Chronic infusion of norepinephrine and clonidine into the hypothalamic paraventricular nucleus.

Previous experiments have shown that acute injection of NE and CLON into the PVN initiates a short-term feeding response in satiated rats. This study examined, in brain-cannulated rats, the impact of remote, chronic injections of NE, CLON, or saline on daily food intake and body weight gain. Over a period of 14 days, NE was infused into the PVN, either continuously at a rate of 12 nm/microliter/hr, or discretely at a rate of 6 nm/microliter/sec. In addition, the alpha 2-adrenergic agonist CLON was infused into the PVN discretely at a rate of 3 nm/0.5 microliter/30 sec. Relative to saline infusion, chronic (continuous or discrete) stimulation of the PVN with either of these drugs was effective in potentiating daily food intake by 12-19% and in increasing body weight gain, from approximately 1.5 g/day to 3.3 g/day. This evidence indicates that medial hypothalamic NE, especially within the PVN, is sufficiently robust to alter long-term feeding patterns and body weight regulation.