Hypothyroidism prolongs mitotic activity in the post-natal mouse brain

Circulating T-4 and T-3 were measured during the first three post-natal wee ks in the mouse and found to increase in a triphasic manner. The first incr ease occurred at post-natal day 6 and was simultaneous with a decrease in b romodeoxyuridine incorporation in areas showing post-natal mitosis. We inve stigated whether there was a causal relationship between increased thyroid hormone levels and decreased proliferation by inducing hypothyroidism in da rns and progeny. Hypothyroidism prolonged mitotic activity in the olfactory bulb, hippocampus, subventricular zone and the cerebellar cortex. This sug gests that the increase in T-3 at the end of the first postnatal week is im plicated in terminating progenitor proliferation in many parts of the mouse brain. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.