Activity changes in mouse brain histidine decarboxylase

Mice were tested for effects of various factors on histidine decarboxylase of whole brain, or major brain regions. Factors included age, sex, fasting and feeding, season of year, time of day, freezing for various time intervals, and intracerebral injection of protein synthesis inhibitors daily for 2-5 days. In the latter test, 5 day treatment with acetoxycycloheximide reduced brain histidine decarboxylase activity. In one experiment, in which a marked activity increase was observed, brain infection seemed to be the stimulus. Brain enzyme activity in normal mice showed large fluctuations over periods of several months to one year; presumably this is of some physiological significance but the causes are obscure.