Thyroid hormones and the acquisition and retention of behavioural responses

Naive rats placed in a plexiglass cylinder from a 15 minute test period show progressive immobility, and retain the immobile response when given a 5-minute retest 24 hours later. In the present study we show that hypothyroidism markedly attenuates the acquisition of the immobile response; that this effect on acquisition is reversed 5-10 minutes after the administration of thyroxine; and that hypothyroid rats treated with a single dose of thyroxine up to 2 hours after the initial test show levels of immobility on re-test indistinguishable from intact rats.