The anatomical synapse in mammals by light and electron microscopy.
The original descriptions of synapses by light microscopy are examined, and their widths and numbers per neuron soma are compared in light and electron micrographs. Electron micrographs show the synaptic cleft very frequently normal to the plane of section. It is rare to find any connection of the synaptic knobs to any dendrite of another axon, and the granular appearance on the surface of unfixed mammalian neurons can be shown to be due to intracellular particles- probably mitochondria. It is concluded that the anatomical synapse is an artifact. This raises questions about the nature of chemical transmission and the vesicle hypothesis. It may require a reinterpretation of transmission, but does not affect physiological or pharmacological findings about the effects of transmitters.
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Hillman
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D002450:Cell Communication; D002462:Cell Membrane / Q000648:ultrastructure; D011232:Chemical Precipitation; D003712:Dendrites / Q000648:ultrastructure; D005189:False Positive Reactions; D006651:Histocytochemistry; D006801:Humans; D007478:Iontophoresis; D008854:Microscopy, Electron; D008954:Models, Biological; D009469:Neuromuscular Junction / Q000502:physiology / Q000648:ultrastructure; D009474:Neurons / Q000648:ultrastructure; D013194:Staining and Labeling; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure*; D013572:Synaptic Vesicles / Q000648:ultrastructure; D013574:Synaptosomes / Q000502:physiology / Q000648:ultrastructure