Alignment and intracytoplasmic disintegration of synaptic vesicles in the brain cortex.

Perfusion fixation with highly concentrated aldehydes suggests that the synaptic vesicles undergo disintegration within the presynaptic ending upon touching the presynaptic membrane rather than being released by exocytosis into the intersynaptic cleft. Three factors have been explored in order to inquire further into the possible significance of the findings: (a) fixative concentration; (b) physiological activity; (c) cell depolarization. The transformation of the vesicles into amorphous, electron-dense material was observed in all experiments in all synapses, including those fixed with the lowest concentration of aldehydes. Besides, after acute ischemia and perfusion of excitatory and depolarizing pharmacological agents, the synaptic vesicles were seen to conflue upon the intersynaptic cleft in well-aligned rows. It was also found that the vesicles flow post mortem towards the intersynaptic cleft with absolute specificity.