A specific clinical protocol for use toward therapy of defective, diseased and damaged neurons in the mammalian brain, of particular usefulness for treatment of neurodegenerative conditions such as Parkinsons disease. The protocol is practiced by directly delivering a definite concentration of a nerve growth factor via delivery of the protein, an expression vector operably encoding the nerve growth factor, or grafting a donor cell containing such an expression vector into the substantia nigra and preferably also the striatum. The method stimulates growth of targeted neurons, and reversal of functional deficits associated with the neurodegenerative disease being treated.
