Rene Couteaux (1909-1999) and the morphological identification of synapses

During a historical research, we realized that Rene Couteaux (1909-1999) was the first histologist who stained the postsynaptic structure of the neuromuscular junction. By means of Janus Green B dye, he revealed the membranous ʹsubneural apparatusʹ related to the ʹsynaptic gutterʹ. Hence, he justified the use of the physiological term ʹsynapseʹ in histology. A few years later, Couteaux localized acetylcholinesterase activity on this subneural apparatus with a histo-enzymatic method. The histochemical staining confirmed his histological observations that the subneural apparatus of the muscle cells was distinct from the nerve terminal. Thus Couteaux not only supported Cajalʹs neuron theory, but also gave decisive morphological basis to the concept of the synapse, thought to be up to that time a physiological entity. These observations were performed several years before the first electron microscopic data obtained in the U.S.A. When the electron microscopy became available in Europe, Couteaux studied the ultrastructural details of the myoneural synapse. He found evidence for the presynaptic ʹactive zoneʹ as a restricted zone of the thickened presynaptic membrane flanked on both sides with synaptic vesicles, some of which were observed to be opening into the synaptic cleft by exocytosis. Furthermore, the synaptic vesicles were shown to be displayed in two rows along the linearly prolonged active zone which is situated just above the ʹtrench-likeʹ junctional folds of the muscle membrane. The discontinuity of the synaptic structure was confirmed by the threedimensional observation of the intraneuronal network of neurofibrils with the first prototype of high-voltage electron microscope.