Cerebral cortex slices in sodium-free medium: depletion of synaptic vesicles.

Rat cerebral cortex slices superfused for 5 min in sodium-free medium after 30-min stabilization and 25-min superfusion periods in sodium-containing medium displayed a well-preserved tissue structure and mostly intact neurons and glial cells. Electron-microscopic morphometry showed the number of presynaptic terminals containing few (less than or equal to 10) vesicles to increase 3-fold after the 5-min depletion of sodium. The 90-min sodium depletion resulted in increased swelling and an additional decrease in synaptic vesicles. The results show that from a morphological point of view the substitution of sodium by choline with brain slice techniques is an eminently suitable method for studies on synaptic neurochemistry.