Immunoreactivity of protein gene product 9.5 (PGP 9.5) in the developing hamster olfactory bulb.

Protein gene product 9.5 (PGP 9.5) is a soluble protein isolated from human brain and recently demonstrated to correspond to ubiquitin carboxyl terminal hydrolase. We examined the PGP 9.5 immunoreactivity in the developing hamster olfactory bulb to determine whether the olfactory bulb expresses PGP 9.5 from the early developmental stage and whether it is a useful marker for investigating the differentiation of bulbar neurons and the development of laminar organization. The developing hamster olfactory bulb was fixed in Bouin's solution without acetic acid or acetic alcohol (95% absolute alcohol with 5% acetic acid) and immunostained with human PGP 9.5 antiserum by the avidin-biotin peroxidase complex (ABC) method. PGP 9.5 immunoreactivity was detected in the axons of olfactory and vomeronasal receptor cells and immature bulbar neurons from embryonic day 13 in the tissue fixed in Bouin's solution without acetic acid and in the immature bulbar neurons from embryonic day 11 in the tissue fixed in acetic alcohol. In some bulbar neurons, PGP 9.5 immunoreactivity was detected not only in the cytoplasm, but also in the nuclei. The pattern of immunostainings for PGP 9.5 became almost the same as in the adult at postnatal day 15. From the immunostaining for PGP 9.5, we found that the short axon cells in addition to mitral, tufted, and mitral/tufted cells were identified in the prenatal period and that the extension of the dendrites, formation of the glomeruli, and completion of the laminar organization were earlier in the main olfactory bulb than in the accessory olfactory bulb. PGP 9.5 can be a useful marker to investigate the differentiation of bulbar neurons and the formation of laminar organization in the developing olfactory bulb.