The dynamics of neuronal activation during food anticipation and feeding in the brain of food-entrained rats

Jul 8, 2008Brain research

Brain cell activity changes during food anticipation and eating in rats trained to expect food

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Abstract

Neuronal activation in multiple brain regions occurs 3 hours before a meal in rats on restricted feeding schedules.

Food-anticipating rats show increased neuronal activation in several brain areas, indicating a distributed network for meal timing.
Key regions involved include the anterior hippocampal continuation, septohippocampal nucleus, paraventricular thalamic nucleus, and dorsomedial hypothalamic nucleus.
Neuronal activation patterns differ after feeding compared to those observed during food anticipation.
An increase in plasma corticosterone during food anticipation does not correlate with increased levels of corticotropin releasing factor mRNA.

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Rats can anticipate a daily mealtime when they are maintained on restricted feeding schedules (RFS). Neural substrates of the food-entrainable oscillator (FEO) are not yet fully understood. The numerous lesions of a single brain region failed to abolish the behavioral anticipation of a daily meal, suggesting that the FEO may be represented by a distributed neuronal network. The present study was designed to detect the dynamics of neuronal activation, using as a marker the expression of c-fos mRNA in the brain of rats subjected to 2-hour daily RFS, 3, 2 and 1 h before the expected meal, at the time of the usual feeding, and 1 h after feeding. We also aimed to clarify whether the increase in plasma corticosterone in food-anticipating rats coincides with the increase in expression of corticotropin releasing factor (CRF) mRNA in the paraventricular hypothalamic nucleus (PVH). The obtained results revealed that the neuronal activation occurring 3 h before the expected meal was not confined to one brain structure, but was evident in the anterior hippocampal continuation and septohippocampal nucleus (AH/SHi), the anterior part of the paraventricular thalamic nucleus (PVTa), and the dorsomedial hypothalamic nucleus (DMH), thus representing distributed septohippocampal-thalamo-hypothalamic circuitry that may act as the FEO. The pattern of neuronal activation after feeding was different from that detected during food anticipation for some specific nucleus or subregions. The increase in plasma corticosterone during food anticipation was not accompanied by an increase in CRF mRNA levels, suggesting that factors other than CRF are involved in the control of adrenocortical secretion under RFS.

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The dynamics of neuronal activation during food anticipation and feeding in the brain of food-entrained rats

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