Thyroid Hormone Regulation of Specific mRNAS in the Developing Brain

In laboratory rats (Rattus norvegicus) aged 1 to 21 days emergence of postural and locomotor skills was studied in the open field and in experimental situations with homing used as motivation. Righting is mediated initially by curving and rocking of the trunk, later head and shoulder are rotated, and lastly the hindlimbs turn and provide co-ordinated support. Pivoting prodominates during the second half of the first week, crawling during most of the second week, and walking or running by the end of the second week. Balancing on narrow paths and compensating for lateral displacement on rotating rods mature later, as do various skills (climbing up or down on inclined surfaces, rods and ropes, and jumping across gaps) that require substantial hindlimb co-ordiantion.