TH-immunoreactivity in the midbrain of (A) saline-treated WT mice, (B) saline-treated GFR α1+/− mice, (C) MPTP-treated WT mice, and (D) MPTP-treated GFR α1+/− mice. (E) Quantification of the average number of SN TH-positive neurons using one-way ANOVA analysis followed by Student-Nuemann-Kuels post-hoc test reveals that 26 month old GFR α1+/− mice treated with saline have significantly fewer SN TH-positive neurons than age-matched WT mice (*p<0.05). Two days after the completion of the subchronic MPTP regimen, no differences existed in the number of SN TH-positive neurons between saline-treated mice and MPTP-treated mice, regardless of genotype. Photomicrograph magnification=10x. N=8 per group. Error bars indicate SEM.