Influence of psychological variables on the activity of the hypothalamic-pituitary-adrenal axis.

Psychobiology is the discipline that attempts to integrate the impact of environmental and psychological variables on biological systems. This paper focuses on the psychobiology of the hypothalamic-pituitary-adrenal (HPA) axis and illustrates several processes that influence the response of the HPA axis. The interaction of the developing rodent or primate with their primary care giver has permanent long-term effects on the HPA axis. Manipulations that alter maternal behavior during critical periods of development permanently modify the HPA axis. The HPA axis can be programmed to be hypo-responsive or hyper-responsive as a function of time and length of maternal separation. In the adult organism, the HPA response to stress is highly dependent on specific psychological factors such as control, predictability, and feedback. In primates, social variables have been shown to diminish or exacerbate the HPA stress response. During the post-natal period of development, the mother appears to actively inhibit the pups' HPA axis. Different aspects of maternal behavior regulate different components of the HPA system.