AbstractThe effect of a single systemic injection of reserpine on tyrosine hydroxylase activity in the locus coeruleus, cerebellum, hypothalamus, and hippocampus was examined. Increases in enzyme activity were seen in all four brain areas; the time‐course of the changes, however, was different in each case. In the locus coeruleus the maximum change in enzyme activity was seen 3 days after drug administration; in the cerebellum, 7‐11 days; in the hypothalamus, 8‐11 days; and in the hippocampus, 21 days. Since tyrosine hydroxylase in the cerebellum and hippocampus is present in terminals of neurons whose cell bodies are located in the locus coeruleus, the delayed increase in enzyme activity in cerebellum and hippocampus probably depends upon the slow rate of transport of TH molecules in these ne