Feeding effects of melanocortin ligands--a historical perspective

Extrahypothalamic Control of Energy Balance and Its Connection with Reproduction: Roles of the Amygdala

Body energy and metabolic homeostasis are exquisitely controlled by multiple, often overlapping regulatory mechanisms, which permit the tight adjustment between fuel reserves, internal needs, and environmental (e.g., nutritional) conditions. As such, this function is sensitive to and closely connected with other relevant bodily systems, including reproduction and gonadal function. The aim of this mini-review article is to summarize the most salient experimental data supporting a role of the amygdala as a key brain region for emotional learning and behavior, including reward processing, in the physiological control of feeding and energy balance. In particular, a major focus will be placed on the putative interplay between reproductive signals and amygdala pathways, as it pertains to the control of metabolism, as complementary, extrahypothalamic circuit for the integral control of energy balance and gonadal function.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Malnourishment during early lactation disrupts the ontogenetic distribution of the CART and α-MSH anorexigenic molecules in the arcuate/paraventricular pathway and lateral hypothalamus in male rats

Developmental malnourishment impacts the energetic metabolism control throughout life. In rat offspring, a 0% protein diet during the first 10 days of lactation results in leptin resistance and in alterations in: feeding behavior, serum leptin and neuropeptide Y (NPY) levels in the hypothalamic arcuate nucleus (ARC)/paraventricular (PVN) pathway. Here, the distributions of alpha-melanocyte stimulating hormone (α-MSH) and cocaine and amphetamine regulated transcript (CART), anorexigenic molecules, were immunohistochemically assessed in the ARC, PVN and lateral hypothalamus (LH) nuclei. Rat dams were subjected to one of the following diet protocols from postnatal day (P) 1-10: 1) Protein-free (PFG, 0% protein chow); 2) Pair-fed (UFG, normoprotein chow); 3) Control group (CG, normoprotein chow). PFG, UFG and CG male offspring were analyzed at different time points, from P5 to P180. In the ARC, PFG α-MSH and CART were increased from P10 to P45 when compared to CG and UFG. In the PVN, α-MSH and CART peaks in PFG animals were delayed from P20 to P30 when compared to CG. In the LH, CART was more intense in PFG animals than in UFG and CG ones by P20, and, by P30, UFG immunostaining became less intense than in CG. In conclusion, aproteic diet altered the ontogenetic distribution of both anorexigenic molecules. In the PVN, the peak was delayed to P30, which coincides with the leptin peak and follows the previously described NPY (orexigenic) peak in this model. The permanent LH CART and α-MSH increase may be associated with the previously observed PFG hypophagia.

Melanocortin Regulation of Inflammation

Adrenocorticotropic hormone (ACTH), and α-, β-, and γ-melanocyte-stimulating hormones (α-, β-, γ-MSH), collectively known as melanocortins, together with their receptors (melanocortin receptors), are components of an ancient modulatory system. The clinical use of ACTH in the treatment of rheumatoid arthritis started in 1949, originally thought that the anti-inflammatory action was through hypothalamus-pituitary-adrenal axis and glucocorticoid-dependent. Subsequent decades have witnessed extensive attempts in unraveling the physiology and pharmacology of the melanocortin system. It is now known that ACTH, together with α-, β-, and γ-MSHs, also possess glucocorticoid-independent anti-inflammatory and immunomodulatory effects by activating the melanocortin receptors expressed in the brain or peripheral immune cells. This review will briefly introduce the melanocortin system and highlight the action of melanocortins in the regulation of immune functions from in vitro, in vivo, preclinical, and clinical studies. The potential therapeutic use of melanocortins are also summarized.

The therapeutic journey of benzimidazoles: a review

Presence of benzimidazole nucleus in numerous categories of therapeutic agents such as antimicrobials, antivirals, antiparasites, anticancer, anti-inflammatory, antioxidants, proton pump inhibitors, antihypertensives, anticoagulants, immunomodulators, hormone modulators, CNS stimulants as well as depressants, lipid level modulators, antidiabetics, etc. has made it an indispensable anchor for development of new therapeutic agents. Varied substitutents around the benzimidazole nucleus have provided a wide spectrum of biological activities. Importance of this nucleus in some activities like, Angiotensin I (AT(1)) receptor antagonism and proton-pump inhibition is reviewed separately in literature. Even some very short reviews on biological importance of this nucleus are also known in literature. However, owing to fast development of new drugs possessing benzimidazole nucleus many research reports are generated in short span of time. So, there is a need to couple the latest information with the earlier information to understand the current status of benzimidazole nucleus in medicinal chemistry research. In the present review, various derivatives of benzimidazole with different pharmacological activities are described on the basis of substitution pattern around the nucleus with an aim to help medicinal chemists for developing an SAR on benzimidazole derived compounds for each activity. This discussion will further help in the development of novel benzimidazole compounds.

Control of food intake by MC4-R signaling in the lateral hypothalamus, nucleus accumbens shell and ventral tegmental area: interactions with ethanol

The melanocortin system is involved in animal models of obesity and anorexia-cachexia and MC4 receptors (MC4-R) are currently a target system for the development of drugs aimed to treat obesity and eating disorders in humans. Previous evidence suggest that feeding peptides might lack their orexigenic activity while stimulate ethanol intake. The present study comparatively evaluated food intake (4-h interval) in Sprague-Dawley (SD) rats drinking ethanol (6% w/v, 2 bottle choice paradigm) (EE group) and ethanol-naïve (EN) rats in response to bilateral infusion of the selective MC4-R antagonist HS014 (0, 0.02 or 0.05 μg/0.5 μl/site) or the selective MC4-R agonist cyclo(NH-CH(2)-CH(2)-CO-His-d-Phe-Arg-Trp-Glu)-NH(2) (0, 0.75 or 1.5 μg/0.5 μl/site), into the lateral hypothalamus (LH), the nucleus accumbens (NAc), or the ventral tegmental area (VTA). The main findings in the study are: (1) LH-infusions of the MC4-R antagonist increased and the agonist reduced feeding and total calories consumed, while ethanol intake remained unaltered. (2) NAc- and VTA-infusions of the selective agonist reduced food, ethanol and total calories intake. (3) NAc- and VTA-infusions of the MC4-R antagonist increased feeding in EN rats, but not in EE animals which showed a mild increase in ethanol intake, while total calories consumed remained unaltered. Present data show that having ethanol available reduces feeding elicited by NAc and VTA-MC4-R blockade. Additionally, while MC4-R signaling in the LH appears to modulate homeostatic aspects of feeding, it may contribute to non-homeostatic aspects of ingestive behaviors in the VTA and the NAc.

Feeding and the rhodopsin family g-protein coupled receptors in nematodes and arthropods

In vertebrates, receptors of the rhodopsin G-protein coupled superfamily (GPCRs) play an important role in the regulation of feeding and energy homeostasis and are activated by peptide hormones produced in the brain-gut axis. These peptides regulate appetite and energy expenditure by promoting or inhibiting food intake. Sequence and function homologs of human GPCRs involved in feeding exist in the nematode roundworm, Caenorhabditis elegans (C. elegans), and the arthropod fruit fly, Drosophila melanogaster (D. melanogaster), suggesting that the mechanisms that regulate food intake emerged early and have been conserved during metazoan radiation. Nematodes and arthropods are the most diverse and successful animal phyla on Earth. They can survive in a vast diversity of environments and have acquired distinct life styles and feeding strategies. The aim of the present review is to investigate if this diversity has affected the evolution of invertebrate GPCRs. Homologs of the C. elegans and D. melanogaster rhodopsin receptors were characterized in the genome of other nematodes and arthropods and receptor evolution compared. With the exception of bombesin receptors (BBR) that are absent from nematodes, a similar gene complement was found. In arthropods, rhodopsin GPCR evolution is characterized by species-specific gene duplications and deletions and in nematodes by gene expansions in species with a free-living stage and gene deletions in representatives of obligate parasitic taxa. Based upon variation in GPCR gene number and potentially divergent functions within phyla we hypothesize that life style and feeding diversity practiced by nematodes and arthropods was one factor that contributed to rhodopsin GPCR gene evolution. Understanding how the regulation of food intake has evolved in invertebrates will contribute to the development of novel drugs to control nematodes and arthropods and the pests and diseases that use them as vectors.

Nr4a1 siRNA expression attenuates α-MSH regulated gene expression in 3T3-L1 adipocytes

Several recent investigations have underscored the growing role of melanocortin signaling in the peripheral regulation of lipid, glucose, and energy homeostasis. In addition, the melanocortins play a critical role in the central control of satiety. These observations, and the latest reports highlighting the emerging role of the nuclear hormone receptor (NR) 4A subgroup in metabolism, have prompted us to investigate the cross talk between [Nle(4), d-Phe(7)] (NDP)-α-MSH and Nr4a signaling in adipose. We have shown that NDP-MSH strikingly and preferentially induces the expression of the NR4A subgroup (but not any other members of the NR superfamily) in differentiated 3T3-L1 adipocytes. Utilization of quantitative PCR on custom-designed metabolic TaqMan low-density arrays identified the concomitant and marked induction of the mRNAs encoding Il-6, Cox2, Pdk4, and Pck-1 after NDP-MSH treatment. Similar experiments demonstrated that the mRNA expression profile induced by cAMP and NDP-MSH treatment displayed unique but also overlapping properties and suggested that melanocortin-mediated induction of gene expression involves cAMP-dependent and -independent signaling. Nr4a1/Nur77 small interfering RNA (siRNA) expression suppressed NDP-MSH-mediated induction of Nr4a1/Nur77 and Nr4a3/Nor-1 (but not Nr4a2/Nurr1). Moreover, expression of the siRNA-attenuated NDP-MSH mediated induction of the mRNAs encoding Il-6, Cox2/Ptgs2, and Pck-1 expression. In addition, Nur77 siRNA expression attenuated NDP-MSH-mediated glucose uptake. In vivo, ip administration of NDP-MSH to C57 BL/6J (male) mice significantly induced the expression of the mRNA encoding Nur77 and increased IL-6, Cox2, Pck1, and Pdk4 mRNA expression in (inguinal) adipose tissue. We conclude that Nur77 expression is necessary for MSH-mediated induction of gene expression in differentiated adipocytes. Furthermore, this study demonstrates cross talk between MSH and Nr4a signaling in adipocytes.

Central mechanisms controlling appetite and food intake in a cancer setting: an update

PURPOSE OF REVIEW

Cachexia, also known as disease-associated wasting, is an important factor in the mortality of many patients with diseases such as cancer, as well as renal and congestive heart failure. Yet the syndrome is not yet well defined, making diagnosis difficult and often subjective on the part of the physician. Nor are the central mechanisms of cachexia fully elucidated. Recent studies have begun to address these gaps by focusing on three areas: the role of cytokines in cachexia, other proteins and peptides that might be involved, and potential treatments for this devastating syndrome.

RECENT FINDINGS

Cachexia can be caused, in the absence of disease, by inflammatory stimuli and some chemotherapy drugs, suggesting possible central mechanisms in cachexia. Promising treatments include melanocortin antagonism and some hormones.

SUMMARY

While more research is necessary to illuminate causal mechanisms and uncover potential therapies of cachexia, several of its major molecular pathways have become elucidated, suggesting directions for therapeutic approaches.

Neuropeptide Y and alpha-melanocyte-stimulating hormone: interaction in obesity and possible role in the development of hypertension

AIM

Obesity and hypertension frequently coexist and both represent important risk factors for cardiovascular disease. The mechanisms implicated in the regulation of food intake have not been completely elucidated. Recent data suggests that peripheral and central neuropeptides play an important role in the maintenance of energy balance. More specifically, leptin, neuropeptide Y (NPY) and alpha-melanocyte-stimulating hormone (a-MSH) appear to be implicated in the pathogenesis of obesity and also contribute to the development of hypertension in obesity.

METHODS

Analysis of the pertinent bibliography published in PubMed database.

RESULTS

Leptin is produced in the adipose tissue directly correlated with fat tissue mass. Leptin acts on two distinct neural populations in the hypothalamus: the first expresses the orexigenic peptides NPY and agouti-related protein (AgRP), the second pro-opiomelanocortin (POMC). The activation of POMC neurons increases the production of the anorexigenic hormone a-MSH and inhibits the release of NPY and AgRP. In addition, the hypothalamus integrates the neuroendocrine systems with the autonomic nervous system and controls the activity of the latter. Stimulation of hypothalamic nuclei elicits sympathetic responses including blood pressure elevation. Both NPY and a-MSH appears to be implicated in the hypothalamic regulation of sympathetic nervous system (SNS) activity.

CONCLUSION

Alterations in leptin, NPY and a-MSH are frequently observed in obesity and might stimulate SNS activity, contributing to the development of hypertension in obese patients. These neuropeptides might provide a pathophysiologic link between excess weight and hypertension. However, more research is needed before the pharmacologic manipulation of these complex neuroendocrine systems can be applied in the treatment of obesity and hypertension.

Identification of a novel series of benzimidazoles as potent and selective antagonists of the human melanocortin-4 receptor

A novel series of benzimidazoles was identified and optimized, leading to the discovery of potent and selective antagonists of the human melanocortin-4 receptor. In addition, compound 5i was shown to cross the blood-brain barrier after intravenous dosing in rats.

Effects of pro-opiomelanocortin (POMC) on food intake and body weight: mechanisms and therapeutic potential?

POMC (pro-opiomelanocortin) is a complex polypeptide precursor which is cleaved into smaller biologically active peptides such as the melanocortins, α-, β- and γ-melanocyte-stimulating hormone. Data from human genetic and murine studies convincingly show that an intact central melanocortin signalling pathway is critical for normal energy homoeostasis. Not only does a loss of normal melanocortin signalling lead to obesity, but there are also data implicating increased melanocortin activity in the pathogenesis of cachexia. The study of POMC biology has lead to some fundamental insights into the mechanisms controlling food intake and body weight. This increased understanding of the physiological roles of the melanocortin system has opened up the potential for the design and development of rational therapies to treat perturbations in energy homoeostasis.

Evidence for increased neuropeptide Y synthesis in mediobasal hypothalamus in relation to parental hyperphagia and gonadal activation in breeding ring doves

Like lactating mammals, male and female ring dove parents increase their food consumption to meet the energetic challenges of provisioning their young. To clarify the neurochemical mechanisms involved, the present study investigated the relationship between parental hyperphagia and changes in activity of the potent orexigen neuropeptide Y (NPY) in the hypothalamus of breeding doves. Changes in NPY-immunoreactive (NPY-ir) cell numbers in the tuberal hypothalamus of male and female doves were examined by immunocytochemistry at six stages of the breeding cycle. Parallel NPY mRNA measurements were recorded in mediobasal hypothalamus (which includes the tuberal hypothalamus) by semiquantitative reverse transcription-polymerase chain reaction using 18S rRNA as the internal standard. NPY mRNA changes were also measured in the mediobasal hypothalamus of nonbreeding doves following intracranial administration of prolactin, an orexigenic hormone that is elevated in the plasma of parent doves, and in response to food deprivation, which mimics the negative energy state that develops in parents as they provision their growing young. NPY-ir cell numbers in the tuberal hypothalamus and NPY mRNA levels in the mediobasal hypothalamus were significantly higher in breeding males and females during the period of parental hyperphagia after hatching than during the late incubation period when food intake remains unchanged. In nonbreeding doves, food deprivation and prolactin treatment increased NPY mRNA in this region by two- to three-fold, which suggests that NPY expression is sensitive to hormonal and metabolic signals associated with parenting. We conclude that NPY synthesis is increased in the mediobasal hypothalamus during the posthatching period, which presumably supports increased NPY release and resulting parental hyperphagia. NPY-ir and mRNA were also high in the mediobasal hypothalamus prior to egg laying when food intake remained unchanged. Several lines of evidence suggest that this elevation in NPY supports the increased gonadal activity that accompanies intense courtship and nest building interactions in breeding doves.

New melanocortin 1 receptor binding motif based on the C-terminal sequence of alpha-melanocyte-stimulating hormone

The C-terminal tripeptide of the alpha-melanocyte stimulating hormone (alpha-MSH11-13) possesses strong antiinflammatory activity without known cellular target. In order to better understand the structural requirements for function of such motif, we designed, synthesized and tested out Trp- and Tyr-containing analogues of the alpha-MSH11-13. Seven alpha-MSH11-13 analogues were synthesized and characterized for their binding to the melanocortin receptors recombinantly expressed in insect (Sf9) cells, infected with baculovirus carrying corresponding MC receptor DNA. We also tested these analogues on B16-F1 mouse melanoma cells endogenously expressing the MC1 receptor for binding and for ability to increase cAMP levels as well as on COS-7 cells transfected with the human MC receptors. The data indicate that HS401 (Ac-Tyr-Lys-Pro-Val-NH2) and HS402 (Ac-Lys-Pro-Val-Tyr-NH2) selectively bound to the MC1 receptor and stimulated cAMP generation in a concentration dependent way while the other Tyr- and Trp-containing alpha-MSH11-13 analogues neither bound to MC receptors nor stimulated cAMP. We have thus identified new MC receptor binding motif derived from the C-terminal sequence of alpha-MSH. The tetrapeptides have novel properties as the both act via MC-ergic pathways and also carry the anti-inflammatory alpha-MSH11-13 message sequence.

Low abundance of NPY in the hypothalamus can produce hyperphagia and obesity

States of increased metabolic demand are associated with up-regulation of NPY and hyperphagia. However, we present some instances of hyperphagia in which NPY is not up-regulated. Ablation or functional disruption of specific sites in the hypothalamus, such as the ventromedial or paraventricular nuclei, or transection of inputs to the hypothalamus from the hindbrain results in hyperphagia and excess body weight gain. However, NPY expression and concentration in these experimental models is either decreased or unchanged. While there is no up-regulation of NPY in these models, there is increased sensitivity to the orexigenic effects of NPY. This enhanced responsiveness to NPY may more than compensate for the reduced levels of NPY and result in hyperphagia and excess body weight gain. The hyper-responsiveness may be due either to an increase in NPY receptors or to other changes in target cells and response pathways that may result from the treatments used in these models.

Increased hypothalamic protein tyrosine phosphatase 1B contributes to leptin resistance with age

Animals at advanced ages exhibit a reduction in central leptin sensitivity. However, changes in growth, metabolism, and obesity risk occur much earlier in life, particularly during the transition from youth to middle age. To determine when initial decreases in central leptin sensitivity occur, leptin-dependent suppression of food intake was tested in 8-, 12-, and 20-wk-old male, chow-fed Sprague Dawley rats. Intracerebroventricular leptin injection (3 microg) suppressed 24-h food intake in 8- and 12-wk-old rats (P < 0.05) but not 20-wk-old rats. To identify potential cellular mediators of this resistance, we focused on protein tyrosine phosphatase 1B (PTP1B), a recently described inhibitor of leptin signaling. PTP1B protein levels, as determined by Western blot, were significantly higher in mediobasal hypothalamic punches collected from 20-wk-old rats, compared with 8-wk-old rats (P < 0.05). When 20-wk-old rats were fasted for 24 h, levels of hypothalamic PTP1B decreased (P < 0.05), coincident with a restoration of leptin sensitivity. To directly test whether inhibition of PTP1B restores leptin sensitivity, 20-wk-old chow-fed rats were pretreated with a pharmacological PTP1B inhibitor 1 h before leptin, and 24-h food intake was recorded. As expected, leptin alone produced a small but nonsignificant reduction in food intake. However, pretreatment with the PTP1B inhibitor resulted in a marked improvement in leptin-dependent suppression of food intake (P < 0.05). These data are consistent with the hypothesis that increases in PTP1B contribute to hypothalamic leptin resistance as rats transition into middle age.

Preference for palatable food is reduced by the gamma-hydroxybutyrate analogue GET73, in rats

Palatability and variety of foods are major reasons for "hedonic" eating, and hence for overeating and obesity. Palatable food and drugs of abuse share a common reward mechanism, and compounds that block the reinforcing effect of drugs of abuse preferentially suppress the intake of palatable foods. This research was aimed at studying the influence of the gamma-hydroxybutyrate analogue N-(4-trifluoromethylbenzyl)-4-methoxybutanamide (GET73) - that inhibits alcohol consumption - on consumption and reinforcing effect of palatable food. Adult male rats were used. For place preference conditioning, sweetened corn flakes were used as the reinforcer, and GET73 (50, 100 and 200mgkg(-1)) or vehicle were orally (p.o.) administered either 30min before each training session and the test session, or only before the test session. To study the influence on consumption, GET73 was given p.o. at the same doses once daily for 12 days to rats given free access to both palatable and varied food (cafeteria diet) or to standard chow. Both acquisition and expression of palatable food-induced conditioned place preference were inhibited by GET73, either administered throughout the conditioning period or only before the test session. GET73 reduced also the consumption of cafeteria food, while that of standard chow was increased. At these doses, GET73 had no detrimental effect on open-field behaviour. GET73 seems to specifically attenuate the gratification produced by varied and palatable food, without affecting the consumption of not particularly palatable chow. Since, overweight and obesity are mostly due to the overeating of palatable and varied foods, drugs like GET73 could represent a somewhat ideal and rational approach to obesity treatment.

A quantitative trait locus on chromosome 18q for physical activity and dietary intake in Hispanic children

OBJECTIVE

Genetic components of energy homeostasis contributing to childhood obesity are poorly understood. Genome scans were performed to identify chromosomal regions contributing to physical activity and dietary intake traits in Hispanic children participating in the VIVA LA FAMILIA Study.

RESEARCH METHODS AND PROCEDURES

We report linkage findings on chromosome 18 for physical activity and dietary intake in 1030 siblings from 319 Hispanic families. Measurements entailed physical activity by accelerometry, dietary intake by two 24-hour recalls, and genetic linkage analyses using SOLAR software.

RESULTS

Significant heritabilities were seen for physical activity and dietary intake, ranging from 0.46 to 0.69, except for vigorous activity (h2 = 0.18). Percentage time in sedentary activity mapped to markers D18S1102-D18S64 on chromosome 18 [logarithm of the odds (LOD) score = 4.07], where melanocortin 4 receptor gene (MC4R) resides. Quantitative trait loci (QTLs) for total activity counts, percentage time in light or in moderate activity, and carbohydrate intake and percentage of energy intake from carbohydrates were detected in the same region (LOD = 2.28, 2.79, 2.2, 1.84, and 1.51, respectively). A novel loss of function mutation in MC4R (G55V) was detected in six obese relatives, but not in the rest of the cohort. Removal of these MC4R-deficient subjects from the analysis reduced the LOD score for sedentary activity to 3.94.

DISCUSSION

Given its role in the regulation of food intake and energy expenditure, MC4R is a strong positional candidate gene for the QTL on chromosome 18 detected for physical activity and dietary intake in Hispanic children.

The hypothalamic paraventricular nucleus is not essential for orexigenic NPY or anorexigenic melanocortin action

Bilateral electrolytic lesions of the paraventricular nucleus of the hypothalamus (PVN) produce hyperphagia with excess weight gain. The orexigenic neuropeptide Y (NPY) system and the anorexigenic melanocortin system act in the PVN to regulate food intake, and participate in mediating the anorexic effects of leptin. We hypothesized that changes in the responsiveness of these systems may contribute to the hyperphagia observed in PVN-lesioned rats. Adult female Sprague-Dawley rats received either sham or electrolytic lesions in the PVN immediately followed by implantation of a guide cannula into the third cerebroventricle. Twenty-five days following surgery groups of sham and hyperphagic PVN-lesioned rats were injected intracerebroventricularly (i.c.v.) with either 118 pmole or 470 pmole of NPY and food intake was measured for 3 h. Food intake in response to NPY was nearly three-fold higher in PVN-lesioned rats as compared to sham rats. However, the response to 5 microg leptin i.c.v. was not different in lesioned versus sham rats. The effect of the melanocortin agonist MTII on food intake was tested in additional rats beginning either 7-14 days or 30-40 days following surgery. Doses of 0.1 nmole or 1.0 nmole of MTII were injected immediately before lights-off and food intake was measured at 2 h, 24 h and 48 h post-injection. Suppression of food intake in PVN-lesioned rats was not different from that in sham-lesioned rats. These data suggest that hyper-responsiveness to NPY may account in part for the hyperphagia observed in PVN-lesioned rats. Furthermore, based on the similarities of responses of PVN-lesioned and sham control rats to the anorexigenic agents MTII and leptin and the hypersensitivity of lesioned rats to NPY, we conclude that the PVN is not essential for NPY stimulation of food intake or for melanocortin suppression of food intake and that NPY and melanocortin receptors outside of the PVN are sufficient to produce these effects.