Developmental changes in expression of a calcium-binding protein (spot 35-calbindin) in the Nervus terminalis and the vomeronasal and olfactory receptor cells.

The detailed localization of spot 35-calbindin and its ontogenic change were studied in Nervus terminalis, the vomeronasal organ and the olfactory epithelium of the rat by immunohistochemistry. At the embryonic days 12 and 13 (E 12-13), calbindin-immunoreactive cells were found in the outermost layer of the presumptive olfactory bulb and within the olfactory placode. At E 14 to the postnatal day 1 (P 1), intense calbindin-immunoreactivity was localized in ganglionated fiber bundles of Nervus terminalis coursing through the mesenchymal spaces on both sides of the nasal septum. Nervus terminalis decreased the immunoreactivity abruptly after P 1 and it showed no distinct immunoreactivity for calbindin at P 7 and thereafter. On the other hand, numerous receptor cells in the olfactory epithelium and the thicker vomeronasal epithelium exhibited weak to moderate immunoreactivity for calbindin at E 18-P 1. Their immunoreactivity decreased in intensity progressively after P 7 and no distinct immunoreactivity for calbindin was detected in most of the receptor cells, whereas moderate immunoreactivity was detected in most of the vomeronasal and olfactory nerves at P 28 and P 63.