Institute of Developmental Biology, Russian Academy of Science, Moscow, Russia

Abstract

In herbivorous pulmonate molluscs, activity of the buccal central pattern generator (CPG) for feeding is generally arrested during activation of CPG for defensive withdrawal. Using a serious of neuromorphological methods including axon backfilling and immunocytochemistry, we have investigated both basommatophoran, fresh-water pulmonates (Lymnaea stagnalis , L.auricularia, Planorbarius corneus) and stylommatophoran, terrestrial ones (Bradibaena fruticum, Helix pomatia, H.lucorum, Limax cinereaniger, Succinea putris), and found that a pair of pleural-buccal projecting neurons, the right and left PlB cells, are responsible for this coordination. Opposite to the feeding-defence hierarchy in pulmonates, defensive responses are inhibited during feeding arousal in a predatory opisthobranch Clione limocina. In spite of this difference, two symmetric neurons similar to the pulmonate PlB cells have been found to occur in the pleural ganglia of C.limacina. Specific features indicating the homology of the Clione PlB neurons to those of pulmonates are FMRFamide-like immunoreactivity and peculiar, indirect route of the axon which traverses the ipsilateral pedal ganglion on its way to the cerebral and buccal one. We conclude that homologous coordinating neurons conserved in gastropod evolution may underlie defence/feeding dominance in an opposite manner.