Abstract
The area postrema (AP) located in the dorsal medulla is one of the circumventricular organs that are characterized by the lack of a blood brain barrier. The neuronal activity of AP neurons contributes to the control of several autonomic functions. The AP have been implicated to contain uniformly shaped small neurons and glia, however, AP cell bodies, which is visually identified in brain slices using Nomarski optics, are different sizes. We, therefore, hypothesized that there may be morphological correlates of the electrophysiological cell classes. Whole-cell recordings were performed to examine the morphological properties of electrophysiologically-classified area postrema (AP) neurons in rat brain slices. Using electrophysiological criteria, AP neurons were subdivided into three groups: 1) cells displaying both the hyperpolarization-activated cation current (Ih) and the fast transient outward current (fast Ito); 2) cells displaying only the fast Ito; and 3) cells displaying only the slow Ito. Majority of group 3 cells showed relatively larger values of the cell soma diameter and the total electrical capacitance. Interestingly, a number of cells from group 1 and 3 but not group 2 were found to extend their dendrites into the nucleus tractus solitarius (NTS) suggesting that AP neurons could receive vagal afferent inputs at their dendritic termini within the NTS. This study indicates the presence of significantly different subpopulations of AP neurons, which are characterized not only electrophysiologically but also morphologically. [Jpn J Physiol 55 Suppl:S14 (2005)]
