Neuronal and fibre organization in neocortical grafts placed in post-ischaemic adult rat brain: a three-dimensional confocal microscopy study.

The dendritic morphology in neocortical grafts was studied with three-dimensional confocal laser scanning microscopy after microinjection of Lucifer Yellow into individual cells. The grafts had been implanted into infarct cavities in the neocortex of hypertensive rats 46 weeks earlier. The carbocyanine dye method was used to identify afferent (host to transplant) and efferent (transplant to host) connections. Pyramidal, nonpyramidal and glial cells were present in the transplants. Some dendrites had an almost normal appearance, but abnormalities (atypical orientation of apical, basal or oblique apical dendrites) were observed. Some bi-apical pyramidal neurons and pyramidal neurons with obliquely oriented apical dendrites were also observed. Carbocyanine dye-labelled fibres of different diameter formed a dense network in the transplant, enabling the border between transplant and host tissue to be clearly recognized. No labelled fibres were observed to enter the host brain. Fibres with "boutons en passant" and no preferential orientation were noted. It is proposed that Lucifer Yellow microinjection may be a useful method in studies aimed at improving graft morphology. Failure to demonstrate host to transplant connections with the carbocyanine dye method was contrary to earlier studies in which tracers were applied in vivo. A combined use of in-vivo and post-mortem tracer techniques is needed to establish the reason for the discrepancy.