¹Laboratoire de Neuropsychobiologie des Désadaptations, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5541, Université Victor Segalen Bordeaux 2, Bordeaux, France

Correspondence: Dr M Flavia Barbano, Laboratoire de Neuropsychobiologie des Désadaptations, CNRS 5541, Unité Mixte de Recherche, Université Victor Segalen Bordeaux 2, 146, rue Léo Saignat, BP 31, 33076 Bordeaux Cedex, France. Tel: +33 5 57 57 15 45; Fax: +33 5 56 90 02 78; E-mail: maria.barbano@etud.u-bordeaux2.fr

Received 13 June 2005; Revised 17 August 2005; Accepted 22 August 2005; Published online 5 October 2005.

Abstract

Various aspects of feeding behavior (eg consumption, motivation and anticipation) are regulated by homeostatic and hedonic systems, and are modulated by dopaminergic and opioid brain systems. Here, we have studied the modulation of these aspects of feeding behavior by opioid and dopaminergic neurotransmission while taking into account food palatability and homeostatic state. Foods that varied in palatability were presented to either food sated or food restricted rats following injections of different doses of naloxone, an opioid receptor antagonist, or flupenthixol, a dopaminergic receptor antagonist, in behavioral paradigms that measured different aspects of feeding. Naloxone decreased food intake in a dose-dependent manner in sated rats given access to palatable food, without modifying food intake in food restricted rats. Flupenthixol did not have any effect on food intake. With regard to motivation, which was tested in a straight alley, naloxone increased the latency to reach the food only in sated rats presented with palatable food. Flupenthixol did not modify the latency of any group. Conditioned locomotor activity to repeated food presentation, a measure of anticipation, is expressed only in food restricted rats. Naloxone did not modify anticipatory activity, whereas flupenthixol decreased it only in food restricted rats presented with palatable food. These results reinforce the idea that the opioid system regulates feeding through the modulation of the perceived palatability of food. The dopaminergic system seems to be more important for the regulation of anticipatory activity related to motivationally relevant stimuli.