Influence of feeding paradigm in rats on temporal pattern of: II. Brain serotoninergic and catecholaminergic systems

The relationship between the feeding paradigm (single diet versus food selection) and central idoleamines and catecholamines was studied. Temporal patterns of the brain parameters in response to presentation of a single diet of fixed composition (20% casein) or a choice between two isocaloric diets (0% and 60% casein) for 2 weeks under 8-h feeding cycles during the dark phase were measured in adult Sprague-Dawley rats. Groups of animals were then killed at the beginning and at 2-h intervals throughout the feeding period. The distribution and the temporal pattern of variation of the serotoninergic and the catecholaminergic parameters studied were significantly affected by the diet paradigms used. A different neurochemical equilibrium was observed before food intake and was characterized by a central serotoninergic predominance in subjects having a dietary selection experience but a central catecholaminergic predominance in animals adapted to a single diet. Hypothalamic and extrahypothalamic serotoninergic and catecholaminergic systems were found to intervene in an interdependent way, sometimes antagonistic according to the feeding paradigm and the related temporal changes in energy intake and macronutrient selection. These results suggest that central serotoninergic and catecholaminergic systems are influenced by the diet paradigm and display characteristic patterns of temporal variations during the feeding cycle. The feeding paradigm, per se, should then be considered as a potential synchronizer of central biological rhythms of monoamines, which in turn may affect food intake and appetite for macronutrients.