Neuromuscular junctions in the leech

Neuromuscular junctions on leech body wall muscle have been described. Based on vesicle morphology, there are two types of junctions, (I) clear vesicle terminals, and (II) dense core vesicle terminals. Further, the dense core terminals are‐of two types, (1) small terminals which appear to directly innervate body wall muscle cells, and (2) large terminals which appear to synapse on clear vesicle terminals which in turn innervate body wall muscle cells. The clear vesicle ending resembles known cholinergic junctions in other systems. The cores in the dense core vesicle terminals are regarded as containing 5‐HT because (1) they are structurally identical with the 5‐HT containing cores in granules of the Retzius cells, (2) they contain a chromaffin substance, and (3) they become radioactive when tritiated 5‐HT is present but not when 5‐HTP or noradrenaline is present.