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

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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.

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