Synaptic neuropil in nerves of the crustacean stomatogastric nervous system: An immunocytochemical and electron microscopical study

Patches of peptide-immunoreactive varicosities have been found in nerves of the stomatogastric nervous system (STNS) of decapod crustaceans. In the pr esent study, these patches were examined in detail in the stomatogastric ne rve (stn) and in the superior oesophageal nerve (son) of the crayfish Chera x destructor by using whole-mount immunocytochemical techniques combined wi th confocal microscopy and, in addition, electron microscopy. Double-labeli ng experiments with antibodies generated against the peptides allatostatin, FMRF-amide and proctolin, combined with an antibody generated against the small vesicle protein synapsin, suggest that each patch contains small syna ptic vesicles in addition to all three peptides. The neuropil regions of th e ganglia of the STNS were also strongly stained by the synapsin antibody. Synapsin-like immunoreactivity was also studied in the crab Cancer pagurus and the lobster Homarus americanus. A similar pattern of staining was found for all three species, but the distribution within the stn varied. In H. a mericanus, a lightly stained weblike structure was found on the surface of nerves including the inferior oesophageal nerve, the son, and the anterior stn. By using electron microscopy, synapses were found in the core of the s tn-son junction of C. destructor, in the same region where the synapsin-lik e and the peptide staining was localized. In addition, putative neurohemal release sites were found in the peripheral sheath of the stn. The presynapt ic profiles found in the core of the stn seem to correspond to the types of presynaptic profiles found in the neuropil of the stomatogastric ganglion. These findings demonstrate that synaptic neuropil is present in the nerves of the STNS of a decapod crustacean. J. Comp. Neurol. 420:373-397, 2000. ( C) 2000 Wiley-Liss, Inc.