Occurrence of Cylindrical Synaptic Vesicles in the Central Nervous System Perfused with Buffered Formalin Solution Prior to OsO<sub>4</sub>-fixation

Abstract

In the brain perfused with buffered formalin solution and post-fixed with OsO4 fixative, there can be found a new type of synaptic vesicles which is not observable in materials simply fixed with OsO4 fixatives. These vesicles are of cylindrical form, 240-300A in diameter and 300-1000A in length. They occur either in terminals of the type of boutons terminaux or in neuronal processes forming synapses en passant, and can be found in various regions of the central nervous system examined, including olfactory bulb, cerebral and cerebellar cortex, hippocampal formation, septal region, habenular nuclei, dorsal nucleus of the lateral geniculate body, lateral pulvinar nucleus, preoptic area, hypothalamic suprachiasmatic and ventromedial nuclei and anterior horn of the spinal cord. The terminals containing such vesicles make synaptic junctions both with neuronal perikarya and with dendrites. There, the synaptic cleft is somewhat narrower and the thickening of the synaptic membranes are less marked than at synapses the presynaptic component of which does not contain cylindrical vesicles. Sometimes synaptic junction is formed between a terminal with cylindrical vesicles and that exclusively with ordinary, spherical vesicles. In the majority of these axo-axonal synapses the presynaptic component does not contain cylindrical vesicles but spherical ones solely.The terminals with cylindrical vesicles occur in a considerably constant freguency in a given area of the central nervous system. For example, it was estimated as 18% of all the terminals in the lateral pulvinar nucleus and 25% in the caudate nucleus.A possible explanation on the occurrence of these synaptic vesicles only in the perfused materials was presented and some comments on the perfusion technique were also made.