Sequential developmental acquisition of cotransmitters in identified sensory neurons of the stomatogastric nervous system of the lobsters, Homarus americanus and Homarus gammarus

We studied the developmental acquisition of three of the cotransmitters fou nd in the gastropyloric receptor (GPR) neurons of the stomatogastric nervou s systems of the lobsters Homarus americanus and Homarus gammarus. By using wholemount immunocytochemistry and confocal microscopy, we examined the di stribution of serotonin-like, allatostatin-like, and FLRFNH2-like immunorea ctivities within the stomatogastric nervous system of embryonic, larval, ju venile, and adult animals. The GPR neurons are peripheral sensory neurons t hat send proprioceptive information to the stomatogastric and commissural g anglia. In H. americanus, GPR neurons of the adult contain serotonin-like, allatostatin-like. and Phe-Leu-Arg-Phe-amide (FLRFNH2)-like immunoreactivit ies. In the stomatogastric ganglion (STG) of the adult H. americanus and H. gammarus, all of the serotonin-like and allatostatin-like immunoreactivity colocalizes in neuropil processes that are derived exclusively from ramifi cations of the GPR neurons. In both species, FLRFNH2-like immunoreactivity was detected in the STG neuropil by 50% of embryonic development (E50). All atostatin-like immunoreactivity was visible first in the STG at approximate ly E70-E80. In contrast, serotonin staining was not clearly visible until l arval stage I (LI) in H. gammarus and until LII or LIII in H. americanus. T hese data indicate that there is a sequential acquisition of the cotransmit ters of the GPR neurons. (C) 1999 Wiley-Liss, Inc.