Chapter 54: Neurophysiological analysis of mechanisms for subfornical organ and area postrema involvement in autonomic control

Abstract

Two examples of circumventricular organs (CVOs) with the ability to sense circulating substances and influence central nervous system (CNS) function as the result of actions on the neural substrate of these structures relate to peptidergic actions in the subfornical organ (SFO) and the area postrema (AP). Anatomical, biochemical, pharmacological and physiological evidence has implicated these structures as CNS sites at which angiotensin (ANG), atrial natriuretic peptide (ANP), vasopressin (VP) and endothelin (ET) act to influence neuroendocrine and other more classical autonomic functions. This chapter focuses on neurophysiological studies that have attempted to describe factors, neural and circulating, controlling the activity of neurons in these CVOs. The functional nature of neural pathways through which SFO and AP neurons influence neuroendocrine and cardiovascular control systems is described. Electrophysiological studies have provided convincing evidence that changes in circulating peptide concentrations influence the activity of AP and SFO neurons. In addition, SFO neurons influence neuroendocrine and cardiovascular systems through efferent projections to hypothalamic nuclei such as the SON and PVN. Considerable evidence now suggests that two separate functional populations of AP neurons may exist which play opposing roles in the control of blood pressure.