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

Involvement of the caudal raphe nuclei (raphe pallidus, RPa; raphe magnus, RMS, and raphe obscurus, ROb) in feeding behavior of adult rats was studied by measuring c-Fos protein expression, in animals submitted to the "meal-f eeding" model of food restriction in which the rats were fed ad libitum onl y from 7:00 to 9:00 h, for 15 days. The experimental groups submitted to ch ronic fasting, named 'search for food' (SF), 'ingestion of food' (IF) and ' satiety of food' (SaF) were scheduled after a previous study in which the b ody weight and the general and feeding behaviors were evaluated by daily mo nitoring. Acute, 48-h fasting (AF) was used as control. In the chronic grou p, 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. Ent rainment of the sleep-wake cycle to the schedule of food presentation was a lso observed. The RPa was the most Fos immunopositive nucleus in the chroni c fasting group, followed by the RMg. The ANOVA and Tukey test (P<0.05) con firmed these results. The IF group was significantly different from the oth er three groups, as also was the number of labeled cells in the RPa in SF a nd 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 t o observe that the groups in which the animals were more active, searching for or ingesting food, presented a larger number of labeled cells. These re sults suggest a different involvement of the caudal raphe nuclei in the som atic and autonomic events of feeding behavior, corroborating the functions reported for them earlier.