Example of melanin-positive neurons and NRTN-immunostaining in PD substantia nigra, pars compacta (SNc). While many clusters of melanin-positive, dopaminergic perikarya were observed in nigra (A: low magnification and B: high magnification), only rarely did any nigral neurons show evidence for NRTN staining (e.g., C: high magnification). Panels A and B illustrate the general failure of nigrostriatal neurons to retrogradely transport NRTN to nigral perikarya following intraputaminal delivery of AAV2-NRTN, whereas Panel C illustrates a rare example of NRTN in the nigra from successful retrograde transport. Scale bar represents 220 μm in panel A and 22 μm in panels B and C.