Evidence for neurosecretory cells in the cestode Hymenolepis microstoma

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Abstract
EM of the neck region of the cestode H. microstoma revealed neurons with the characteristics of neurosecretory cells. The neurosecretory cells differ from the other nerve cells by the presence of .alpha.-glycogen in the neurites, by their content of large electron-dense vesicles and by the ultrastructural manifestation of neurosecretory release sites. The dense neurosecretory vesicles, 915 .+-. 151 .ANG. to 1040 .+-. 201 .ANG. (1 .ANG. = 0.1 nm) in diameter, are formed at the Golgi complexes and accumulate in the axon varicosities or boutons, the synaptoid release sites. .omega.-Profiles, electron-dense focal sites, neurosecretory vesicles with contents of variable electron density and small electron-lucent vesicles set in a fine granular matrix are observed at the release sites. Neurosecretory material is released from the electron-dense vesicles into the intercellular spaces. Neurosecretory synapses are described.