A gene named HCS2 has been isolated from single molluscan neurons involved in control of withdrawal behavior. The predicted amino acid sequence of the HCS2 protein contains precursor for neuropeptides with a C-terminal signature sequence YPRx. These peptides called were synthesized and polyclonal antibodies were raised. Recently homological to HSC2 gene was sequenced in Aplysia; immunochemical study has shown presence of CNP-IR neurons in the CNS of this mollusk. Another molluscan peptide, previously described as Mytilus SCP, also have an YPRL sequence, characteristic for CNP superfamily. CNP have a significant overlap with sequence of insect neuropeptides superfamily, called pyrokinins/PBAN. With the aid of antibodies we've found CNP homologues in nervous system in various families of Mollusca, in several representative species of Insecta and Annelida. Using the immunohistochemistry technique we delineated a map of the CNP-IR neurons in leech, Hirudo medicinalis. We performed intracellular recordings of CNP-IR neurons HE (heart exciter) in semi-intact preparation, and found inhibitory responses of the MNs and of the heart tube to peptide CNP4 application. Time parameters and direction of CNP4 effects on snail heart activity are very similar to the effects found in leech. Supported by RFBR, INTAS 01-2117.