Behavioural experiments were carried out on adult rats made hypothyroid and hyperthyroid. The hypothyroid rats in an "open field" situation reduced the number of squares crossed and boluses defecated, the hyperthyroid rats reduced the number of squares crossed. A swimming endurance was conducted to evaluate the physical resistance of the rats: only hypothyroidism affected the performance. 2. Two operant tests were studied: a) an "extinction" trial (60 min), in which the rats trained in a fixed ratio schedule (FR 1:10), were no longer rewarded with pellets of food and b) the "reversal" test in which the contingency for food delivery was switched four times from one lever, where responses were previously reinforced, to the other lever where responses had no programmed consequences. 3. Both hypo and hyperthyroid conditions caused a lower rate of responses during the "extinction" trial, while in the "reversal" test only hyperthyroid rats showed improved performances. 4. Our data clearly demonstrate behavioural changes in adult hypothyroid and hyperthyroid rats.
