ABSTRACT
This study investigated the effects of local injections of 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX, AMPA-kainate receptor antagonist, 0.8 and 2.7 nmol) and MK-801 (NMDA receptor antagonist, 1.8 and 6.0 nmol) into the nucleus taeniae of the amygdala (TnA) and the arcopallium intermedium (AI) on ingestive and non-ingestive behaviors in free-feeding pigeons. Injections of DNQX into the TnA or into the AI failed to consistently affect feeding behavior; DNQX vehicle (DMSO) affected drinking when injected into the TnA. MK-801 injections into the AI produced a delayed increase in food and water intake. In the TnA, MK-801 increased water intake in the first two hours after the treatment. These data indicate that glutamatergic circuits in arcopallial structures in the pigeon, comparable to the mammalian medial amygdala, are involved in the inhibitory control of ingestive behaviors, suggesting that this can represent a conserved functional attribute in the amniote prosencephalon.
Subject(s)
Columbidae/physiology , Dizocilpine Maleate/pharmacology , Feeding Behavior/drug effects , Prosencephalon/drug effects , Quinoxalines/pharmacology , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Amygdala/drug effects , Amygdala/physiology , Analysis of Variance , Animals , Dose-Response Relationship, Drug , Drinking/drug effects , Eating/drug effects , Male , Prosencephalon/physiology , Reaction Time/drug effectsABSTRACT
This study examined the acute changes in feeding and drinking behaviours of free-feeding and free-drinking pigeons, in response to local injections of metergoline (MET, 5-HT(1/2) receptor antagonist; 7 and 20 nmol), GR46611 (GR, 5-HT(1B/1D) agonist; 2 and 6 nmol) or vehicle, into two components of the arcopallium: the nucleus taeniae of the amygdala (TnA) and the arcopallium intermedium (AI). In the TnA, the highest MET dose elicited a short-lived hyperphagy, without affecting drinking or non-ingestive behaviours during the first hour after injection. In contrast, all MET doses promptly increased drinking when injected in the AI, without affecting feeding; this effect was still evident 3 and 24 h after the treatment. When injected in the TnA, the highest GR dose promptly increased both food and water intake; these effects persisted 24 h after the treatments. GR injections in the AI evoked long-lasting increases in drinking, but not in feeding. Injections of these drugs into other arcopallial nuclei evoked no significant ingestive effects. These data indicate the presence of a tonic inhibitory influence of serotonergic inputs, partially mediated by 5-HT(1B/1D) receptors, on feeding- and drinking-related TnA circuits and on mechanisms controlling drinking in the AI. Compared to data from the rodent medial amygdala, our results suggest that a tonic inhibitory 5-HTergic control of feeding (but not drinking) behaviour, mediated by 5-HT(1/2) receptors and exerted in the medial amygdaloid area, may represent a broadly conserved functional attribute in the amniote brain, but probably involves many important taxa-specific neural mechanisms.