Regeneration of retinal axons in grafts of peripheral and central nervous tissue in the adult rat

1999

J. Comp. Neurol.

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This study examined whether prior regenerative growth through peripheral nerve (PN) bridging grafts influenced the specificity with which lesioned adult rat retinal ganglion cell (RGC) axons grew into co‐grafts of developing target tissue (fetal superior colliculus). Growth into nontarget (muscle) tissue was also examined. Autologous PN was grafted onto the transected optic nerve. After 14 days, the distal ends of the PNs were placed next to, or inserted into, embryonic tectal tissue or into autologous muscle grafts placed in frontal cortex cavities. Host retinal projections were examined 3–8 months later using anterograde and retrograde tracing techniques. In rats in which there was good apposition between PN and tectal tissue, small numbers of RGC axons were observed growing into the tectal grafts (maximum distance of 180 μm). No evidence of specific innervation of appropriate target regions within tectal grafts was detected, even though such regions (identified by acetylcholinesterase histochemistry) were often located close to the PN grafts. In rats with PN/muscle co‐grafts, the extent of retinal axon outgrowth was greater (up to 465 μm from the PN tip) and labelled profiles that resembled motor endplates were seen contacting muscle fibres. Previous studies have shown that spontaneously regenerating RGC axons consistently and selectively innervate appropriate target areas in fetal tectal tissue grafted directly into optic tract lesion cavities. Together, the data suggest that exposure to a PN environment may have reduced the extent of adult retinal axon growth into fetal tectal transplants and affected the way regenerating axons responded to specific developmental cues expressed by target cells in the co‐grafted tissue. J. Comp. Neurol. 412:617–632, 1999. © 1999 Wiley‐Liss, Inc.

contrasting

confidence: 44%

Section: Discussionmentioning

confidence: 99%

Section: Materials and Methods Surgerymentioning

confidence: 99%

mentioning

confidence: 91%

mentioning

confidence: 99%

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Retinal axon regeneration in peripheral nerve, tectal, and muscle grafts in adult rats

Tan

1999

J. Comp. Neurol.

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The morphology and connectivity of dissociated and reaggregated fetal tectal tissue transplanted to the midbrain of newborn rats

Bairstow

1992

Exp Brain Res

Tectal tissue from E15 or E16 Wistar rat embryos was dissociated and reaggregated (DR) prior to transplantation on to the midbrain of newborn host rats. We wished to determine how complete disruption of the donor tissue (i) affected the subsequent morphological development of the grafts in the host brain, and (ii) whether this procedure affected the selectivity with which host retinal axons innervated target regions in the tectal transplants. Forty-three to 135 days after transplantation, host rats received binocular injections of wheatgerm agglutinin-conjugated horseradish peroxidase. After perfusion, frozen sections of the grafts and underlying host brainstem were cut and reacted with tetramethylbenzidine to identify retinal projections, or stained for either acetylcholinesterase (AChE), Nissl or neurofibrils. All host brains contained identifiable DR grafts. Each brain contained at least one large transplant and numerous smaller pieces of graft tissue. The fragmentation of DR grafts was greater than that seen in direct, undissociated tectal transplants; however the morphology of individual DR grafts was markedly similar to direct grafts. Of particular interest was the presence in DR grafts of localized, often oval or circular regions, that possessed high AChE activity and contained mostly small (5 to 10 microns) close-packed neurons. AChE-dense patches were found both superficially and deep within DR grafts and appeared identical to those seen in direct transplants. These regions are thought to be homologous to the superficial, retinorecipient layers of normal superior colliculus (SC) and it is likely that the formation of these localized areas resulted from the selective association of presumptive SGS neurons within the reaggregating neuropil. In almost all cases, host retinal input to DR grafts was confined to the localized AChE-dense patches, suggesting that despite the dissociation procedure, specific retinal innervation of regions containing at least some of the appropriate target cells was maintained in DR tectal grafts.

The migration and intermixing of donor and host glia on nitrocellulose polymers implanted into cortical lesion cavities in adult mice and rats

Intl J of Devlp Neuroscience

Fan

Connor

et al. 1993

The fate of neonatal glia (mostly glial fibrillary acidic protein-positive astrocytes), cultured on nitrocellulose papers and implanted into cortical lesion cavities, was examined in adult mice and rats. In mice, a Y-chromosome-specific probe and in situ hybridization techniques were used to identify male cells. Male-female grafts allowed visualization of donor glia and their behaviour after transplantation; female-male grafts allowed an analysis of how host cells responded to the presence of the implants. There was substantial intermixing of cells, with many donor glia migrating away from the implants and host cells migrating onto both sides of the nitrocellulose paper. In rats, donor glia were labelled with fluorescein-conjugated latex microspheres prior to transplantation on nitrocellulose polymers. The rat data were broadly consistent with those obtained from the mouse; moreover, immunohistochemical studies in rats suggested that the majority of host cells migrating onto the previously cell-coated papers were astrocytes. In a number of studies, glia-coated polymers have been used in an attempt to promote the regrowth of axons across lesion sites in the brain and spinal cord. The present work suggests that both transplanted and host glia may influence the regenerative growth seen in such implants.