Behavioral consequences of perinatal hypothyroidism in postnatal and adult rats

The long-term effects of perinatal hypothyroidism on spontaneous locomotor behaviors were assessed after exposure to the antithyroid drug, methimazole. Perseveration was observed in methimazole-treated rats in a spatial maze. Locomotor activity in residential mazes was examined at 6 weeks, 4 months, and 6 months of age. Treated rats were hypoactive at some intervals compared with controls and were hyperactive at others. These paradoxical differences resulted from changes in exploratory, diurnal, and nocturnal locomotor activity in control rats both with increasing age and on repeated exposures to residential mazes; rats after perinatal hypothyroidism had relatively constant levels of activity on repeated days of exposure to residential mazes and at different ages. These results may be related to perseveration noted in the spatial maze. In an analysis of walking patterns, treated rats tended to have a more pronounced asymmetry in gait than controls.