Effects of fluoxetine administration on hypothalamic melanocortin system in obese Zucker rats

The aim of the present work was to study the potential involvement of melanocortin system in the anorectic mechanism of fluoxetine, a selective serotonin reuptake inhibitors, in obese Zucker rats. Male obese Zucker (fa/fa) rats were administered fluoxetine (10 mg/kg; i.p.) daily for two weeks. The control group was given 0.9% NaCl solution. RT-PCR for pro-opiomelanocortin (POMC), Agouti gene related peptide (AgRP) and melanocortin receptor 4 (MC4-R) in the hypothalamus, as well as regional immunostaining for alpha-melanocyte stimulating hormone (alpha-MSH) and MC4-R were carried out. Fluoxetine administration increased POMC expression and reduced MC4-R expression in the hypothalamus, without changes in AgRP mRNA levels. Moreover, an increase in the numbers of alpha-MSH positively immunostained neural cells in the hypothalamic arcuate nucleus (ARC), as well as a significant decrease in the numbers of neural cells positively immunostained for MC4-R in the paraventricular nucleus (PVN), without changes in lateral hypothalamic area (LHA), were observed. These results suggest the involvement of alpha-MSH in central fluoxetine anorectic action.     

Effects of melanocortin receptor ligands on thyrotropin-releasing hormone release: evidence for the differential roles of melanocortin 3 and 4 receptors

The hypothalamic melanocortin system is important in the central regulation of food intake and body weight. We have previously demonstrated that intracerebroventricular administration of alpha-melanocyte stimulating hormone (alpha-MSH), a nonselective MC3 and MC4 receptor agonist, stimulated plasma thyroid-stimulating hormone, and agouti-related protein (AgRP), an MC3 and MC4 receptor antagonist, suppressed it. In this study, we investigated the effects of MC3 and MC4 receptor (MC3-R and MC4-R) selective agonists and antagonists on the release of thyrotropin-releasing hormone (TRH) from hypothalamic explants in vitro. alpha-MSH stimulated TRH release from the rat hypothalamic explants (alpha-MSH 100 nm 230 +/- 22.9% basal, P < 0.005). In contrast, gamma 2-MSH, a selective MC3-R agonist, suppressed TRH release (gamma 2-MSH 10 microns 76.2 +/- 7.4% basal, P < 0.05). AgRP (83-132), a nonselective MC3/4-R antagonist, induced no change in TRH release whilst JKC-363 (cyclic [Mpr11, D-Nal14, Cys18, Asp22-NH2]-beta-MSH 11-22), a selective MC4-R antagonist, suppressed it (JKC-363 10 nm 57.2 +/- 11.5% basal, P < 0.05). Both AgRP (83-132) and JKC-363 blocked alpha-MSH stimulated TRH release but only AgRP (83-132) blocked the inhibitory effect of gamma 2-MSH on TRH release. These data suggest differential roles for the MC3 and MC4 receptors in TRH release; MC3-R agonism inhibiting and MC4-R agonism stimulating TRH release.     

Elevated hypothalamic neuropeptide Y levels in rats with dorsomedial hindbrain lesions

Lesions centered on the area postrema (AP) and adjacent nucleus of the solitary tract (AP/mNTS-lesions) are reported to result in increased consumption of highly palatable diets. Recent studies suggest that neuropeptide Y (NPY) may cause a preference for carbohydrate-rich diets. Thus, it is possible that NPY may play a role in the enhanced intake of highly palatable diets by AP/mNTS-lesioned rats. In the studies reported here, we found that lesions centered on the AP result in increased levels of NPY-immunoreactivity in the paraventricular nucleus of the hypothalamus. Additionally, steady-state NPY mRNA in the basomedial hypothalamus including the arcuate nucleus was elevated. Enhanced NPY was not found throughout the hypothalamus however, as NPY-immunoreactivity was not elevated in the lateral hypothalamus or the tissue bordering the anteroventral third ventricle. These data suggest the possibility that elevated hypothalamic NPY, particularly in the arcuate and paraventricular nuclei, may contribute to the altered food intake and energy balance observed in rats with lesions centered on the AP.     

The effect of morphine on MC4 and CRF receptor mRNAs in the rat amygdala and attenuation of tolerance after their blockade

The relationships between the CRF, which enhances the proopiomelanocortin (POMC) biosynthesis, and POMC-derived peptides (opioids and melanocortins) might be a new target for rational treatment of morphine tolerance. In the present study, we investigated the effect of acute and chronic morphine administration on the level of CRF1 and melanocortin 4 receptor (MC4-R) mRNAs in the rat amygdala by quantitative real-time PCR method. Moreover, we investigated the effect of antagonists of melanocortin and CRF receptors, SHU9119 and -helical CRF (h-CRF), respectively, administered bilaterally into the central nucleus of the amygdala, on morphine tolerance using tail-flick and paw withdrawal tests. Our study demonstrated that acute morphine administration decreased the level of MC4-R mRNA in the rat amygdala. This decrease was attenuated following chronic morphine administration, and mRNA level of MC4 receptors was gradually increased and, on 9th day of morphine administration, i.e. in the period when morphine tolerance already developed, the level was significantly increased in comparison with control and with the effect after single morphine dose. In contrast, morphine did not affect the CRF receptor. In behavioral study, we demonstrated that SHU9119 and h-CRF significantly increased the antinociceptive effect of morphine, when they were injected into the amygdala prior to morphine administration in tolerant rats. We have shown for the first time the contribution of amygdalar melanocortin receptors to morphine tolerance, and we conclude that the altered melanocortin receptor function may play an important role in the development of morphine-induced tolerance. CRF and melanocortin peptides can modulate the phenomena in the same direction, in opposition to opioids. Therefore, antagonists of melanocortin receptors may be regarded as possible therapeutic modulators of morphine tolerance.     

Effects of paraventricular hypothalamic microinjections of phenylpropanolamine and d-amphetamine on mash intake in rats

The present experiment compared the effects of unilateral microinjections (40, 80 and 160 nmol/0.5 microliter) of phenylpropanolamine (PPA: d,l-norephedrine) and d-amphetamine sulfate within the paraventricular hypothalamus (PVN) on consumption of a palatable sweetened-mash diet in 15-hour food-deprived adult male rats. Intracranial microinjections were administered 5 minutes prior to each 30-minute feeding trial. PPA, at a dose of 160 nmol, suppressed feeding by 42%, whereas a similar dose of amphetamine suppressed feeding by 49%. Amphetamine or PPA doses of 40 and 80 nmol were without significant effect on feeding behavior. A relatively high dose of 160 nmol amphetamine was required to suppress feeding after injection into the PVN whereas much lower amphetamine concentrations are required to suppress feeding after injection into the perifornical hypothalamus. In contrast, PPA has some anorexic activity within the PVN but not within the perifornical hypothalamus.     

Melanin-concentrating hormone, melanocortin receptors and regulation of luteinizing hormone release

Melanin-concentrating hormone (MCH) is a neuropeptide, identified by its ability to either mimic or antagonize the melanin-dispersing action of alpha-melanocyte stimulating hormone (alphaMSH) on skin melanophores. MCH and alphaMSH also have antagonistic actions in the brain affecting feeding behaviour, aggression, anxiety, arousal and reproductive function through the release of luteinizing hormone (LH). It is not clear, however, how they exert their opposite effects in the central nervous system (CNS). One possibility is that they act via a common receptor. In this study we have examined the effect of a number of MC receptor antagonists, with relative selectivity for the MC3, 4 and 5 subtypes, on the actions of MCH on LH release. We confirmed that bilateral administration of MCH (100 and 200 ng/side) into the medial preoptic area of oestrogen-primed (oestradiol benzoate 5 microgram) ovariectomized anaesthetized rats, stimulated the release of LH. This effect was blocked by the concomitant administration into the medial preoptic area of the MC4/5 antagonist ([D-Arg8]ACTH(4-10) and the MC3/5 antagonist ([Ala6]ACTH(4-10)-both at 500 ng/side-but not by the MC3/4 antagonist, SHU9119 (200 ng/side). Furthermore, the MC3 agonist [Nle3]-gamma2 MSH failed to affect LH release. These results indicate that the MC3 and MC4 receptors are not involved in mediating the action of MCH but are consistent with an action via the MC5 subtype. Preputial glands, which express MC5 receptors, were also stimulated by MCH which is in keeping with this idea. In HEK293 cells transfected with the MC5 receptor MCH increased the production of IP3. However, it was much less potent than alphaMSH and unlike alphaMSH, had no effect on the production of cAMP. MCH (10-10 to 10-5 M) also failed to displace I125NDP-MSH from cells transfected with MC5 receptors indicating that it was not acting as a competitive antagonist and its binding site was distinct from that of alphaMSH. Thus while MCH may function as an agonist at the MC5 receptor, its stimulation of LH release is more likely to be mediated via a specific MCH receptor that has common properties with the MC5 receptor.     

Impact of hypothalamic d-norfenfluramine and peripheral d-fenfluramine injection on macronutrient intake in the rat

Previous research with hypothalamic injection of serotonin (5-HT) has suggested that this monoamine may act within the medial hypothalamus to suppress carbohydrate intake in a selective, phasic and circadian-related fashion. To explore further the action of 5-HT in the brain, the present studies tested the serotonergic stimulants, d-norfenfluramine (DNF) and d-fenfluramine (DF), in freely feeding, brain-cannulated animals maintained on pure macronutrient diets (protein, carbohydrate and fat) and tested at different times of the diurnal cycle. The results show that administration of DNF into the paraventricular nucleus (PVN) potently influences appetite for a specific nutrient at a particular time of the light-dark cycle. Specifically, DNF injection at the onset of the nocturnal (active) period selectively and dose-dependently suppresses carbohydrate consumption, while leaving protein and fat intake unchanged. This drug, however, has no effect, even at high doses, on macronutrient intake in the middle and late h of the dark phase, strongly implicating a function for hypothalamic 5-HT in the control of carbohydrate ingestion at the beginning of the nocturnal cycle. The possibility that peripherally injected DF may act, in part, through this endogenous serotonergic system is supported by the additional finding that, at low doses of 0.06-0.5 mg/kg, DF preferentially modulates carbohydrate ingestion exclusively at the onset of the nocturnal period. However, at doses above 0.5 mg/kg, this compound produces a potent and general suppression of feeding of all macronutrients. In animals with brain cannulas aimed at different hypothalamic nuclei, the feeding-suppressive effect of DNF is found to be site specific; it is localized to the medial hypothalamic nuclei, including the ventromedial, suprachiasmatic and dorsomedial nuclei as well as the PVN. Serotonin in these nuclei may function to produce satiety specific for carbohydrate and, through the suprachiasmatic nucleus, control energy intake in a circadian-related manner.     

Effects of neuropeptide Y deficiency on hypothalamic agouti-related protein expression and responsiveness to melanocortin analogues

Central administration of neuropeptide Y (NPY) potently induces feeding and its abundance in the hypothalamus increases when energy stores fall. Consequently, NPY is considered to be a physiological effector of feeding behavior. Surprisingly, NPY-deficient (NPY-/-) mice feed and grow normally with ad libitum access to food and manifest a normal hyperphagic response after fasting, suggesting that other feeding effectors may compensate for the lack of NPY. Agouti-related protein (AgRP), a melanocortin receptor antagonist, can also stimulate feeding behavior when administered centrally and is coexpressed in a majority of hypothalmamic NPY-ergic neurons, making AgRP a candidate compensatory factor. To test this possibility, we evaluated AgRP mRNA and protein expression, as well as responsiveness to centrally administered AgRP in NPY-/- mice. These studies demonstrate that hypothalamic AgRP mRNA and immunoreactivity are upregulated with fasting and that these increases are not affected by NPY deficiency. Interestingly, NPY-/- mice are hypersensitive to central administration of AgRP(83-132), yet exhibit a normal response to centrally administered MTII, a melanocortin receptor agonist. These data suggest that if AgRP compensates for the lack of NPY in NPY-/- mice, it is not at the level of AgRP synthesis and may instead involve alterations in the postsynaptic signaling efficacy of AgRP. Moreover, the effects of AgRP are not limited to its actions at the melanocortin-4 receptor (MC4R), because MC4R-deficient (MC4R-/-) mice manifest a significant response to centrally administered AgRP. These data imply that AgRP has additional targets in the hypothalamus.     

Feeding and drinking elicited by central injection of neuropeptide Y: Evidence for a hypothalamic site(s) of action

Neuropeptide Y (NPY), which exists in very high concentrations in the brain, has been shown to elicit a powerful feeding response and a small drinking response in satiated rats. In order to delineate the brain sites sensitive to these effects, NPY was injected through chronic guide cannulas into seven different brain regions, and the food and water intake of satiated rats was measured one hr postinjection. Injection of NPY (78 pmoles) into hypothalamic areas, namely the paraventricular nucleus (PVN), ventromedial hypothalamus (VMH), and lateral hypothalamus (LH), elicited a strong feeding response; in contrast, injections into extra-hypothalamic areas, namely the amygdala, thalamus, and periaqueductal gray, were completely ineffective. Administration of NPY into the PVN and VMH also elicited a small drinking response; however, all other areas, including the LH, were insensitive to this effect. The findings that NPY was effective in the hypothalamus, as opposed to sites anterior, posterior, lateral or dorsal to this structure, suggest a hypothalamic site(s) of action for this neuropeptide.     

The role of the melanocortin system and the melanocortin-4 receptor in ring dove (Streptopelia risoria) feeding behavior

The melanocortin-4 receptor (MC4-R) is an important mediator of the effects of two melanocortin system ligands, alpha melanocyte stimulating hormone (-MSH) and agouti-related peptide (AGRP), on feeding behavior and energy balance in mammals. Although an avian homologue of the mammalian MC4-R has recently been identified, there is little information on the role of this receptor and the melanocortin system in avian feeding and body weight regulation. In these studies, we measured changes in feeding behavior in ring doves (Streptopelia risoria) following intracerebroventricular (i.c.v.) injection of various melanocortin receptor agonists and antagonists. The selective MC4-R antagonist HS014 elevated food intake within 4 h at all three doses tested (0.02, 0.2, and 2 nmol). A 1 nmol dose of the endogenous antagonist AGRP also stimulated feeding but only after a post-injection interval of 10 h. Surprisingly, the MC3-R and MC4-R antagonist SHU9119 not only failed to stimulate food intake at the same doses as HS014, but actually inhibited food intake at 8 h after injection. Whether this was due to toxicity effects or differences in the pharmacology of avian and mammalian melanocortin receptors remains to be determined. Food-deprived doves showed a fourfold increase in the number of AGRP-immunoreactive cells in the tuberal region of the hypothalamus and 5 ng of the MC3-R and MC4-R agonist MTII significantly attenuated the amount of food consumed by food-deprived birds that were allowed to re-feed. These data support a role for the melanocortin system and the melanocortin-4 receptor in the ring dove feeding behavior.     

Neuropeptide Y immunoreactivity and corticotropin-releasing hormone mRNA level are increased in the hypothalamus of mouse bearing a human oral squamous cell carcinoma

We examined gene expression of corticotropin-releasing hormone and neuropeptide Y level in the hypothalamic paraventricular nucleus of mouse bearing a human oral squamous cell carcinoma. A cell line derived from a human oral squamous cell carcinoma was inoculated into the lower dorsal area of nude mice. Body weight, tumor size and daily food intake were recorded every morning. Mice were sacrificed for corticotropin-releasing hormone mRNA in situ hybridization and neuropeptide Y immunohistochemistry, when the tumor ratio reached to 11-13% of real body weight. The results were compared with the age-matching non-tumor controls injected with saline instead of carcinoma cell. Body weight gain was significantly reduced in tumor bearing mice, however, no compensatory hyperphagia was found, i.e. daily food intake of the tumor mice did not differ from the non-tumor mice. Both neuropeptide Y immunoreactivity and corticotropin-releasing hormone mRNA level were significantly increased in the hypothalamic paraventricular nucleus of tumor mice. These results suggest that a human oral squamous cell carcinoma may induce anorexia, at least partly, via increasing the hypothalamic expression of corticotropin-releasing hormone in the tumor subjects. Additionally, neuropeptide Y-induced feeding appears to be inhibited in this tumor anorexia model, and this may correlate with increased expression of corticotropin-releasing hormone.     

Fos induction in selective hypothalamic neuroendocrine and medullary nuclei by intravenous injection of urocortin and corticotropin-releasing factor in rats

CRF and urocortin, administrated systemically, exert peripheral biological actions which may be mediated by brain pathways. We identified brain neuronal activation induced by intravenous (i.v.) injection of CRF and urocortin in conscious rats by monitoring Fos expression 60 min later. Both peptides (850 pmol/kg, i.v.) increased the number of Fos immunoreactive cells in the paraventricular nucleus of the hypothalamus, supraoptic nucleus, central amygdala, nucleus tractus solitarius and area postrema compared with vehicle injection. Urocortin induced a 4-fold increase in the number of Fos-positive cells in the supraoptic nucleus and a 3.4-fold increase in the lateral magnocellular part of the paraventricular nucleus compared with CRF. Urocortin also elicited Fos expression in the accessory hypothalamic neurosecretory nuclei, ependyma lining the ventricles and choroid plexus which was not observed after CRF. The intensity and pattern of the Fos response were dose-related (85, 255 and 850 pmol/kg, i.v.) and urocortin was more potent than CRF. Neither CRF nor urocortin induced Fos expression in the lateral septal nucleus, Edinger-Westphal nucleus, dorsal raphe nucleus, locus coeruleus, or hypoglossal nucleus. These results show that urocortin, and less potently CRF, injected into the circulation at picomolar doses activate selective brain nuclei involved in the modulation of autonomic/endocrine function; in addition, urocortin induces a distinct activation of hypothalamic neuroendocrine neurons.     

Paraventricular nucleus lesions exaggerate dietary obesity but block photoperiod-induced weight gains and suspension of estrous cyclicity in Syrian hamsters

Lesions of the paraventricular nucleus (PVN) of the hypothalamus block short photoperiod-induced testicular regression in Syrian hamsters. We examined the effects of PVN or sham lesions on the short photoperiod-induced increases in body weight and adiposity in female Syrian hamsters. PVN lesions did not affect body weight when hamsters were housed in a long photoperiod (LD, 16:8) and fed Purina laboratory rodent chow (No. 5001). However, when fed a high-fat diet both groups gained weight, and the hamsters with PVN lesions gained approximately twice as much as the sham-operated controls. When the hamsters were exposed to a short photoperiod (LD, 8:16), only the hamsters with sham lesions displayed the typical increase in body weight. No further increase in body weight or parametrial fat pad weight was seen when the hamsters with PVN lesions were exposed to the short photoperiod. The lack of a short photoperiod-induced increase in body weight gain in hamsters with PVN lesions seems unlikely to be due to a "ceiling effect" on body weight gain because we have routinely observed neurally intact, melatonin-treated female Syrian hamsters with body weight in excess of 250 g. Finally, the short photoperiod interrupted estrous cyclicity in sham-lesioned hamsters but not in those with PVN lesions. Thus, PVN lesions exaggerate dietary obesity but prevent short photoperiod-induced weight gains and vaginal acyclicity in female Syrian hamsters.     

Intracerebroventricular injection of dibutyryl cyclic adenosine 3′,5′-monophosphate increases hypothalamic levels of neuropeptide Y

This investigation examined in vivo the relationship between the nucleotide cAMP and hypothalamic levels of two peptides, neuropeptide Y (NPY) and galanin (GAL), which are known to potentiate feeding behavior. In brain-cannulated rats, third ventricular injections of N⁶,2′-O-dibutyryl cyclic adenosine 3′,5′-monophosphate ((Bu)₂cAMP, 25 μg), compared to saline, caused a significant increase in NPY levels in the arcuate nucleus (ARC) and medial parvocellular portion of the paraventricular nucleus (mPVN), while having no impact in other hypothalamic areas. These site-specific changes in NPY occurred in the absence of any alteration in circulating levels of insulin, corticosterone, aldosterone or glucose, or of changes in hypothalamic levels of GAL. These findings implicate cAMP as having regulatory functions within specific hypothalamic NPY-synthesizing neurons, projecting from the ARC to the mPVN, that are believed to be involved in energy homeostasis.     

Regulation of the hypothalamic pituitary adrenal axis during chronic stress: responses to repeated intraperitoneal hypertonic saline injection

Chronic osmotic stress inhibits, while repeated physical stress can increase pituitary ACTH responsiveness to a novel stress. The interaction between these effects was studied in rats subjected to repeated i.p. injection of hypertonic saline, a strong aversive stimulus with osmotic and painful and psychological stress components, for 14 days. Hypertonic saline injection caused marked drinking responses, transient increases in plasma vasopressin (VP), and marked increases in VP mRNA and irVP in magnocellular cell bodies in the hypothalamus. Parvicellular activity was also enhanced as indicated by increases in VP immunostaining in the external zone of the median eminence and CRH mRNA and irCRH in the PVN. Plasma ACTH levels increased 10-fold after 30 min hypertonic saline injection, returning to basal levels in 4 h, and there was no desensitization of the ACTH responses after repeated injections (from basal values of 76 ± 10to782 ± 57, 788 ± 83and779 ±31pg/ml30 min after the first, 4th and 14th injection, respectively). Basal ACTH levels were normal 24 h after the last injection, but pituitary POMC mRNA levels were increased by 95%, and ACTH responses to a novel stress (15 min immobilization) were significantly larger than in controls (P < 0.01) despite increases in morning plasma corticosterone levels (1.5 ± 0.4and9.2 ± 3.1μg/dl) in controls and stressed rats, respectively). Enhancing the osmotic component of the stress by daily withdrawal of the drinking water for 8 h following the injection, or by administration of 0.9% saline as drinking fluid, did not prevent the increases in CRH mRNA and hypersensitivity of the ACTH response to the novel stress. The data show that physical and psychological components of the stress overcome the inhibitory effect of chronic osmotic stimulation on ACTH secretion, and emphasizes the relationship between parvicellular activation and HPA hypersensitivity during chronic stress.     

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.     

The effects of serotonin1A receptor on female mice body weight and food intake are associated with the differential expression of hypothalamic neuropeptides and the GABAA receptor

Both common eating disorders anorexia nervosa and bulimia nervosa are characteristically diseases of women. To characterize the role of the 5-HT_1A receptor (5-HT_1A-R) in these eating disorders in females, we investigated the effect of saline or 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) treatment on feeding behavior and body weight in adult WT female mice and in adult 5-HT_1A-R knockout (KO) female mice. Our results showed that KO female mice have lower food intake and body weight than WT female mice. Administration of 8-OH-DPAT decreased food intake but not body weight in WT female mice. Furthermore, qRT-PCR was employed to analyze the expression levels of neuropeptides, γ-aminobutyric acid A receptor subunit β (GABA_A β subunits) and glutamic acid decarboxylase in the hypothalamic area. The results showed the difference in food intake between WT and KO mice was accompanied by differential expression of POMC, CART and GABA_A β2, and the difference in body weight between WT and KO mice was associated with significantly different expression levels of CART and GABA_A β2. As such, our data provide new insight into the role of 5-HT_1A-R in both feeding behavior and the associated expression of neuropeptides and the GABA_A receptor.     

Mapping of hypothalamic sites involved in the effects of NPY on body temperature and food intake

The objective of the present study was to identify hypothalamic sites that might be implicated in the effects of neuropeptide Y (NPY) on both body temperature and food intake. For this purpose, the effects of direct microinjections of NPY in several doses (0.156–20 μg) into discrete hypothalamic nuclei on body temperature were examined in rats. To examine specificity of effects, food consumption of animals following injections was also measured. Results indicate that the influence of NPY on body temperature varies with the hypothalamic region where the peptide is administered. NPY had no effect on temperature after administration into the ventromedial (VMH) and the perifornical hypothalamus (PeF). However, a significant hypothermia was seen following administration into the preoptic (POA) and arcuate nucleus (Arc), and hyperthermia was seen after injection into the paraventricular nucleus (PVN). Finally, a biphasic effect was observed after injection into the lateral hypothalamus (LH): hyperthermia with relatively small doses and hypothermia with higher doses. Similar effects were obtained when administred into the third ventricle (3V) but in an inverted dose-related fashion: hypothermia at low and hyperthermia at higher doses. For feeding, NPY consistently increased food intake in all regions examined, with the strongest effect obtained after administration into the PeF. The present results clearly dissociate the effects of NPY on food intake and body temperature, and demonstrate that these effects are related to specific hypothalamic nuclei.