Pharmacological stimulation of brain carnitine palmitoyl-transferase-1 decreases food intake and body weight

Inhibition of brain carnitine palmitoyl-transferase-1 (CPT-1) is reported to decrease food intake and body weight in rats. Yet, the fatty acid synthase (FAS) inhibitor and CPT-1 stimulator C75 produces hypophagia and weight loss when given to rodents intracerebroventricularly (icv). Thus roles and relative contributions of altered brain CPT-1 activity and fatty acid oxidation in these phenomena remain unclarified. We administered compounds that target FAS or CPT-1 to mice by single icv bolus and examined acute and prolonged effects on feeding and body weight. C75 decreased food intake rapidly and potently at all doses (1-56 nmol) and dose dependently inhibited intake on day 1. Dose-dependent weight loss on day 1 persisted through 4 days of postinjection monitoring. The FAS inhibitor cerulenin produced dose-dependent (560 nmol) hypophagia for 1 day, weight loss for 2 days, and weight regain to vehicle control by day 3. The CPT-1 inhibitor etomoxir (32, 320 nmol) did not alter overall day 1 feeding. However, etomoxir attenuated the hypophagia produced by C75, indicating that CPT-1 stimulation is important for C75's effect. A novel compound, C89b, was characterized in vitro as a selective stimulator of CPT-1 that does not affect fatty acid synthesis. C89b (100, 320 nmol) decreased feeding in mice for 3 days and produced persistent weight loss for 6 days without producing conditioned taste aversion. Similarly, intraperitoneal administration decreased feeding and body weight without producing conditioned taste aversion. These results suggest a role for brain CPT-1 in the regulation of energy balance and implicate CPT-1 stimulation as a pharmacological approach to weight loss.     

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.     

Physiologic estradiol levels enhance hypothalamic expression of the long form of the leptin receptor in intact rats

Estradiol is a potent hypophagic agent that reduces food intake and body weight without a concomitant fall in plasma leptin levels. We investigated whether the hypophagic effect of estradiol is mediated by stimulating POMC and/or inhibiting NPY neuronal pathways in the hypothalamus, which respectively inhibit and stimulate feeding. We examined hypothalamic gene expression of Ob-Rb, NPY, POMC, MC4-R, and AgRP in intact Wistar rats treated with estradiol for 48 hours. Food intake and body weight were reduced in estradiol-treated rats but fat mass was unchanged; plasma leptin and insulin levels were not significantly different from untreated, freely fed controls. In untreated rats that were pair-fed to match the estradiol-treated group, body weight was also reduced without changes in fat mass, although leptin and insulin levels decreased significantly. Ob-Rb expression was increased in both hypophagic groups despite serum leptin were only decreased in pair-fed animals, suggesting an estradiol-stimulating effect on Ob-Rb expression. No significant differences were found in POMC, AgRP, or MC4-R expression among any of the experimental groups. A significant but small decrease in NPY expression was also found in both hypophagic groups; this was explained by the combined effect of both surgery and reduced food intake. These results indicate that estradiol mediated hypophagia in intact rats could be brought about by an enhanced hypothalamic leptin sensitivity but is unlikely to be driven by changes in NPY or melanocortin system.     

Nicotine's attenuation of body weight involves the perifornical hypothalamus

Previously we showed that intermittent administration of nicotine (NIC) in the dark phase decreased food intake and body weight and this could be blocked when the NIC receptor antagonist mecamylamine was infused into the fourth ventricle. Catecholaminergic neurons adjacent to the fourth ventricle contain NIC receptors and directly innervate the perifornical hypothalamus (PFH) which has been shown to be involved in regulation of feeding. This study explored whether NIC regulates feeding behavior by modulating catecholaminergic input to the PFH. Epinephrine and norepinephrine neuronal input was ablated within the PFH by infusion of 6-hydroxydopamine hydrobromide (6-OHDA), while bupropion was infused to protect dopaminergic neurons. After recovery of body weights to pre-surgery levels, food intake, meal size, meal number and body weight were measured after intermittent NIC injections. The results showed the PFH lesioned animals did not exhibit the typical prolonged drop in food intake, meal size and body weight normally associated with NIC administration. High performance liquid chromatography analyses demonstrated that compared to control rats, 6-OHDA administration significantly reduced PFH norepinephrine and epinephrine levels, but not dopamine levels. These results are consistent with NIC reducing food intake in part by acting through catecholaminergic neurons within or extending through the PFH.     

Changes in lipogenesis and lipolysis associated with recovery from reversible obesity in mature female rats

Reversible obesity provides a model for demonstration of weight regulation in mature animals. Changes in body composition and in vitro adipose and hepatic lipid synthesis and adipose lipolysis of rats recovering from enforced weight gain were examined to determine whether correction of weight was facilitated by metabolic changes independent of those resulting from hypophagia and negative energy balance. Female Sprague-Dawley rats (200 g) were divided into three groups. Controls ate ad libitum, tube-fed control rats were weight matched to controls. Two-hundred percent-fed rats were tube-fed twice control intake. After 26 days tube feeding stopped and a subgroup from each treatment was killed for determination of body composition and in vitro tissue metabolism. Further subgroups were examined 5, 10, 15, and 36 days later. At the end of overfeeding 200%-fed rats were hypophagic and had high rates of adipose and hepatic lipid synthesis, which soon returned to normal. Gross changes in body fat mass were corrected by hypophagia and increased adipose lipolysis. The remaining small excess in body fat appeared to be corrected by decreased basal and insulin-stimulated adipose fatty acid synthesis when food intake had returned to normal.     

Cyclic estradiol treatment normalizes body weight and restores physiological patterns of spontaneous feeding and sexual receptivity in ovariectomized rats

Hypothalamic-pituitary-gonadal axis function strongly influences feeding and body weight in cycling females in many species. To test the sufficiency of cyclic variations in plasma estradiol to reproduce normal patterns of spontaneous feeding, food intake, and body weight, ovariectomized Long-Evans rats were subcutaneously injected every fourth day with 2 microg estradiol benzoate or with the oil vehicle alone. Cyclic estradiol treatment completely normalized the trajectory of body weight gain and total food intake through seven treatment cycles. The hyperphagia of ovariectomized rats was expressed as an increase in spontaneous meal size. Meal frequency decreased, but not enough to compensate for the increase in meal size. Estradiol treatment normalized both parameters. In addition, cyclic estradiol treatment produced a further phasic decrease in meal size (and increase in meal frequency) and a decrease in food intake during the second night after injection. This phasic change is similar to the feeding changes occurring during estrus in intact rats. Sexual receptivity was measured during the eighth estradiol treatment cycle, 4 h after injection of 0.5 mg progesterone. Lordosis scores at the time of the treatment cycle modeling estrus were maximal, and scores at the time modeling diestrus were slightly increased over those of rats that did not receive estradiol. Finally, plasma estradiol levels, measured during the ninth treatment cycle, revealed a near-normal cyclic pattern of plasma estradiol levels. These results provide the first demonstration that the induction of a cyclic, near-physiological pattern of plasma estradiol is sufficient to maintain normal levels of body weight, spontaneous feeding patterns, total food intake, and (together with progesterone) sexual receptivity in ovariectomized rats.     

Increase in hypothalamic AMPK phosphorylation induced by prolonged exposure to LPS involves ghrelin and CB1R signaling

Acute administration of lipopolysaccharide (LPS) from Gram-negative bacteria induces hypophagia. However, the repeated administration of LPS leads to desensitization of hypophagia, which is associated with increased hypothalamic p-AMPK expression. Because ghrelin and endocannabinoids modulate AMPK activity in the hypothalamus, we hypothesized that these neuromodulators play a role in the reversal of tolerance to hypophagia in rats under long-term exposure to LPS. Male Wistar rats were treated with single (1 LPS, 100 μg/kg body weight, ip) or repeated injections of LPS over 6 days (6 LPS). Food intake was reduced in the 1 LPS, but not in the 6 LPS group. 6 LPS rats showed an increased serum concentration of acylated ghrelin and reduced ghrelin receptor mRNA expression in the hypothalamus. Ghrelin injection (40 μg/kg body weight, ip) increased food intake, body weight gain, p-AMPK hypothalamic expression, neuropeptide Y (NPY) and Agouti related peptide (AgRP) mRNA expression in control animals (Saline). However, in 6 LPS rats, ghrelin did not alter these parameters. Central administration of a CB1R antagonist (AM251, 200 ng/μl in 5 μl/rat) induced hypophagia in 6 LPS animals, suggesting that the endocannabinoid system contributes to preserved food intake during LPS tolerance. In the presence of AM251, the ability of ghrelin to phosphorylate AMPK in the hypothalamus of 6 LPS group was restored, but not its orexigenic effect. Our data highlight that the orexigenic effects of ghrelin require CB1R signaling downstream of AMPK activation. Moreover, CB1R-mediated pathways contribute to the absence of hypophagia during repeated exposure to endotoxin.     

Gastric emptying in Limanda limanda (L.) and the return of appetite

Limanda limanda (35–225 g) fed during daytime when trained to use demand feeders under natural photoperiods. Under continuous illumination different feeding rhythms developed which were detected by periodogram analysis. Interfeeding periods (P hours) varied with body weight (W grams) and temperature (T° C) over the range 6.5–15° C as: In P=4.4 – 0.167 (In W) – 0.05 T. Daily food intake (D grams increased with both temperature and size (In D = 0.099 T + 0.579 In W – 3.49). Relative daily intake (R as % body weight, b.w) increased with temperature but decreased with size (In R = 0.099T–0.41 In W + 1.05). These changes in daily intake are primarily caused by changes in feeding frequency; the amount eaten at a meal is relatively constant save at low temperatures (6.5° C) when appetite is suppressed. Dilution of the food with kaolin (from 4.8 to 2.2 kcal/g) did not cause a compensatory increase in meal size or frequency. Gastric emptying time (GET hours) measured by X-radiography changed with body weight, temperature and relative meal size (M % b.w.) as In GET = 0.68 In M + 0.39 In W – 0.035T + 1.46. With the exception of the lowest temperature (6.5° C) interfeeding periods closely followed GET (P = 1.09 GET – 2.6) supporting the proposal that stomach fullness is a major factor controlling appetite in the dab.     

Leptin resistance and desensitization of hypophagia during prolonged inflammatory challenge

Acute exposure to bacterial lipopolysaccharide (LPS) is a potent inducer of immune response as well as hypophagia. Nevertheless, desensitization of responses to LPS occurs during long-term exposure to endotoxin. We induced endotoxin tolerance, injecting repeated (6LPS) LPS doses compared with single (1LPS) treatment. 1LPS, but not 6LPS group, showed decreased food intake and body weight, which was associated with an increased plasma leptin and higher mRNA expression of OB-Rb, MC4R, and SOCS3 in the hypothalamus. Hypophagia induced by 1LPS was associated with lower levels of 2-arachidonoylglycerol (2-AG), increased number of p-STAT3 neurons, and decreased AMP-activated protein kinase (AMPK) activity. Desensitization of hypophagia in the 6LPS group was related to high 2-AG, with no changes in p-STAT3 or increased p-AMPK. Leptin decreased food intake, body weight, 2-AG levels, and AMPK activity and enhanced p-STAT3 in control rats. However, leptin had no effects on 2-AG, p-STAT3, or p-AMPK in the 1LPS and 6LPS groups. Rats treated with HFD to induce leptin resistance showed neither hypophagia nor changes in p-STAT3 after 1LPS, suggesting that leptin and LPS recruit a common signaling pathway in the hypothalamus to modulate food intake reduction. Desensitization of hypophagia in response to repeated exposure to endotoxin is related to an inability of leptin to inhibit AMPK phosphorylation and 2-AG production and activate STAT3. SOCS3 is unlikely to underlie this resistance to leptin signaling in the endotoxin tolerance. The present model of prolonged inflammatory challenge may contribute to further investigations on mechanisms of leptin resistance.     

Hyperphagia and obesity in OLETF rats lacking CCK-1 receptors

The brain-gut peptide cholecystokinin (CCK) inhibits food intake following peripheral or site directed central administration. Peripheral exogenous CCK inhibits food intake by reducing the size and duration of a meal. Antagonist studies have demonstrated that the actions of the exogenous peptide mimic those of endogenous CCK. Antagonist administration results in increased meal size and meal duration. The feeding inhibitory actions of CCK are mediated through interactions with CCK-1 receptors. The recent identification of the Otsuka-Long-Evans-Tokushima Fatty (OLETF) rat as a spontaneous CCK-1 receptor knockout model has allowed a more comprehensive evaluation of the feeding actions of CCK. OLETF rats become obese and develop non-insulin dependent diabetes mellitus (NIDDM). Consistent with the absence of CCK-1 receptors, OLETF rats do not respond to exogenous CCK. OLETF rats are hyperphagic and their increased food intake is characterized by a large increase in meal size with a decrease in meal frequency that is not sufficient to compensate for the meal size increase. Deficits in meal size control are evident in OLETF rats as young as 2 days of age. OLETF obesity is secondary to the increased food intake. Pair feeding to amounts consumed by intact control rats normalizes body weight, body fat and elevated insulin and glucose levels. Hypothalamic arcuate nucleus peptide mRNA expression in OLETF rats is appropriate to their obesity and is normalized by pair feeding. In contrast, pair fed and young pre-obese OLETF rats have greatly elevated dorsomedial hypothalamic (DMH) neuropeptide Y (NPY) mRNA expression. Elevated DMH NPY in OLETF rats appears to be a consequence of the absence of CCK-1 receptors. In intact rats NPY and CCK-1 receptors colocalize to neurons within the compact subregion of the DMH and local CCK administration reduces food intake and decreases DMH NPY mRNA expression. We have proposed that the absence of DMH CCK-1 receptors significantly contributes to the OLETF's inability to compensate for their meal size control deficit leading to their overall hyperphagia. Access to a running wheel and the resulting exercise normalizes food intake and body weight in OLETF rats. When given access to running wheels for 6 weeks shortly after weaning, OLETF rats do not gain weight to the same degree as sedentary OLETF rats and do not develop NIDDM. Exercise also prevents elevated levels of DMH NPY mRNA expression, suggesting that exercise exerts an alternative, non-CCK mediated, control on DMH NPY. The OLETF rat is a valuable model for characterizing actions of CCK in energy balance and has provided novel insights into interactions between exercise and food intake.     

Dorsomedial hypothalamic corticotropin-releasing factor mediation of exercise-induced anorexia

Running wheel access and resulting voluntary exercise alter food intake and reduce body weight. The neural mechanisms underlying these effects are unclear. In this study, we first assessed the effects of 7 days of running wheel access on food intake, body weight, and hypothalamic gene expression. We demonstrate that running wheel access significantly decreases food intake and body weight and results in a significant elevation of CRF mRNA expression in the dorsomedial hypothalamus (DMH) but not the paraventricular nucleus. Seven-day running wheel access also results in elevated arcuate nucleus and DMH neuropeptide Y gene expression. To assess a potential role for elevated DMH CRF activity in the activity-induced changes in food intake and body weight, we compared changes in food intake, body weight, and hypothalamic gene expression in rats receiving intracerebroventricular (ICV) CRF antagonist alpha-helical CRF or vehicle with or without access to running wheels. During a 4-day period of running wheel access, we found that exercise-induced reductions of food intake and body weight were significantly attenuated by ICV injection of the CRF antagonist. The effect on food intake was specific to a blockade of activity-induced changes in meal size. Central CRF antagonist injection further increased DMH CRF mRNA expression in exercised rats. Together, these data suggest that DMH CRF play a critical role in the anorexia resulting from increased voluntary exercise.     

Intraperitoneal injections of low doses of C75 elicit a behaviorally specific and vagal afferent-independent inhibition of eating in rats

Central and intraperitoneal C75, an inhibitor of fatty acid synthase and stimulator of carnitine palmitoyl-transferase-1, inhibits eating in mice and rats. Mechanisms involved in feeding inhibition after central C75 have been identified, but little is yet known about how systemic C75 might inhibit eating. One issue is whether intraperitoneal C75 reduces food intake in rats by influencing normal physiological controls of food intake or acts nonselectively, for example by eliciting illness or aversion. Another issue relates to whether intraperitoneal C75 acts centrally or, similar to some other peripheral metabolic controls of eating, activates abdominal vagal afferents to inhibit eating. To further address these questions, we investigated the effects of intraperitoneal C75 on spontaneous meal patterns and the formation of conditioned taste aversion (CTA). We also tested whether the eating inhibitory effect of intraperitoneal C75 is vagally mediated by testing rats after either total subdiaphragmatic vagotomy (TVX) or selective subdiaphragmatic vagal deafferentations (SDA). Intraperitoneal injection of 3.2 and 7.5 mg/kg of C75 significantly reduced food intake 3, 12, and 24 h after injection by reducing the number of meals without affecting meal size, whereas 15 mg/kg of C75 reduced both meal number and meal size. The two smaller doses of C75 failed to induce a CTA, but 15 mg/kg C75 did. The eating inhibitory effect of C75 was not diminished in either TVX or SDA rats. We conclude that intraperitoneal injections of low doses of C75 inhibit eating in a behaviorally specific manner and that this effect does not require abdominal vagal afferents.     

Increased short-term food satiation and sensitivity to cholecystokinin in neurotrophin-4 knock-in mice

Neurotrophin-4 (NT-4) knockout mice exhibited decreased innervation of the small intestine by vagal intraganglionic laminar endings (IGLEs) and reduced food satiation. Recent findings suggested this innervation was increased in NT-4 knock-in (NT-4KI) mice. Therefore, to further investigate the relationship between intestinal IGLEs and satiation, meal patterns were characterized using solid and liquid diets, and cholecystokinin (CCK) effects on 30-min solid diet intake were examined in NT-4KI and wild-type mice. NT-4KI mice consuming the solid diet exhibited reduced meal size, suggesting increased satiation. However, compensation occurred through increased meal frequency, maintaining daily food intake and body weight gain similar to controls. Mutants fed the liquid diet displayed a decrease in intake rate, again implying increased satiation, but meal duration increased, which led to an increase in meal size. This was compensated for by decreased meal frequency, resulting in similar daily food intake and weight gain as controls. Importantly, these alterations in NT-4KI mice were opposite, or different, from those of NT-4 knockout mice, further supporting the hypothesis that they are specific to vagal afferent signaling. CCK suppressed short-term intake in mutants and controls, but the mutants exhibited larger suppressions at lower doses, implying they were more sensitive to CCK. Moreover, devazepide prevented this suppression, indicating this increased sensitivity was mediated by CCK-1 receptors. These results suggest that the NT-4 gene knock-in, probably involving increased intestinal IGLE innervation, altered short-term feeding, in particular by enhancing satiation and sensitivity to CCK, whereas long-term control of daily intake and body weight was unaffected.     

Long-term effects of a fatty acid synthase inhibitor on obese mice: food intake, hypothalamic neuropeptides, and UCP3

Short-term treatment of lean and obese mice with the fatty acid synthase (FAS) inhibitor, C75, alters expression of hypothalamic neuropeptides thereby reducing food intake, body weight, and body fat. Here we report the long-term effects of C75 on obese (Ob/Ob) mice. A low dose of C75 administered every third day for 30 days reduced food intake by 62% and body weight by 43% whereas body weight of ad lib-fed controls increased by 11%. Loss of body weight correlated with decreased adipose and liver tissue mass. Decreased food intake correlated with decreased expression of hypothalamic neuropeptide mRNAs for NPY, AgRP, and MCH and an increased expression of neuropeptide mRNAs for alphaMSH (i.e., POMC) and CART. Consistent with increased energy expenditure, C75 treatment caused greater weight loss than pair-fed controls and increased expression of skeletal muscle UCP-3 mRNA. Lowered blood glucose was due largely to restriction of food intake. C75 blocked the normal fasting-induced rise in blood free fatty acids and ketones due either to decreased adipose tissue lipolysis and hepatic ketogenesis or increased fatty acid and ketone utilization by peripheral tissues, notably skeletal muscle.     

Pharmacological glycerol-3-phosphate acyltransferase inhibition decreases food intake and adiposity and increases insulin sensitivity in diet-induced obesity

Storage of excess calories as triglycerides is central to obesity and its associated disorders. Glycerol-3-phosphate acyltransferases (GPATs) catalyze the initial step in acylglyceride syntheses, including triglyceride synthesis. We utilized a novel small-molecule GPAT inhibitor, FSG67, to investigate metabolic consequences of systemic pharmacological GPAT inhibition in lean and diet-induced obese (DIO) mice. FSG67 administered intraperitoneally decreased body weight and energy intake, without producing conditioned taste aversion. Daily FSG67 (5 mg/kg, 15.3 μmol/kg) produced gradual 12% weight loss in DIO mice beyond that due to transient 9- to 10-day hypophagia (6% weight loss in pair-fed controls). Continued FSG67 maintained the weight loss despite return to baseline energy intake. Weight was lost specifically from fat mass. Indirect calorimetry showed partial protection by FSG67 against decreased rates of oxygen consumption seen with hypophagia. Despite low respiratory exchange ratio due to a high-fat diet, FSG67-treated mice showed further decreased respiratory exchange ratio, beyond pair-fed controls, indicating enhanced fat oxidation. Chronic FSG67 increased glucose tolerance and insulin sensitivity in DIO mice. Chronic FSG67 decreased gene expression for lipogenic enzymes in white adipose tissue and liver and decreased lipid accumulation in white adipose, brown adipose, and liver tissues without signs of damage. RT-PCR showed decreased gene expression for orexigenic hypothalamic neuropeptides AgRP or NPY after acute and chronic systemic FSG67. FSG67 given intracerebroventricularly (100 and 320 nmol icv) produced 24-h weight loss and feeding suppression, indicating contributions from direct central nervous system sites of action. Together, these data point to GPAT as a new potential therapeutic target for the management of obesity and its comorbidities.     

Stimulation of the hypothalamic ventromedial nuclei by pituitary adenylate cyclase-activating polypeptide induces hypophagia and thermogenesis

Numerous studies have demonstrated that the hypothalamic ventromedial nuclei (VMN) regulate energy homeostasis by integrating and utilizing behavioral and metabolic mechanisms. The VMN heavily express pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptors (PAC1R). Despite the receptor distribution, most PACAP experiments investigating affects on feeding have focused on intracerebroventricular administration or global knockout mice. To identify the specific contribution of PACAP signaling in the VMN, we injected PACAP directly into the VMN and measured feeding behavior and indices of energy expenditure. Following an acute injection of PACAP, nocturnal food intake was significantly reduced for 6 h after injections without evidence of malaise. In addition, PACAP-induced suppression of feeding also occurred following an overnight fast and could be blocked by a specific PAC1R antagonist. Metabolically, VMN-specific injections of PACAP significantly increased both core body temperature and spontaneous locomotor activity with a concurrent increase in brown adipose uncoupling protein 1 mRNA expression. To determine which signaling pathways were responsive to PACAP administration into the VMN, we measured mRNA expression of well-characterized hypothalamic neuropeptide regulators of feeding. One hour after PACAP administration, expression of pro-opiomelanocortin mRNA was significantly increased in the arcuate nuclei (ARC), with no changes in neuropeptide Y and agouti-related polypeptide mRNA levels. This suggests that PAC1R expressing VMN neurons projecting to pro-opiomelanocortin neurons contribute to hypophagia by involving melanocortin signaling. While the VMN also abundantly express PACAP protein, the present study demonstrates that PACAP input to the VMN can influence the control of energy homeostasis.     

Antagonism of corticotrophin-releasing factor receptors in the fourth ventricle modifies responses to mild but not restraint stress

Repeated restraint stress (RRS; 3 h of restraint on 3 consecutive days) in rodents produces temporary hypophagia, but a long-term downregulation of body weight. The mild stress (MS) of an intraperitoneal injection of saline and housing in a novel room for 2 h also inhibits food intake and weight gain, but the effects are smaller than for RRS. Previous exposure to RRS exaggerates hypophagia, glucocorticoid release, and anxiety-type behavior caused by MS. Here we tested the involvement of brain stem corticotrophin-releasing factor receptors (CRFR) in mediating energetic and glucocorticoid responses to RRS or MS and in promoting stress hyperresponsiveness in RRS rats. Administration of 1.3 nmol alphahCRF(9-41), a nonspecific CRFR antagonist, exaggerated hypophagia and weight loss in both RRS and MS rats, whereas 0.26 nmol had no effect in RRS or MS rats. In contrast, 2 nmol of the nonspecific antagonist astressin had no effect on weight loss or hypersensitivity to subsequent MS in RRS rats, but blocked weight loss and inhibition of food intake caused by MS alone. MS rats infused with 3 nmol antisauvagine-30, a CRFR2 antagonist, did not lose weight in the 48 h after MS, but 0.3 nmol did not prevent weight loss in MS rats. These data suggest that inhibition of food intake and weight loss induced by RRS or by MS involve different pathways, with hindbrain CRFR mediating the effect of MS on body weight and food intake. Hindbrain CRFR do not appear to influence stress-induced corticosterone release in RRS rats.     

Brain-derived neurotrophic factor in the hypothalamic paraventricular nucleus increases energy expenditure by elevating metabolic rate

Brain-derived neurotrophic factor (BDNF) decreases food intake and body weight, but few central sites of action have been identified. The hypothalamic paraventricular nucleus (PVN) is important in energy metabolism regulation, and expresses both BDNF and its receptor. We tested three hypotheses: 1) PVN BDNF reduces feeding and increases energy expenditure (EE), 2) PVN BDNF-enhanced thermogenesis results from increased spontaneous physical activity (SPA) and resting metabolic rate (RMR), and 3) PVN BDNF thermogenic effects are mediated, in part, by uncoupling protein 1 (UCP1) in brown adipose tissue (BAT). BDNF (0.5 microg) was injected into the PVN of Sprague-Dawley rats; and oxygen consumption, carbon dioxide production, food intake, and SPA were measured for 24 h in an indirect calorimeter. SPA was also measured in open-field activity chambers for 48 h after BDNF injection. Animals were killed 6 or 24 h after BDNF injection, and BAT UCP1 gene expression was measured with quantitative real-time PCR. BDNF significantly decreased food intake and body weight gain 24 h after injection. Heat production and RMR were significantly elevated for 7 h immediately after BDNF injection. BDNF had no effect on SPA, but increased UCP1 gene expression in BAT at 6 h, but not 24 h after injection. In conclusion, PVN BDNF reduces body weight by decreasing food intake and increasing EE consequent to increased RMR, which may be due, in part, to BAT UCP1 activity. These data suggest that the PVN is an important site of BDNF action to influence energy balance.