Functional effects of fetal striatal transplants.

Much interest has been generated in recent years by the finding that fetal brain tissue transplants into adult brain can survive and grow in the host brain. Most work has been done transplanting relatively homogeneous populations of dopaminergic nigral neurons. However, it is now clear that the more complex fetal striatal tissue, which contains multiple neuronal types, will also survive and grow when transplanted into excitotoxin-lesioned adult striatum. We review herein studies demonstrating that the fetal striatal transplants are functional in that they can elicit changes in behavior in the transplant recipients. The striatal transplants reverse the locomotor hyperactivity characteristic of bilateral excitotoxin lesions. However, there is some controversy about the reversal of the abnormal apomorphine- and amphetamine-induced locomotor responses by fetal striatal transplants into excitotoxin-lesioned striatum and the presence of absence of dopamine receptors within the transplanted tissue. We review the evidence for and against the existence of neuroanatomical connections between the host brain and the transplanted fetal striatal tissue. We also point out the possibility of neurotrophic factors mediating the recovery of spontaneous locomotor activity in light of recent evidence that neurotrophic factors may mediate the functional recovery following transplants of adrenal medulla tissue into dopaminergic deafferented striatum.