Figure 1.

Complex IV activity within injured demyelinated axons. (A–E) In the active rim of chronic active multiple sclerosis lesions, identified by the loss of Luxol Fast Blue (A) and presence of MHC class II positive cells (B) in serial sections, the complex IV activity is at an intermediate level compared with normal appearing white matter and relatively inactive lesion centre (C). Surprisingly complex IV activity is increased in the inactive area of chronic lesions. There are a number of ovoid shaped structures containing intense complex IV activity in the active rim (C and insert). When the same serial section used for COX histochemistry (C) is immunofluorescently labelled for amyloid precursor protein (APP) (D), the complex IV active ovoid structures are APP-positive (D, E). However, not all APP reactive ovoids show complex IV activity (red, E). (F–I) The APP-positive linear segments of demyelinated axons without terminal ovoids (red in F and G) in chronic lesions are devoid of complex IV activity, brown punctate elements apparent at 100× magnification (F, arrows). The lack of complex IV activity in APP-positive demyelinated axons is not due to the lack of mitochondria as shown by the presence of porin reactive elements (green) in x–y and x–z confocal images (G arrows and inserts). In a separate chronic lesion, the immunofluorescent labelling of non-phosphorylated neurofilaments (SMI32) identifies an injured demyelinated axon (red in H and I) which also lacks complex IV active elements (H, arrowheads). The SMI32 (red) reactive axon lacking complex IV active elements contain numerous porin (green) reactive elements (I, arrowheads). x– y and x–z; confocal images of APP and porin immunoreactivity in x–y and x–z planes. Asterisk indicates inactive area of chronic multiple sclerosis lesion.