THYROXINE REDUCES THE PRODUCTION-RATE OF BRDU-LABELED CELLS IN THE VENTRICULAR ZONE OF THE ADULT CANARY BRAIN

When the canary reaches adulthood, neuron production continues in the lateral ventricular zone (VZ) of the forebrain. The effect of thyroxine injection on the cell production rate in the VZ during adulthood was studied immunohistochemically using bromodeoxyuridine (BrdU). The rate of occurrence of BrdU-labeled cells was reduced by thyroxine injection (1 mg/body). Hyperthyroidism usually promotes increased mitotic activity, but in the present study this was not the case. The decrease in the number of BrdU-labeled cells in the VZ appears to have resulted from, premature termination of cell proliferation due to early initiation of cell differentiation. Our results suggest that the production rate of cells in the VZ of the adult canary changes seasonally, decreasing in the summer when the plasma level of thyroxine increases.