Involvement of the caudal raphe nuclei in the feeding behavior of rats.

L.F Takase,J.R Barone,M.I Nogueira

doi:10.1590/s0100-879x2000000200010

Abstract

Involvement of the caudal raphe nuclei (raphe pallidus, RPa; raphe magnus, RMg, and raphe obscurus, ROb) in feeding behavior of adult rats was studied by measuring c-Fos protein expression, in animals submitted to the "meal-feeding" model of food restriction in which the rats were fed ad libitum only from 7:00 to 9:00 h, for 15 days. The experimental groups submitted to chronic fasting, named 'search for food' (SF), 'ingestion of food' (IF) and 'satiety of food' (SaF) were scheduled after a previous study in which the body weight and the general and feeding behaviors were evaluated by daily monitoring. Acute, 48-h fasting (AF) was used as control. In the chronic group, the animals presented a 16% reduction in body weight in the first week, followed by a continuous, slow rise in weight over the subsequent days. Entrainment of the sleep-wake cycle to the schedule of food presentation was also observed. The RPa was the most Fos immunopositive nucleus in the chronic fasting group, followed by the RMg. The ANOVA and Tukey test (P<0.05) confirmed these results. The IF group was significantly different from the other three groups, as also was the number of labeled cells in the RPa in SF and IF groups. Nevertheless, no significant difference was observed between RMg and RPa, or RMg and ROb in the SaF and AF. However, it is interesting to observe that the groups in which the animals were more active, searching for or ingesting food, presented a larger number of labeled cells. These results suggest a different involvement of the caudal raphe nuclei in the somatic and autonomic events of feeding behavior, corroborating the functions reported for them earlier.

Highlights

We performed experiments using c-Fos expression methods and the restriction food model, known as meal-feeding that limits feeding to a fixed period of the day to further characterize the involvement of the caudal raphe nuclei in feeding behavior [15]
This model of chronic fasting uniformizes feeding conditions compared to spontaneous feeding, and appears to constitute a suitable tool to explore the strategies employed by an organism to cope with its homeostatic requirements when submitted to a starvation schedule
To choose the experimental parameters, a preliminary study was carried out in which the alterations in body weight, the amount of food consumed, the duration of ingestion, and general behavior were monitored daily. These data formed the basis for the designation of three chronic fasting groups: search for food (SF), in which food was presented to the animals, but these were prevented from reaching it; ingestion of food (IF), in which the animals were allowed to eat for 30 min, and the satiety of food (SaF) group, in which the animals ate for 2 h

Summary

Introduction

We performed experiments using c-Fos expression methods and the restriction food model, known as meal-feeding that limits feeding to a fixed period of the day to further characterize the involvement of the caudal raphe nuclei in feeding behavior [15]. Microscopic analysis of c-Fos expression revealed that cells of different sizes were involved in feeding behavior and that their number varied along the anteroposterior axis in each of the three caudal raphe nuclei.

Results

Conclusion