The presynaptic active zone protein Bassoon as a marker for synapses between Type lll cells and afferent nerve fibers in taste buds

Taste buds are receptor organs for gustation. Two types of taste receptor cells have been identified in taste buds: Type II and Type III cells. Type III cells connect with afferent fibers through conventional chemical synapses. In the present study on taste buds, we used immunocytochemistry to examine the distribution pattern of Bassoon, a scaffolding protein of the cytomatrix at the active zones of conventional synapses. Bassoon was predominantly detected as small puncta in Type III cells. Bassoon-immunoreactive puncta were observed in proximity to or partially overlapping with intragemmal nerve fibers. Immunoelectron microscopy showed Bassoon at the active zones of the conventional synapses of Type III cells. The present results demonstrated that Bassoon is a marker for synapses between Type III cells and afferent fibers in taste buds.