Distribution of calmodulin, calbindin-D28k and calretinin among rat olfactory nerve bundles.

Calmodulin, calbindin-D28k and calretinin are calcium-binding proteins largely distributed in the bipolar olfactory receptor cells. In the olfactory epithelium their distribution seemed to be random. Using immunohistochemistry we have examined their localization in rat olfactory axons extending to the olfactory bulb. Sections were analyzed both horizontally and vertically. Almost all fibers were immunoreactive for one of the three intracellular calcium-binding proteins whose distribution was not random among the bundles. Three different subclasses of fibers could be detected: calbindin-D28k and calretinin immunoreactivities were restricted to external fibers whereas calmodulin immunoreactivity was intense, abundant and largely distributed throughout the internal portion of the olfactory nerve. This additional degree of organization detected in the olfactory axons might play a role in odor discrimination.