Protein gene product 9.5 in the developing and mature rat vomeronasal organ.

Protein gene product 9.5 (PGP 9.5) was immunocytochemically identified in structures of the developing and mature rat vomeronasal organ (VNO). This study started with embryos at 17 days of gestation. By this stage, PGP 9.5 was immunolocalized within both the receptor cells of the neuroepithelium and cells of the receptor-free epithelium, located on the opposite side of the lumenal space. Nerve fibers surrounding the nascent vomeronasal vein also showed PGP 9.5 immunoreactivity. Labeling was retained in the neuroepithelium and nerve fibers around the vein during development and into adulthood. Within the pool of receptor cells of the adult neuroepithelium, labeling was observed within the cytoplasm of the somata and dendrites; some receptor cells also expressed nuclear labeling. The number of immunoreactive cells in the receptor-free epithelium appeared to increase postnatally but by adulthood immunoreactivity virtually was absent. These results suggest a role for PGP 9.5 in development and maturation of the VNO and a continuing role within the steadily renewing receptor cell population found in the mature neuroepithelium. The findings of this study also suggest that PGP 9.5 is localized within the nerve fibers surrounding the vomeronasal vein from early in development through adulthood.