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

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. Feeding behavior is a complex group of functions that comprise the search, capture and ingestion of the organic and inorganic matter necessary for the sustenance of life. This behavior consists of many different components, and different brain systems are involved in the regulation of its specific aspects. As a biological rhythm, feeding behavior is organized mainly in the diencephalon by the lateral and medial hypothalamus subdivisions and the paraventricular nucleus (1-3). The lateral hypothalamus seems to control blood glucose homeostasis through glucoreceptors (also present in the nucleus tractus solitarius and the liver). Once stimulated, these receptors trigger reflexes that restore glycemia through metabolic activity of the liver, which in turn, initiates feeding behavior, particularly the searching and ingestion phases (4). Satiety, however, seems to be driven by the ventromedial hypothalamic subdivision through the release of gut hormones and cholecystokinin, and also by the distension of the gastrointestinal tract

Serotonin and circadian rhythms.

“…The synthesis of melatonin, a hormone derived from 5-HT, undergoes phase advances in rats subjected to food restriction (Challet, Pevet, Vivien-Roels, & Malan, 1997). In an experiment with rats subjected to food restriction and divided into three groups (one group that had no access to food but had olfactory and visual contact; one group that had food access for 30 min; and one group with food access for 2 h), an increase in c- fos expression was observed in the caudal raphe nuclei of the pallid raphe nucleus, nucleus raphe magnus, and nucleus raphe obscurus during the period of food exposure (Takase, Barone, & Nogueira, 2000).…”

Envolvimento dos núcleos da rafe nas respostas adaptativas a alterações de volume sangüineo em ratos, estudo através da expressão de Fos

“…Os núcleos da rafe realizam múltiplas conexões com núcleos encefálicos que estão envolvidos na regulação do sistema cardiovascular (BAUSBAUM et al, 1978;SATOH, 1979;VAN DE KAR e LORENS, 1979;LOEWY, 1981aLOEWY, , 1981bHOLSTEGE e KUYPERS, 1982a;ROSS et al, 1985;BOWKER, 1986;ALSTERMARK et al, 1987;HOLSTEGE e KUYPERS, 1982b;MARTIN et al 1990;BACON et al, 1990;NICHOLAS e HANCOCK, 1990;JACOBS e AZMITIA, 1992;EVANS e BLAIR, 1993;WANG e LOVICK, 1993;INUI et al, 1994;VERTES e KOCSIS, 1994;VERTES et a1., 1999;NOGUEIRA et al, 2000).…”

“…Assim, a proteína Fos tem sido utilizada como um método de marcação da atividade do neurônio para mapear circuitos neurais que se relacionem funcionalmente e que respondam a estímulos específicos (KRUIJER e SCHUBERT, 1985;SAGAR et al, 1988 BADOER et al, 1993;LI e DAMPNEY, 1994;MIURA et al, 1994;GRAHAM et al, 1995;POLSON et al, 1995;HIROOKA et al, 1997;POTTS, 1997;HORIUCHI et al, 1999;POTTS et al, 2000;TAKASE et al, 2000;LOHMEIER et al, 2001;POLSON et al, 2002;LOHMEIER et al, 2003). Sendo assim, este trabalho utiliza a expressão e quantificação desta proteína para avaliar a participação dos núcleos da rafe na resposta frente a alterações de volume sangüíneo.…”