Quantitative analysis of tooth pulp afferent terminals in the rat brain stem.

This study analyzed quantitatively the ultrastructural features of tooth pulp afferent terminals and their presynaptic axonal endings (p-endings) in the trigeminal principal (Vp), dorsomedial oral (Vdm), and caudal nuclei (Vc). Mitochondrial volume, active zone area, apposed surface area, and vesicle number were highly correlated with afferent bouton volume. The afferent bouton volume varied widely in Vp, compared to that in Vdm and Vc. The values of all parameters of p-endings were within a narrow range, and were smaller than those of afferent boutons. The afferent bouton volume correlated with the number of postsynaptic dendrites and p-endings. These results suggest that pulpal afferent information is regulated in a unique manner in the each trigeminal sensory nucleus.