title: Electrophysiological actions of peripheral hormones on melanocortin neurons.
abstract: Neurons of the arcuate nucleus of the hypothalamus (ARH) appear to be sites of convergence of central and peripheral signals of energy stores, and profoundly modulate the activity of the melanocortin circuits, providing a strong rationale for pursuing these circuits as therapeutic targets for disorders of energy homeostasis. Recently, tremendous advances have been made in identifying genes and pathways important to regulating energy homeostasis, particularly the hormone leptin and its receptor. This hormone/receptor pair is expressed at high levels in the so-called satiety centers in the hypothalamus, and at lower levels elsewhere in the body. Recent studies in our lab and those of our collaborators have shown that leptin modulates different populations of hypothalamic cells in different ways, rapidly activating POMC neurons and inhibiting NPY/AgRP neurons. In this report, we outline an integrated model of leptin's action in the arcuate nucleus of the hypothalamus, derived from our electrophysiological studies of brain slice preparations taken from transgenic mice that have been bred to express a variety of fluorescent proteins in specific cell types. We also discuss the recently withdrawn obesity drug fenfluramine, which appears to act on POMC neurons via the serotonin 2C receptor. Nutrient-sensing serotonin neurons may project from the raphe nuclei in the brainstem to the hypothalamus; within the arcuate nucleus, serotonin signals are integrated with others such as leptin, ghrelin, and peptide YY(3-36) from the gut, to produce a coordinated response to nutrient state. Finally, we review the current inquiries into the ability of the hormone ghrelin to stimulate appetite by its action of NPY neurons and inhibition of POMC neurons.
authors.affiliation: Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Sciences University, Beaverton, Oregon 97006, USA. cowleym@ohsu.edu
authors.forename: Michael A
authors.initials: MA
authors.lastname: Cowley
authors.forename: Roger  D
authors.initials: R
authors.lastname: Cone
authors.forename: Pablo
authors.initials: P
authors.lastname: Enriori
authors.forename: Ingrid
authors.initials: I
authors.lastname: Louiselle
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Williams
authors.forename: Anne E
authors.initials: AE
authors.lastname: Evans
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology / Q000378:metabolism; D004594:Electrophysiology; D004734:Energy Metabolism / Q000502:physiology; D005277:Fenfluramine / Q000378:metabolism; D054439:Ghrelin; D006706:Homeostasis; D006801:Humans; D020738:Leptin / Q000378:metabolism*; D008954:Models, Biological; D009474:Neurons / Q000378:metabolism*; D009478:Neuropeptide Y / Q000378:metabolism*; D036361:Peptide Hormones / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism; D018490:Serotonin Agents / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D054439:Ghrelin; D020738:Leptin; D009478:Neuropeptide Y; D036361:Peptide Hormones; D018490:Serotonin Agents; D005277:Fenfluramine; D012701:Serotonin; D005680:gamma-Aminobutyric Acid; D011333:Pro-Opiomelanocortin