Fig. 3

VTA DA neurons in the Tg2576 mice show mitochondrial alterations at 3 months of age. A Representative confocal images of AIF labeling in TH⁺ neurons from WT and Tg2576 mice at 3 months of age (scale: 10 μm). B The graph shows the % of AIF⁺ nuclei in DA neurons of the VTA (n = 4 mice per genotype; Unpaired t-test: **p = 0.0018). C TEM representative images of normal, swollen, and vacuolated mitochondria (upper row; original magnification 92.000x) from osmium-free TH-stained post-embedded VTA of 3-month-old WT (panels of middle row) and Tg2576 mice (lower row; original magnification 24.000x). Normal-appearing mitochondria (n in all panels) display a smooth outer membrane and well-preserved cristae filled with a regular electron density of the mitochondrial matrix. Swollen (s) and vacuolated-appearing (v) mitochondria exhibit dilation of the intermembrane space, vacuolization of the inner compartment, and an irregular appearance of matrix and cristae. Entirely vacuolized mitochondria (V) contain an amorphous substance or appear as empty vacuoles of various sizes. Although mitochondrial swelling and vacuolization are detectable in WT neurons, Tg2576 neurons show an increase of mitochondria at different stages of swelling and/or vacuolization (plots D-G). In all TEM panels, blue arrowheads point to TH-coding gold particles (scale bar: 30 nm for upper panels, and 130 nm for middle and lower panels; WT: n = 53 TH⁺ neurons; from 3 mice; Tg2576 mice: n = 51 TH⁺ neurons, from 3 mice. D Total density of mitochondria (0.68/μm² ± 0.05 and 0.76/μm² ± 0.04); E density of normal mitochondria (0.55/μm² ± 0.04 and 0.34/μm² ± 0.02; Mann-Whitney test: ***p = 0.0003), F density of swollen/vacuolated mitochondria (0.12/μm² ± 0.01 and 0.42/μm² ± 0.03; Mann-Whitney test: ****p < 0.0001), and G ratio of swollen-vacuolated/normal mitochondria (Mann-Whitney test: ****p < 0.0001)