The role of stress in the pathophysiology of the dopaminergic system

In this review, we will examine the most recent preclinical evidence in sup port of the fact that both acute and chronic stress may have a detrimental impact on the normal function of the dopaminergic system. In recent decades , the term stress has changed its meaning from that of a 'non-specific body response' to a 'monitoring system of internal and external cues'; that is a modality of reaction of the mammalian central nervous system (CNS) which is critical to the adaptation of the organism to its environment. Compellin g results have demonstrated that the dopaminergic system is important not o nly for hedonic impact or reward learning but also, in a broader sense, for reactivity to perturbation in environmental conditions, for selective info rmation processing, and for general emotional responses, which are essentia l functions in the ability (or failure) to cope with the external world. In this, stress directly influences several basic behaviors which are mediate d by the dopaminergic system such as locomotor activity, sexual activity, a ppetite, and cross sensitization with drugs of abuse. Studies using rat lin es which are genetically different in dopamine (DA) physiology, have shown that even small alterations in the birth procedure or early life stress eve nts may contribute to the pathophysiology of psychiatric disorders-in parti cular those involving central DA dysfunction-and may cause depression or ps ychotic derangement in the offspring. Finally, the fact that the dopaminerg ic system after stress responds, preferentially, in the medial prefrontal c ortex (MFC), is thought to serve, in humans, as a protection against positi ve psychotic symptoms, since the increased DA activity in the MFC suppresse s limbic DA transmission. However, excessive MFC dopaminergic activity has a negative impact on the cognitive functions of primates, making them unabl e to select and process significant environmental stimuli. Thus it appears that a critical range of DA turnover is necessary for optimal cognitive fun ctioning after stress, in the response of the CNS to ever-changing environm ental demands.