Meal-synchronized CEA in rats: effects of meal size, intragastric feeding,and subdiaphragmatic vagotomy

Within a feeding schedule of intermittent food access, large meals have the ability to induce activity at the same time the next day [circadian ensuin g activity (CEA)]. In these experiments, we evaluated the minimum meal size necessary to induce CEA and whether oral-pharyngeal factors and afferent v agal activity played necessary roles in the induction of the underlying pro cess. Tn experiment 1, every 33 h rats were given two meals separated by a 2-h interval. The size of the first meal was varied, while total intake eve ry feeding cycle was held constant;. When the initial meal was <10 g (34 kc al) CEA occurred later, indicating that such a meal size was subthreshold f or inducing CEA. In experiment 2, rats were given intragastric (IG) meals e very 33 h, before and after complete subdiaphragmatic vagotomy. IG nutrient meals induced CEA, indicating that extensive oral-pharyngeal experience wa r; not necessary for CEA induction. CEA occurred in vagotomized rats but, c ompared with intact rats, appeared to occur later relative to nutrient infu sion, indicating that afferent vagal activity may be sufficient but not nec essary to induce CEA.