Infusion of the 5-hydroxytryptamine agonists RU24969 and TFMPP into the paraventricular nucleus of the hypothalamus causes hypophagia

Abstract

The 5-HT_1B agonist RU24969 when given either systemically (1 mg/kg SC) or by infusion (0.5, 1.0, 2.0 μg) into the region of the paraventricular nucleus of the hypothalamus caused dose-dependent hypophagia in rats previously deprived of food for 18 h. Similar results were obtained at the above dosages of 1-[3-(trifluoromethyl) phenyl] piperazine (TFMPP), which acts on 5-HT_1B and possibly also on 5-HT_1C receptors. Neither drug significantly affected locomotion following central administration. Food intake was significantly decreased when the 5-HT_1A agonist 8-OH-DPAT was given systemically (1 mg/kg SC) to rats previously deprived of food but was unaffected when 8-OH-DPAT (1 μg) was infused into the paraventricular nucleus of both food-deprived and free feeding rats. Therefore, hypophagia occurs when hypothalamic 5-HT_1B (and possibly 5-HT_1C) but not 5-HT_1A receptors are activated.