Microdialysis analysis of norepinephrine levels in the paraventricular nucleus in association with food intake at dark onset.

It has been proposed that norepinephrine (NE) in the paraventricular nucleus (PVN) acts to stimulate carbohydrate feeding specifically at the start of the active (dark) cycle in rats. This study used microdialysis to examine the relationship between endogenous levels of NE in the PVN at dark onset and the amount of food consumed at this time. The results indicated that: (1) in satiated rats on a lab chow diet, NE levels in the PVN, as opposed to sites anterior or lateral to this nucleus, were significantly higher during large meals around dark onset then they were during small meals or during intervals that preceded the large meals, and (2) in food-deprived animals given a pure carbohydrate diet at dark onset, PVN levels of NE just before the initiation of the meal were significantly higher in animals that consumed a relatively large carbohydrate meal (> 2.0 g) during the first dark hour, and they were significantly correlated across animals with the size of their carbohydrate meal. These findings are consistent with other evidence linking endogenous PVN NE to food intake at the beginning of the natural feeding cycle.