insulin-infused groups) and lard ingestion on the patterns of c-Fos(+) cells in the brain, termed insulin- and lard-associated patterns, respectively. Insulin-associated changes in c-Fos(+) cell numbers were evident in the arcuate nucleus, bed nucleus of the stria terminalis and substantia nigra pars compacta, concomitant with elevated leptin levels and reduced chow intake. Lard-associated changes in c-Fos(+) cell numbers were observed in the nucleus of the tractus solitarius, lateral parabrachial nucleus, central nucleus of the amygdala, ventral tegmental area, nucleus accumbens shell and the prefrontal cortex, and were associated with lower levels of triglycerides and free fatty acids. The anterior paraventricular thalamic nucleus exhibited both patterns. These data collectively fit into a framework for food intake and reward and provide targets for pharmacological manipulation to influence the choice of food intake.

Causes of obesity: looking beyond the hypothalamus

The brain takes a primary position in the organism. We present the novel view that the brain gives priority to controlling its own adenosine triphosphate (ATP) concentration. It fulfils this tenet by orchestrating metabolism in the organism. The brain activates an energy-on-request system that directly couples cerebral supply with cerebral need. The request system is hierarchically organized among the cerebral hemispheres, the hypothalamus, and peripheral somatomotor, autonomic-visceromotor, and the neuroendocrine-secretomotor neurons. The system initiates allocative behavior (i.e. allocation of energy from body to brain), ingestive behavior (intake of energy from the immediate environment), or exploratory behavior (foraging in the distant environment). Cerebral projections coordinate all three behavioral strategies in such a way that the brain's energy supply is guaranteed continuously. In an ongoing learning process, the brain's request system adapts to various environmental conditions and stressful challenges. Disruption of a cerebral energy-request pathway is critical to the development of obesity: if the brain fails to receive sufficient energy from the peripheral body, it compensates for the undersupply by increasing energy intake from the immediate environment, leaving the body with a surplus. Obesity develops in the long term.

Chronic stress-induced effects of corticosterone on brain: direct and indirect

Acutely, glucocorticoids act to inhibit stress-induced corticotrophin-releasing factor (CRF) and adrenocorticotrophic hormone (ACTH) secretion through their actions in brain and anterior pituitary (canonical feedback). With chronic stress, glucocorticoid feedback inhibition of ACTH secretion changes markedly. Chronically stressed rats characteristically exhibit facilitated ACTH responses to acute, novel stressors. Moreover, in adrenalectomized rats in which corticosterone was replaced, steroid concentrations in the higher range are required for facilitation of ACTH responses to occur after chronic stress or diabetes. Infusion of corticosterone intracerebroventricularly into adrenalectomized rats increases basal ACTH, tends to increase CRF, and allows facilitation of ACTH responses to repeated restraint. Therefore, with chronic stressors, corticosterone seems to act in brain in an excitatory rather than an inhibitory fashion. We believe, under conditions of chronic stress, that there is an indirect glucocorticoid feedback that is mediated through the effects of the steroid +/- insulin on metabolism. Increased energy stores feedback on brain to inhibit hypothalamic CRF and decrease the expression of dopamine-beta-hydroxylase in the locus coeruleus. These changes would be expected to decrease the level of discomfort and anxiety induced by chronic stress. Moreover, central neural actions of glucocorticoids abet the peripheral effects of the steroids by increasing the salience and ingestion of pleasurable foods.

Sucrose intake and corticosterone interact with cold to modulate ingestive behaviour, energy balance, autonomic outflow and neuroendocrine responses during chronic stress

In adrenalectomized (ADX) rats, either corticosterone replacement or increased sucrose intake will restore body weight gain, uncoupling protein-1, fat depot mass, food intake and corticotropin-releasing factor mRNA expression to normal. Here, we tested the potential interactions between sucrose intake and circulating corticosterone on behavioural, metabolic, autonomic and neuroendocrine responses to the stress of cold. Rats were left intact, sham-ADX, or ADX and replaced with pellets that provided normal, basal (30%B) or high stress (100%B) constant circulating concentrations of corticosterone +/- sucrose. More calories were consumed in cold than at room temperature (RT), provided that corticosterone concentrations were elevated above mean daily basal values in cold. Neither increased sucrose nor increased chow ingestion occurred in cold if the rats were ADX and replaced with 30%B. However, sucrose drinking in this group markedly ameliorated other responses to cold. By contrast, ADX30%B rats not drinking sucrose fared poorly, and none of the metabolic or endocrine variables were similar to those in sham-ADX controls. ADX100%B group in cold, resembled intact rats without sucrose; however, this group was metabolically abnormal at RT. We conclude that drinking sucrose lowers stress-induced corticosterone secretion while reducing many responses to cold; elevated corticosterone concentrations in the stress-response range are essential for the normal integrated cold-induced responses to occur.

Resistance to glucocorticoid feedback in obesity

Increased hypothalamo-pituitary-adrenal axis drive has been reported in obese subjects but with paradoxically low or normal levels of plasma cortisol. Our current study was designed to investigate whether glucocorticoid feedback was altered in obesity, both under basal and stressed conditions. Plasma ACTH and cortisol concentrations in male control or obese subjects (age range 20-50 yr) were measured at frequent intervals over 24 h during infusion of saline or hydrocortisone at two physiological doses (7.5 and 15 mg/d) designed to occupy predominantly mineralocorticoid rather than glucocorticoid receptors. The same subjects then underwent insulin-induced hypoglycemia either in the morning or the evening. Obese subjects had significantly higher basal ACTH and lower cortisol concentrations throughout the 24 h infusion period, compared with controls (P < 0.05, two-way ANOVA followed by Newman-Keuls posthoc analysis). Basal plasma ACTH was decreased in obese groups given low- or high-dose hydrocortisone during the day (P < 0.05) but not during the night, unlike controls who responded to hydrocortisone both during the day and at night (P < 0.05). Obese subjects also showed resistance to steroid-induced inhibition of the ACTH response to hypoglycemia, compared with controls (P < 0.05). These data clearly show that obesity is associated with a relative insensitivity to glucocorticoid feedback, which is most marked during the night, and suggest that this condition is characterized by a decreased mineralocorticoid receptor response to circulating corticosteroids.

Corticosterone exerts site-specific and state-dependent effects in prefrontal cortex and amygdala on regulation of adrenocorticotropic hormone, insulin and fat depots

Chronic stress stimulates corticosterone secretion and recruits brain pathways that regulate energy balance (caloric acquisition and deposition) and facilitate hypothalamic-pituitary-adrenal responsiveness to new stressors. We implanted corticosterone or cholesterol bilaterally either near the central nucleus of the amygdala (CeA) or in the prefrontal cortex to determine whether high concentrations of the steroid act at either site, with or without chronic stress. Rats were adrenalectomized and treated systemically with low doses of corticosterone. Half were maintained at room temperature and the other half were exposed to 5 degrees C cold for 5 days before all rats were restrained. There was limited diffusion of corticosterone from brain implants. Corticosterone in prefrontal cortex, but not CeA, decreased plasma insulin and adrenocorticotropic hormone (ACTH) responses to acute restraint in both control and chronically cold stressed rats. Corticosterone implants near CeA decreased the weight of fat depots only in cold; corticosterone implants in prefrontal cortex were ineffective. We conclude that (i) corticosterone inhibits insulin and ACTH secretion by an action in prefrontal cortex but not CeA; (ii) high concentrations of corticosterone secreted during chronic stress alter metabolism through (autonomic) outputs of the CeA and prefrontal cortex in site- and variable-specific fashion; and (iii) the amygdala is a component of a stress-recruited, state-dependent pathway.

Sucrose ingestion normalizes central expression of corticotropin-releasing-factor messenger ribonucleic acid and energy balance in adrenalectomized rats: a glucocorticoid-metabolic-brain axis?

Both CRF and norepinephrine (NE) inhibit food intake and stimulate ACTH secretion and sympathetic outflow. CRF also increases anxiety; NE increases attention and cortical arousal. Adrenalectomy (ADX) changes CRF and NE activity in brain, increases ACTH secretion and sympathetic outflow and reduces food intake and weight gain; all of these effects are corrected by administration of adrenal steroids. Unexpectedly, we recently found that ADX rats drinking sucrose, but not saccharin, also have normal caloric intake, metabolism, and ACTH. Here, we show that ADX (but not sham-ADX) rats prefer to consume significantly more sucrose than saccharin. Voluntary ingestion of sucrose restores CRF and dopamine-beta-hydroxylase messenger RNA expression in brain, food intake, and caloric efficiency and fat deposition, circulating triglyceride, leptin, and insulin to normal. Our results suggest that the brains of ADX rats, cued by sucrose energy (but not by nonnutritive saccharin) maintain normal activity in systems that regulate neuroendocrine (hypothalamic-pituitary-adrenal), behavioral (feeding), and metabolic functions (fat deposition). We conclude that because sucrose ingestion, like glucocorticoid replacement, normalizes energetic and neuromodulatory effects of ADX, many of the actions of the steroids on the central nervous system under basal conditions may be indirect and mediated by signals that result from the metabolic effects of adrenal steroids.

Androgens alter corticotropin releasing hormone and arginine vasopressin mRNA within forebrain sites known to regulate activity in the hypothalamic-pituitary-adrenal axis

To reveal direct effects of androgens, independent of glucocorticoids, we studied the effects of gonadectomy (GDX) in adrenalectomized (ADX) rats with or without androgen replacement on corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) mRNA expression within various forebrain sites known to regulate the hypothalamic-pituitary-adrenal axis. These included the medial parvocellular portion of the paraventricular nucleus of the hypothalamus (mp PVN), the central and medial nuclei of the amygdala and bed nuclei of the stria terminalis (BNST). In the mp PVN, ADX stimulated both CRH and AVP mRNA expression. Combined ADX + GDX inhibited only AVP, and testosterone and dihydrotestosterone (DHT) restored AVP mRNA. In the central nucleus of the amygdala, ADX decreased CRH mRNA expression, and this response was unaffected by GDX +/- testosterone or DHT replacement. In the medial amygdala, AVP mRNA expression was decreased by ADX, abolished by ADX + GDX, and restored by androgen replacement. ADX had no effect on CRH and AVP mRNA expression in the BNST. GDX + ADX, however, reduced CRH mRNA expression only within the fusiform nuclei of the BNST and reduced the number of AVP-expressing neurones in the posterior BNST. Androgen replacement reversed both responses. In summary, in ADX rats, AVP, but not CRH mRNA expression in the amygdala and mp PVN, is sensitive to GDX +/- androgen replacement. Both CRH- and AVP-expressing neurones in the BNST respond to GDX and androgen replacement, but not to ADX alone. Because androgen receptors are not expressed by hypophysiotropic PVN neurones, we conclude that glucocorticoid-independent, androgenic influences on medial parvocellular AVP mRNA expression are mediated upstream from the PVN, and may involve AVP-related pathways in the medial amygdala, relayed to and through CRH- and AVP-expressing neurones of the BNST.

Manipulation of androgens causes different energetic responses to cold in 60- and 40-day-old male rats

Previous studies suggested that adults respond differently than pubertal male rats to cold stress. To test the role of androgens in this difference, we adrenalectomized and replaced with corticosterone either 60- or 40-day-old male rats, then sham gonadectomized (Intact), gonadectomized (GDX), or GDX and replaced with testosterone (T; GDX+T) or dihydrotestosterone (DHT). One-half remained at room temperature (RT), and one-half lived in cold for 5 days. Cold reduced T in adult but not in pubertal Intacts. In 60-day-old rats, GDX with or without T replacement had minor effects on body weight (BW) and food intake (FI) at RT and cold. In 40-day-old rats at RT, androgens had slight effects; however, androgens affected almost all variables in cold. Separation of 40-day-old T-treated rats into two groups (moderate T levels, 1.4 ng/ml; high T levels, 1.9 ng/ml) revealed major differences between the groups. Moderate T (and DHT) prevented cold-induced loss of BW and increased FI. No T and high T induced decreased BW and FI in cold. We conclude that at 40 days of age, partial resistance to stress-induced reduction of T and high sensitivity to small changes in T have markedly positive effects on threatened energy balance.

Haploinsufficiency of steroidogenic factor-1 in mice disrupts adrenal development leading to an impaired stress response

Adrenal steroids are essential for homeostasis and survival during severe physiological stress. Analysis of a patient heterozygous for the steroidogenic factor-1 (SF-1) gene suggested that reduced expression of this nuclear receptor leads to adrenal failure. We therefore examined SF-1 heterozygous (+/-) mice as a potential model for delineating mechanisms underlying this disease. Here we show that SF-1 +/- mice exhibit adrenal insufficiency resulting from profound defects in adrenal development and organization. However, compensatory mechanisms, such as cellular hypertrophy and increased expression of the rate-limiting steroidogenic protein StAR, help to maintain adrenal function at near normal capacity under basal conditions. In contrast, adrenal deficits in SF-1 heterozygotes are revealed under stressful conditions, demonstrating that normal gene dosage of SF-1 is required for mounting an adequate stress response. Our findings predict that natural variations leading to reduced SF-1 function may underlie some forms of subclinical adrenal insufficiency, which become life threatening during traumatic stress.

Disruption of arcuate/paraventricular nucleus connections changes body energy balance and response to acute stress

The mediobasal hypothalamus regulates functions necessary for survival, including body energy balance and adaptation to stress. The purpose of this experiment was to determine the contribution of the arcuate nucleus (ARC) in controlling these two functions by the paraventricular nucleus (PVN). Circular, horizontal cuts (1.0 mm radius) were placed immediately above the anterior ARC to sever afferents to the PVN. In shams the knife was lowered to the same coordinates but was not rotated. Food intake and body weight were monitored twice daily, at the beginning and end of the light cycle, for 1 week. On the final day the animals were restrained for 30 min. Lesioned animals had increased food intake in light and dark periods, higher weight gain per day, and more body fat as compared with shams. There was no difference in caloric efficiency. Unlike shams, lesioned rats had no predictable relationship between plasma insulin and leptin. Plasma ACTH was increased at 0 min in lesioned rats but was decreased 15 and 30 min after restraint as compared with shams. There was no difference in plasma corticosterone. Immunostaining revealed that alpha-melanocortin (alphaMSH) and neuropeptide Y (NPY) accumulated below the cuts, and both were decreased in PVN. Food intake and body weight were correlated negatively to alphaMSH, but not NPY in PVN. There was no difference in proopiomelanocortin (POMC) mRNA, but NPY mRNA was reduced in the ARC of lesioned animals. We conclude that ARC controls body energy balance in unstressed rats, possibly by alphaMSH input to PVN, and that ARC also is necessary for PVN regulation of ACTH.

A cholecystokinin-mediated pathway to the paraventricular thalamus is recruited in chronically stressed rats and regulates hypothalamic-pituitary-adrenal function

Chronic stress alters hypothalamic-pituitary-adrenal (HPA) responses to acute, novel stress. After acute restraint, the posterior division of the paraventricular thalamic nucleus (pPVTh) exhibits increased numbers of Fos-expressing neurons in chronically cold-stressed rats compared with stress-naive controls. Furthermore, lesions of the PVTh augment HPA activity in response to novel restraint only in previously stressed rats, suggesting that the PVTh is inhibitory to HPA activity but that inhibition occurs only in chronically stressed rats. In this study, we further examined pPVTh functions in chronically stressed rats. We identified afferent projections to the pPVTh using injection of the retrograde tracer fluorogold. Of the sites containing fluorogold-labeled cells, neurons in the lateral parabrachial, periaqueductal gray, and dorsal raphe containing fluorogold also expressed cholecystokinin (CCK) mRNA. We then examined whether these CCKergic inputs to the pPVTh were involved in HPA responses to acute, novel restraint after chronic stress. We injected the CCK-B receptor antagonist PD 135,158 into the PVTh before restraint in control and chronically cold-stressed rats. ACTH responses to restraint stress were augmented by PD 135,158 only in chronically stressed rats but not in controls. In addition, CCK-B receptor mRNA expression in the pPVTh was not altered by chronic cold stress. We conclude that previous chronic stress specifically facilitates the release of CCK into the pPVTh in response to acute, novel stress. The CCK is probably secreted from neurons in the lateral parabrachial, the periaqueductal gray, and/or the dorsal raphe nuclei. Acting via CCK-B receptors in pPVTh, CCK then constrains facilitated ACTH responses to novel stress in chronically stressed but not naive rats. These results demonstrate clearly that chronic stress recruits a new set of pathways that modulate HPA responsiveness to a novel stress.

Bottomed out: metabolic significance of the circadian trough in glucocorticoid concentrations

Mild chronic stressors characteristically increase circadian trough corticosteroid concentrations in rats and man. The elevation in trough concentrations is often accompanied by a reduction in peak concentrations and no change in the daily mean values. Here we point out that elevation of trough glucocorticoids, probably through daily increases of glucocorticoid receptor occupancy, has major metabolic effects that bias organisms toward storage of calories as fat. Thus, chronic mild stress, by overriding the normal mineralocorticoid receptor-mediated corticosteroid feedback regulation of trough CRF and ACTH secretion, facilitates development of the metabolic syndrome.

Corticosterone facilitates saccharin intake in adrenalectomized rats: does corticosterone increase stimulus salience?

Unlike normal rats, adrenalectomized rats do not voluntarily drink sweet saccharin solutions. To test whether this is a function of corticosterone in the circulation, and if corticosterone also increases the impetus for drinking saccharin after a period of withdrawal, we performed the following experiments. Young male rats were sham adrenalectomized (sham) or adrenalectomized (ADX); the ADX rats were provided with subcutaneous pellets containing (percent replacement of corticosterone, %B) 0%B, 15%B, 30%B or 100%B. Sham and ADX rats were immediately provided with saline (0.5%) and saccharin (2 mM) bottles in their home cages. Saccharin was allowed for 4 days on, 3 days off, 4 days on, 3 days off and a final day on, over the 15 days experiment. The dose of corticosterone determined both how much saccharin was voluntarily drunk by the ADX rats and the degree of overshoot after days off. Corticosterone also determined energy balance of the groups of ADX rats. The 30%B pellets restored food intake, body weight gain, insulin and caloric efficiency to the normal levels observed in sham rats. White fat depot weights and uncoupling protein concentration in brown adipose tissue were restored to sham levels by 100%B, suggesting that these variables which depend on activity in the sympathetic nervous system require considerable glucocorticoid receptor occupancy. We conclude that corticosterone increases the willingness to ingest sweetened water in a unimodal, dose-related manner, while moderate doses of corticosterone restore energy balance.

Plasma membrane calcium pump isoform 1 gene expression is repressed by corticosterone and stress in rat hippocampus

Glucocorticoids (GCs) are critical to learning and memory, in large part because of their actions in the hippocampus. Chronic high levels of GCs have profound effects on hippocampal structure and function and can even result in irreversible neurodegeneration. Hippocampal GC actions are mediated by intracellular receptors that modulate the transcription of specific target genes. In a screen for genes repressed by GCs in rat hippocampus, we identified plasma membrane calcium pump isoform 1 (PMCA1), a plasma membrane calcium ATPase. In Northern blots, PMCA1 was repressed approximately 33% after a high, but not a low dose of the GC, corticosterone (B), suggesting glucocorticoid (but not mineralocorticoid) receptor-mediated repression. Furthermore, in situ hybridization demonstrated that B significantly downregulated PMCA1 mRNA in all brain regions examined. Repression of PMCA1 was also observed in cultured hippocampal neurons, but only when the cells were in the differentiated state. Stress also repressed PMCA1 expression in hippocampus of adrenal-intact animals, and a clear inverse correlation between B level and PMCA1 mRNA could be discerned. However, other non-B-dependent factors appeared to be involved in the response of PMCA1 to stress because, unlike exogenous B, cold stress did not repress PMCA1 in brain regions other than hippocampus. Moreover, in the presence of constant B (B-replaced, adrenalectomized animals), cold stress led to increased hippocampal PMCA1 expression. These observations suggest that repression of PMCA1 represents one molecular mechanism by which corticosteroids regulate Ca(2+) homeostasis and hence influence neuronal activity. Moreover, other stress-related neurohumoral factors appear to counter the repressive effects of B. Defects in the balance between GC-mediated and non-GC-mediated effects on PMCA1 expression may have adverse effects on neuronal function and ultimately result in irreversible neuronal damage.

Voluntary sucrose ingestion, like corticosterone replacement, prevents the metabolic deficits of adrenalectomy

We tested whether corticosterone replacement causes increased sucrose drinking in adrenalectomized (ADX) rats compared to sham-ADX (sham) rats. ADX rats given high doses of corticosterone drank as much sucrose as sham rats, whereas at three lower doses of corticosterone, drinking was similar between groups and was only approximately 40% of that ingested by shams. Compared to sham rats, ADX rats drinking saline, or saline and saccharin, gain weight more slowly, contain less white adipose tissue, and have higher sympathetic outflow as assessed by uncoupling protein content in brown adipose tissue. Allowing sucrose as well as saline to drink restored all of these variables to normal in ADX rats with no- or low-corticosterone. All endpoints from sucrose-drinking ADX rats with no-or low-corticosterone were indistinguishable from those in water-drinking shams. By contrast, sucrose-drinking ADX rats that were given high doses of corticosterone exhibited the usual catabolic effects of corticosterone on body weight gain and, unlike sucrose-drinking shams, were obese. We conclude that (i) high corticosterone stimulates the potability of sucrose and inhibits sympathetic stimulation of uncoupling protein; (ii) sucrose, without corticosterone, normalizes metabolic deficits in ADX rats probably through actions mediated both peripherally and by the central nervous system; and (iii) ADX rats have a distinct sucrose appetite.

Transcriptional repression of the 5-HT1A receptor promoter by corticosterone via mineralocorticoid receptors depends on the cellular context

The diverse effects of the corticosteroid hormones are mediated in large measure by the mineralocorticoid and glucocorticoid receptors, two closely related members of the nuclear receptor superfamily. In the brain, corticosteroids regulate neuronal excitability and responses to neurotransmitters in a cell type-specific manner. The 5-HT1A receptor, for example, is highly expressed in the hippocampus and raphe but transcription is repressed by corticosterone (the principal glucocorticoid in rodents) only in hippocampus. We have used transient transfection of cultured cells to study the transcriptional regulation of the 5-HT1A receptor promoter by activators and repression by glucocorticoids. We find that transcription factors Sp1 and NF-kB subunit p65, both of which are coexpressed in hippocampus with the 5-HT1A receptor in vivo, synergistically activate a reporter driven by receptor 5'-flanking region. Primer extension data suggest that the multiple transcription initiation sites used in reporter gene transcription correlate with those used in transcription of the endogenous gene which has a TATA-less promoter. Repression of transcription by corticosteroids was found to be mediated by both mineralocorticoid and glucocorticoid receptors, but not identically. While glucocorticoid receptors potently inhibited both p65- and p65/Sp1-stimulated transcription, repression via mineralocorticoid receptors (MR) depended on the transcriptional activators that were present: p65-stimulated reporter activity was not repressed via MR, whereas a similar level of transcription resulting from synergistic activation by p65/Sp1-stimulation was repressed via MR. The context-dependence of these MR-mediated effects provides a model for the cell-type and state-dependent actions of corticosterone in the brain.

Hypothalamic-pituitary-adrenal dysfunction in Apoe(-/-) mice: possible role in behavioral and metabolic alterations

Several neurological diseases are frequently accompanied by dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis. The HPA axis regulates the secretion of glucocorticoids (GCs), which play important roles in diverse brain functions, including cognition, emotion, and feeding. Under physiological conditions, GCs are adaptive and beneficial; however, prolonged elevations in GC levels may contribute to neurodegeneration and brain dysfunction. In the current study, we demonstrate that apolipoprotein E (apoE) deficiency results in age-dependent dysregulation of the HPA axis through a mechanism affecting primarily the adrenal gland. Apoe(-/-) mice, which develop neurodegenerative alterations as they age, had an age-dependent increase in basal adrenal corticosterone content and abnormally increased plasma corticosterone levels after restraint stress, whereas their plasma and pituitary adrenocorticotropin levels were either unchanged or lower than those in controls. HPA axis dysregulation was associated with behavioral and metabolic alterations. When anxiety levels were assessed in the elevated plus maze, Apoe(-/-) mice showed more anxiety than wild-type controls. Apoe(-/-) mice also showed reduced activity in the open field. Finally, Apoe(-/-) mice showed age-dependent increases in food and water intake, stomach and body weights, and decreases in brown and white adipose tissues. These results support a key role for apoE in the tonic inhibition of steroidogenesis and HPA axis activity and have important implications for the behavioral analysis of Apoe(-/-) mice.

Effects of streptozotocin-induced diabetes and insulin treatment on the hypothalamic melanocortin system and muscle uncoupling protein 3 expression in rats

Hypothalamic melanocortins are among several neuropeptides strongly implicated in the control of food intake. Agonists for melanocortin 4 (MC-4) receptors such as alpha-melanocyte-stimulating hormone (alpha-MSH), a product of proopiomelanocortin (POMC), reduce food intake, whereas hypothalamic agouti-related protein (AgRP) is a MC-4 receptor antagonist that increases food intake. To investigate whether reduced melanocortin signaling contributes to hyperphagia induced by uncontrolled diabetes, male Sprague-Dawley rats were studied 7 days after administration of streptozotocin (STZ) or vehicle. In addition, we wished to determine the effect of diabetes on muscle uncoupling protein 3 (UCP-3), a potential regulator of muscle energy metabolism. STZ diabetic rats were markedly hyperglycemic (31.3 +/- 1.0 mmol/l; P < 0.005) compared with nondiabetic controls (9.3 +/- 0.2 mmol/l). Insulin treatment partially corrected the hyperglycemia (18.8 +/- 2.5 mol/l; P < 0.005). Plasma leptin was markedly reduced in STZ diabetic rats (0.4 +/- 0.1 ng/ml; P < 0.005) compared with controls (3.0 +/- 0.4 ng/ml), an effect that was also partially reversed by insulin treatment (1.8 +/- 0.3 ng/ml). Untreated diabetic rats were hyperphagic, consuming 40% more food (48 +/- 1 g/day; P < 0.005) than controls (34 +/- 1 g/day). Hyperphagia was prevented by insulin treatment (32 +/- 2 g/day). In untreated diabetic rats, hypothalamic POMC mRNA expression (measured by in situ hybridization) was reduced by 80% (P < 0.005), whereas AgRP mRNA levels were increased by 60% (P < 0.01), suggesting a marked decrease of hypothalamic melanocortin signaling. The change in POMC, but not in AgRP, mRNA levels was partially reversed by insulin treatment. By comparison, the effects of diabetes to increase hypothalamic neuropeptide Y (NPY) expression and to decrease corticotropin-releasing hormone (CRH) expression were normalized by insulin treatment, whereas the expression of mRNA encoding the long form of the leptin receptor in the arcuate nucleus was unaltered by diabetes or insulin treatment. UCP-3 mRNA expression in gastrocnemius muscle from diabetic rats was increased fourfold (P < 0.005), and the increase was prevented by insulin treatment. The effect of uncontrolled diabetes to decrease POMC, while increasing AgRP gene expression, suggests that reduced hypothalamic melanocortin signaling, along with increased NPY and decreased CRH signaling, could contribute to diabetic hyperphagia. These responses, in concert with increased muscle UCP-3 expression, may also contribute to the catabolic effects of uncontrolled diabetes on fuel metabolism in peripheral tissues.

The paraventricular nucleus of the thalamus alters rhythms in core temperature and energy balance in a state-dependent manner

Exposure to chronic stress facilitates activity within the hypothalamic-pituitary-adrenal (HPA) axis and is associated with enhanced neuronal activity in a discreet set of brain regions, including the posterior division of the paraventricular nucleus of the thalamus (pPVTh). Because HPA function is intimately associated with systems that regulate metabolism, including core temperature and energy balance, we examined the effects of chronic stress on circadian rhythms in temperature, locomotor activity, body weight gain and food intake and adipose depot weights in rats. We also examined the potential role of the pPVTh in mediating these functions using ibotenate lesions of this nucleus. Chronic stress lowered the amplitude of core temperature rhythms, and lesions of the pPVTh blocked this effect in chronically stressed animals, but did not affect the amplitude of temperature rhythms in unstressed controls. In addition, lesions of the pPVTh increased cumulative food intake and overall body weight gain in controls but they increased subcutaneous white adipose depot weight in chronically stressed animals. Thus, the functional paraventricular nucleus of the thalamus appears to inhibit both temperature rhythms and specific white adipose depots only in chronically stressed animals. Together with our previous results, we show that the PVTh affects rhythms in food intake and body weight and is a nexus that differentially regulates core temperature rhythms/HPA activity/specific white adipose depots depending on the stress state of the animal.

Repeated, but not acute, stress suppresses inflammatory plasma extravasation

Clinical findings suggest that inflammatory disease symptoms are aggravated by ongoing, repeated stress, but not by acute stress. We hypothesized that, compared with single acute stressors, chronic repeated stress may engage different physiological mechanisms that exert qualitatively different effects on the inflammatory response. Because inhibition of plasma extravasation, a critical component of the inflammatory response, has been associated with increased disease severity in experimental arthritis, we tested for a potential repeated stress-induced inhibition of plasma extravasation. Repeated, but not single, exposures to restraint stress produced a profound inhibition of bradykinin-induced synovial plasma extravasation in the rat. Experiments examining the mechanism of inhibition showed that the effect of repeated stress was blocked by adrenalectomy, but not by adrenal medullae denervation, suggesting that the adrenal cortex mediates this effect. Consistent with known effects of stress and with mediation by the adrenal cortex, restraint stress evoked repeated transient elevations of plasma corticosterone levels. This elevated corticosterone was necessary and sufficient to produce inhibition of plasma extravasation because the stress-induced inhibition was blocked by preventing corticosterone synthesis and, conversely, induction of repeated transient elevations in plasma corticosterone levels mimicked the effects of repeated stress. These data suggest that repetition of a mild stressor can induce changes in the physiological state of the animal that enable a previously innocuous stressor to inhibit the inflammatory response. These findings provide a potential explanation for the clinical association between repeated stress and aggravation of inflammatory disease symptoms and provide a model for study of the biological mechanisms underlying the stress-induced aggravation of chronic inflammatory diseases.

Interactions among chronic cold, corticosterone and puberty on energy intake and deposition

We have shown that chronic cold stress strongly interacts with corticosterone (B) to determine subsequent regulation of the hypothalamo-pituitary-adrenal (HPA) axis responses to novel stress. These studies, using the same 2 sets of rats, show that chronic cold also interacts with B and testosterone on signals of energy balance. The two groups of rats differed in weight by 20% and in age by 2 weeks (44-59 days of age). Adrenalectomized rats, replaced with varying doses of B, were exposed to cold or served as controls. Food intake and body weight during the experiments and hormones, metabolites and fat depots were measured on day 5. B, but not cold, affected food intake in the younger rats; by contrast, cold, but not B, affected food intake in the older rats. Testosterone was higher in older control rats and was markedly depressed by cold; younger rats had lower testosterone that was minimally affected by cold. Weight gain decreased in all rats at room temperature with increasing B, whereas they all lost weight in cold independently of B. Cold stimulated and B inhibited interscapular brown adipose tissue DNA content (reflecting sympathetic stimulation of thermogenesis). B stimulated insulin, whereas cold inhibited leptin and insulin; B also increased white adipose tissue weight gain in controls and inhibited its loss in cold. Leptin was unrelated to white adipose tissue depots in older control rats but was strongly related to these stores in younger rats and in all rats in cold. We conclude that: 1. By decreasing signals that act centrally to inhibit food intake (insulin, leptin and testosterone) cold allows B to stimulate food intake; 2. B inhibits weight gain although it causes accrual of fat; 3. Cold, probably through sympathetic stimulation of white adipose tissue, causes fat loss which is modulated by the inhibitory effect of B on sympathetic outflow; and, 4. The slope of the relationship between fat depot size and leptin becomes flatter in cold, possibly because of increased sympathetic outflow to these depots.

Warning! Nearby construction can profoundly affect your experiments

This is meant to alert people to potentially major effects of construction projects on research results. Because we study the effects of stress on regulation of ACTH and corticosterone secretion and of serotonin receptors and stress on energy balance, we serve as an early warning system when things go awry. Most of our experiments include taking daily, or twice daily, measurements of rat or mouse weights and food intake as well as stress hormone levels. We are highly sensitized to environmental disruption and we've shown previously the effects of construction on stress hormones (1). However, we did not anticipate the change and disruption in energy balance that may occur in response to environmental perturbation. We provide two examples of these, below.

Rats with hypothalamic obesity are insensitive to central leptin injections

Genetically determined obesities, involving leptin- and melanocortin-signaling pathways, have focused attention on the four medial hypothalamic nuclei as primary sources of feeding- and metabolically-based obesity. All four medial cell groups contain leptin receptors. To determine which of these cell groups normally mediates the effects of leptin on food intake and body weight gain, we injected colchicine bilaterally into each nucleus and determined the pathophysiological effects of disruption and responsivity to leptin injected intracerebroventricularly. Intracerebroventricular injections of leptin in sham-lesioned rats decreased food intake during the dark period, but not during the light period. Lesions of the arcuate (ARC), paraventricular (PVN), and ventromedial (VMN) nuclei all resulted in leptin insensitivity; by contrast, lesions of the dorsomedial nuclei (DMN) augmented sensitivity to leptin on feeding and body weight gain. Although rats with ARC and PVN lesions were obese, they were still capable of reducing caloric efficiency over the 5 days of study and increasing uncoupling protein content in interscapular brown adipose tissue. Caloric efficiency and uncoupling protein content were unchanged in rats with VMN and DMN lesions. Finally, the slope of the relationship between leptin and mesenteric white adipose tissue was increased in rats with VMN lesions and abolished in rats with ARC lesions. Thus, lesions of the ARC, PVN, and VMN produced obesity via separate pathways. We conclude that the medial hypothalamic cell groups, each with a different role in energy balance, are all necessary for normal leptin responsiveness.

Starvation: early signals, sensors, and sequelae

To identify the sequences of changes in putative signals, reception of these and responses to starvation, we sampled fed and starved rats at 2- to 6-h intervals after removal of food 2 h before dark. Metabolites, hormones, hypothalamic neuropeptide expression, fat depots, and leptin expression were measured. At 2 h, insulin decreased, and FFA and corticosterone (B) increased; by 4 h, leptin and glucose levels decreased. Neuropeptide Y messenger RNA (mRNA) increased 6 h after food removal and thereafter. Adrenal and plasma B did not follow ACTH and were elevated throughout, with a nadir at the dark-light transition. Leptin correlated inversely with adrenal B. Fat stores decreased during the last 12 h. Leptin mRNA in perirenal and sc fat peaked during the dark period, resembling plasma leptin in fed rats. We conclude that 1) within the first 4 h, hormonal and metabolic signals relay starvation-induced information to the hypothalamus; 2) hypothalamic neuropeptide synthesis responds rapidly to the altered metabolic signals; 3) catabolic activity quickly predominates, reinforced by elevated B, not driven by ACTH, but possibly to a minor extent by leptin, and more by adrenal neural activity; and 4) leptin secretion decreases before leptin mRNA or fat depot weight, showing synthesis-independent regulation.

Hypothalamic obesity: multiple routes mediated by loss of function in medial cell groups

Cell groups of the medial hypothalamus are key to the regulation of energy balance. Functional disruption by colchicine injected in the hypothalamic arcuate (ARC), paraventricular (PVN), and ventromedial (VMN) cell groups produced increased food intake and obesity; disruption of the dorsomedial nuclei (DMN) produced decreased food intake. Colchicine in ARC or PVN increased food intake during both light and dark periods and increased cumulative food intake. By contrast, colchicine in VMN increased food intake only during the light, and cumulative food intake was not increased. Both leptin and insulin were elevated in the obese rats. Compared with sham, the slope of regression of leptin on insulin was increased by disruption of PVN and DMN but was not altered by disruption of VMN. ARC disruption abolished the relationship between leptin and insulin. Colchicine injected in the DMN did not cause obesity but altered feeding and the normal relationship between leptin, fat, and insulin, suggesting that blockade of signals, for example, from the lateral hypothalamus to DMN may disinhibit the normal medial hypothalamic drive to decrease energy stores. Changes in caloric efficiency with time after colchicine injections suggest that rats with both ARC and PVN disruption respond to signals of obesity, whereas rats with VMN disruption do not. These studies distinguish among functions in the four medial hypothalamic nuclei and suggest that interactions among them normally serve to regulate energy balance through alterations in food acquisition and storage.

Independent and overlapping effects of corticosterone and testosterone on corticotropin-releasing hormone and arginine vasopressin mRNA expression in the paraventricular nucleus of the hypothalamus and stress-induced adrenocorticotropic hormone release

Adrenocorticotropin (ACTH) release is regulated by both glucocorticoids and androgens; however, the precise interactions are unclear. We have controlled circulating corticosterone (B) and testosterone (T) by adrenalectomy (ADX) +/- B replacement and gonadectomy (GDX) +/- T replacement, comparing these to sham-operated groups. We hoped to reveal how and where these neuroendocrine systems interact to affect resting and stress-induced ACTH secretion. ADX responses. In gonadal-intact rats, ADX increased corticotropin-releasing factor (CRH) and vasopressin (AVP) mRNA in hypothalamic parvocellular paraventricular nuclei (PVN) and ACTH in pituitary and plasma. B restored these toward normal. GDX blocked the increase in AVP but not CRH mRNA and reduced plasma, but not pituitary ACTH in ADX rats. GDX+T restored increased AVP mRNA in ADX rats, although plasma ACTH remained decreased. Stress responses. Restraint-induced ACTH responses were elevated in ADX gonadally intact rats, and B reduced these toward normal. GDX in adrenal-intact and ADX+B rats increased ACTH responses. Without B, T did not affect ACTH; together with B, T restored ACTH responses to normal. The magnitude of ACTH responses to stress was paralleled by similar effects on the number of c-fos staining neurons in the hypophysiotropic PVN. We conclude that gonadal regulation of ACTH responses to ADX is determined by T dependent effects on AVP biosynthesis, whereas CRH biosynthesis is B-dependent. Stress-induced ACTH release is not explained by B and T interactions at the PVN, but is determined by B- and T-dependent changes in drive to PVN motorneurons.

Leptin-independent hyperphagia and type 2 diabetes in mice with a mutated serotonin 5-HT2C receptor gene

Brain serotonin and leptin signaling contribute substantially to the regulation of feeding and energy expenditure. Here we show that young adult mice with a targeted mutation of the serotonin 5-HT2C receptor gene consume more food despite normal responses to exogenous leptin administration. Chronic hyperphagia leads to a 'middle-aged'-onset obesity associated with a partial leptin resistance of late onset. In addition, older mice develop insulin resistance and impaired glucose tolerance. Mutant mice also responded more to high-fat feeding, leading to hyperglycemia without hyperlipidemia. These findings demonstrate a dissociation of serotonin and leptin signaling in the regulation of feeding and indicate that a perturbation of brain serotonin systems can predispose to type 2 diabetes.

Stress-related cortisol secretion in men: relationships with abdominal obesity and endocrine, metabolic and hemodynamic abnormalities

Abdominal obesity has been suggested to be associated with perturbations of the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. In a population of 51-yr-old men (n = 284) salivary cortisol concentrations were determined on repeated (n = 7) occasions over a random working day, and perceived stress was reported in parallel. Cortisol values were then related to reported stress (stress-related cortisol). A standardized lunch was used as a physiological challenge. A low dose (0.5 mg) dexamethasone suppression test was also performed as well as determinations of testosterone and insulin-like growth factor I (IGF-I). Body mass index [weight (kilograms)/height (meters)2]; waist/hip circumference ratio (WHR); sagittal trunk recumbent diameter (D); fasting insulin; blood glucose; triglycerides; and total, low density (LDL), and high density (HDL) lipoprotein cholesterol were also determined. Cortisol concentrations were highest in the morning, and lunch was followed by a peak (P = 0.044). Two types of diurnal cortisol curves were identified, one characterized by a high variability with high morning values, and another with low variability and low morning values. Both correlated strongly with suppression of salivary cortisol by dexamethasone (P < 0.001). Stress-related cortisol secretion was associated with D (P = 0.051), low IGF-I (P = 0.006), and diastolic blood pressure (P = 0.078). When the type of diurnal cortisol curve was taken into consideration by statistical weighting, stress-related cortisol secretion in subjects with high variability showed associations with testosterone (P < 0.001), D, total and LDL cholesterol, diastolic blood pressure (P < 0.001), fasting insulin (P = 0.039), and glucose (P = 0.030) as well as, negatively, triglycerides (P < 0.001). When weighted for a low variability of diurnal cortisol secretion, stress-related cortisol secretion showed strong negative relationships with IGF-I, testosterone, and HDL. Furthermore, strong, consistent relationships (all P < 0.001) were found with obesity factors (body mass index, WHR, and D), and with metabolic (insulin, glucose, triglycerides, and total and LDL cholesterol) as well as hemodynamic variables (systolic and diastolic blood pressure and heart rate). These results clearly show interactions between diurnal cortisol secretion related to perceived stress and anthropometric, endocrine, metabolic, and hemodynamic variables. This seems to occur with apparently normal regulation of the HPA axis (high morning peaks and variability as well as dexamethasone suppression of cortisol), where other endocrine variables are not affected. With a low diurnal cortisol variation and blunted dexamethasone suppression, indicating abnormal regulation of the HPA axis, perceived stress-dependent cortisol values were strongly related to perturbations of other endocrine axes as well as abdominal obesity with metabolic and hemodynamic abnormalities. Perturbations of the regulations of the HPA axis such as those described in combination with low dexamethasone suppressibility are known to follow long term overactivation of the axis by factors such as environmental stress.

The effects of prior chronic stress on cardiovascular responses to acute restraint and formalin injection

Exposure to acute stressors activates both the hypothalamic-pituitary-adrenal (HPA) and cardiovascular systems. Prior chronic stress enhances HPA responses to novel, acute stressors, but whether it alters cardiovascular responsivity to novel, acute stress is unknown. In the present study, we examined mean arterial blood pressure (MAP) and heart rate (HR) to two distinct stimuli, restraint and formalin, following prior exposure to 7 days of intermittent cold. In two sets of control and chronically stressed animals, we measured MAP and HR for 60 min following onset of 30 min restraint and MAP, HR and behavioral responses to intraplantar injection of formalin. Chronic stress raised MAP and HR under resting conditions and elevated HR during, but not following termination of, restraint. These increases in HR during restraint were due to the differences in resting levels of HR, since both control and chronically stressed animals exhibited similar increases from resting levels in HR during restraint. Conversely, chronically stressed animals exhibited lower changes in MAP and HR from resting levels following termination of restraint. Formalin produced the characteristic biphasic pattern of cardiovascular and behavioral responses. Prior chronic stress did not alter behavior, but increased MAP and HR in Interphase and only MAP in Phase 2. The increases in MAP during Interphase and Phase 2 were a result of the elevations in resting levels of MAP, but even when differences in resting levels were taken into account, HR remained elevated in the Interphase in chronically stressed animals. Together, these data demonstrate that prior chronic intermittent cold stress modifies cardiovascular function both under resting conditions and, in very specific ways, under stimulated conditions produced by restraint and formalin. We propose that these modifications are produced by brain regions that are known to regulate cardiovascular function and which are activated by chronic stress.

Stress-related cortisol secretion in men: relationships with abdominal obesity and endocrine, metabolic and hemodynamic abnormalities

Abdominal obesity has been suggested to be associated with perturbations of the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. In a population of 51-yr-old men (n = 284) salivary cortisol concentrations were determined on repeated (n = 7) occasions over a random working day, and perceived stress was reported in parallel. Cortisol values were then related to reported stress (stress-related cortisol). A standardized lunch was used as a physiological challenge. A low dose (0.5 mg) dexamethasone suppression test was also performed as well as determinations of testosterone and insulin-like growth factor I (IGF-I). Body mass index [weight (kilograms)/height (meters)2]; waist/hip circumference ratio (WHR); sagittal trunk recumbent diameter (D); fasting insulin; blood glucose; triglycerides; and total, low density (LDL), and high density (HDL) lipoprotein cholesterol were also determined. Cortisol concentrations were highest in the morning, and lunch was followed by a peak (P = 0.044). Two types of diurnal cortisol curves were identified, one characterized by a high variability with high morning values, and another with low variability and low morning values. Both correlated strongly with suppression of salivary cortisol by dexamethasone (P < 0.001). Stress-related cortisol secretion was associated with D (P = 0.051), low IGF-I (P = 0.006), and diastolic blood pressure (P = 0.078). When the type of diurnal cortisol curve was taken into consideration by statistical weighting, stress-related cortisol secretion in subjects with high variability showed associations with testosterone (P < 0.001), D, total and LDL cholesterol, diastolic blood pressure (P < 0.001), fasting insulin (P = 0.039), and glucose (P = 0.030) as well as, negatively, triglycerides (P < 0.001). When weighted for a low variability of diurnal cortisol secretion, stress-related cortisol secretion showed strong negative relationships with IGF-I, testosterone, and HDL. Furthermore, strong, consistent relationships (all P < 0.001) were found with obesity factors (body mass index, WHR, and D), and with metabolic (insulin, glucose, triglycerides, and total and LDL cholesterol) as well as hemodynamic variables (systolic and diastolic blood pressure and heart rate). These results clearly show interactions between diurnal cortisol secretion related to perceived stress and anthropometric, endocrine, metabolic, and hemodynamic variables. This seems to occur with apparently normal regulation of the HPA axis (high morning peaks and variability as well as dexamethasone suppression of cortisol), where other endocrine variables are not affected. With a low diurnal cortisol variation and blunted dexamethasone suppression, indicating abnormal regulation of the HPA axis, perceived stress-dependent cortisol values were strongly related to perturbations of other endocrine axes as well as abdominal obesity with metabolic and hemodynamic abnormalities. Perturbations of the regulations of the HPA axis such as those described in combination with low dexamethasone suppressibility are known to follow long term overactivation of the axis by factors such as environmental stress.

Hypothalamic ventromedial nuclei amplify circadian rhythms: do they contain a food-entrained endogenous oscillator?

Several endogenous oscillators determine circadian rhythms. One, light-entrained, is in the suprachiasmatic nuclei (SCN), the others, food-entrained, are in unknown sites. To determine how the hypothalamic ventromedial nuclei (VMN) and feeding affect rhythms, we compared nocturnally active rats fed either ad libitum or for 2 hr/d during light [restricted feeding (RF)] and either with or without colchicine-induced disruption of VMN. We measured rhythms in temperature, locomotor activity, feeding, drinking, corticosterone, and the numbers of cells expressing c-Fos in light/dark in hypothalamic nuclei, the suprachiasmatic nuclei, and two major SCN targets, the subparaventricular zone (sPVNz) and paraventricular thalamus (pvTHAL). c-Fos cells were always light > dark in SCN, whereas the VMN and sPVNz lacked light/dark differences except after RF and RF plus VMN disruption, respectively. Controls fed ad libitum had high-amplitude rhythms and, generally, c-Fos cells dark > light. In RF controls, a c-Fos pattern dark > light occurred in VMN; generally, c-Fos cell numbers increased elsewhere maintaining dark > light. By contrast, levels of corticosterone peaked before food. In rats fed ad libitum, VMN with colchicine markedly reduced rhythm amplitudes, not phase. c-Fos patterns were abolished except in pvTHAL and SCN. In RF, VMN disruption blocked corticosterone and light/dark c-Fos patterns in all nuclei but produced a pattern in the sPVNz like SCN. We conclude that VMN amplify rhythmic output from the SCN, and the RF-induced rhythm in VMN enhances c-Fos activity driven by the SCN. The VMN may contain a food-entrained oscillator, and the sPVNz may integrate output from several oscillators.

Pituitary-adrenocortical responses to persistent noxious stimuli in the awake rat: endogenous corticosterone does not reduce nociception in the formalin test

Although glucocorticoids inhibit inflammation and are used to treat painful inflammatory rheumatic diseases, the contribution, if any, of endogenous pituitary-adrenocortical activity to the control of pain remains unclear. We report that injection of dilute formalin into the hindpaw not only evokes inflammation and pain-related behavior, but it also increases ACTH and corticosterone to a greater extent than restraint and saline injection alone. This difference was particularly robust during the final periods of pain-related behavior in the formalin test, when the ACTH and corticosterone (B) levels in the restraint/saline control group had returned to normal. These results indicate that formalin-evoked increases in ACTH and B reflect nociceptive input, rather than the stress associated with handling. To test the hypothesis that the formalin-induced increase in corticosterone reduces pain and inflammation, we next evaluated the effect of adrenalectomy (to prevent activation of glucocorticoid receptors) or high-dose dexamethasone (to saturate glucocorticoid receptors) on nociceptive processing in the formalin test. Neither adrenalectomy nor dexamethasone changed behavioral or cardiovascular nociceptive responses. Furthermore, the increases in blood pressure and heart rate produced by formalin may not be mediated by adrenomedullary catecholamine release. In addition, we conclude that the nociceptive component of the formalin stimulus is sufficient to activate the pituitary-adrenocortical system in the awake rat, but that the resulting release of corticosterone does not feed back and reduce nociceptive processing.

High-fat feeding alters both basal and stress-induced hypothalamic-pituitary-adrenal activity in the rat

High-fat feeding induces insulin resistance and increases the risk for the development of diabetes and coronary artery disease. Glucocorticoids exacerbate this hyperinsulinemic state, rendering an individual at further risk for chronic disease. The present studies were undertaken to determine whether dietary fat-induced increases in corticosterone (B) reflect alterations in the regulatory components of the hypothalamic-pituitary-adrenal (HPA) axis. Adult male rats were maintained on a high-fat (20%) or control (4%) diet for varying periods of time. Marked elevations in light-phase spontaneous basal B levels were evident as early as 7 days after fat diet onset, and B concentrations remained significantly elevated up to 21 days after fat diet onset compared with controls. In contrast, there were no significant effects on any parameters of spontaneous growth hormone secretory profiles, thus providing support for the specificity of the effects on the HPA axis. In a second study, all groups of rats fed the high-fat diet for 1, 9, or 12 wk exhibited significantly elevated levels of plasma adrenocorticotropic hormone, B, fatty acid, and glucose before, during, and/or at 20, 60, and/or 120 min after the termination of a restraint stress. Furthermore 12-wk fat-fed animals showed a significant resistance to insulin compared with normally fed controls. There were no differences in negative feedback efficacy in high-fat-fed rats vs. controls. Taken together, these results suggest that dietary fat intake acts as a background form of chronic stress, elevating basal B levels and enhancing HPA responses to stress.

Evidence that elevated plasma corticosterone levels are the cause of reduced hypothalamic corticotrophin-releasing hormone gene expression in diabetes

Uncontrolled diabetes mellitus causes both a sustained activation of the hypothalamic-pituitary-adrenal (HPA) axis and reduced expression of corticotrophin-releasing hormone (CRH) mRNA in the hypothalamic paraventricular nucleus (PVN). To investigate the role of glucocorticoids in the regulation of CRH mRNA expression in the PVN of diabetic rats, we studied surgically adrenalectomized (ADX) and sham-operated male Sprague-Dawley rats 4 days after i.v. injection of streptozotocin (STZ; 65 mg/kg i.v.) or vehicle. Among sham-operated animals, AM plasma corticosterone levels were significantly increased in diabetic as compared to nondiabetic animals (1.46+/-0.54 vs. 0.22+/-0.05 microg/dl; P <0.05), and were positively correlated to both plasma ACTH levels (r = 0.74; P = 0.015) and adrenal gland weight (r = 0.70; P = 0.025). In contrast, CRH mRNA levels measured in the PVN by in situ hybridization were inversely related to the plasma corticosterone level (r = -0.68; P = 0.045). In a second experiment, both diabetic and nondiabetic ADX rats received a continuous subcutaneous infusion of either corticosterone at one of two doses or its vehicle for 4 days. Among vehicle-treated ADX animals, STZ diabetes raised hypothalamic CRH mRNA levels, in contrast to the tendency for diabetes to lower CRH mRNA in intact rats in the first experiment. Corticosterone administration lowered CRH mRNA comparably in both diabetic and nondiabetic ADX rats. In contrast, diabetes reduced arginine vasopressin (AVP) mRNA levels in the PVN of ADX rats and blunted the inhibitory effect of glucocorticoids on AVP mRNA levels in this setting. We conclude (1) glucocorticoids are necessary for the effect of diabetes to reduce hypothalamic CRH gene expression, since diabetes causes a paradoxical increase in CRH mRNA levels in adrenalectomized animals; (2) glucocorticoid inhibition of hypothalamic CRH gene expression is intact in diabetic rats; and (3) the activation of the HPA axis by diabetes is associated with a proportionate decrease in PVN CRH gene expression. These findings support a model in which hypothalamic factors additional to CRH activate the HPA axis in uncontrolled diabetes, and inhibit CRH gene expression indirectly by negative glucocorticoid feedback.

Chronic cold in adrenalectomized, corticosterone (B)-treated rats: facilitated corticotropin responses to acute restraint emerge as B increases

Small elevations in corticosterone (B) administered exogenously exert potent inhibitory effects on both basal and stress-induced ACTH secretion. However, under conditions of chronic stress with chronic elevations in B, the hypothalamo-pituitary-adrenal system appears to balance the negative feedback signal of B with central neural facilitation so that the system remains fully responsive to acute stressors. In these studies, we tested whether: 1) circulating B concentrations affect responses to acute restraint in rats exposed to 5 days at 5-7 C (cold), compared with room temperature (control); and 2) facilitated ACTH secretion can be explained by increased CRF or vasopressin messenger RNA (mRNA) levels in the hypothalamic parvocellular paraventricular nuclei (PVN). Rats were adrenalectomized and supplied with B in doses that fixed plasma B at constant levels between approximately 2 and 20 microg/dl; rats were placed in cold or remained as controls. Increasing concentrations of fixed B decreased basal ACTH similarly in both groups. By contrast, as B levels increased, ACTH responses to restraint also increased in cold vs. control rats. Semiquantitative analysis of CRF mRNA by in situ hybridization revealed decreases of similar magnitude in both groups with increasing fixed B. Vasopressin mRNA levels also decreased with increasing fixed B in both groups, but with slightly less sensitivity to inhibition by B in cold exposed rats. Taken together, the decreases in mRNA for these major ACTH neuropeptide secretogogues in the parvocellular PVN are unlikely to explain facilitated ACTH responses in chronically stressed rats. We conclude that a brain site is stimulated by B that is proximal to the PVN; feedforward, positive effects of B are thus implicated in mediation of prior stress-induced facilitation of acute hypothalamo-pituitary-adrenal responses to stress.

Dopamine-beta-hydroxylase activity is necessary for hypothalamo-pituitary-adrenal (HPA) responses to ether, and stress-induced facilitation of subsequent HPA responses to acute ether emerges as HPA responses are inhibited by increasing corticosterone (B)

To determine a role of norepinephrine (NE) in stress-induced HPA function, young male rats were treated with diethyldithiocarbamide (DDC) which inhibits dopamine-beta-hydroxylase, the enzyme that synthesizes NE from dopamine (DA). DDC injected 5 h prior to ether stress stimulated ACTH and corticosterone (B) during this time, and there was no further HPA response to ether. To control for elevated B feedback in DDC effects on HPA responses to ether, rats were adrenalectomized (Adx) and replaced with no (0% B), moderate (40% B) and high (80% B) levels of steroid 5 d prior to DDC or saline with ether stress 5 h later; Sham-Adx rats were included. In Adx rats increasing B inhibited thymus weight, median eminence CRF content, pituitary and plasma ACTH. In saline-treated rats, ether 5 h later caused increased CRF content and plasma ACTH in Sham-Adx and Adx, 0% B, increased ACTH in Adx, 40% B, and no response in Adx, 80% B. B treatment did not alter catecholamine content, and DDC treatment reduced NE content in the paraventricular nuclei by 50-60% in all groups. 5 h after DDC, pituitary ACTH was decreased in all rats with B and plasma ACTH was increased in sham-Adx and Adx, 40% B; thus DDC caused significant, prolonged stress which should facilitate subsequent HPA responses to acute stress. There was no HPA response to ether in Sham-Adx, Adx, 0% or 40% B groups, but there was a marked ACTH response to ether in the Adx, 80% B group treated with DDC. We conclude that: 1) the HPA response to ether stress is probably mediated by catecholamines; 2) DDC does not stimulate responses in the HPA axis in the absence of B; and, 3) facilitation of HPA responses to acute stress depends on increased steady-state B signals. Facilitated responses are probably not mediated by catecholamines. The consequence of facilitation is that under conditions of chronic stress and elevated B concentrations, as in depression or anorexia nervosa in man, or adjuvent-induced arthritis in rats, the HPA axis is continually responsive to new stimuli.

A hypercaloric load induces thermogenesis but inhibits stress responses in the SNS and HPA system

Caloric overingestion generates a sympathetic nervous system (SNS)-mediated increase in brown adipose tissue (BAT) thermogenesis; its effect on the hypothalamo-pituitary-adrenal (HPA) axis is unknown. To determine whether metabolic activation affects the HPA axis, male rats were provided palatable sucrose ad libitum. After 5 or 10 days of sucrose ingestion, BAT and basal and restraint-induced HPA variables were measured. Some rats were instrumented with temperature probes. BAT temperature and HPA axis responses to restraint were measured. Although caloric intake increased > or = 18%, body weight gain did not change after sucrose ingestion; DNA, protein, and uncoupling protein increased in BAT depots, and white adipose tissues were heavier after both 5 and 10 days. During days 5-10, the BAT-core temperature difference was +0.30 degrees C in sucrose rats and -0.46 degrees C in controls (P < 0.05); this, together with the biochemical changes, shows persistent activation of BAT by excess calories. Basal HPA measures were not altered. The sucrose group exhibited smaller BAT temperature and HPA responses to restraint on day 10; there was no HPA difference on day 5. We conclude that calorically mediated increases in BAT thermogenesis are independent of basal HPA activity; however, both systems respond concordantly to restraint stress. The diminished response to restraint in both systems in sucrose-fed rats may result from signals indicating increased energy stores.

Elevated corticosterone is not required for the rapid induction of neuropeptide Y gene expression by an overnight fast

Fasting stimulates corticosterone (B) secretion and the expression and secretion of hypothalamic neuropeptide Y in rats. These studies tested the hypothesis that the rapid and marked fasting-induced increases in plasma B are responsible for stimulation of neuropeptide Y (NPY) gene expression. Plasma leptin and insulin were measured because they are also signals known to affect NPY messenger RNA (mRNA). Intact or adrenalectomized rats given a low fixed level of corticosterone (B replaced) were fasted for 48 h. NPY mRNA in the mediobasal hypothalamus, measured by nuclease protection assay, was elevated similarly above ad lib-fed controls in both intact and B replaced groups at 15 and 48 h after the onset of fasting. NPY immunoreactivity in the mediobasal hypothalamus increased between 3 and 48 h after onset of the fast in intact but not in B replaced groups. The fasting-induced decreases in leptin observed in intact rats at 48 h did not occur in B replaced rats. Fasting-induced decreases in insulin occurred in B replaced rats but not in intact rats. We conclude that: 1) elevated B is not required for fasting-induced increases in hypothalamic NPY gene expression; and 2) decreases in neither leptin nor insulin alone signal the changes that occur in NPY mRNA in fasted rats.

The hypothalamic ventromedial nuclei couple activity in the hypothalamo-pituitary-adrenal axis to the morning fed or fasted state

Function in the adrenocortical system is markedly altered by availability of food. Basal activity is lowest and stress responsivity highest in the morning when nocturnal rats eat approximately 90% of their daily calories during the dark. After an overnight fast, basal corticotrophin and corticosteroid levels are elevated, and responsivity to stressors is decreased. Central neural sites that control these changes are unidentified. The hypothalamic ventromedial nuclei (VMN) appear to signal satiety; lesions result in increased food intake, obesity, and elevated basal insulin and corticosteroids. Thus, the VMN are good candidates for calorically mediated control of adrenocortical system function in satiated rats. We injected colchicine into the VMN to cause reversible inhibition of activity (Avrith and Mogenson, 1978) and tested the effects on basal and stimulated function in the adrenocortical system. Colchicine-injected rats that fed ad libitum exhibited increased basal but reduced corticotrophin and corticosterone responses to restraint in the morning compared with controls. By contrast, after an overnight fast, control rats had increased basal adrenocortical hormones and decreased stress responses that did not differ from colchicine-injected rats. Colchicine was visualized within cells in the VMN for up to 5 d using fluorescein/colchicine, and the treatment did not cause increased gliosis; moreover, the functional effects of the injections were reversed within 15 d. We conclude that (1) the VMN serve to couple activity in the adrenocortical system to energy intake and (2) discrete colchicine injections provide a behaviorally and neuroendocrinologically useful period of inhibition without causing permanent functional damage.

Hyperinsulinemia in rats with obesity-inducing amygdaloid lesions

Electrolytic lesions of the posterodorsal aspects of the medial division of the extended amygdala in female rats result in hyperphagia and excessive weight gain. In the present study, the effects of such lesions on plasma insulin, glucose, corticosterone, and adrenocorticotropic hormone were assessed during a period of food restriction and again after a 15-day period of food ad libitum. Compared with control animals, the rats with amygdaloid lesions were hyperinsulinemic under both conditions and gained substantially more weight when fed ad libitum. No difference between groups was observed for the other hormones. It is concluded that damage to the posterodorsal aspects of the medial amygdala results in a primary metabolic dysfunction that accounts, at least in part, for the overeating and excessive weight gain.

Behavioral, endocrine, and hypothalamic responses to involuntary overfeeding

The suppression of food intake after a period of forced overfeeding is potent and long lasting, yet little is known of the underlying mechanisms for this regulatory response. Rats were overfed via a surgically implanted gastrostomy tube. During overfeeding, plasma insulin and corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus of the hypothalamus were elevated compared with controls and with overfed rats allowed 3 days to recover from the overfeeding regimen such that body weight returned to the level of controls. In contrast, rats that were not overfed but were pair-fed to the low spontaneous food intake of previously overfed rats lost weight and had significantly reduced plasma insulin and elevated mRNA for neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus. The results indicate that overfeeding produces an activation of hypothalamic CRH system that may contribute to the hypophagia that accompanies involuntary overfeeding. Furthermore, the hypothalamic NPY response to food restriction is not tied to low food intake per se, but rather to negative energy balance.

Predominately glucocorticoid agonist actions of RU-486 in young specific-pathogen-free Zucker rats

Previous studies have demonstrated antiglucocorticoid actions for the progesterone receptor antagonist RU-486. In one study, daily administration of this drug for 2 wk decreased food intake (FI) and body weight gain (delta BW) in obese, but not lean, conventionally housed 5-wk-old female Zucker rats. We recently found that 2-wk administration of RU-486 attenuated delta BW in lean but not obese 12-wk-old male Zucker rats without affecting FI. To examine the actions of RU-486 and its effects on FI and delta BW in young (5 wk old) specific-pathogen-free (SPF) male and female Zucker rats, RU-486 was administered at 30 mg.kg-1.day-1 subcutaneously for 14 days. RU-486 did not affect FI in obese or lean male or female rats. RU-486 increased adrenal weight (P < 0.05) overall and in lean female rats and modestly decreased inguinal fat weight overall and in obese female rats (P < 0.01), suggesting some antiglucocorticoid activity in these animals. However, RU-486 also decreased thymus weight by 18-31% (P < 0.0001), increased plasma glucose by 10-16 mg/dl (P < 0.002), and increased plasma insulin by 47% in obese male rats (P < 0.028), demonstrating glucocorticoid agonist actions for the drug. Plasma corticosterone (B) and adrenocorticotropic hormone (ACTH) were elevated in vehicle-treated obese female and male rats by 150-360% (P < 0.0025) and 32-38% (P < 0.05), respectively, compared with lean rats. RU-486 treatment lowered the elevated plasma B and ACTH levels in obese female and male rats (both P < 0.02 vs. vehicle), a glucocorticoid agonist effect. We conclude that in young SPF Zucker rats 1) RU-486 administration does not alter FI or delta BW, 2) RU-486 has predominately glucocorticoid agonist actions in several tissues, 3) obese animals have increased hypothalamic-pituitary-adrenal (HPA) axis activity (plasma B and ACTH), and 4) RU-486 administration suppresses the HPA axis in obese rats.

Clamped Corticosterone (B) Reveals the Effect of Endogenous B on Both Facilitated Responsivity to Acute Restraint and Metabolic Responses to Chronic Stress

To determine the effects of both corticosterone (B) and chronic stressors on acute ACTH responses to restraint, young male rats were exposed to streptozotocin-induced diabetes, cold (5-7 degreesC) or intracerebroventricular (icv) neuropeptide Y (NPY) for 5 d and then exposed to restraint within 2 h after lights on. Two groups of rats were studied: intact and adrenalectomized replaced with B pellets that maintained plasma B in the normal mean 24-h range of intact rats. In addition to ACTH and B responses to restraint on d 5, body weight, food intake, fat depots, glucose and other hormones were measured to determine the role of stress-induced elevations in B on energy balance. ACTH responses to restraint were normal in intact rats subjected to diabetes or cold. By contrast, there was no ACTH or B response to restraint in NPY-infused intact rats. All 3 groups of chronically stimulated adrenalectomized rats with clamped B had facilitated ACTH responses to restraint compared to their treatment controls. Overall food intake increased in all groups of stressed rats; however, augmented intake occurred only during the light in intact rats and equally in the light and dark in B-clamped rats. White adipose depot weights were decreased by both diabetes and cold and increased by NPY in intact rats; the decreases with cold and increases with NPY were both blunted and changes in fat stores were not significant in adrenalectomized, B-clamped rats. We conclude that: 1. diabetes- and cold-induced facilitation of restraint-induced afferent input to hypothalamic control of the hypothalamo-pituitary-adrenal (HPA) axis is opposed in intact rats by the elevated feedback signal of B secretion; 2. NPY does not induce facilitation of afferent stress pathways; 3. chronic stimulation of the HPA axis induces acute hyperresponsiveness of hypothalamic neurons to restraint provided that the afferent input of this acute stimulus is not prevented by B feedback; 4. stimulus-induced elevations in B secretion result in day-time feeding; 5. insensitivity of both caloric efficiency and white fat stores to chronic stress in adrenalectomized, B-clamped rats results from loss of normally variable B levels.

The neural network that regulates energy balance is responsive to glucocorticoids and insulin and also regulates HPA axis responsivity at a site proximal to CRF neurons

The structure of a large neural system that responds to and regulates energy balance and that encompasses that PVN and activity of the HPA axis has begun to emerge from these experiments (Fig. 6). Several large loops have been delineated within this context of the maintenance of energy balance. Corticosteroids stimulate both feeding and insulin secretion. The actions of corticosteroids in the periphery are catabolic, causing mobilization of energy stores; their actions in the central nervous system are stimulatory to energy acquisition (food intake). By contrast, the action of insulin in the periphery is anabolic, causing energy storage; its action in the central nervous system is inhibitory to energy acquisition (food intake). At the level of the CNS, insulin inhibits and corticosteroids stimulate expression of NPY mRNA in the arcuate nuclei, and these actions may explain, in part, the reciprocal actions of the hormones on energy acquisition. Thus over the long term, stimulation of insulin secretion by corticosteroids tends to supply an automatic brake on the effects of corticosteroids on feeding. The neural system that controls energy balance and responds to the reciprocal signals of corticosterone and insulin also regulates responsivity to restraint stress in the HPA axis. The low-amplitude ACTH responses to restraint, corticosteroid feedback, and prior stress-induced facilitation that are observed under conditions of relative fasting in the PM can be produced in the AM by a 14-h, overnight fast. By contrast, NPY injected ivt stimulates identical ACTH responses in the AM in fed rats and in rats fasted overnight, suggesting that NPY acts to stimulate CRF secretion at a site closer to the PVN than the stress of restraint, which is filtered through the neural energy balance system. In the periphery, corticosteroids and insulin also have reciprocal effects on energy storage; effects that are opposite those exerted in the CNS on energy acquisition. Thus, together, the two hormones may be construed as a bihormonal system that regulates overall energy balance. Although under normal conditions this system is well designed to accomplish energy balance, and provides a mechanism by which total energy stores may be increased appropriately (e.g., prior to hibernation or migration), it seems probable that under conditions of chronic stress, this regulatory system may be maladaptive. Chronic stress and glucocorticoid treatment cause increases in mean daily concentrations of both corticosteroids and insulin. Increases in the absolute levels of both hormones, with the normal ratio between them maintained, results in remodeling of body energy stores-away from muscle stores and toward fat stores, particularly abdominal fat stores. It seems quite likely that some conditions of abdominal obesity in man may be explained, at least in part, by increased activity in the HPA axis. Because abdominal obesity is associated with cardiovascular diseases, these responses, when they persist, are clearly maladaptive. Exploration of the role and control of the HPA axis in and by the larger neural network that regulates energy balance has to date been instructive. Clearly this work has just begun and is primarily still at the level of phenomenology. However, once the phenomenology is understood, mechanistic work can be performed that will flesh out our understanding of this very large and physiologically essential system.

Corticosterone regulation of insulin-like growth factor I, IGF-binding proteins, and growth in streptozotocin-induced diabetic rats

The experiments reported herein were conducted to determine how corticosterone regulates growth and plasma insulin-like growth factor (IGF) I and IGF-binding protein (IGFBP) concentrations in normal and streptozotocin (STZ)-induced diabetic rats. Males were bilaterally adrenalectomized (Ax) or sham Ax and given intravenous injections of 0, 30, or 65 mg STZ per kg body wt (0, 30, or 65 STZ) to induce varying degrees of insulin deficiency and implanted with 100-mg pellets containing 0, 40, or 80% corticosterone in cholesterol. Changes in plasma IGFBP concentrations were determined by Western ligand blotting or immunoblots. Neither IGFBP-5 nor IG-FBP-6 was detected in any of the treatment groups. Plasma IGFBP-2 was elevated and IGF-I was reduced in the nondiabetic Ax rats compared with sham Ax controls, but plasma IGFBP-3 and -4 were not significantly changed. Adrenalectomy had no affect on tibial growth or plasma IGFBP-1 in these animals. Plasma IGF-I, IGFBP-1 and -3, and tibial growth were equal among 0, 30, and 65 STZ Ax rats that did not receive corticosterone. Plasma IGFBP-4 was inversely related to the amount of STZ injected in these animals, and IGFBP-2 was elevated in those given the high dose of STZ. In the 0 STZ Ax rats, plasma IGF-I and IGFBP-3 increased in proportion to the corticosterone implant dose, but IGFBP-1 was unaffected. By contrast, IGF-I and IGFBP-3 were unaltered by corticosterone in the 30 STZ Ax rats, and IGFBP-1 increased in proportion with the dose of corticosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic response to starvation: implications for the study of wasting disorders

Weight loss is a potent stimulus to food intake in normal individuals. The persistence of anorexia in wasting disorders, therefore, implies a failure of this adaptive feeding response. We describe a model for the normal hypothalamic response to starvation composed of the stimulation of neuronal pathways that promote energy intake and storage coupled with the inhibition of pathways that exert opposing effects. This model provides a framework for investigating disturbances of the normal hypothalamic response to weight loss and suggests a specific mechanism by which cytokines contribute to wasting in acquired immune deficiency syndrome and other cachexic disorders.

Glucocorticoids and insulin: complex interaction on brown adipose tissue

Glucocorticoids and insulin effect long-term reciprocal changes in food intake and body weight. We tested the interactions of corticosterone and insulin on caloric efficiency, white adipose tissue (WAT) stores, and brown adipose tissue (BAT). Two experiments were performed: 1) adrenalectomized rats were treated with corticosterone with or without streptozotocin-induced diabetes and 2) adrenalectomized, corticosterone-treated, diabetic rats were treated with insulin. By 4-5 days later, > or = 50% of the variance in caloric efficiency, plasma triglycerides, and WAT stores was explained by regression of these variables on corticosterone (catabolic) and insulin (anabolic). When the ratio of the hormones was normal, but concentrations high, overall gain of energy stores decreased and energy was redistributed to fat. Both hormones were anabolic on BAT lipid storage; the hormones played a complex role in the regulation of uncoupling protein (UCP) in BAT. Although corticosterone inhibited and insulin stimulated UCP, these effects were only evident in diabetics and with normoglycemia, respectively. For BAT variables, < or = 50% of the variance was explained by regression on corticosterone and insulin, suggesting that the effects of these hormones are mediated through an intermediate such as sympathetic nervous system input to BAT.