Alterations of the synaptosomal membrane 'microviscosity' in the brain cortex of rats during aging and centrophenoxine treatment.

Synaptosomal and myelin fractions were isolated from the brain cortex of young, adult and old male CFY rats (2, 12 and 24 mth, respectively). The purity of the fractions was tested by transmission electron microscopy and marker enzyme assays. The cholesterol content of the fractions was also determined. Samples of the fractions were labelled with diphenylhexatriene (DPH) and the fluorescence anisotropy (r) of the label was measured at various optical densities. The values of r extrapolated to zero optical density were compared in the age groups and used for calculating the 'microviscosity' of the membranes. The 'microviscosity' of synaptosomal membranes displayed a significant age-dependent increase: from 2.3 +/- 0.02 (SD) in the young group it increased to 2.6 +/- 0.03 poise by the age of 24 mth at 37 degrees C. Most of this increase occurred between the adult and old age. The cholesterol content of the synaptosomes also increased significantly during aging. Centrophenoxine (CPH)-treatment with 100 mg/kg body weight daily dose for 2 mth was able to reverse the age-dependent alterations of both the membrane 'microviscosity' and the cholesterol content in the synaptosomes: the values returned nearly to the adult level. The results obtained are interpreted in terms of the membrane hypothesis of aging attributing to primary role to the free-radical induced membrane damage in cellular aging.