Functions of peptide CNP4, encoded by the HCS2 gene, in the nervous system of Helix lucorum.

The aims of the present work were to study the role of neuropeptide CNP4, encoded by the HCS2 gene (which is expressed mainly in parietal command interneurons), in controlling the activity of the respiratory system, and also to study the effects of this neuropeptide on isolated defensive behavior neurons in prolonged culture. The influence of the command interneuron on the pneumostoma included a direct effect consisting of closure and a delayed effect consisting of intensification of respiratory movements. Application of neuropeptide CNP4 produced a pattern similar to the delayed effects seen on stimulation of the command interneuron, i.e., significant increases in the frequency and intensity of pneumostoma movements and strengthening of the rhythmic activity of the pneumostoma motoneuron. Studies of the effects of neuropeptide CNP4 on isolated neurons after prolonged culture showed that neuron process growth correlated with the presence of the neuropeptide in the medium. Identification of the location of the HCS2 precursor protein and neuropeptide CNP4 in isolated command interneurons after prolonged culture showed that that only those parts of the cell showing active process growth were immunopositive. Thus, neuropeptide CNP4 appears to be a secreted neuropeptide controlling respiratory system activity, which may also be involved in rearrangements of the network controlling defensive behavior in Helix snails.