Abstract
Clinical trials of cell replacement therapy in Huntington's disease have shown its safety, feasibility, and potentially long-lasting effects. However, more needs to be known regarding the conditions that stimulate plasticity and compensation achieved by neural grafts to maximize posttransplantation recovery of such neurorehabilitative therapies. The effects of enriched environment (EE), behavioral experience, and transplantation can each separately influence neuronal plasticity and recovery of function after brain damage, and the mechanisms by which these factors interact to modify the survival, integration, or function of grafted tissues are at present unknown. To investigate the effects of variable housing conditions and duration on morphological and cellular changes within embryonic striatal transplants, rats received unilateral excitotoxic lesions of the striatum, followed by E15 whole-ganglionic eminence suspension grafts. The rats were divided into three groups according to housing: full-time EE, 1 h/day exposure to EE, or standard laboratory cages. The experimental design included “early” (7 weeks postgrafting) and “late” (13 weeks postgrafting) survival time points to explore the effects of exposure lengths to the three housing conditions. The morphological and cellular effects on the grafts were analyzed using immunohistochemistry, cell morphology, image analysis, and enzyme-linked immunoassay. Both the duration of the exposure and the housing conditions were seen to influence multiple parameters of grafted cell morphology. The factors acted either independently (e.g., on graft size), complementarily (e.g., on spine density), or had no distinctive effect (e.g., on lesion size) on graft development. Features of embryonic striatal grafts and their trophic milieu were influenced both by the complexity of the environmental conditions and by the length of exposure to them. The data suggest that neurorehabilitation should be a feature of clinical trials of cell transplantation in order to exploit the underlying mechanisms that promote anatomical integration of the grafted cells and maximize transplant-mediated functional recovery.