Analysis of spontaneous regeneration of olfactory structures with emphasis on myelination and re-innervation of cortical areas

Abstract

Regeneration of the lateral olfactory tract (LOT) occurs spontaneously after transection in developing rats. In neonatally LOT-transected rats, we observed a newly-formed myelinated tract near the rhinal sulcus. The aim of this study was to analyze the precise re-innervated cortical areas and to demonstrate ectopic LOT myelination in neonatally LOT-transected rats. Neonatal rats were subjected to unilateral LOT transection and simultaneous injection of a retrograde fluorescent tracer into the posterior olfactory cortex to evaluate the degree of transection. After 8 weeks, bilateral olfactory bulbs of the rats were subjected to multiple injections of an anterograde neuronal tracer to determine the extent of the regenerated fibers. In the completely LOT-transected rats, the regenerated fibers were distributed in the anterior olfactory cortices; the anterior olfactory nucleus, the olfactory tubercle, and the rostral part of the piriform cortex.Ectopic myelination of LOT was evident immediately below the rhinal sulcus in the completely and incompletely LOT-transected rats. We concluded that the regenerated bulbar fibers were confined to the regions of the anterior olfactory cortices and that ectopic myelination of the regenerated LOT occurred only at a specific site near the rhinal sulcus.

Acetyl-l-carnitine enhances myelination of regenerated fibers of the lateral olfactory tract

“…LOT transection was performed in P2 pups (n = 70) unilaterally on the left side, as described previously [11][12][13]. Briefly, the LOT was transected at the posterior half of the olfactory stria by inserting the tip of a knife (Ophthalmic Scleral MVR Knife, 25 gauge; Alcon, Tokyo, Japan) from the ventrolateral aspect of the head.…”

“…The lateral olfactory tract (LOT) is the main fiber tract of the central olfactory system and exclusively consists of myelinated axon fibers. We have recently demonstrated that the neonatally transected LOT can be replaced by newly-formed axon fibers connecting the olfactory bulb and the olfactory cortex (the olfactory tubercle and piriform cortex) via the transected site at a later stage [11][12][13][14]. Because the regenerated LOT is primarily composed of unmyelinated axon fibers, LOT injury is a good animal model to examine the effects of ALC on myelin formation in the developing brain.…”