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American Zoologist 1973 13(2):315-319; doi:10.1093/icb/13.2.315
© 1973 by The Society for Integrative and Comparative Biology
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Insect Neuromuscular Synapses

THOMAS SMYTH, JR., MARY HELEN GREER and DAVID J. G. GRIFFITHS
Departments of Entomology and Biophysics, The Pennsylvania State University University Park, Pennsylvania 16802

Miniature end-plate potentials were used in studying several aspects of the neuromuscular systems in the cockroach femur. The similar sizes and time courses of miniatures associated with fast and slow type excitatory axons suggest that they employ the same transmitter. There is other evidence also indicating that the essential difference between these two excitatory systems is in the number of packets of transmitter released per nerve impulse rather than different transmitter substances. From the shapes of miniatures it was suspected that typical muscle fibers might have a branching structure. This was confirmed by histological examination, intracellular stimulation, and intracellular dye injection. That inhibitory transmission is quantal is indicated by hyperpolarizing miniatures which occur at random time intervals. Inhibitory transmission can be made to fail and recover in a stepwise manner by manipulating the Ca/Mg ratio. In studies of toxins which affect transmitter release at vertebrate motor end-plates, botulinal toxin was found to be without effect at either excitatory or inhibitory junctions in cockroach muscle. However, black widow spider venom acted as it does in vertebrates, promoting massive release of transmitters and then permanent inactivation of the junctions.


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