Perinatal hypothyroidism effects on step-through passive avoidance task in rats

Previous studies have documented a decrease in the ability of neonatal hypothyroid animals to learn and habituate to maze tests, and an increase in spontaneous activity. However, there is little information about the effects of perinatal (i.e., prenatal and postnatal) hypothyroidism on behaviour. The present study was designed to assess whether perinatal hypothyroidism in rats induces alteration on acquisition and/or short- and long-term retention of a learned response in male Wistar rats. Perinatal hypothyroidism was induced by prolonged (E9-P21) exposure of pregnant and lactating dams to methimazole (administered orally in drinking water, 0.2 mg/ml). Cognitive function was tested at 50 days by means of a step-through passive avoidance task. The effects of perinatal hypothyroidism on the retention of the passive avoidance response are long lasting being, however, highly dependent on the retention after the original training. Our results showed that methimazole-treated rats performed more poorly when retention was tested at long-term (24 h and 7 days) retention interval. Instead, methimazole-treated rats showed longer retrieval latencies than the control ones did when retention was tested at short term (1 h).