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 f etal neocortical tissue blocks placed in ischemic brain infarcts of ad ult rats would be enhanced in rats housed in an enriched environment. We also investigated whether the enriched housing conditions could enh ance the postischemic and postgrafting functional outcome, in terms of motor behavior. This part of the study has been published recently. T he middle cerebral artery was ligated on the right side in 37 inbred, adult male spontaneously hypertensive rats. The rats were placed at ra ndom either in an enriched environment (groups A and B) or in standard laboratory cages (group C), Three weeks after the artery occlusion, b locks of fetal sensorimotor cortex (Embryonic Day 17) were transplante d into the infarct cavity of rats from groups B and C. After 9 weeks a ll transplanted rats received an injection, into the graft, of a mixtu re containing the two tracers Fluoro-Gold and biotinylated Dextran ami ne. The transplants revealed a structured morphology with whorls and b ands of cells reminiscent of normal neocortex. Tracing of efferent tra nsplant to host fibers with biotinylated Dextran amine showed pronounc ed intrinsic transplant projections, as well as fibers, although signi ficantly 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 ad ult rats develop a morphology reminiscent of normal neocortex and that both afferent and efferent neural connections, although sparse, are e stablished with the host brain, whether the rats are reared under enri ched housing conditions Or not. (C) 1996 Academic Press, Inc.