Aging Aging

Damage to Mitochondria 229sity (no. of particles/µm 3 of tissue) of synaptic mitochondria decreases significantlywith aging, their average size (average mitochondrial volume) increasesto reach a complete recovery of the total volume in a µm 3 of tissue (volumedensity) (8–10). These findings appear to be significant if referred to the limitedspecific volume where sampling has been carried out. In conclusion, itseems reasonable to assume that the data obtained by many laboratories priorto the introduction of the dissector procedure may still be trusted when theconclusions drawn refer not to quantitation of the total number of structuresbut to the relationships present among the structures (e.g., number of mitochondriafound in a synapse cross-section).4. Notes1. The buffer solutions should be prepared the day before their use. Freshly preparedsolutions are stable for a week if stored at 4°C.2. To prevent spontaneous polymerization during storage, commercial formalin containsmore than 10% methanol. Thus, to yield a high-purity solution, it is preferredto prepare the fixative for electron microscopy by depolymerizingpowdered paraformaldehyde.3. The commercially available glutaraldehydes have varying amounts of impuritieswhich can affect tissue fixation to a high extent. Although it is more expensive, theuse of glutaraldehyde of optimal purity is more advantageous to obtain a goodpreservation of biological samples. Glutaraldehyde is supplied as a 50% or 25%solution that stays relatively stable for long periods of time if stored in the cold. Ifthe solution turns yellow, some polymerization has occurred and the chemicalshould not be used unless it is purified with charcoal. However, the purificationprocedure implies that the concentration of the final clear, oily solution must bechecked with a recording spectrometer. Therefore, we recommend purchasing theright amount of glutaraldehyde to be used in a reasonably short period of time.4. Osmium tetroxide is volatile, and its fumes are very toxic and able to fix biologicaltissues. Thus, any manipulation involving this chemical should be performedin a fume cupboard. Exposure to the vapor should be kept to an absolute minimumand contact with hands and face should be avoided. Great care should betaken to avoid any contamination by dust particles or light, which would result ina striking decrease in the fixing capacity of the solution.5. Osmium vapors readily leak out of many containers, and in many electron microscopylaboratories a typical sign of this contamination is the black precipitatefound on the inside of refrigerator walls. To prevent this leakage, osmium solutionsshould be stored in glass vacuum-type blood collection tubes. Plugging themwith rubber stoppers prevents contamination of the surrounding environment.6. Before disposing of the used solutions of osmium tetroxide, neutralize them bytwice the volume of corn oil, a product that has a high percentage of unsaturatedbonds. Confirmation that the toxic osmium tetroxide has been completely inactivatedcan be obtained by soaking a piece of filter paper in corn oil and then