Small cardioactive peptide gene: structure, expression and mass spectrometric analysis reveals a complex pattern of co-transmitters in a snail feeding neuron.

The small cardioactive peptides (SCPs) are an important group of neural cotransmitters in molluscs where they are known to play both central and peripheral modulatory roles in the control of feeding behaviour. Here we show that in the snail Lymnaea the SCP gene exists in one interrupted copy that produces a single species of transcript which encodes a prepropeptide containing two structurally related SCPs SGYLAFPRMamide (SCP(A)) and pQNYLAFPRMamide (SCP(B)). In situ hybridization was used to localize expression specifically to the soma of several types of motoneurons in the feeding system of Lymnaea, including the giant B2 foregut motoneurons. The peptide content of individual B2 cell bodies was analysed by matrix-assisted laser desorption/ionization mass spectrometry and the structures of the SCPs predicted from the cloned gene were confirmed in these cells by post-source decay fragmentation analysis. Identical stimulatory activity for the two SCP peptides was demonstrated by their application to the isolated foregut, suggesting that their co-release from the B2 cells may play an important part in the co-modulation of gut motility, together with acetylcholine and the myomodulin family of peptides.

Molecular characterization of NOS in a mollusc: expression in a giant modulatory neuron.

Here we report on the molecular characterization of the first molluscan NOS in the CNS of the pond snail Lymnaea stagnalis. This Lymnaea NOS (Lym-nNOS) which is expressed preferentially in the CNS is most similar to mammalian neuronal NOS but contains tandem repeats of a seven amino acid motif not found in any other known NOS. We have localized Lym-nNOS to the serotonergic cerebral giant cells (CGCs) which modulate synaptic transmission within a neural network that generates feeding behavior. Our results suggest that the CGCs employ both NO and serotonin in the modulation of the central neural network underlying feeding.