ABSTRACT
The theory of stress was developed as being of a merely endocrine character and suggested the involvement of noxious stimuli of physical or chemical nature as stressors (Selye, 1935). Subsequent research demonstrated that psychological stimuli were as strong activators of the neuroendocrine system as the physical ones (Mason, 1968) and provided ample evidence for the involvement of brain and behavioral mechanisms in the organization of stress responses (Mason, 1971). At the same time, it became clear that the brain is an important target of stress hormones. Following the first report by Torda and Wolff (1952), a number of investigations suggested that stress hormones like adrenocorticotropin (ACTH) and adrenocortical steroids (Woodbury, 1958) profoundly influence brain excitability. From the early 1960s a vast amount of literature supported the view that behavioral plasticity as defined by studies of learning and memory processes is influenced by stress hormones. Following investigations about the role of adrenal cortical hormones and ACTH and related peptides in adaptive behaviors (e.g., Bohus & De Wied, 1980), increasing interest was directed toward the involvement of adrenal catecholamines and a novel generation of stress hormones like vasopressin, oxytocin, prolactin, and endorphins in learning and memory processes (e.g., Martinez & Kesner, 1991).
