FMRFAMIDE-RELATED PEPTIDES, PARTIAL SEROTONIN DEPLETION, AND OSMOREGULATION IN HELISOMA-DURYI (MOLLUSCA, PULMONATA)

Serotonergic neurons were studied by specific histological methods, an d neurons containing Phe-Met-Arg-Phe-NH2 (FMRFamide)-related heptapept ides were identified with an antiserum specific for these substances i n the central nervous system of the freshwater snail Helisoma duryi. S erotonergic neurons and their axons are present in all of the ganglia (paired buccal, cerebral, pedal, pleural, parietal, and single viscera l) and major nerves of the central nervous system. Large neurons conta ining FMRFamide-related peptide immunoreactivity are located in the le ft parietal and visceral ganglia, whereas a few small neurons are loca ted in the cerebral and pedal ganglia. Both serotonergic and FMRFamide -related peptide-immunoreactive dendrites and varicosities were observ ed in the kidney. A second antiserum with high affinity for FMRFamide- related heptapeptides was used to measure the levels of the immunoreac tive material in various tissues, and such material was found in every tissue analyzed. When snails were exposed to a medium isosmotic to th eir hemolymph, the levels of immunoreactive FMRFamide-related peptides increased in the hemolymph, central nervous system, mantle, and kidne y. Injection of dihydroxytryptamine, which is known to deplete seroton in content in the snail, also reduced the levels of FMRFamide-related- immunoreactive material in the above tissues. Therefore, serotonin may influence the levels of FMRFamide-related peptides in tissues by regu lating the rate of their synthesis, axonal transport, or release. Both serotonin and FMRFamide-related peptides could be involved in osmoreg ulation. J. Comp. Neurol. 393:25-33, 1998. (C) 1998 Wiley-Liss, Inc.