Journal of neural transplantation最新文献

Tectal tissue was removed from rats at embryonic ages (E) E15, E18, E20 and postnatal day 0 (P0) and grafted onto the midbrain of newborn host rats. Six to 24 weeks after transplantation we examined 1) the growth characteristics of the grafts, 2) their morphology and 3) the pattern of retinal innervation of the grafted tissue. Graft survival was markedly affected by donor age. Transplants from E15 and E18 donors showed a survival rate of 90% which decreased to 35% when tissue was taken from E20 animals. Only one graft could be definitively identified in the P0 group. The ultimate volume of the graft was inversely related to donor age; grafts taken from E15 donors grew in size and produced the largest grafts, whereas E20 grafts showed a reduction in tissue volume from the time of implantation. Host retinal input was found in surviving grafts from all fetal donor ages (E15-E20). This input was always restricted to localized areas in the grafts containing high AChE activity; these areas are believed to contain presumptive superior collicular cells from the superficial layers. Thus, in tissue taken from fetal rats, it appears that altering the donor age does not affect the selectivity with which host retinal axons grow into and innervate specific areas within tectal grafts.

Vibrissal follicles on one side of the mouse whiskerpad are topologically connected to barrels in the contralateral somatosensory cortex. Barre's develop from postnatal day 3 to 6. Recently, I have observed that the barrelfields still develop in pieces of parietal cortex that were removed and reimplanted, in the same place and with the original orientation, on the day of birth, or on postnatal days 1 or 3. Now, two questions were asked: (i) Can the barrelfield form and/or remain in place after interrupting thalamocortical connections at different ages (from birth to postnatal day 9)? (ii) How does the cortex behave, in terms of cellular layers, after the interruption of thalamocortical connections? To answer these questions the parietal cortex was removed and reimplanted in the same place with the original orientation, in 79 mice from a C3H strain. Fifty-one mice survived and were processed for histology. Their brains were cut coronally to facilitate the identification of the limits of the reimplanted cortex and of its cellular layering. In 29 cases the reimplanted cortex could be identified, and in 17 cases barrel-like structures had developed. The "barrelfields" were obtained from coronal sections of each piece of reimplanted cortex, by means of a computer program which permitted reconstructing these pieces of cortex and rotating them in space. In this way, barrel-like structures and "barrelfields" could be visualized as if obtained from sections made tangential to the parietal cortex. "Barrelfields" were found in pieces of cortex reimplanted at different ages up to postnatal day 9. Cortical layers appeared to be more close to normal in cases operated after postnatal day 5.

Adult rats that sustained unilateral motor cortical lesions at birth demonstrated deficits in traversing an elevated narrow beam. These deficits, manifested by hindlimb slips off the edge of the beam, were not spared in animals that received fetal cortical transplants into the lesion cavity immediately after lesion placement.

The immunohistochemical detection of the thymidine analog, 5-bromo-2'-deoxyuridine (BrdU) is shown to be a useful and reliable method to positively identify fetal brain transplants in standard histological preparations. This technique offers several advantages over the [3H]thymidine autoradiographic method, including being much more rapid and avoiding the use of radionuclides.

The previous companion paper detailed a technique which allowed embryonic retinal ganglion cell axons to grow from the anterior eye chamber across a PNS bridge, and enter the adult host forebrain. Embryonic eyes of E11, E14, E18 and E21 animals were sutured to a PNS bridge, the embryonic eye implanted into an adult host eye, and the distal end of the bridge implanted into the host forebrain. Results indicate that when eyes of all ages are used for implantation, axons could be observed to grow from the embryonic retina, through the bridge and into the adult host forebrain. The axons extend for long distances in the host brain, reach various layers of the cortex and in a few animals enter the caudate/putamen complex. Control studies show that the bridge is used exclusively as the conduit to the brain, as opposed to the degenerated host optic nerve. Thus, the results presented in this paper indicate that successful grafting and transplantation is possible using the aforementioned technique. The results suggest that the described visual system reconstruction technique can be used for the study of development and transplantation in this system.

Blindness from retinal disease is often the consequence of extensive damage to the photoreceptor cell population, while other cell types which form the neural retina are relatively spared. In this setting, transplantation of photoreceptor cells could offer hope for the restoration of some degree of visual function. We tested the feasibility of this approach by transplanting immature retinal cells into the eyes of adult rats affected by late stage phototoxic retinopathy, which are almost totally devoid of photoreceptor cells. Dissociated neuroretinal cells from newborn rats were injected into the hosts' retinas. These cells were labelled with the fluorescent tracer Fast-blue for identification within the host eye. Survival time ranged from 3 to 100 post-transplantation days. Fundus examination of light-irradiated eyes showed pallor caused by a considerable reduction of the retino-choroidal vascular bed after light irradiation. Histologically the hosts exhibited decimation of the elements forming the outer layers throughout the entire retina. As visualized by light and electron microscopic procedures, we report the differentiation of clusters of transplanted photoreceptor cells, and the integration of these cells within the adjacent areas of the host retina. Fluorescence microscopy showed these clusters to be formed by fluorescently labelled cells developing in intimate contact with the unlabelled host retina. Electron microscopically it was possible to determine that these photoreceptors had established synaptic contacts. These observations indicate that successful transplantation of immature retinal cells is feasible into adult eyes that have suffered extensive retino-choroidal damage. These findings also support the concept that retinal transplantation is a procedure which may open new avenues into the study of retinal repair.

Studies of myelination after transplantation of mature oligodendrocytes to cerebellar cultures in which oligodendrocyte maturation and myelination had been irreversibly inhibited by exposure to cytosine arabinoside were reviewed. Transplanted oligodendrocytes were derived from three sources, including cerebellar explants treated with kainic acid, dissociated oligodendrocyte cultures, and optic nerve fragments. Oligodendrocytes from all sources migrated into the host explants and myelinated appropriate axons. The time of appearance of myelin and the percentage of host cultures myelinated differed for the three sources of oligodendrocytes, however. Myelin was visible earliest and in the highest percentage of host explants transplanted with cultured dissociated oligodendrocytes, which were presumably the most free to migrate into the host tissue, and latest and in the lowest percentage of host cultures transplanted with optic nerve, from which oligodendrocytes were presumably least free to migrate. Some myelin-like membranes unassociated with axons appeared in cerebellar cultures transplanted with cultured dissociated oligodendrocytes, and not in cerebellar explants transplanted with oligodendrocytes from other sources. The formation of such myelin-like membranes was interpreted as a manifestation of oligodendrocyte hyperreactivity induced by culture in isolation.

Various techniques have been explored to determine the uses and limitations of techniques that enable the adult CNS to regenerate, but relatively little attention has been given to the consideration of a "reconstructed" visual system. Using this approach, one can design experiments to study the uses of exogenous tissues in reestablishing neuronal circuits that have been damaged. Toward this end, experiments were designed to determine whether embryonic retinal ganglion cells can project axons into a grafted PNS "bridge", and enter adult host targets that were partially deafferented. Embryonic eyes of E11, E14, E18 and E21 rats were sutured to peripheral nerve segments which served as bridges between the host eye and frontal cortex. Projections between the developing retina and the host brain could then be evaluated using HRP tracing techniques. From a methodological standpoint, the preparations are 65% effective; i.e., a viable bridge results between the embryonic eye and the host forebrain. The results presented in the accompanying paper demonstrate that the technique can yield results indicative of embryonic retinal development and axonal projection through the graft and into the host brain. This partial reconstruction of the visual system may prove a useful tool in understanding the uses and limitations of grafting in the CNS.

Neuropeptide receptors were visualized in homografts of fetal cortex (E14) into adult rat cortex (immediate or 7 day delay) and spinal cord using in vitro autoradiographic techniques to explore the expression of peptide receptors in the same graft tissue in different central nervous system implantation sites. Receptors for bombesin (BN)-like peptides developed in the grafts by 3 weeks postimplantation regardless of location or age of implantation pocket in host. After 4 weeks, the density of BN receptors was confined to the graft. In grafts to spinal cord, however, high densities of BN-like receptors were not confined to the graft but were distributed throughout the spinal cord. In contrast, the density of vasoactive intestinal polypeptide (VIP) and substance P (SP) receptors was moderate and low to undetectable in the fetal grafts. The development of the peptide receptors studied was graft donor tissue specific since they were not altered by central nervous system implantation site.

Rats which receive injections of kainic acid (KA) into the striatum show many of the anatomical, biochemical and behavioral abnormalities seen in patients with Huntington's disease. Recently, it has been reported that fetal striatal transplants into the lesioned striatum could normalize the neurological and behavioral abnormalities produced by the KA lesion. The present study examined the issue of transplant integration in producing behavioral recovery. In one experiment, lesioned animals with transplants located within the lateral ventricle were compared against parenchymally transplanted rats. It was found that unless the ventricular transplant grew into the lesioned striatum there was no recovery. The second experiment demonstrated that electrolytic destruction of a successful fetal striatal transplant could reverse the transplant-induced behavioral recovery. These results suggest that the integrity of the transplant is important in maintaining behavioral recovery. A continuing functional interaction between the host brain and transplanted tissue may be a vital element in the success of the fetal striatal transplant.