Effect of Psychosocial Stimulation on the Enzymes Involved in the Biosynthesis and Metabolism of Noradrenaline and Adrenaline

Abstract

Various groups of CBA mice were exposed to differing levels of psychosocial stimulation by mutual confrontation for 6 months after reaching maturity. Their experiences ranged from individual isolation, through standard boxing, to a colony life in an intercommunicating box system containing males and females. The blood pressures of the socially stimulated groups increased to 170 ± 20 mmHg; those of the boxed and isolated animals remained a normal 126 ± 12 mmHg. Adrenal weights, adrenal noradrenaline and adrenaline, monoamine oxidase, tyrosine hydroxylase (the rate-limiting enzyme in catecholamine synthesis) and phenylethanolamine-N-methyltransferase (PNMT, the enzyme that converts noradrenaline to adrenaline) were all increased in the stimulated groups. A significant decrease in the two latter enzymes was observed in the isolated animals. It is suggested that the increase in catecholamine-forming enzymes resulting from psychosocial stimulation may be neuronally mediated, and that it is not an immediate response as in the case of a sudden discharge of noradrenaline and adrenaline in states of anger, fear or aggression.