RESUMEN
The possible involvement of glutamatergic mechanisms in the control of food intake was studied in free-feeding and in 24-h food-deprived (FD24) pigeons for 1 h after intracerebroventricular (i.c.v.) treatment with glutamate (Glu, 0, 50, 150, 300, and 600 nmol). Glu injections dose dependently induced decreases (30-65%) in food intake (FI) and feeding duration (FD), and increases in latency to start feeding (LSF) in FD24 animals, but not in free-feeding ones. None of these treatments affected noningestive behaviors (locomotion, sleep, and preening). In FD24 pigeons, i.c.v. treatments with N-methyl-D-aspartic acid (NMDA, 0.1, 1, 4, 8, or 16 nmol) or D,L-alpha-amino-3-hydroxy-isoxazole proprionic acid (AMPA, 0.1, 1, 4, or 8 nmol) decreased FI and FD, but left LSF unchanged compared to vehicle-treated FD24 controls. Kainic acid (0.1, 0.5, and 1 nmol), or [trans-(1S,3R)-ACPD-(5NH4OH)] (ACPD, 0.1, 1, 4, 8, and 16 nmol) left unchanged the ingestive profile of FD24 pigeons. Pretreatment with the NMDA receptor antagonist MK-801 (15 nmol) and the AMPA-kainate receptor antagonist CNQX (390 nmol), 20 min before an i.c.v. injection of Glu (300 nmol) induced a partial blockade of the Glu-induced decreases in FI and FD and completely inhibited the Glu-induced increase in LSF in FD24 pigeons. I.c.v. injections of MK-801 (30 nmol) and of CNQX (780 nmol) increased FI and FD and reduced LSF in free-feeding pigeons. A lower dose of MK-801 (15 nmol) increased FI and FD, but not LSF. Conversely, a lower dose of CNQX (390 nmol) reduced LSF without changing FI or FD. These findings indicate the involvement of Glu as a chemical mediator in the regulation of food intake in the pigeon, possibly acting on multiple central mechanisms in this species through NMDA- and AMPA-sensitive Glu receptors.
Asunto(s)
Encéfalo/efectos de los fármacos , Ingestión de Alimentos/efectos de los fármacos , Ácido Glutámico/farmacología , Receptores AMPA/fisiología , Receptores de Glutamato/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , 6-Ciano 7-nitroquinoxalina 2,3-diona/farmacología , Animales , Columbidae , Relación Dosis-Respuesta a Droga , Inyecciones Intraventriculares , MasculinoRESUMEN
The effects of local injections of adrenaline (Adr, 6 nmol) or noradrenaline (Nor, 16 nmol) into the paraventricular nucleus (PVN) and into other anterior hypothalamic districts on feeding behavior were examined in satiated pigeons bearing a chronically implanted cannula. When infused into the PVN, both Adr and Nor reliably elicited feeding responses during the first hour after the injection. Feeding responses to Adr injections were significantly higher than those evoked by Nor. Other behavioral measurements (sleep, exploratory, and preening) were not affected by these treatments. Local pretreatment with phentolamine (20 nmol) but not with propranolol (20 nmol) abolished the feeding response induced by both Adr and Nor into the PVN. Lateral hypothalamic sites were also shown to respond to catecholamine injections with an increase in feeding, followed also by an increased sleep-like behavior duration. Together with other evidence, the present results indicate that adrenergically mediated circuits into the avian PVN play an important role in the mechanisms of food intake control, equivalent to that observed in mammalian species.