Fine structural localization of acetylcholinesterase in sensory and motor neurons of the muscle receptor organ in Homarus

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Abstract
Histochemical techniques with the electron microscope for the localization of specific acetylcholinesterase and non‐specific cholinesterases have been applied to preparations of the abdominal muscle receptor organ, or stretch receptor, of the lobster. Reaction product specific for AChE was found to be localized in a discrete but interrupted fashion on the external surface of the cell membranes of both the fast and slow sensory neurons at the levels of axon, cell body, large and small dendritic processes, and fine dendritic terminations. Reaction product specific for AChE was also found on the external surface of the limiting membranes of motor axons, but not at neuromuscular endings. Non‐specific ChE was limited to cytoplasmic vacuoles and cisternae of the Schwann cells of the neural sheaths. These findings lend support to the hypothesis that in the lobster the ACh system may mediate membrane excitability of nerve fibers. Furthermore, at the level of dendritic terminations this system may mediate the transduction of mechanical into electrical energy via reversible permeability changes.