TrkA expression in mouse olfactory tract following axotomy of olfactory nerves

The olfactory bulb is one of the brain regions that synthesizes the nerve g rowth factor (NGF). Functional roles of the bulbar NGF remain to be determi ned. The aim of the present study was, using an antibody specific to the hi gh-affinity NGF receptor (trkA), to examine immunohistochemically the distr ibution of the NGF receptor in the mouse olfactory tract, under normal cond itions and during regenerative processes. In normal mouse olfactory epithel ia, trkA immunoreactive cell bodies were only seen in basal cells. Cell bod ies of olfactory receptor cells did not express trkA immunoreactivity, but their neuronal processes (olfactory nerve fibres and bundles in the olfacto ry mucosa and the olfactory bulb) displayed trkA immunoreactivity. After ax otomy of olfactory nerves, regenerating olfactory cells (basal cells and ol factory receptor cells) expressed trkA immunoreactivity in intramucosal and intrabulbar neuronal processes of olfactory receptor cells. These results suggest involvement of the bulbar NGF in the process of synaptogenesis and/ or regeneration of the olfactory nervous system.