Feeding behavior after metergoline or GR-46611 injections into the paraventricular nucleus of the hypothalamus in the pigeon.
The present study examined changes in spontaneous behavior of free-feeding pigeons in response to local injections of metergoline (MET, an antagonist of 5-HT(1/2) receptors; 5, 10 and 20 nmol), GR-46611 (GR, a 5-HT(1B/1D) agonist; 0.6 and 6 nmol) or vehicle into the paraventricular hypothalamic nucleus (PVN). When infused into the PVN, MET and GR promptly and reliably elicited feeding at their higher doses, without affecting drinking or non-ingestive behaviors (locomotion, exploration, preening, sleep) during the first hour after injection. Both GR- and MET-evoked ingestive responses were associated only with an increase in feeding duration, with no changes in latency to start feeding. In a second series of experiments, the effective doses of MET (20 nmol) and GR (6 nmol) were injected into other diencephalic areas. This exploratory study revealed that intense feeding responses to both MET and GR local injections are also observed in the n. medialis hypothalami posterioris and in the adjacent n. lateralis hypothalami posterioris (PMH/PLH complex, in the caudoventral hypothalamus) and in the n. magnocellularis preopticus (PPM, in the caudal preoptic region). The behavioral profiles associated with these hyperphagic responses were nucleus-specific: in the PMH/PLH, MET-induced feeding was accompanied by an increase in total feeding duration and by a reduction in the latency to start feeding, while ingestive responses evoked by MET in the PPM were associated only with an increase in feeding duration (similar to that observed in the PVN experiments). No ingestive effects were observed after intracerebroventricular (ICV, lateral ventricle) injections of MET (10, 30, 100 or 300 nmol), while ICV injections of GR (3, 15 or 30 nmol) increased feeding only at the higher dose [Da Silva RA, De Oliveira ST, Hackl LPN, Spilere CI, Faria MS, Marino-Neto J, Paschoalini MA. Ingestive behaviors and metabolic fuels after central injections of 5-HT1A and 5-HT1D/1B receptors agonists in the pigeon. Brain Res, 2004;1026:275-283]. These data indicate the presence of a tonic inhibitory influence on feeding behavior exerted by 5-HT afferents on these hypothalamic areas, and suggest that these inputs, possibly mediated by non-rodent-type 5-HT1D/1B receptors, can affect both satiety and satiation mechanisms.
Da Silva
Renata A
RA
Department of Physiological Sciences - CCB, Federal University of Santa Catarina, 88040-900 Florianópolis, SC, Brazil.
Da Silva
Aderley S S
AS
Poffo
Marine Josiane
MJ
Ribas
Déborah C
DC
Faria
Moacir Serralvo
MS
Marino-Neto
José
J
Paschoalini
Marta A
MA
D000178:Acrylamides / Q000008:administration & dosage / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D010856:Columbidae; D004305:Dose-Response Relationship, Drug; D005247:Feeding Behavior / Q000187:drug effects* / Q000502:physiology; D007211:Indoles / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008711:Metergoline / Q000008:administration & dosage / Q000494:pharmacology*; D008845:Microinjections; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects* / Q000502:physiology; D011985:Receptors, Serotonin / Q000145:classification / Q000187:drug effects / Q000502:physiology; D012702:Serotonin Antagonists / Q000008:administration & dosage / Q000494:pharmacology*
D000178:Acrylamides; C119994:GR 46611; D007211:Indoles; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D008711:Metergoline