Influence of thyroid hormones on myelin proteins in the developing rat brain.

This communication describes developmental changes in myelin proteins prepared from control, hypothyroid, and hyperthyroid rat brain. In the 10- to 37-day postnatal period studied, total myelin protein was found to double, and this change mainly reflected the increase in proteolipid and basic protein constituents. Thyroid states affect differentially the various myelin proteins. Hypothyroidism decreases the proteolipid and slow-moving basic protein, but has no effect on the fast basic or minor proteins. In hyperthyroidism, an increase was observed in proteolipid as well as both slow- and fast-moving proteins. The protein alterations were correlated to the changes previously found in lipid composition of myelin consequent upon hypo- and hyperthyroidism, and the role of thyroid hormones in brain development.