INFLUENCE OF SOCIAL STRESS ON BRAIN CATECHOLAMINE MECHANISMS

Abstract

Prolonged social isolation is a method to induce aggressiveness in male animals of various species. The phenomenon has been studied in mice that fight each other intensively when brought together after individual housing for about 4 weeks. The effect of isolation on the synthesis and turnover of brain monoamines has been the subject of several investigations. The turnover of noradrenaline (NA) and 5-hydroxytryptamine has been found to be lower in isolated than in grouped mice. Studies on the turnover of brain dopamine (DA) during isolation are contradictory. The rate of depletion of DA after tyrosine hydroxylase inhibition has been reported to be either decreased or increased. The catecholamine (CA) synthesis is retarded in isolated animals, when estimated in vivo as the accumulation of DA and NA after monoamine oxidase (MAO) inhibition. The tyrosine hydroxylase activity, measured in vitro in midbrain and striatum, has been reported to be increased. Fighting among previously isolated animals has been reported to be without significant effect on the synthesis and turnover of brain CA when estimated as their accumulation after MAO inhibition and depletion after tyrosine hydroxylase inhibition. These findings were taken as support for the hypothesis that stress induces a partial and reversible inhibition of mitochondrial MAO in the brain.