Circadian release of hypothalamic norepinephrine in rats in vivo is depressed during early L-lysine deficiency

Rats rapidly recognize an amino acid-deficient diet, presumably via central mechanisms that involve hypothalamic circuits. We evaluated the effects of a deficiency of the essential amino acid, L-lysine, on the ventromedial hypothalamus (VMH) norepinephrine (NE) circadian release in free-moving, nonstressed rats. A dialysis probe was implanted into the VMH of male Wistar rats. Continuous microdialysis measurement was done during the first 26 h of L-lysine (Lys) deficiency in rats that had free access to food and fluid. The dark phase was from 1900 to 0700 h. Rats were divided into six groups according to their food and fluid intakes. They were fed either normal (Lys sufficient) or Lys deficient powdered food and provided with distilled water, glycine (Gly, 400 mmol/L) or Lys solution (400 mmol/L). In control rats, VMH NE release showed a diurnal pattern, with the lowest levels measured at the onset of the dark phase. In Lys-deficient rats, the release was significantly depressed from the early morning (0500 h) compared with Lys-sufficient rats, without any differences in food and fluid intakes. A normal pattern of VMH NE was restored by the provision of 400 mmol/L Lys solution to deficient rats. The results suggest that the VMH NE release is involved in the early integration of signals about amino acid deficiency.