Nerve growth factor receptor and the transplanted rat olfactory bulb.

Nerve growth factor receptor (NGFR) in the rat olfactory system is developmentally regulated, localizing to the olfactory nerve (ON) in the young rat, and to the olfactory bulb (OB) glomeruli in the adult (Vickland et al. 1991. Brain Res., in press). This pattern of immunoreactivity (IR) may indicate the state of axon growth in the young ON and synaptogenesis in the adult glomeruli. Additional experiments in our laboratory involving lesions to the ON in adult rats have shown a recapitulation of the developmental pattern of expression: NGFR-IR is again found along the ON. Longer survival times after lesioning show the reexpression of the adult pattern of NGFR-IR. This phenomenon was further explored in a transplant (TX) model to determine the changes in NGFR-IR in both the host and TX tissue. A fetal OB labeled with [3H]thymidine is placed into the space created by the removal of the OB of a neonatal rat. After survival times of 1, 2, 8, and 13 weeks, the host animal is sacrificed and the OB TX is processed using monoclonal antibody 192 IgG for NGFR. The host ON shows strong NGFR-IR in TX of 1- and 2-week survival times. In TX survival times of 8 weeks or more, NGFR-IR is observed in glomerulus-like structures. All of these glomerulus-like structures are near groups of neurons in the TX tissue, indicating that they may be functional, with appropriate synapses. Therefore, even though the adult pattern of NGFR-IR takes longer to become established than in normal rats, we have demonstrated that this pattern does so in the TX OB model.