Reversal of delayed myelinogenesis in experimental hypothyroidism.

Neonatal hypothyroidism has been shown to induce delayed myelinogenesis in the developing rat brain. This delay in myelin formation is most prominent during the critical 3 - 4 week postnatal period and the heavy myelin fraction is more selectively affected. The experimental animals, however, continue active myelin formation and by 6 weeks post natum, they do not differ significantly from littermate controls. Myelin protein analysis by SDS acrylamide gels and densitometer methods revealed a decreasing proportion of high molecular weight protein and no significant change in either proteolipid or basic protein in developing myelin. The data suggest that neonatal hypothyroidism induces a reversible delay without qualitative change in myelinogenesis.