COMPARTMENTAL MODELING OF RAT MACULAR PRIMARY AFFERENTS FROM 3-DIMENSIONAL RECONSTRUCTIONS OF TRANSMISSION ELECTRON-MICROGRAPHS OF SERIAL SECTIONS

1. We cut serial sections through the medial part of the rat vestibular macula for transmission electron microscopic (TEM) examination, computer-assisted three-dimensional (3-D) reconstruction, and compartmental modeling. The ultrastructural research showed that many primary vestibular neurons have an unmyelinated segment, often branched, that extends between the heminode [putative site of the spike initiation zone (SIZ)] and the expanded terminal(s) (calyx, calyces). These segments, termed the neuron branches, and the calyces frequently have spinelike processes of various dimensions that morphologically are afferent, efferent, or reciprocal to other macular neural elements. The purpose of this research was to determine whether morphometric data obtained ultrastructurally were essential to compartmental models [i.e., they influenced action potential(AP) generation,latency, or amplitude] or whether afferent parts could be collapsed into more simple units without markedly affecting results. We used the compartmental modeling program NEURON for this research.old decreased AP peak latency by less than or equal to 54%.