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Leptin and Neuropeptide Y Have Opposing Modulatory Effects on Nucleus of the Solitary Tract Neurophysiological Responses to Gastric Loads: Implications for the Control of Food Intake

Bourne Behavioral Research Laboratory, Department of Psychiatry, WMC Cornell University (G.J.S.), White Plains, New York 10605; and Department of Psychiatry and Behavioral Sciences, The Johns Hopkins University School of Medicine (T.H.M.), Baltimore, Maryland 21205

Address all correspondence and requests for reprints to: Gary J. Schwartz, Ph.D., Bourne Behavioral Research Laboratory, WMC Cornell University, 21 Bloomingdale Road, White Plains, New York 10605. E-mail: gjs2001{at}med.cornell.edu.

Leptin is an adiposity hormone that modulates the activity of multiple hypothalamic signaling pathways involved in the control of food intake. The present experiments were designed to evaluate whether central administration of leptin or one of its downstream mediators, neuropeptide Y (NPY), could affect food intake by modulating the brain stem neurophysiological response to ascending meal-related feedback signals in the nucleus of the solitary tract (NTS) in anesthetized male Long-Evans rats. NTS neurons at the rostrocaudal level of the area postrema were dose-dependently activated by gastric loads ranging from 2–10 ml, and leptin and NPY had opposite modulatory effects on this load volume/activity relationship: leptin significantly increased NTS responses to gastric loads, whereas NPY reduced the potency and efficacy with which gastric loads activated NTS neurons. These effects were probably not mediated by peripheral effects of centrally administered peptides or by the gastrokinetic effects of central NPY or leptin, because the dose-response relationship between gastric load volume and neurophysiological firing rate was unchanged in gastric load-sensitive vagal afferent fibers. These data suggest a mechanistic framework for considering how feeding behavior occurring in meals is altered by challenges to energy homeostasis, such as fasting and overfeeding.