Hyperactivity and spatial maze learning impairment of adult rats with temporary neonatal hypothyroidism

Temporary hypothyroidism was induced in neonatal rats by 0.02% propylthiouracil (PTU) administration to lactating dams during days 0–19 after delivery, and its effects on the behavior and learning of their male offspring were examined. The serum T 4 (thyroxine) level was returned to normal around 1 week after the last PTU administration, but the body weight gain was still depressed. The open field and Biel water maze tests at the age of 6 weeks showed an increased number of ambulations and an increase in errors with prolonged swimming time in the PTU rats. The radial arm maze test started at 13 weeks revealed that the PTU animals required more trials until they showed the first well-performed trial. The total number of choices was also larger, with less correct choices, and treatment effects on the response distribution and pattern were significant. Thus, the rats, which had suffered from temporary hypothyroidism in the neonatal period, showed hyperactivity and irreversible impairment in maze learning. These results suggest an involvement of temporary neonatal hypothyroidism in hippocampal dysfunction.