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 hy pothalamus (VMH) norepinephrine (NE) circadian release in free-moving, nons tressed rats. A dialysis probe was implanted into the VMH of male Wistar ra ts. 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. T he dark phase was from 1900 to 0700 h. Rats were divided into six groups ac cording to their food and fluid intakes. They were fed either normal (Lys s ufficient) 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 signif icantly depressed from the early morning (0500 h) compared with Lys-suffici ent rats, without any differences in food and fluid intakes. A normal patte rn of VMH NE was restored by the provision of 400 mmol/L Lys solution to de ficient rats. The results suggest that the VMH NE release is involved in th e early integration of signals about amino acid deficiency.