Potentiation of amphetamine-induced hyperactivity in the adult mouse following neonatal thyroxine administration

In order to examine possible long-term effects of neonatal hyperthyroidism on catecholamine (CA) neural systems, mice receiving saline or thyroxine injections during the neonatal period were subsequently injected with d-amphetamine or saline immediately prior to testing for locomotor activity at 100 days of age. Thyroxine-treated males were more active than control males following amphetamine injections, but thyroxine-treated and control females did not differ in this regard. In general, the results suggest that neonatal hyperthyroidism may have long-lasting effects on CA function that, at least at the age tested, may be limited to the male mouse.