Paraventricular nucleus injections of naloxone methiodide inhibit NPY's effects on energy substrate utilization

Microinjection of neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus stimulates eating and increases respiratory quotient. In contrast, administration of opioid receptor antagonists reduces food intake and suppresses NPY-induced feeding. The present study examined whether naloxone methiodide, an opioid antagonist, would suppress the potentiation of NPY on energy substrate utilization, when injected into the PVN. Naloxone methiodide was injected at doses of 0.1 and 1.0 g, 10 min prior to NPY treatment. NPY was administered immediately prior to the start of the nocturnal period and RQ was determined using an open-circuit calorimeter. Doses of 50 and 100 pmol NPY alone evoked reliable increases in RQ within 30min of treatment. Following naloxone methiodide pretreatment, the stimulatory action of NPY was significantly attenuated. These data indicate that opioid receptors in the PVN influence the action of NPY on energy substrate utilization.     

Effects of three neurochemical stimuli on delayed feeding and energy metabolism

Infusions of norepinephrine (NE), the gamma-aminobutyric acid agonist, muscimol (MUS), or neuropeptide Y (NPY) into the paraventricular nucleus (PVN) of the hypothalamus all increase food intake. Such feeding may be due to direct activation of behavioral processes driving ingestion and/or to alterations in nutrient metabolism that feeding serves to normalize. To examine these possibilities, male Sprague-Dawley rats received PVN infusions of vehicle, 20 nmol NE, 1 nmol MUS or 100 pmol NPY at dark onset, then food intake was measured under three feeding conditions: (1) 1 and 2 h immediately after injections, (2) 1 h after a 1 h delay between injections and access to food, and (3) 1 h after a 1 h feeding delay, but with injections occurring just before presenting food. Measures of energy expenditure (EE) and respiratory quotients (RQs) in the absence of food were made over 2 h in parallel experiments. Results confirmed that NE, MUS and NPY all increased dark-onset feeding, but only NPY increased intake above control levels after a 1 h feeding delay. No neurochemically-induced changes in EE were observed, nor were there changes in RQs after NE or MUS. However, NPY reliably enhanced RQs from 30 to 120 min of testing. Our findings imply that NE and MUS initiate relatively immediate, short-term feeding that is not associated with changes in nutrient metabolism and does not summate with cues stimulated by delayed access to food. NPY initiates more protracted feeding temporally linked to enhanced carbohydrate metabolism. This may indicate that part of NPY's feeding stimulatory effects are secondary to physiological processes driving ingestion.     

Blockade of natural and neuropeptide Y-induced carbohydrate feeding by a receptor antagonist PYX-2.

Neuropeptide Y (NPY injected into the paraventricular nucleus (PVN) of rats has a potent stimulatory effect specifically on carbohydrate intake. This study examined the behavioral effects of a newly synthesized NPY antagonist, PYX-2. After PVN injection of PYX-2 (50-900 pmoles) alone, a strong dose-dependent reduction in spontaneous carbohydrate intake at the onset of the dark cycle was observed in freely-feeding rats. Moreover, at even lower doses (12.5 and 25.0 pmoles), PYX-2 also blocked the stimulatory action of PVN NPY (100 pmoles) on carbohydrate ingestion. These results provide the first evidence for the existence of endogenous NPY receptors in mediating the action of exogenous NPY in the hypothalamus. They also constitute a crucial step in demonstrating a physiological function of these PVN NPY receptors specifically in controlling carbohydrate ingestion at the onset of the natural feeding cycle.     

5-HT(2A/2C) receptor antagonists in the paraventricular nucleus attenuate the action of DOI on NPY-stimulated eating.

Hypothalamic neuropeptide Y (NPY) and serotonin (5-HT)-containing neurons are believed to exert an interactive effect on ingestive behavior. The present study examined the ability of two serotonergic antagonists, spiperone (SPIP), a 5-HT2A antagonist, and mianserin (MIAN), a 5-HT(2A/2C) antagonist, to block the inhibitory action of the 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) on NPY-stimulated eating. Drugs were injected directly into the paraventricular nucleus (PVN), the perifornical (PFH) or the ventromedial hypothalamus (VMH) at the onset of the dark cycle. PVN, PFH and VMH injections of NPY potentiated food intake although only PVN pretreatment with DOI (5-20 nmol) suppressed NPY-induced eating. SPIP or MIAN, injected immediately prior to PVN DOI, reversed the suppressive effect of DOI on NPY feeding. These findings are consistent with other recent data showing that 5-HT2A receptors within the PVN modulate NPY's effect on food intake at the start of the nocturnal period.     

Paraventricular nucleus anandamide signaling alters eating and substrate oxidation

In the central nervous system, the endocannabinoid anandamide [N-arachidonoylethanolamine (AEA)] is believed to increase food intake through on-demand activation of hypothalamic circuits. The present study examined the effects of hypothalamic paraventricular nucleus (PVN) injections of AEA (25-400 pmol) on food intake and energy substrate oxidation [respiratory quotient (RQ)]. PVN administration of AEA increased eating behavior and RQ, indicating enhanced carbohydrate oxidation. Further, PVN administration of the cannabinoid type 1 receptor inverse agonist AM251 (5-10 μg) attenuated both the eating and the RQ responses elicited by AEA (100 pmol). AM251 administered alone did not alter food intake or RQ. Overall, these findings are consistent with a role for PVN cannabinoid type 1 receptors in the regulation of eating and energy homeostasis.     

Metabolic effects of neuropeptide Y injected into the sulcal prefrontal cortex

The metabolic effects of 10, 39 and 156 pmol doses of neuropeptide Y (NPY) injected into the sulcal prefrontal cortex (SPC) were investigated in an open-circuit calorimeter. The 39 pmol dose produced a large and long lasting increase in respiratory quotient indicating both increased utilization of carbohydrate as an energy substrate and the synthesis of fat from carbohydrate. The 10 and 39 pmol doses produced an inhibition of energy expenditure that was still evident 24 hours following the 10, but not the 39 pmol, dose. These energy expenditure effects appeared to reflect an inhibition of thermogenesis as they were not systematically related to changes in locomotor activity. In separate tests, 39 pmol NPY reliably enhanced food intake. This combination of effects, namely increased carbohydrate utilization, fat synthesis and food intake with reduced energy expenditure, shows NPY to be a potent anabolic force. In addition, these results indicate both the functional significance of NPY at a cortical level and the important role of the SPC in the control of energy balance.     

Action of MT-II on ghrelin-induced feeding in the paraventricular nucleus of the hypothalamus

Ghrelin is a 28 amino-acid peptide that has been shown to induce positive energy balance when administered both peripherally and centrally. This effect appears to occur by increasing food intake and by reducing fat utilization. Ghrelin injected into the PVN increases food intake dose-dependently. The NPY receptor has been implicated in the orexigenic effect of ghrelin, but until now, the role of melanocortins on the effect of ghrelin in the PVN has not been reported. Sprague-Dawley rats were stimulated to eat by PVN ghrelin. Pre-injection of 10 pmol of MT II into the PVN caused a significant decrease in ghrelin-induced feeding in both 0-1 h and 0-4 h food intake studies. This finding indicates that MC 3/4-R signaling appears to be recruited by ghrelin, in the PVN, in its role to induce feeding.     

Diurnal variations in the feeding responses to norepinephrine, neuropeptide Y and galanin in the PVN.

The feeding responses elicited by injection of norepinephrine (NE), neuropeptide Y (NPY) and galanin (GAL) into the paraventricular nucleus (PVN) were studied at two different times of the dark (active) cycle in male Sprague-Dawley rats maintained ad lib on pure nutrient diets. The feeding response elicited by NE in the PVN, characterized by a potent and selective stimulatory effect on ingestion of the carbohydrate diet, was significantly stronger during the early dark period (+11.7 kcal over vehicle baseline) relative to the late dark period (+7.6 kcal). A similar pattern of effects was observed with NPY in the PVN, which also selectively potentiated carbohydrate ingestion. The effects of GAL were different from those observed with NE and NPY. Whereas the total amount of food consumed after PVN GAL injection was similar in the early and late dark periods, the macronutrient selection patterns exhibited at these two times were different. During the early dark period, PVN GAL had a small stimulatory effect on carbohydrate, in addition to a strong enhancement of fat intake; in the late dark period, in contrast, GAL stimulated intake only of the fat diet. These findings may reflect differential functions of these hypothalamic neurotransmitters in controlling nutrient ingestion at different periods of the circadian cycle.     

Altered functionality of the corticotrophin-releasing hormone receptor-2 in the hypothalamic paraventricular nucleus of hyperphagic maternally separated rats

Early-life stress induces endocrine and metabolic alterations that increase food intake and overweight in adulthood. The stress response activates the corticotropin-releasing hormone (CRH) and urocortins' (Ucns) system in the hypothalamic paraventricular nucleus (PVN). These peptides induce anorexic effects through CRH-R2 receptor activation; however, chronic stressed animals develop hyperphagia despite of high PVN CRH expression.We analyzed this paradoxical behavior in adult rats subjected to maternal separation (MS) for 180 min/daily during post-natal days 2–14, evaluating their body weight gain, food intake, serum corticosterone and vasopressin concentrations, PVN mRNA expression of CRH-R1, CRH-R2, CRH, Ucn2, Ucn3, vasopressin and CRH-R2 protein levels.MS adults increased their feeding, weight gain as well as circulating corticosterone and vasopressin levels, evincing chronic hyperactivity of the stress system. MS induced higher PVN CRH, Ucn2 and CRH-R2 mRNA expression and protein levels of CRH-R2 showed a tendency to decrease in the cellular membrane fraction. An intra-PVN injection of the CRH-R2 antagonist antisauvagine-30 in control adults increased receptor's mRNA expression, mimicking the observed PVN receptor's up-regulation of early-life MS adults.An injection of Ucn-2 directly into the PVN reduced food intake and increased PVN pCREB/CREB ratio in control animals; in contrast, Ucn-2 was unable to reduce food intake and enhance phosphorylated-CREB levels in PVN of MS rats.In conclusion, the chronic hyperactivity of the stress axis and PVN CRH-R2 resistance to Ucn2 effects, supported impaired receptor functionality in MS animals, probably due to its chronic stimulation by CRH or Ucn2, induced by early-life stress.     

Neonatal immune challenge affects the regulation of estrus cyclicity and feeding behavior in female rats

A single immune challenge with lipopolysaccharide (LPS) in the neonatal period has a long-lasting influence on immune response. Using female Sprague–Dawley rats, we examined whether neonatal LPS challenge influences the life-long neuroendocrine sensitivity of reproductive function and feeding behavior to LPS, and whether stress-related neuropeptides and their receptors are involved in neonatal LPS-induced physiological change. On day 10 after birth, all pups were injected with LPS (100 μg/kg, i.p.) or saline. Then, in Experiment 1, LPS (100 μg/kg, i.p.) or saline was injected at diestrous in adulthood, and the length of the estrous cycle, 24 h food intake and body weight change were recorded. In Experiment 2, the mRNA expression levels of corticotropin-releasing hormone (CRH), urocortin (UCN), urocortin 2 (UCN2), CRH receptor type 1 (CRH-R1) and CRH receptor type 2 (CRH-R2) in the hypothalamus were measured using real-time PCR. LPS injection in adulthood prolonged the estrous cycle in neonatal LPS-injected rats. LPS injection in adulthood decreased food intake and body weight in both neonatal LPS- and saline-injected rats, more so in the latter. Basal expressions of UCN2 and CRH-R2 mRNA were higher in neonatal LPS-injected rats than in saline-injected rats. These findings indicate that neonatal immune challenge influences the anti-stress regulation of the estrous cycle and feeding behavior in adulthood. Increased expression of UCN2 and CRH-R2 might enhance the sensitivity of the estrous cycle in suppressing the effects of LPS.     

Ghrelin is an orexigenic peptide and elicits anxiety-like behaviors following administration into discrete regions of the hypothalamus

Previous evidence indicates that peripherally administered ghrelin significantly increases corticotropin releasing hormone (CRH) mRNA and serum corticosterone. In addition, intraventricular administration of ghrelin has been reported to elicit anxiety-like behaviors suggesting that the peptide plays a role in mediating neuroendocrine and behavioral responses to stress. In the present study, we characterized the orexigenic, metabolic, and anxiogenic actions of ghrelin following microinjection into the arcuate nucleus (ARN), paraventricular nucleus (PVN), perifornical hypothalamus (PFH), and ventromedial nucleus (VMN). To assess ghrelin's role in anxiogenic behavior, rats were injected with vehicle or 50-800 pmol of ghrelin and then placed in an elevated plus maze (EPM) for 10 min. Each test was performed as a single trial per animal. In separate behavioral testing we measured the induction of stereotypic behaviors. Doses of 200 pmol or higher administered into the ARN and PVN elicited anxiety-like behaviors, including an increased avoidance of the open arms of the EPM. However, in the PFH and VMN, higher doses of ghrelin (400-800 pmol) were required to induce anxiety. Ghrelin doses as low as 50 pmol stimulated eating and altered energy substrate oxidation (respiratory quotient; RQ) when injected into the ARN and PVN. Injections into the PFH and VMN elicited more modest effects on eating and RQ at doses of 400 pmol or greater. Our findings indicate that regions of the hypothalamus appear to be differentially sensitive and responsive to the feeding-stimulant, metabolic, and anxiogenic actions of ghrelin and that the ARN and PVN, in particular, exert a primary role in mediating these effects.     

Substance P is associated with hypothalamic paraventricular nucleus activation that coincides with increased urotensin 2 mRNA in chicks

Exogenous administration of substance P (SP) exerts anorexigenic effects in both chicks and rats, but the central mechanism mediating this response is poorly understood. Therefore, this study was designed to elucidate mechanisms of SP-induced anorexia using chicks as models. Chicks that received intracerebroventricular (ICV) injections of SP dose-dependably reduced their food intake with no effect on water intake. Next, the diencephalon was isolated from SP-injected chicks and mRNA expression of neuropeptide Y (NPY), corticotropin releasing factor (CRF), urocortin 3 (UCN 3) and CRF receptors were measured but were not affected. When measured in the hypothalamus, mRNA abundance of these and NPY receptors, urotensin 2 (UTS2) and melanocortin receptor 4 (MCR4) were not affected by SP-injection. Quantification of c-Fos immunoreactivity in appetite-associated hypothalamic nuclei demonstrated that the paraventricular nucleus (PVN) was activated in SP-injected chicks. Finally, in the PVN isolated from SP-injected chicks, there was increased expression of UTS2 mRNA while CRF and UCN3 were not affected. Thus, the anorexigenic effects of SP appear to be mediated by PVN activation and may involve UTS2.     

Tonic inhibition of food intake during inactive phase is reversed by the injection of the melanocortin receptor antagonist into the paraventricular nucleus of the hypothalamus and central amygdala of the rat

Melanocortins inhibit food intake and melanocortin 4 receptor (MC(4)R) antagonists stimulate feeding behaviour. These effects may occur due to stimulation or blockade of MC(4) receptors in the hypothalamus. To test the validity of this hypothesis, a cyclic peptide, the MC(4)R selective antagonist HS014 (20, 100 and 500 pmol), or vehicle, was injected unilaterally into the paraventricular nucleus of the hypothalamus (PVN). As MC receptors are expressed also in extrahypothalamic sites involved in the regulation of feeding behaviour, HS014 was injected bilaterally into the vicinity of the central nucleus of the amygdala (CA) and the nucleus accumbens region (Acc). All doses of HS014 induced a dose-dependent increase in food intake when injected into the PVN. Intra-amygdalar injections of HS014 (50 and 250 pmol/side) also stimulated food intake, whereas a 10-pmol dose was inactive. Local microinjections of HS014 into the Acc failed to stimulate feeding. These data suggest that endogenous melanocortin receptor agonists exert a tonic inhibitory influence on food consumption by stimulating MC(4) receptors in the hypothalamus and amygdala.     

Long‐term Infusion of Brain‐Derived Neurotrophic Factor Reduces Food Intake and Body Weight via a Corticotrophin‐Releasing Hormone Pathway in the Paraventricular Nucleus of the Hypothalamus

Brain‐derived neurotrophic factor (BDNF) has been implicated in learning, depression and energy metabolism. However, the neuronal mechanisms underlying the effects of BDNF on energy metabolism remain unclear. The present study aimed to elucidate the neuronal pathways by which BDNF controls feeding behaviour and energy balance. Using an osmotic mini‐pump, BDNF or control artificial cerebrospinal fluid was infused i.c.v. at the lateral ventricle or into the paraventricular nucleus of the hypothalamus (PVN) for 12 days. Intracerebroventricular BDNF up‐regulated mRNA expression of corticotrophin‐releasing hormone (CRH) and urocortin in the PVN. TrkB, the receptor for BDNF, was expressed in the PVN neurones, including those containing CRH. Both i.c.v. and intra‐PVN‐administered BDNF decreased food intake and body weight. These effects of BDNF on food intake and body weight were counteracted by the co‐administration of α‐helical‐CRH, an antagonist for the CRH and urocortin receptors CRH‐R1/R2, and partly attenuated by a selective antagonist for CRH‐R2 but not CRH‐R1. Intracerebroventricular BDNF also decreased the subcutaneous and visceral fat mass, adipocyte size and serum triglyceride levels, which were all attenuated by α‐helical‐CRH. Furthermore, BDNF decreased the respiratory quotient and raised rectal temperature, which were counteracted by α‐helical‐CRH. These results indicate that the CRH‐urocortin‐CRH‐R2 pathway in the PVN and connected areas mediates the long‐term effects of BDNF to depress feeding and promote lipolysis.     

Metabolic effects of neuropeptide Y injections into the paraventricular nucleus of the hypothalamus

The metabolic effects of single injections of neuropeptide Y (NPY) into the paraventricular hypothalamus were investigated in an open-circuit calorimeter. Wistar rats were tested, with no food available during the tests. Over the dose range of 10-156 pmol NPY had large effects on respiratory quotient (RQ) while having no effect on energy expenditure or locomotor activity. The effects of NPY on RQ were unusual both in respect to their dose-response and time-dose-response characteristics. The lowest dose (10 pmol) produced a very low latency reduction in RQ which indicates a decreased utilization of carbohydrates as an energy substrate. The next higher dose (20 pmol) had no effect, whereas the next three doses (39, 78 and 156 pmol) produced increases in RQ which indicate an increased utilization of carbohydrates as an energy substrate. Surprisingly, the latencies of the increased RQs were dose-dependent over the range of 30 min to 20 h with the highest dose producing the longest latency effect. The finding of a positive relation of dose to response latency over a time range of from a few minutes to 20 h is unprecedented and appears to represent a neuromodulatory effect of NPY that acts in concert with its neurotransmitter effects. These data highlight the central role of NPY in modulating energy substrate utilization and indicate the importance of elucidating time-dose-response relationships when investigating the effects of NPY.     

Suppression of neuropeptide Y-elicited eating by adrenalectomy or hypophysectomy: reversal with corticosterone

Neuropeptide Y (NPY) injected into the paraventricular hypothalamus (PVN) stimulates a robust eating response in the satiated rat. To examine whether the NPY-feeding system interacts with the pituitary-adrenal axis, the eating response to PVN injections of NPY (78 pmol) was tested in adult male rats before and after sham surgery, adrenalectomy (ADX), hypophysectomy (HYPX), and/or corticosterone (CORT) replacement therapy. In unoperated or sham groups, NPY elicited 5.7-8.8 g of food intake in 1 h as compared to 0.4-1.1 g for vehicle-injected animals. In ADX groups, the NPY-elicited response was reduced by 60-71%, to between 2.4 and 2.8 g. Likewise, the average response of the HYPX group was reduced by 69%, to 1.7 g. Corticosterone replacement, via subcutaneous implant of a 100 mg CORT pellet, normalized the NPY-induced feeding response in both the ADX and HYPX groups. These findings suggest that the hypothalamic NPY-feeding system is largely dependent upon circulating CORT and that no other adrenal or pituitary hormone is essential.     

Urocortin in the ventromedial hypothalamic nucleus acts as an inhibitor of feeding behavior in rats

Urocortin (UCN), a member of the corticotropin-releasing factor (CRF) family, inhibits food intake when it is injected intracerebroventricularly in rats. To explore the site of action of UCN in feeding behavior, we examined the effects of injection of UCN into various hypothalamic nuclei on food and water intake in 24-h fasted rats. Injection of UCN into the ventromedial hypothalamic nucleus (VMH) significantly inhibited food and water intake over 3 h without sedative effect, but no significant effect was observed following injection either into the lateral hypothalamic area, or the paraventricular nucleus of the hypothalamus. To further explore the physiological significance of endogenous UCN of the VMH in feeding behavior, the effect of immunoneutralization of hypothalamic UCN on food intake was examined. Injection of anti-rat UCN rabbit gamma-globulin into the bilateral VMH in freely fed rats significantly potentiated food and water intake compared with rats that received normal rabbit gamma-globulin. These results suggest that endogenous UCN in the VMH exert inhibitory control on ingestive behavior.     

Anorectic Effect of Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) in Rats: Lack of Evidence for Involvement of Hypothalamic Neuropeptide Gene Expression

We investigated the effect of centrally administered pituitary adenylate cyclase activating polypeptide (PACAP) on feeding in rats, and the involvement of hypothalamic neuropeptide gene expression using in situ hybridization. lntracerebroventricular injection of PACAP (1000  pmol/rat) significantly decreased food intake in a dose-dependent manner. In PACAP-treated rats, neuropeptide Y (NPY) mRNA levels in the arcuate nucleus and galanin mRNA levels in the paraventricular nucleus increased, and corticotropin-releasing hormone (CRH) mRNA levels in the paraventricular nucleus decreased. In rats fasted for 72  h, NPY mRNA levels increased, and CRH mRNA levels decreased, but galanin mRNA levels were unchanged. These results indicate that the anorectic function of PACAP is not mediated by NPY or CRH, and that PACAP increases galanin synthesis.     

Neuropeptide Y (NPY) May Integrate Responses of Hypothalamic Feeding Systems and the Hypothalamo-Pituitary-Adrenal Axis

Neuropeptide Y (NPY) is a powerful stimulus to food intake in the rat. Exogenous NPY given into the third ventricle or into the paraventricular nucleus (PVN) of the hypothalamus stimulates both food consumption as well as the hypothalamus-pituitary-adrenal (HPA) axis. Presumably NPY activates the adrenocortical system through direct stimulation of CRF containing cells in the PVN. Food intake is also a major regulator of adrenocortical activation. Rhythms in HPA axis activity follow rhythms in food consumption, and rats that have been food deprived overnight have inhibited HPA axis responses to restraint stress and corticosteroid feedback the following morning. To investigate the interaction of NPY with both feeding and HPA axis activation three sets of experiments were performed: Animals fed ad lib were injected icv with NPY (2.5 μg) and allowed access to food or not post injection; animals were fasted overnight prior to NPY injection; finally, dose response experiments were performed to examine the relative sensitivities of feeding and HPA axis activation to exogenous NPY. Ad lib fed animals allowed access to food after NPY injection had slightly greater ACTH responses to NPY while glucocorticoid and insulin responses were not significantly different from ad lib fed animals not allowed access to food post injection. Animals allowed to eat post injection had significantly decreased food consumption the night following injection, however, total 24 h food consumption was not different between these animals and those given food 8 h post NPY injection. In overnight fasted animals NPY injections produced ACTH responses of equal magnitude to those in ad lib fed animals. Insulin responses to NPY were significantly elevated compared to CSF controls in overnight fasted animals. Dose response studies revealed that the adrenocortical system responds to icv NPY with at least as great sensitivity as feeding systems. NPY is discussed as a potential integrator of feeding and responsiveness in the HPA axis.     

Effects of NPY and NPY2–36 on body temperature and food intake following administration into hypothalamic nuclei

Our previous in vivo structure-activity studies suggested that the putative receptors mediating the effects of NPY and NPY_2–36 on food intake and body temperature are pharmacologically different [17]. In the present study, we examined and compared dose-related effects of NPY and NPY_2–36 on ad lib food intake and rectal temperature after administration into discrete hypothalamic nuclei of the rat. Results indicate that NPY and NPY_2–36 have opposite effects on body temperature to those of NPY when injected in the preoptic area (POA): hypothermia and hyperthermia, respectively. When administered in the paraventricular nucleus (PVN), both increased body temperature. When injected into the third ventricle (3V), NPY produced a biphasic effect: hypothermia at low doses and hyperthermia at high doses. Similar effects were obtained with NPY_2–36, but in an inverted dose-related fashion: hyperthermia at low and hypothermia at higher doses. In the arcuate nucleus (Arc), NPY induced a significant hypothermia whereas NPY_2–36 had no effect. Finally, neither peptide affected body temperature when injected into the ventromedial (VMH) and perifornical (PeF) nuclei. Both NPY and NPY_2–36 increased food intake after injection in all regions examined. In general, NPY was more potent and efficacious than NPY_2–36. The present results clearly dissociate the effects of NPY on food intake and body temperature. Furthermore, the data support the hypothesis that the putative receptors underlying the effects of NPY and NPY_2–36 on food intake are similar, whereas those mediating the effects on body temperature are pharmacologically different.