Administration of small doses of apomorphine attenuates feeding in non-deprived pigeons

The dopamine agonist apomorphine was administered peripherally at small doses of 25, 50 or 100 micrograms to non-deprived pigeons, either in the morning or in the afternoon. The food and water consumption of the birds was then measured at 4 times (30, 60, 90 and 120 min) after the injection. In the control condition (injection of saline), the pigeons ate less in the morning than in the afternoon, whereas a reverse situation was observed for drinking. Administration of apomorphine attenuated the food consumption in a dose-related fashion, at both times of the day, and for no longer than 90 min post-injection; the reduction of feeding was relatively larger when the drug was given in the morning than in the afternoon, and it was not accompanied by consistent changes of the water consumption. These results show that in pigeons, the feeding-like responses to apomorphine treatment (pecking, swallowing, mandibulating) which have been described previously are not associated with an actual enhancement of the food intake. Possible mechanisms and loci of action of dopamine agonists on these 2 types of behaviors are discussed.