Neural grafting to experimental neocortical infarcts improves behavioral outcome and reduces thalamic atrophy in rats housed in enriched but not in standard environments.

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Abstract
Background and Purpose The purpose of this study was to evaluate whether grafting of fetal neocortical tissue 1 week after focal brain ischemia improved behavioral outcome and reduced secondary thalamic atrophy. Methods One week after distal ligation of the right middle cerebral artery in spontaneously hypertensive male rats, blocks of fetal neocortex (embryonic day 17) were homografted to rats housed in standard or enriched environments. Control infarcted nongrafted rats were housed in the enriched environment. Behavioral outcome was repeatedly tested until the rats were killed 20 weeks after the ligation. Ten days earlier, a mixture of 2% Fluoro-Gold and 10% biotinylated dextran amine was injected into the transplants for retrograde and anterograde tracing of graft-host connections. Results Grafted and nongrafted rats with enriched housing performed significantly better than grafted rats with standard housing on a rotating pole and a prehensile traction test. Grafted “enriched” rats were moreover significantly better than grafted “standard” rats and nongrafted enriched rats in a rotation test and a postural and locomotor tail position test. In the latter test, nongrafted enriched rats performed significantly better than grafted standard rats. The lesion-induced atrophy in posterior thalamus with its major sensorimotor cortex relay nuclei was significantly reduced in grafted enriched rats compared with nongrafted enriched rats. Afferent and efferent graft-host connections were identified in both grafted groups. Graft volumes did not differ. Conclusions Neural grafting enhanced functional outcome and reduced thalamic atrophy only when combined with housing in enriched environments.