Mytilus inhibitory peptides (MIP) in the central and peripheral nervous system of the pulmonate gastropods, Lymnaea stagnalis and Helix pomatia: distribution and physiological actions

The distribution and neuroanatomy of Mytilus inhibitory peptides (MIP)-cont aining neurons in the central nervous system and their innervation pattern in the peripheral nervous system of the pulmonate snail species, Lymnaea st agnalis and Helix pomatia, have been investigated immunocytochemically. by applying an antibody raised to GSPMFVamide. A significant number of immunor eactive neurons occurs in the central nervous system of both species (Lymna ea: ca 600-700, Helix: ca 400-500), but their distribution is different. In Lymnaea, labeled neurons are found in all central ganglia where a number o f large and giant neurons, previously identified physiologically, reveal MI P immunoreactivity. In Helix, most of the immunolabeled neurons are small ( 12-30 mu m) and concentrated in the buccal and cerebral ganglia; the pariet al ganglia are free of labeled cells. In both species, the ganglionic neuro pils, peripheral nerves, connectives, and commissures are richly supplied w ith immunolabeled fibers. The MIP-immunoreactive innervation pattern in the heart, intestine, buccal mass and radula, and foot is similar in both spec ies, with labeled axonal bundles and terminal-like arborizations (buccal ma ss, foot) or a network of varicose fibers (heart, intestine). Intrinsic neu rons are not present in these tissues. The application of GSPYFVamide inhib its the spontaneous contractions of the esophageal longitudinal musculature in Helix, indicating the bioactivity of the peptide. An outside-out patch- clamp technique has demonstrated that GSPYFVamide opens the K+ channels in central nerve cells of Helix. Injection of CSPYFVamide into the body cavity inhibits the feeding of starved Helix. A wide modulatory role of MIP at ce ntral and peripheral levels is suggested in Lymnaea and Helix, including th e participation in intercellular signalling processes and remote neurohormo nal-like control effects.