Ultrastructural study on the release of neurosecretory material from the sinus gland of the land crab,Gecarcinus lateralis

Summary Sites of release of neurosecretory material were examined in a neurohemal organ of decapod crustaceans, the sinus gland of the land crab, Gecarcinus lateralis. Such discharge into the circulation seems to occur primarily at interfaces between the neurosecretory axons and the acellular stromal sheath which is interposed between parenchyma and hemolymph. The evidence obtained from electron micrographs of adult specimens indicates that more or less intact secretory granules are released into the extraaxonal space primarily by the process of exocytosis. Synaptic-type vesicles are clustered in parts of neurosecretory axons facing the stromal sheath. Such vesicles are thought to result from rearrangement of membranes temporarily fused at the release site and to a minor degree from fragmentation of neurosecretory vesicles within the axon. The presence of nonmarginal vesicles and the occasional appearance of free intraaxonal dense material are interpreted as indications of a second, probably less frequent, mode of release of neurosecretory material.Supported by grants AM-3984, NB-00840, and NB-05219 from the U.S.P.H.S., administered by Dr. Berta Scharrer.I am greatly indebted to Mrs. Sarah Wurzelmann for her excellent technical assistance. I thank Dr. Dorothy E. Bliss for contributing the animals used in this study, and Mr. Murray Altmann for technical advice.