THE ROLE OF LIMBIC-HYPOTHALAMIC SYSTEMS IN METABOLIC RESPONSES OF PHENYLALANINE TO REPEATED COLD EXPOSURES IN RABBITS

In this study we examine the effects of lesions to limbic or hypothala mic structures on the metabolic responses of phenylalanine in liver sl ices prepared from rabbits exposed to cold stress (-20-degrees-C) for 12 hours at a fixed time once a day. The results were as follows: 1. T he 1st cold exposure (cold exposure on the 1st day) had marked and var ious effects on phenylalanine metabolism, and the metabolic responses of phenylalanine to cold exposure gradually decreased and then complet ely disappeared with repetitions of exposure in intact rabbits. 2. The metabolic patterns and responses of phenylalanine to the 1st cold exp osure were altered by lesioning the periventricular arcuate nucleus (A RC), ventromedial hypothalamus (VMH), stria terminalis (ST) or dorsal fornix (FX). 3. The complete abolishment of the metabolic responses to cold exposure by its repetition was observed in rabbits with lesions in the ARC or VMH as well. 4. In contrast, metabolic responses of phen ylalanine to cold exposure in rabbits with lesions in the ST or FX rem ained even after six exposures. These results suggest that the ARC, VM H, amygdala (AMYG)-ST system and dorsal hippocampus (HPC)-FX system pl ayed a role in the metabolic regulation of phenylalanine and in the me tabolic responses of phenylalanine to the 1st cold exposure and that t he AMYG-ST and HPC-FX systems, but not the ARC or VMH, participated in the process of the metabolic adaptation of phenylalanine to cold expo sure.