Transection Of Lateral Olfactory Tract Research Articles

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

It is well known that acetyl-l-carnitine (ALC) has various neuroprotective effects against neurodegenerative diseases. In addition, it has been reported that ALC facilitates myelination of regenerated axons after peripheral nerve injuries. We previously reported that spontaneous regeneration of the lateral olfactory tract (LOT), the main fiber tract of the central olfactory system, consistently occurred in newborn rats and a majority of these regenerated fibers were unmyelinated in neonatally LOT-transected young adult rats. To investigate the effects of ALC treatment on myelination in LOT, neonatal rats were treated with ALC after LOT transection. Immunohistochemistry for myelin basic protein showed more positive areas in ALC-treated rats than in control rats. Moreover, the number of myelinated axons of regenerated fibers was assessed using electron microscopy and was found to be statistically higher in ALC-treated rats compared to control rats. The study revealed that ALC accelerates myelination of regenerated fibers in neonatally LOT-injured young adult rats.

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

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.

Re-evaluation of spontaneous regeneration of the lateral olfactory tract

Spontaneous regeneration of the lateral olfactory tract (LOT) was re-evaluated in newborn rats using a fluorescent retrograde neuronal tracer as objective indicators of complete LOT transection. Complete LOT transection was evidenced by the loss of the white myelinated band characteristic for adult LOT and the total lack of retrograde neuronal labeling of mitral cells by Fast Blue that was injected during LOT transection. In completely LOT-transected young adult rats, mitral cells were retrogradely labeled consistently only by Fluoro-Gold that was injected into the olfactory cortex at the adult stage. Moreover, an anterograde neuronal tracer, biotinylated dextran amine (BDA), was demonstrated to pass from the neonatally LOT-transected bulb, through the transected retrobulbar site, towards the olfactory cortex, far caudally at a level near the optic chiasm. The regenerated structures lacked immunoreactivity for myelin basic protein and electron-dense myelinated axon bundles, and were also characterized by the thinness of the BDA(+) terminal zone within the olfactory cortex and the lack of its caudal extension. Young adult rats subjected to unilateral bulbectomy contralateral to the neonatally LOT-transected side showed perfect ability to discriminate cycloheximide solution by olfaction. From these findings, we conclude that the spontaneously regenerated olfactory system is functional despite structural incompleteness.

Expression of the Gene Encoding the Chemorepellent Semaphorin III Is Induced in the Fibroblast Component of Neural Scar Tissue Formed Following Injuries of Adult But Not Neonatal CNS

This study evaluates the expression of the chemorepellent semaphorin III (D)/collapsin-1 (sema III) following lesions to the rat CNS. Scar tissue, formed after penetrating injuries to the lateral olfactory tract (LOT), cortex, perforant pathway, and spinal cord, contained numerous spindle-shaped cells expressing high levels of sema III mRNA. The properties of these cells were investigated in detail in the lesioned LOT. Most sema III mRNA-positive cells were located in the core of the scar and expressed proteins characteristic for fibroblast-like cells. Neuropilin-1, a sema III receptor, was expressed in injured neurons with projections to the lesion site, in a subpopulation of scar-associated cells and in blood vessels around the scar. In contrast to lesions made in the mature CNS, LOT transection in neonates did not induce sema III mRNA expression within cells in the lesion and was followed by vigorous axonal regeneration. The concomitant expression of sema III and its receptor neuropilin-1 in the scar suggests that sema III/neuropilin-1-mediated mechanisms are involved in CNS scar formation. The expression of the secreted chemorepellent sema III following CNS injury provides the first evidence that chemorepulsive semaphorins may contribute to the inhibitory effects exerted by scars on the outgrowth of injured CNS neurites. The vigorous regrowth of injured axons in the absence of sema III following early neonatal lesions is consistent with this notion. The inactivation of sema III in scar tissue by either antibody perturbation or by genetic or pharmacological intervention could be a powerful means to promote long-distance regeneration in the adult CNS.

Short-Term Odor Memory: Effects of Posterior Transection of the Lateral Olfactory Tract in the Rat

Thanos, P. K., B. M. Slotnick. Short-Term Odor Memory: Effects of Posterior Transection of the Lateral Olfactory Tract in the Rat. Physiol Behav 61(6) 903–906, 1997.—Rats were trained on a series of novel 2-odor discrimination problems before and after combined unilateral bulbectomy and posterior transection of the contralateral lateral olfactory tract. In postoperative tests, experimental rats performed as well as controls when a short intertrial interval (30 seconds) was used but, in contrast to controls, failed to learn a 2-odor discrimination when the intertrial interval was 10 minutes. When tested on a reversal task, controls showed memory for original learning by making many errors while experimental rats quickly acquired the task. The results suggest that lateral olfactory tract afferents to posterior olfactory cortex may play a significant role in short-term memory for odors.

In goldfish the qualitative discriminative ability for odors rapidly returns after bilateral nerve axotomy and lateral olfactory tract transection

After amino acid discrimination training (Arg vs. Gln) in 5 groups of 2 fish the olfactory nerves and in 5 groups the lateral olfactory tracts were intracranially and bilaterally dissected. Immediately after this operation both groups of fish were unable to discriminate concentration differences and contaminated stimuli. Two weeks after the operation, following functional regeneration, both groups again were able to discriminate stimulus concentration differences and contaminations as they did before the operation. Therefore functional regeneration of the olfactory nerves (peripheral regeneration) and lateral olfactory subtracts (central regeneration) is highly specific.

Developmental changes in the astrocytic response to lateral olfactory tract section.

When the lateral olfactory tract (LOT) of the golden hamster, Mesocricetus auratus, is transected in the first week of postnatal life, axons can grow back past the lesion and achieve functional reinnervation of caudal projection regions. In contrast, when the tract is sectioned after postnatal day 7 (P7), axons do not reinnervate regions caudal to the cut. The experiments reported here investigated whether regenerative failure after tract section in pups older than P7 is accompanied by developmental changes in the astrocytic response. LOT transections were performed at P3 and P9 and the glial reaction was observed at survival times ranging from 12 hr to 2 weeks. Immunocytochemistry with glial fibrillary acidic protein (GFAP) was employed for histological visualization of astrocytic reactivity. Staining for GFAP immunoreactivity showed an appreciable glial reaction after tract section at both P3 and P9, but the extent of astrocytic hypertrophy and proliferation of glial processes was considerably greater and more extensive after tract section at P9. Radial glial cells were observed 2 weeks after LOT transection at P3 but were absent after lesions made at P9. The results from this study suggest that the developmental loss of regenerative capacity after LOT transection may be related to maturational changes in the glial response. In particular, the presence of radial glial elements after P3 lesions could serve to establish a more favorable microenvironment for axonal elongation.

Developmental factors affecting regeneration in the central nervous system: early but not late formed mitral cells reinnervate olfactory cortex after neonatal tract section

If the lateral olfactory tract (LOT) of the golden hamster is transected in the first week of postnatal life, axons will grow back through the cut and reinnervate the terminal regions. Functional recovery occurs only when the terminal regions are reinnervated. The experiments reported here tested the hypothesis that reinnervation is due to neogenesis: the continued growth of newly formed axons which were not severed by the lesion. In the first experiment the birth dates of the mitral and tufted cells were determined in the hamster. It was found that mitral cells are formed on gestational days 11 and 12 (E11 and E12) and tufted cells on E11 to E14. Experiment 2 involved the combination of [3H]thymidine labeling, for the time of cell formation, with the retrograde transport of horseradish peroxidase (HRP), at a time when the LOT projections are not yet complete. The axons of early formed cells were found to reach the olfactory cortex before those of later formed cells. Experiment 3 examined the possibility that the axons which grow through an early LOT transection are new axons that had not yet reached the level of the cut. Animals were given [3H]thymidine to label the times of formation of mitral and tufted cells and then were given a transection of the LOT on postnatal day 3 (P3). After a recovery period sufficient to allow axonal regrowth and reinnervation, HRP was placed in the olfactory projection region caudal to the prior LOT section. The original hypothesis was not supported. Cells that are formed early and send out their axons early are able to reinnervate the olfactory cortex, whereas late formed cells do not. The results of this experiment suggest that the factors which prevent the regrowth of axons when the LOT is cut after P7 may depend on the stage of development of the tissue into which the axons are growing, rather than in the cells of origin and their axons.

Transmission and integration of biologically meaningful olfactory information after bilateral transection of the lateral olfactory tract in the rat

The contribution of the olfactory inputs conveyed by the lateral olfactory tract (LOT) to the central olfactory areas in the onset of behavioral and electrophysiological responses i.e. multiunit activity of mitral cells was studied in rats which were submitted to a bilateral transection of LOT. The characteristic emotional reactions elicited in sham-operated rats by biologically meaningful odorants — odors of predator or of conspecific — were no longer observed after such lesion. At the olfactory bulb level, the differential habituation of mitral cell electrical responses according to the biological meaning of the stimuli disappeared in the rats with a bilateral section of LOT. However the awaking influence of the odorants when stimulations occurred during slow wave sleep remained unchanged: all the rats were more often awakened by the odor of predator than by the other stimuli. On the other hand, an inhibitory centrifugal influence of LOT on mitral cell electrical responses was noted in rats with a unilateral transection of LOT. The results are discussed in relation to the two olfactory pathways (lateral and medial). During wakefulness, LOT seems essential to the olfactory information processing; in slow wave sleep, the medial olfactory pathways appear to mediate olfactory discrimination and to elicit adapted arousal.

Components of mating dissociated by lateral olfactory tract transection in male hamsters

Components of mating dissociated by lateral olfactory tract transection in male hamsters