Fig. 1

Ultrastructural characterization of OPN in the lesion core 3 days after lesion induction by 3-nitropropionic-acid. Confocal microscopic image of a semi-thin section double-labeled with OPN and Iba1 (a), images of confocal data overlaid onto the corresponding electron microscopic image (b), and the corresponding transmission electron microscopic images obtained from the same field (c–g). a, b Confocal data shows the two different OPN-positive profiles based on their localization and shape: puncta scattered among the activated microglia/macrophages (arrowheads), and puncta localized to the perinuclear region of brain macrophages (arrow). c–d Higher-magnification views of the boxed areas in a. Note that silver-enhanced immunogold particles are specifically localized to the saccules and tubules in the Golgi complex, but not in the mitochondria (m). N, nucleus of an Iba1-positive brain macrophage. e–g Higher-magnification views of the boxed areas in b and e, respectively. Note that the OPN-positive puncta are indeed the swollen mitochondria (m in f and g) with disorganized cristae in the neurites or OPN-coated degenerating neurites containing small and highly electron-dense mitochondria (asterisk in g). Also, note that adjacent unlabeled neurites contain mitochondria that appear normal (m in inset of g). Cell nuclei appear blue after DAPI staining. Scale bars = 2 μm for a, b; 1 μm for c; 0.2 μm for d, f, g and g inset; and 0.5 μm for e