Hepatic vagotomy alters limbic and hypothalamic neuropeptide responses to insulin-dependent diabetes and voluntary lard ingestion.

Hypothalamic anorexigenic [corticotropin-releasing factor (CRF) and proopiomelanocortin] peptides decrease and the orexigen, neuropeptide Y, increases with diabetic hyperphagia. However, when diabetic rats are allowed to eat lard (saturated fat) as well as chow, both caloric intake and hypothalamic peptides normalize. These neuropeptide responses to lard require an intact hepatic vagus [la Fleur et al. (2003) Diabetes, 52, 2321-2330]. Here, we delineate temporal interactions after lard consumption +/- hepatic vagotomy (HV) between feeding and brain neuropeptide expression in insulin-dependent diabetic rats. CRF-mRNA was reduced in the paraventricular nuclei (PVN) by 6 h after presentation of lard, before caloric intake increased in HV-diabetic rats, and did not increase at 30 or 36 h, as it did in shamHV-diabetic rats eating lard. CRF-mRNA was increased in the bed nuclei of the stria terminalis of HV-diabetic rats compared with shamHV-diabetic rats only when caloric intake was high at 30 or 36 h. At 36 h, shamHV-diabetic rats eating chow had increased CRF-mRNA in the central amygdala but diabetic rats eating lard had decreased CRF-mRNA, whereas HV-diabetic rats eating chow or lard had normal CRF-mRNA in the central amygdala. We conclude that eating lard restores peptide expression to normal in the hypothalamus of diabetic rats, and because decreased CRF-mRNA in the PVN precedes the increase in caloric intake in HV-diabetic rats eating lard, that the loss of a hepatic vagal signal to PVN may be responsible for increased intake; moreover, CRF-mRNA in limbic structures is also sensitive to both HV and lard ingestion in diabetic rats.

Time-dependent alterations in mRNA expression of brain neuropeptides regulating energy balance and hypothalamo-pituitary-adrenal activity after withdrawal from intermittent morphine treatment.

Chronic stressors alter brain function and may leave traces after their relief. We used intermittent morphine treatment to examine the relationships between stress-induced changes in energy balance and hypothalamo-pituitary-adrenal (HPA) activity and the recovery thereafter. We studied the effects of morphine injections on energy balance, hormones and fat stores, brain neuropeptide expression, and the ACTH and corticosterone responses to restraint 12 hr after the final injection and 8 d later during recovery. Weight gain, food intake, and caloric efficiency decreased at morphine onset, and these were maintained throughout the morphine injections. At 12 hr, fat stores, leptin, insulin, and testosterone concentrations were reduced. Subsequently, body weight gain and food intake increased and caloric efficiency was above control during the final days. By the eighth recovery day, fat stores and peripheral hormones were no longer depressed. At 12 hr, an over-response of CRF mRNA to restraint occurred in the hypothalamus, similar to the facilitated ACTH and corticosterone responses. On day 8, the hypothalamic CRF mRNA response to restraint was still facilitated, opposite to inhibited ACTH responses. Hypothalamic CRF mRNA correlated highly with mesenteric fat weight in morphine-treated rats. We conclude that there is a prolonged recovery from chronic stressors involving interrelated changes in energy balance and HPA activity. Nonetheless, 8 d after withdrawal from morphine, rats still display facilitated central stress responses, similar to the HPA symptoms described in posttraumatic stress disorder patients. Repeated partial withdrawal associated with intermittent morphine treatment, compounded by complete withdrawal associated with termination of the treatment, is likely required for these metabolic and HPA derangements.

Interaction between corticosterone and insulin in obesity: regulation of lard intake and fat stores.

Passive elevations in glucocorticoids result in increased insulin and abdominal obesity with peripheral wasting, as observed in Cushing's syndrome, with little effect on chow intake. In the absence of insulin (streptozotocin-induced diabetes) diabetic rats markedly increase their chow intake in proportion to glucocorticoids. Given a choice of lard or chow, diabetic rats first eat lard, then reduce caloric intake to normal for 48 h before returning to hyperphagia on chow alone. We performed three experiments to determine the relationship of corticosterone and insulin to lard intake, chow intake, body weight, hormones, and fat depots. The results of these studies clarify the actions of both circulating glucocorticoids and insulin on caloric intake in adult male rats. Our experiments show that glucocorticoids provoke dose-related increases in total caloric intake that persist for days and weeks; the results also suggest that increasing insulin concentrations stimulated by glucocorticoids determine the amount of fat intake. Furthermore, we show that lard intake is associated with increasing insulin concentrations. Additionally, the results in adrenalectomized and adrenalectomized, streptozotocin-induced diabetic rats strongly suggest that it is a combination of corticosterone and insulin that increases abdominal fat depot weight. Independently of the hormonally manipulated rats, the results also show that intact rats voluntarily eat a considerable and stable proportion of their daily calories as lard when given a choice between lard and chow. These results suggest that some human obesities may result from elevated glucocorticoids and insulin increasing the proportional intake of high density calories.

Androgen-sensitive changes in regulation of restraint-induced adrenocorticotropin secretion between early and late puberty in male rats.

Regulation of ACTH secretion changes between early (40 d) and late (60 d) puberty in male rats. We tested whether this occurs because of activating effects of testosterone on the brain. We measured testosterone and ACTH responses to repeated restraint in adrenalectomized, corticosterone-replaced rats entering and leaving puberty with or without treatment with flutamide, a nonsteroidal androgen-receptor antagonist. Flutamide increased testosterone. ACTH responses were high and suppressed by flutamide at 40 d. At 60 d, ACTH responses were low and increased by flutamide. On d 4, basal arginine vasopressin (AVP) mRNA was increased by restraint, but not age, in the medial parvicellular paraventricular nucleus (mpPVN) and medial amygdala and increased with age in the bed nucleus of the stria terminalis. We counted numbers of AVP-immunoreactive (AVP-ir) and corticotropin-releasing factor (CRF)-ir neurons. In medial amygdala, there was no change in AVP+ cells. With restraint, CRF+ cells in the central nucleus decreased at 40 d and increased at 60 d. Flutamide did not affect the response at 40 d but blocked restraint-induced increases at 60 d. After restraint, the bed nucleus of the stria terminalis AVP-ir correlated negatively with mpPVN CRF-ir at 40 d and with mpPVN AVP-ir at 60 d. In PVN, there were no effects on CRF+ cells. However, AVP+ cells increased only with restraint plus flutamide at 40 d and tended to increase with restraint and decrease with restraint plus flutamide at 60 d. We conclude that during puberty testosterone induces marked changes in regulation of neuropeptides in pathways known to determine autonomic, neuroendocrine, and behavioral responses to chronic stress.

Chronic stress and obesity: a new view of "comfort food".

The effects of adrenal corticosteroids on subsequent adrenocorticotropin secretion are complex. Acutely (within hours), glucocorticoids (GCs) directly inhibit further activity in the hypothalamo-pituitary-adrenal axis, but the chronic actions (across days) of these steroids on brain are directly excitatory. Chronically high concentrations of GCs act in three ways that are functionally congruent. (i) GCs increase the expression of corticotropin-releasing factor (CRF) mRNA in the central nucleus of the amygdala, a critical node in the emotional brain. CRF enables recruitment of a chronic stress-response network. (ii) GCs increase the salience of pleasurable or compulsive activities (ingesting sucrose, fat, and drugs, or wheel-running). This motivates ingestion of "comfort food." (iii) GCs act systemically to increase abdominal fat depots. This allows an increased signal of abdominal energy stores to inhibit catecholamines in the brainstem and CRF expression in hypothalamic neurons regulating adrenocorticotropin. Chronic stress, together with high GC concentrations, usually decreases body weight gain in rats; by contrast, in stressed or depressed humans chronic stress induces either increased comfort food intake and body weight gain or decreased intake and body weight loss. Comfort food ingestion that produces abdominal obesity, decreases CRF mRNA in the hypothalamus of rats. Depressed people who overeat have decreased cerebrospinal CRF, catecholamine concentrations, and hypothalamo-pituitary-adrenal activity. We propose that people eat comfort food in an attempt to reduce the activity in the chronic stress-response network with its attendant anxiety. These mechanisms, determined in rats, may explain some of the epidemic of obesity occurring in our society.

The hepatic vagus mediates fat-induced inhibition of diabetic hyperphagia.

Diabetic rats both overeat high-carbohydrate diet and have altered hypothalamic neuropeptide Y (NPY) and corticotropin-releasing factor (CRF). In contrast, a high-fat diet reduces caloric intake of diabetics to normal, reflected by normal hypothalamic NPY and CRF content. How the brain senses these changes in diet is unknown. To date, no hormonal changes explain these diet-induced changes in caloric intake. We tested whether the common branch of the hepatic vagus mediates the fat signal. We presented fat in two ways. First, diabetic and vehicle-treated rats were offered a cup of lard in addition to their normal high-carbohydrate diet. Second, we switched diabetic rats from high-carbohydrate diet to high-fat diet, without choice. In streptozotocin-treated rats, both methods resulted in fat-induced inhibition of caloric intake and normalization of hypothalamic neuropeptides to nondiabetic levels. Strikingly, common branch hepatic vagotomy (unlike gastroduodenal vagotomy) entirely blocked these fat-induced changes. Although a shift in hepatic energy status did not explain the lard-induced changes in diabetic rats, the data suggested that common hepatic branch vagotomy does not interfere with hepatic energy status. Furthermore, common branch hepatic vagotomy without diabetes induced indexes of obesity. Abnormal function of the hepatic vagus, as occurs in diabetic neuropathy, may contribute to diabetic obesity.

Intermittent morphine administration induces dependence and is a chronic stressor in rats.

Although constant treatment with morphine (implanted pellets) does not activate the hypothalamic-pituitary-adrenal (HPA) axis, intermittent injections of morphine may constitute a chronic stressor in rats. To test this hypothesis, we compared the effects of morphine in escalating doses (10-40 mg/kg, s.c.) or saline injected twice daily for 4 days on energy balance, hormones, HPA responses to novel restraint and central corticotropin-releasing factor (CRF) mRNA 12 h and 8 days after the last morphine injection in adult male Sprague-Dawley rats. Weight gain stopped at the onset of morphine, weight loss was marked 36 h postmorphine; thereafter, body weight gain paralleled saline controls. At 12 h, insulin, leptin, and testosterone concentrations were reduced but normalized by 8 days. Restraint and tail nicks caused facilitated ACTH responses at 12 h, under-responsiveness at 8 days. CRF mRNA, measured only at 12 h, was increased in the paraventricular (PVN) and Barrington's nuclei (BAR), decreased in the bed nuclei of the stria terminalis (BNST) and unchanged in the amygdala (CeA) in morphine-treated rats. After stress, CRF mRNA increased in PVN in both groups, increased in BAR and decreased in BNST in saline but not morphine groups, and was unchanged in CeA in both groups. Results from all variables characterize intermittent morphine injections as a chronic stressor. In contrast to constant treatment, injected morphine probably allows some withdrawal during each 12 h interval, causing repeated stress. Drug addicts treat themselves intermittently, and stress causes relapse after withdrawal. Thus, intermittent morphine, itself, may promote relapse.

A spoonful of sugar: feedback signals of energy stores and corticosterone regulate responses to chronic stress.

To begin to understand the effects of chronic stress on food intake and energy stores, the effects of increased activity in the hypothalamo-pituitary-adrenal (HPA) axis and glucocorticoids (GCs) on the body and brain must first be understood. We propose two major systems that are both GC sensitive: a metabolic feedback that is inhibitory and a direct central GC drive. Under basal conditions, the metabolic feedback signal to brain is dominant, although infusion of GC into a lateral brain ventricle blocks the effects of the metabolic feedback. Chronic stress activates GC secretion and brain nuclear GC receptor occupancy, markedly changing the normal relationships between these two major corticosteroid-activated systems. The stressor-induced switch in the relative strengths of these signals determines subsequent brain regulation of stress responses (behavioral, neuroendocrine and autonomic outflows). The metabolic feedback effects of GCs are mimicked by voluntary sucrose ingestion in adrenalectomized rats, and experiments suggest that the metabolic feedback also inhibits the stressor-induced direct GC drive on brain. We speculate that the interaction between peripheral and central GC-sensitive signaling systems may be coupled through the inhibitory actions of endogenous opiatergic inputs on corticotropin-releasing factor (CRF) neurons.

Corticosterone infused intracerebroventricularly inhibits energy storage and stimulates the hypothalamo-pituitary axis in adrenalectomized rats drinking sucrose.

When allowed to drink sucrose, bilaterally adrenalectomized (ADX) rats exhibit normal weight gain, food intake, sympathetic neural activity, and ACTH compared with sham-ADX rats. Furthermore, ADX rats drinking sucrose have normal corticotropin-releasing factor (CRF) mRNA throughout brain. In ADX rats without sucrose, all of these variables are abnormal. Systemic corticosterone (B) replacement also restores these variables in ADX rats to normal. To test whether B acts centrally, we infused B or saline intracerebroventricularly into ADX rats under basal conditions and after repeated restraint. Rats were exposed to no stress or 3 h/d restraint for 3 d. Body weights and food and fluid intakes were measured. Brains were analyzed using immunocytochemistry against glucocorticoid receptors (GR) and CRF. Intracerebroventricular B blocked the positive effects of sucrose on metabolism, increased basal ACTH concentrations, and augmented ACTH responses to restraint on d 3. B-infused rats exhibited nuclear GR staining in perirhinal cortex, hippocampus, and hypothalamic paraventricular nuclei, showing that infused B spreads effectively. CRF staining in the paraventricular nucleus of the hypothalamus was higher in B- than in saline-infused rats. We conclude that under basal conditions B acts systemically, but not in the brain, to restore metabolism and neuropeptides after adrenalectomy. By contrast, tonic GR occupancy in brain initiates metabolic and ACTH responses characteristic of stress.