Immunocytochemical localization of calretinin in the olfactory system of the adult lamprey, Lampetra fluviatilis.

The distribution of calretinin immunoreactive (CR-ir) structures in the adult lamprey (Lampetra fluviatilis) olfactory system was studied by using immunocytochemical techniques. In the olfactory epithelium, a subpopulation of olfactory receptor cells was CR-ir. In the olfactory bulbs, three different cell populations were observed. Large CR-ir cells (mitral cells) were located medially to the olfactory glomeruli and occasionally between them. In the inner cellular layer, two types of CR-ir perikarya were found: numerous small CR-ir cells (granule cells) and some medium-sized CR-ir cells (putative displaced periglomerular cells). In addition, different intensities of CR-ir fibers were present in particular rootlets of the olfactory nerves, as well as in particular glomeruli. The presence of CR-ir cells and fibers in all layers of the lamprey olfactory bulbs supports the idea that this protein is present in pathways underlying the processing of sensory information throughout evolution.