Chronic norepinephrine injection into the hypothalamic paraventricular nucleus produces hyperphagia and increased body weight in the rat.

A single injection of norepinephrine (NE) into the paraventricular nucleus (PVN) is known to elicit a feeding response in the satiated rat. Through repeated NE injections, the present study set out to determine whether chronic noradrenergic stimulation of the PVN is effective in producing changes in total daily food intake, as well as in body weight gain. The results indicate that repeated injections of NE (20 nmoles/injection given 4 times/day) cause a stimulation of eating with each injection and consequently produce a significant increase in total daily food intake. This stimulatory effect on feeding behavior occurs under food-restricted conditions, where food is available only at times (in the daytime) when NE is injected, and also under food-satiated conditions were food is available essentially ad lib. This hyperphagia results in a gradual increase in body weight which develops over the course of a 5-day sequence of repeated NE injections. There is some evidence to suggest that the overeating produced by NE throughout the day may be attributed specifically to an increase in meal size rather than to a change in meal frequency. This evidence suggests that medial hypothalamic NE, particularly within the PVN, may play a role in long-term feeding behavior and body weight regulation.