NEUROPEPTIDES MYOMODULIN, SMALL CARDIOACTIVE PEPTIDE, AND BUCCALIN INTHE CENTRAL-NERVOUS-SYSTEM OF LYMNAEA-STAGNALIS - PURIFICATION, IMMUNOREACTIVITY, AND ARTIFACTS

The neuropeptides myomodulin, small cardioactive peptide (SCP), and bu ccalin are widely distributed in the phylum Mollusca and have importan t physiological functions. Here, we describe the detailed distribution of each class of peptide in the central nervous system (CNS) of the s nail Lymnaea stagnalis by the use of immunocytochemical techniques com bined with dye-marking of electrophysiologically identified neurons. W e report the isolation and structural characterization of a Lymnaea my omodulin, PMSMLRLamide, identical to myomodulin A of Aplysia californi ca. Myomodulin immunoreactivity was localized in all 11 ganglia, in th eir connectives, and in peripheral nerves. In many cases, myomodulin i mmunoreactivity appeared localized in neuronal clusters expressing FMR Famide-like peptides, but also in a large number of additional neurons . Double-labelling experiments demonstrated myomodulin immunoreactivit y in the visceral white interneuron, involved in regulation of cardior espiration. SCP-like immunoreactivity also appeared in all ganglia, an d double-labelling experiments revealed that in many locations it was specifically associated with clusters expressing distinct exons of the FMRFamide gene that are differentially expressed in the CNS. Characte rization of the two types of SCP-antisera used in this study, however, suggested that they cross-reacted with both FMRFamide and N-terminall y extended FMRFamide-like peptides. Selective preadsorption with these cross-reacting peptides resulted in elimination of the widespread sta ining and retention of bona fide SCP immunoreactivity in the buccal an d pedal ganglia only. Buccalin immunoreactivity was limited to the buc cal and pedal ganglia. It did not coincide with the distribution of ei ther myomodulin or SCP. Most immunoreactive clusters were found in the pedal ganglia. (C) 1994 Wiley-Liss, Inc.