ABSTRACT
The research field of psychoneuroimmunology, or neuroimmunology, has experienced rapid growth and development during the past 25 years. The idea of bi-directional communication between the brain and the immune system, as originally proposed by Besedovsky et al. (1979a, b, 1983, 1984, 1986), continues to provide a primary conceptual framework for analysing the complex interactions among the three fundamental regulatory systems of the body, the central nervous system, the endocrine system and the immune system. Multidisciplinary approaches and techniques have characterized this research field and have provided the basis for advancements in our understanding of this fundamental and complex regulatory network. Despite the intrinsic difficulties presented by attempts to integrate these diverse regulatory systems into a unitary theoretical framework, there are several constituent elements that provide the foundation for any conceptual model of the neuroimmune regulatory system. Similar to other homeostatic physiological processes, the hypothalamus and its connections comprise the central integrative and regulatory elements for this proposed regulatory system. The dual efferent arms of this central regulatory system are composed of the endocrine and autonomic nervous systems. Thus, any actions by the nervous system on any immunological processes, by necessity, must be mediated by neuroendocrine responses and/or changes in sympathetic nerve activity. Within the hypothalamus, the paraventricular nucleus (PVN) has been proposed as a nodal region for the regulation of brain-immune interactions (Nance and MacNeil, 2001). Focus on the PVN is due to the fact that the cell bodies that produce the neuroendocrine releasing factor CRF are primarily localized within this nucleus and that the immunomodulatory actions of adrenal steroids are well established (Selye, 1950; Rivier, 2001). In addition, the PVN has efferent connections with brain stem and spinal cord autonomic nuclei indicating that this same hypothalamic region can directly modulate the activity of both the sympathetic and parasympathetic nervous systems (Swanson, 1985). Thus, both neuroanatomical and functional evidence suggest that the PVN and it’s connections are strategically positioned to simultaneously regulate the two efferent arms of the neuroimmune regulatory system.
