FOCAL ACCUMULATION OF INTRAAXONAL MITOCHONDRIA IN DEMYELINATION OF THE CAT OPTIC-NERVE

Mitochondrial accumulation has been reported at sites of degenerating nerve fibres. The reason for focal accumulation of mitochondria within axons has not previously been investigated. The aim of this study was to quantitate changes in mitochondrial concentration within demyelina ted axons and determine if these changes were due to obstruction of th e free passage of organelles within the fibre. The average number of m itochondria per unit area of axon within axons of normal cat optic ner ve and optic nerve in which demyelination had been induced with anti-g alactocerebroside (GC) was determined using transmission electron micr oscopy. Increased numbers of mitochondria were demonstrated at the sit e of demyelination, peaking at approximately two and a half times the value for normal non-lesioned nerves at 6-7 days after anti-CC adminis tration [0.66 +/- 0.06 (SD) mitochondria per mu m(2) of axon compared to 0.28 +/- 0.04 in controls; P < 0.05]. The mitochondrial concentrati on gradually decreased over the next 20 days towards normal values. Th e concentration of mitochondria within non-myelinated axons of cat ret ina (0.55 +/- 0.18) was also determined and shown to be comparable to the values for the demyelinated optic axons (0.66 +/- 0.06). It is pro posed that the accumulation of mitochondria within demyelinated axons reflects the adaptive process of the axon during the early restoration of impulse conduction rather than the obstruction of the free passage of organelles within the fibre.