Tolerance to drum stress and its relationship to dopamine turnover

Abstract

The biphasic increase in latency to tonic extension following maximal electroshock, observed in mice stressed in a revolving drum for 7.5 min, was reduced markedly in animals which had been stressed prior to study (1 min per day for 3–5 days). In addition, previously stressed mice were found to be less susceptible (‘stress-tolerant’) to lethal amount of drum stress. α-Methyltyrosine, given prior to a 7.5 min stress, prevented the increase in latency to tonic extension, independent of previous stress; however, when given after stress, it prevented this increase only in ‘stress-tolerant’ animals and not in those stressed for the first time. Following a 7.5 min drum stress, both ‘stress-tolerant’ and non-tolerant groups elicited a marked increase in brain dopamine levels. However the rate of fall of dopamine, but not norepinephrine, following α-methyltyrosine was markedly accelerated in ‘stress-tolerant’ mice as compared with normal animals. It is suggested that exposure to prior stress markedly accelerates the turnover of brain dopamine and protects mice against the physiological alterations induced by more severe stress.