Postnatal action of growth and thyroid hormones on the retarded cerebral myelinogenesis of Snell dwarf mice (dw).

Snell dwarf mice (dw) showed a lower CNPase activity (59% of the normal controls) only in the cerebrum among different parts of the CNS, and a strikingly reduced level of spontaneous locomotion activity with an indistinct diurnal periodicity in a 24-h record at 40 days of age. Daily administration of bGH and T4 to the dwarfs during the first 40 days of postnatal life restored CNPase activity to the level of the normal controls, and was accompanied by normalization of the pattern of spontaneous locomotion activity. Daily administration of bGH alone also restored CNPase activity and spontaneous locomotion, but to a lesser extent. The daily administration of thyroid stimulating hormone (TSH) alone, however, failed to restore CNPase activity, in spite of the fact that the thyroid glands of the TSH-treated dwarfs were indistinguishable from the normal controls in organization and appearance. These results indicate that the restoration of both the retarded myelinogenesis and abnormal behavior of the Snell dwarf mice might essentially depend upon GH levels and the synergistic effects of T4.