Some Features of the Submicroscopic Morphology of Synapses in Frog and Earthworm

Abstract

Electron micrographs are presented of synaptic regions encountered in sections of frog sympathetic ganglia and earthworm nerve cord neuropile. Pre- and postsynaptic neuronal elements each appear to have a membrane 70 to 100 A thick, separated from each other over the synaptic area by an intermembranal space 100 to 150 A across. A granular or vesicular component, here designated the synaptic vesicles, is encountered on the presynaptic side of the synapse and consists of numerous oval or spherical bodies 200 to 500 A in diameter, with dense circumferences and lighter centers. Synaptic vesicles are encountered in close relationship to the synaptic membrane. In the earthworm neuropile elongated vesicles are found extending through perforations or gaps in the presynaptic membrane, with portions of vesicles appearing in the intermembranal space. Mitochondria are encountered in the vicinity of the synapse, and in the frog, a submicroscopic filamentary component can be seen in the presynaptic member extending up to the region where the vesicles are found, but terminating short of the synapse itself.

Observations on the Fine Structure and Cytochemistry of Mouse and Human Intercostal Neuromuscular Junctions

“…The axoplasm of the terminal axon branches contained moderate numbers of mitochondria, approximately 0.2 × 1 #, that were filled with transverse cristae. The axoplasm in well fixed preparations was finely granular and contained variable numbers of round or oval profiles of "synaptic vesicles" (14). The vesicles, which measured approximately 300 A in diameter, were usually most prominent on the axoplasmic surface overlying the sarcolemma.…”

The basis for silver staining of synapses of the mammalian spinal cord: a light and electron microscope study

“…Also in some regions they mark the terminal parts of axons, where they form characteristic rings, clubs and reticulated structures, the classical 'boutons terminauX' (Cajal, 1911;Bartelmez & Hoerr, 1933;Bodian, 1937). Neurofilaments, fine osmiophilic threads 60-100A in diameter, have been described in electron micrographs by Schmitt & Green (1950), Fernandez-Moran (1954), de Robertis & Bennet (1955) and Palay & Palade (1955). These authors have suggested that the neurofilaments form the basis of the neurofibrillae of light microscopists.…”

Evidence that protons act as neurotransmitters at vestibular hair cell–calyx afferent synapses

“…synaptic transmission | indefatigable I nformation transmission in the nervous system occurs primarily through chemical signaling by small molecules packaged in synaptic vesicles and released quantally (1,2) and gaseous free radicals that diffuse through 3D tissue volumes, oblivious to membrane boundaries (3)(4)(5). These two chemical modes of neurotransmission often act synergistically and in some systems, are augmented by electrical ephaptic interactions (6) and gap junctions (7).…”