Delivery of neuroactive compounds to the brain: potential utility of genetically modified cells.

Several methods for chronic delivery of compounds to the central nervous system (CNS) now exist. Peripheral drug administration is generally safest, but not always effective. If direct CNS delivery of a substance is required, then CNS implantation of drug-delivery systems or grafting of various cell types to the brain can be performed, although none of these interventions are yet of consistent, proven benefit in Alzheimer's disease and other neurodegenerative disorders. Grafting of genetically modified cells to the brain may be an alternative delivery system of some substances to the CNS.