The Effect of Neuropeptide Y on Hypothalamic Serotonin Overflow

Intracerebroventricular injections of Neuropeptide Y stimulate orexigenic behaviors (food intake) in satiated animals. Several investigators have shown that the ventromedial, paraventricular, and other specific hypothalamic sites mediate the action of Neuropeptide Y to stimulate feeding. The present study used in vivo microdialysis to describe the time course of the changes in ventromedial hypothalamic serotonin and its metabolite, 5-hydroxy-3-indoleacetic acid subsequent to Neuropeptide Y administration in adult male Sprague-Dawley rats. Dialysates were collected before and after Neuropeptide Y injection using a 1 mm microdialysis probe placed in the ventromedial nucleus of the hypothalamus and were analyzed with High Performance Liquid Chromatography equipped with an ESA electrochemical detector. Two and half-hours after Neuropeptide Y injection, the perfusion fluid was changed so as to contain 10 μM of fluoxetine, a serotonin uptake inhibitor. Neuropeptide Y decreased extracellular serotonin concentration on average 30 to 50 percent from baseline. 5-hydroxy-3-indoleacetic acid overflow remained constant. Fluoxetine did not change the serotonin suppression. These observations suggest that Neuropeptide Y might be acting at the presynaptic terminal to prevent vesicular release of serotonin.