Bombesin-like immunoreactivity in specific neurones of the snail Helix aspersa and an example of the coexistence of substance P and serotonin in an invertebrate neurone.

Serial sections of the suboesophageal ganglia from Helix aspersa were processed immunohistochemically for the localisation of bombesin-, substance P-, cholecystokinin-, vasoactive intestinal polypeptide- and serotonin-related substances. All of these substances were localized in specific neurones and processes. Bombesin-like immunoreactivity was found in both perikarya and terminals throughout the suboesophageal ganglia. In the visceral ganglion two giant neurones were discovered to contain both substance P- and serotonin-like immunoreactivity. We could not demonstrate the coexistence of pairs of the other substances in any other neurone in the suboesophageal ganglia.