Regeneration of the olfactory tract following neonatal lesion in rats.

Neuronal regeneration following early postnatal olfactory tract transection (OTS) was investigated in newborn Wistar rats. Olfactory tract lesioned rats were sacrificed at different time periods and the brains processed for Nissl staining. This was used to study the neural cell architecture; fiber tracts (myelinated fibers) were examined with Luxol Fast Blue staining. In addition, a neuronal tracing technique (i.e., retrograde labeling) was employed to study the reestablishment of connections with the target sites following transection of the tract. Degeneration of the olfactory tract was evident at the 7th day following lesion. Regeneration of the tract was not apparent even up to 60 days following transection. However, by 240 days, the olfactory tract had regenerated and the tract fibers had reestablished connection. This was confirmed by retrograde labeling of mitral cells of the olfactory bulb with Fast Blue (FB) injected into the piriform cortex, the target site of these neurons. In this study, we show that mammalian olfactory tract can regenerate spontaneously if the olfactory tract is lesioned neonatally. The results suggest that the olfactory tract is an excellent model to investigate some issues related to central nervous system regeneration.