Influence of anterior pituitary on avoidance learning and escape behavior

Abstract

Adenohypophysectomized rats were subjected to an avoidance learning procedure. Only 6 of 21 adenohypophysectomized rats achieved the conditioning criterion against 14 of 18 sham-operated controls. The treatment with a long-acting ACTH preparation (ACTH(A1)Zn) during avoidance training resulted in an improvement in the rate of conditioning, which was most optimal following the administration of 1.5 IU. The injection of replacement therapy with cortisone, testosterone, and thyroxine also improved the ability of adenohypophysectomized rats to acquire an avoidance response. The speed with which adenohypophysectomized rats escaped a noxious stimulus in a runway was significantly lower than that of sham-operated controls, indicating that the motor and sensory capacities of this animal were seriously impaired. Administration of ACTH (A1)Zn or of the replacement therapy restored the escape speed toward normal. Accordingly, the deficiency in learning capacity of adenohypophysectomized rats does not seem to depend on the absence of ACTH but on a general debilitation of the adenohypophysectomized organism.