Effects of hydrocortisone and electric footshock on mouse brain tyrosine hydroxylase activity and tyrosine levels.

Tyrosine hydroxylase (TH) activity and levels of tyrosine were measured in whole brains from mice subjected to brief electric foot shock or to single or multiple injections of hydrocortisone acetate (HCA; 20 mg/kg). Adult brain tyrosine levels showed a rapid increase after either foot shock or a single injection of HCA; TH activity was also rapidly increased by foot shock but not by HCA. Multiple injections of HCA over three days increased brain TH activity in neonatal mice, but had no effect in adults. These results suggest that glucocorticoid hormone may have a regulatory influence on brain TH during the neonatal period, and that the hormone may also affect brain tyrosine. The acute effect of foot shock stress on brain TH activity is not a glucocorticoid-mediated event, but can be interpreted as enzyme activation due to neural stimulation.