The brain and subarachnoid space as possible sites for endocrine tissue transplantation

Embryonic neural transplants across a major histocompatibility barrier: survival and specificity of innervation

The ability of embryonic tissue to survive cross-transplantation between histologically incompatible rat strains was examined by transplanting septal neurons from Sprague Dawley fetuses to adult Wistar rats (Ag-B6 to Ag-B2 histocompatibility haplotype). Transplants were found to survive without rejection over a period of 3 months. Furthermore, the laminar pattern of cholinergic innervation was similar to that of homogenic septal transplants and of intrinsic septal projections. These results suggest that embryonic neural tissue transplanted across major histocompatibility barriers are capable of survival for extended periods of time, and are in support of the concept of the privileged nature of embryonic tissue as a source of material for cross-transplantation.

Transplantation of reaggregates of embryonic neural retinae to neonatal rat brain: differentiation and formation of connections

Embryonic day 14 neural retinae were dissociated into single cells and reaggregated prior to transplantation over the superior colliculi of newborn rats. One month after transplantation, the brains of the host rats were examined for transplant differentiation and the formation of projections from the transplant to the host brain. All reaggregated retinal transplants differentiated in the host brain, showing normal lamination and cellular morphology. Electron microscopic examination demonstrated normal synaptology with the transplanted retinal neuropil. Horseradish peroxidase injections into the host superior colliculus retrogradely filled cells within the transplant. These cells were found in the lamina corresponding to the ganglion cell layer and displayed a morphology characteristic of normal ganglion cells. Lesions of the transplants confirmed the projection of the reaggregated retinal transplants to superior colliculus. Degeneration was also traced into a number of ther nuclei that are normally retinorecipient. The presence of degenerating synaptic terminals resembling those seen after eye removal in control rats was confirmed by electron microscopic examination. It appears that despite disruption of initial cell-cell associations early in retinal development and prior to transplantation, the reaggregated transplants retain the ability to differentiate and form appropriate connection with the host brain.