ULTRASTRUCTURAL-LOCALIZATION OF ANTHO-RWAMIDE-I AND ANTHO-RWAMIDE-II AT NEUROMUSCULAR SYNAPSES IN THE GASTRODERMIS AND ORAL SPHINCTER MUSCLE OF THE SEA-ANEMONE CALLIACTIS-PARASITICA

Light microscopic studies have shown that the sea anemone neuropeptide s Antho-R Wamides I (<Glu-Ser-Leu-Arg-Trp-NH2) and II (<Glu-Gly-Leu-Ar g-Trp-NH2) are located in neurons associated with the oral sphincter m uscle of the sea anemone Calliactis parasitica. In the present ultrast ructural study, using the immunogold technique, we found Antho-R Wamid e-like material in the granular vesicles of neurons that make synaptic contacts with the myonemes of both gastrodermal and oral sphincter mu scle cells of Calliactis. Gastrodermal nerve cells contained immunorea ctive granular vesicles averaging 149.3 +/- 4.1 nm in diameter; smalle r granular vesicles (47.5 +/- 2.5 nm) were present at a labelled synap se. Neurites associated with the sphincter muscle had immunoreactive g ranular vesicles averaging 78.8 +/- 3.3 nm in diameter with smaller gr anular vesicles (63 +/- 4.4 nm) at three labelled neuromuscular synaps es. All Antho-R Wamide-immunoreactive vesicles were irregularly granul ar, unlike the typical dense-cored vesicles observed at some other syn apses in sea anemones. No evidence was found of storage or release at nonsynaptic sites (paracrine secretion). The Antho-R Wamide immunoreac tive neurites innervate the sphincter muscle fibers directly rather th an through intermediate neuronal pathways. This is the first ultrastru ctural evidence of a neuropeptide at a coelenterate neuromuscular syna pse.