Figure 3.

Retrograde degeneration of SNc dopaminergic neurons. (A) Dopaminergic projections to the striatum (Str), NAc and OT. The diagram delineates these regions. Sections were stained with TH antibody to label dopaminergic projections (brown pigment). At 3 weeks of age, Mfn2 mutant animals show decreased TH-immunoreactive terminals in the dorsolateral striatum (outlined region). Later time points reveal widespread loss in the striatum. VTA projections to the NAc and OT are still present, albeit reduced, at 11 and 14 weeks (outlined regions in bottom two panels). (B) Dopaminergic neurons at the SNc and VTA. Sections of the midbrain were stained with TH and counterstained with Cresyl violet (blue) to identify dopaminergic neurons. At 11 and 14 weeks, the Mfn2 mutants exhibit reduced staining in the SNc, whereas the VTA is relatively preserved. The SNc and VTA regions are outlined. (C) Quantification of TH-staining. Measured values of the TH-positive signal from heterozygous and homozygous animals were normalized to wild-type controls. For each animal, three sections were measured. The Student's t-test was used to obtain P-values (*P < 0.05; **P < 0.001; n = 3–6), and the error bars represent the propagated error. (D) Quantitation of dopaminergic cell loss in the SNc. Counts from heterozygous and homozygous animals were normalized to wild-type controls (n = 3 for each genotype). For each animal, nine sections spanning the rostro-caudal extent of the midbrain were manually counted. Statistical analysis was performed as in (C). (E) Magnified images of (B) showing the loss of dopaminergic neurons and processes in Mfn2 mutant animals.