Opiomelanocortins, Learning and Memory: Significance of Multiple Behavioural Information in One Polypeptide Molecule

Abstract

The concept that peptide hormones of pituitary or brain origin are important modulators of behavioural adaptation stems from a unified endocrine and behavioural view of coping with environmental demands. The stress theory of SELYE [1] suggested that pituitary-adrenal response to noxious, physically damaging stimuli facilitates coping with the given environmental challenge. Observations of both animals and men from the 1950s onward led to the recognition that environmental stimuli that induce fear, anxiety, rage, and disappointment are among the most powerful stimuli for activating pituitary adrenocorticotrophic hormone (ACTH) release [2, 3]. The recognition of the central nervous control of the pituitary gland, in particular the role of the limbic system herein [see 4 for references], was an important step in linking endocrine activity and learning, memory and cognition that are closely related to limbic system function [5]. The idea that the brain is a target of ‘stress hormones’ received support from a few experimental studies demonstrating behavioural changes following the removal of the pituitary or the adrenal gland in animals. In addition, clinical observations suggested mood alterations and changes in the electrical activity of the brain following ACTH or corticosteroid therapy [see 6 for review]. Extensive research on the influences of peptide hormones related to ACTH, α- and β-melanocyte stimulating hormone (MSH) in the 1960s [e. g. 7,8]led to the recognition of a number of important neurobiological ‘rules’.