Neonatal thyroxine administration, behavioral maturation, and brain growth in mice of different brain weight.
L-thyroxine in amounts of .5, 1, and 2 mug was injected daily from age 5 through 14 days in 3 lines of mice selected for high (H), medium (M), or low (L) brain weight. Controls (injected with vehicle only) of these lines differed in ages of eye-opening, first auditory startle, and perfection of a surface-righting response. Thyroxine at .5 mug/day accelerated the maturation of eye-opening, auditory startle, and aerial-righting response, but had no effect on a grasping response or open-field activity. Brain weights were depressed significantly in all thyroxine treated groups except in the 9k-mug dosage in  H mice.
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development*; D001921:Brain / Q000033:anatomy & histology / Q000254:growth & development*; D004305:Dose-Response Relationship, Drug; D005106:Exploratory Behavior / Q000187:drug effects; D005260:Female; D007323:Instinct; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009929:Organ Size; D010641:Phenotype; D012018:Reflex / Q000187:drug effects; D013216:Reflex, Startle / Q000187:drug effects; D013974:Thyroxine / Q000008:administration & dosage / Q000494:pharmacology*
D013974:Thyroxine