Helix Command Specific 2 (HCS2) gene is constantly expressed in parietal premotor (command) interneurons involved in control of the terrestrial snail Helix lucorum withdrawal behavior as a trigger element. It is also expressed under noxious conditions in other neurons presumably involved in withdrawal behavior. In this study we addressed the role of neuropeptide CNP4, encoded by gene HCS2, in the regulation of activity of the respiratory system, and in the influence on growth of isolated neurons in culture. It was shown that activity of the premotor interneuron elicits a direct effect (pneumostome closure), and a delayed intensification of respiratory movements. Application of CNP4 mimicked the delayed effects. Presence of the peptide CNP4 in solution for cultured neurons led to increase of neuronal growth. Immunochemical localization of the protein precursor encoded by gene HCS2 and peptide CNP4 in the cultured premotor interneurons revealed their preferential presence in the growth cones. The obtained results suggest that CNP4 may be secreted and involved in synergic regulation of behavior of a snail.