Fig. 2.

Ultrastructure of axonal mitochondria by transmission electron microscopy of chemically fixed and high-pressure frozen optic nerves. Mitochondria are highlighted in blue. A) Axonal mitochondria in a chemically fixed WT optic nerve are characterized by a small diameter and rather dark contrast probably induced by the strong heavy metal staining applied to obtain sufficient contrast in the SEM. B) Mitochondria in a high-pressure frozen WT optic nerve. Note that the cristae structure is clearly visible. C) Mitochondria in a chemically fixed Plp^−/Y optic nerve. D) Mitochondria in a high-pressure frozen optic nerve in Plp^−/Y. In both preparations mitochondria with abnormal morphology are detected when PLP is lacking. As in the WT samples, in the HPF prepared Plp^−/Y samples the structure of the cristae is better preserved as judged by the narrow alignment of inner and outer membrane, the shape of the cristae and the smoothness of the membranes. This quality of preservation allows a judgement of distinct ultrastructural changes at the resolution of the TEM. Scale bars 500 nm.