Thyroxine replacement in an animal model of congenital hypothyroidism

This study examined the effects of thyroxine (T4) treatment on spatial learning and memory in congenitally hypothyroid (CH) rats. Forty CH male offspring of methimazole-treated dams were randomly divided into three groups: no T4 (vehicle) treatment (n = 12), T4 treatment commencing on postnatal day (P-) 7 (n = 14), and T4 treatment commencing on P-21 (n = 14). Normal male rats were used as a control group (n = 14). T4 was administered daily (sc, 0.02 μg/g) to the treatment groups for 30 days. A water-maze was used to assess behaviour at 42, 70 and 98 days of age. T4 treatment beginning at P-7 improved learning and memory associated with CH at 70 and 98 days of age but T4 treatment beginning at P-21 did not improve CH-impaired learning and memory.