Thyroxine regulates the activity and the concentration of synaptic plasma membrane Na,K-ATPase in the developing rat brain cortex.

The administration of thyroxine to neonatal rats stimulates the activity of synaptic membrane Na,K-ATPase in the brain cortex of euthyroid and hypothyroid animals. Thyroxine also increases NA,K-ATPase activity of isolated neuronal perikarya in neonatal rats. Binding studies employing [3H]ouabain indicate that the hormone increases the amount of Na,K-ATPase in the synaptic membranes of two-week-old rats. Thyroxine treatment however did not affect synaptic membrane Na,K-ATPase in rats aged 30 days. The results suggest that thyroid hormones are important for the maturation of the synaptic plasma membrane during the critical period of rat brain development.