Summary
The ultrastructure of neuromuscular junctions in various organs of a starfish and a holothurian was studied. All neurons were found to contain large (100–250 nm), densecore vesicles.
Cytochemical tests for acetylcholinesterase were negative for these neurons. The presence of proteinaceous neurosecretory material was contested by enzymatic digestion (pepsin) which did not attack the dense-core vesicles, as well as by incubation in phosphotungstic acid (PTA) which did not stain these structures. Staining with dichromate produced a positive reaction for 5-hydroxytryptamine.
In the absence of synaptic modifications even after specific staining with PTA, the transmission of nervous impulses is effectuated through exocytosis of 5-hydroxytryptamine at nerve endings in the muscle tissue.
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Dolder, H. An ultrastructural and cytochemical study of neuromuscular junctions in echinoderms. Histochemistry 44, 313–322 (1975). https://doi.org/10.1007/BF00490368
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DOI: https://doi.org/10.1007/BF00490368