Fetal neocortical tissue blocks implanted in brain infarcts of adult rats interconnect with the host brain

The purpose of the present study was to study if the connectivity of fetal neocortical tissue blocks placed in ischemic brain infarcts of adult rats would be enhanced in rats housed in an enriched environment. We also investigated whether the enriched housing conditions could enhance the postischemic and postgrafting functional outcome, in terms of motor behavior. This part of the study has been published recently. The middle cerebral artery was ligated on the right side in 37 inbred, adult male spontaneously hypertensive rats. The rats were placed at random either in an enriched environment (groups A and B) or in standard laboratory cages (group C). Three weeks after the artery occlusion, blocks of fetal sensorimotor cortex (embryonic day 17) were transplanted into the infarct cavity of rats from groups B and C. After 9 weeks all transplanted rats received an injection, into the graft, of a mixture containing the two tracers Fluoro-Gold and biotinylated Dextran amine. The transplants revealed a structured morphology with whorls and bands of cells reminiscent of normal neocortex. Tracing of efferent transplant to host fibers with biotinylated Dextran amine showed pronounced intrinsic transplant projections, as well as fibers, although significantly fewer, to the host ipsilateral sensorimotor cortex, striatum, and thalamus. Host to transplant projections were revealed by Fluoro-Gold-labeled cells found in the ipsilateral host sensorimotor cortex, the basal nucleus of Meynert, the thalamic ventrobasal, ventrolateral and posterior nuclei, and in the dorsal raphe nuclei. We conclude that fetal frontal neocortical block grafts placed in brain infarcts of adult rats develop a morphology reminiscent of normal neocortex and that both afferent and efferent neural connections, although sparse, are established with the host brain, whether the rats are reared under enriched housing conditions or not.