Dopaminergic neuroprotection and regeneration by neurturin assessed by using behavioral, biochemical and histochemical measurements in a model of progressive Parkinson's disease

Abstract

Trophic effects of neurturin, a member of the glial cell line-derived neurotrophic factor-family, have been demonstrated on mesencephalic dopaminergic neurons, suggesting its therapeutic potential for Parkinson's disease. This study was designed to test the neuroprotective and regenerative effects of an intrastriatal injection of neurturin based on behavioral, neurochemical and histochemical changes in a rat model of progressive Parkinson's disease. An extensive and progressive dopaminergic lesion was unilaterally made by intrastriatal convection-enhanced delivery of 6-hydroxydopamine (6-OHDA), in which 20 microg of 6-OHDA dissolved in 20 microl of vehicle was infused at a rate of 0.2 microl/min. For neuroprotection study, recombinant human neurturin (5 microg in 5 microl of vehicle) was stereotaxically injected into the unilateral striatum. The 6-OHDA lesion was made on the ipsilateral side 3 days after the neurturin treatment. Tyrosine hydroxylase (TH)-immunoreactive neurons of the substantia nigra were protected from progressive degeneration in the neurturin-treated animals compared with the vehicle-treated animals 2 and 8 weeks after the 6-OHDA lesion. Eight weeks after the 6-OHDA lesion, dopamine concentration significantly increased in the striatum of neurturin-treated animals with improvement of methamphetamine-induced rotation behavior. For neuroregeneration study, 5 microg of neurturin was injected into the striatum 12 weeks after the 6-OHDA lesion. Four weeks after neurturin or vehicle injection, there were no significant differences in the survival of nigral TH-immunoreactive neurons between the groups. However, TH-immunoreactive fibers were thicker and more abundant in the striatum of the neurturin-treated rats compared to those of the control group, suggesting neurturin-induced growth of the dopaminergic axons. Striatal dopamine levels also significantly increased in the neurturin-treated rats compared with those in the control group of rats, accompanied by the recovery of methamphetamine-induced rotation in the neurturin-treated rats. In conclusion, an intrastriatal injection of neurturin is a useful method to protect nigral dopaminergic neurons from extensive cell death in a model of progressive Parkinson's disease, as well as to promote the axonal regeneration and dopaminergic function.