Fetal tissue transplants in animal models of Huntington's disease: the effects on damaged neuronal circuitry and behavioral deficits

Accumulating evidence indicates that grafts of embryonic neurons achieve th e anatomical and functional reconstruction of damaged neuronal circuitry. T he restorative capacity of grafted embryonic neural tissue is most illustra ted by studies with striatal tissue transplantation in animals with striata l lesions. Striatal neurons implanted into the lesioned striatum receive so me of the major striatal afferents such as the nigrostriatal dopaminergic i nputs and the gluatmatergic afferernts from the neocortex and thalamus. The grafted neurons also send efferents to the primary striatal targets, inclu ding the globus pallidus (GP, the rodent homologue of the external segment of the globus pallidus) and the entopeduncular nucleus (EP, the rodent homo logue of the internal segment of the globus pallidus). These anatomical con nections provide the reversal of the lesion-induced alterations in neuronal activities of primary and secondary striatal targets. Furthermore, intrast riatal striatal grafts improve motor and cognitive deficits seen in animals with striatal lesions. Since the grafts affect motor and cognitive behavio rs that are critically dependent on the integrity of neuronal circuits of t he basal ganglia, the craft-mediated recovery in these behavioral deficits is most likely attributable to the functional reconstruction of the damaged neuronal circuits. The fact that the extent of the behavioral recovery is positively correlated to the amount of grafted neurons surviving in the str iatum encourages this view. Based on the animal studies, embryonic striatal tissue grafting could be a viable strategy to alleviate motor and cognitiv e disorders seen in patients with Huntington's disease where massive degene ration of striatal neurons occurs. (C) 2000 Elsevier Science Ltd. All right s reserved.