Distribution of calbindin D-28k immunoreactivity in the cochlear nucleus of the young adult chinchilla.

Calbindin is a 28 kD calcium-binding protein found in neural tissue. Although its functional role in nerve cell physiological processing is still uncertain, previous investigations have suggested that because of its intracellular calcium buffering and regulation properties, it could influence temporal precision of neuronal firing to subserve temporal processing in the auditory brainstem, or could mediate monaural versus binaural coding, or be involved in synaptic plasticity (learning). The present study demonstrates differential calbindin immunoreactivity in the cochlear nuclear complex of the chinchilla, a rodent with exceptionally good low-frequency hearing. The most intense labeling in the cochlear cochlear nucleus was in somata of cartwheel and fusiform cells of the fusiform cell layer, and somata and process of the molecular layer of the dorsal cochlear nucleus (DCN). Only a relatively few scattered neurons were stained in the deep layers of DCN. In contrast, moderate labeling of neurons and neuropil throughout the ventral cochlear nucleus was seen. For instance, moderately stained spherical and elongate cells of the anteroventral cochlear nucleus were observed in contact with labeled puncta and amidst stained fibers. In the cochlear nerve root region, stained auditory nerve fibers and global cells were noted. In the posteroventral cochlear nucleus, principal cells of elongate and octopus shape were observed, in contact with labeled swellings and surrounded by labeled neuropil.