The influence of the posterior and inter-mediate lobe of the pituitary and pituitary peptides on the maintenance of a conditioned avoidance response in rats

Abstract

The removal of the posterior and intermediate lobe of the pituitary (posterior lobectomy) in rats, facilitates the rate of extinction of a conditioned avoidance response without affecting avoidance learning. The abnormal extinction behaviour of posterior lobectomized rats appeared not to be due to the disturbance in water metabolism resulting from the removal of the posterior pituitary. Pitressin, purified lysine vasopressin, synthetic α-MSH and ACTH (A 1 peptide) admini-stered as long acting preparations during the period of extinction, inhibited the rapid rate of extinction (of the avoidance response) in posterior lobectomized rats. These data indicate that the presence of the posterior and/or intermediate lobe of the pituitary is essential for the maintenance of the avoidance response and that peptides representing these structures are physiologically involved in this process. This behavioural effect suggests an important central action of these peptides.