Figure 1: Tyrosine hydroxylase (TH) immunohistochemistry in the substantianigra (SN) and striatum. (A) Representative immunofluorescent (IF) microphotographs demonstrating extensive loss of midbrain TH+ dopamine (DA) neuronal cell bodies (green) in the SN of RNU-/+ rats 4 weeks after unilateral 6- hydroxydopamine (6-OHDA) lesion. (B) No significant loss is observed in the SN of RNU-/+ rats following saline injection. (C) Quantitative analysis of TH-immunoreactive DA cells confirms a significant loss in cell number induced by 6-OHDA in the ipsilateral SN (ipsi lesion – L) as compared to the contralateral SN (control – CL) of RNU-/+ rats. (D) Immunohistochemical images indicate a depletion of TH-positivefiber density (brown) in the striatum of both RNU-/+ and RNU-/- rats 8 weeks after 6-OHDA injection (lesion – L,non-lesion – NL). (E) Quantitative analysis of TH+ fiber area confirms a significant reduction of ≈40-50% in striatal fiber density in the injected sites (X + SEM, Y + SEM, respectively). (F) Percent reduction of TH-fiber density after 6- OHDA injections does not differ significantly between RNU-/+ and RNU-/- rats; N = 3-4 rats per group.