Immunohistochemical demonstration of peptides, serotonin and dopamine-beta-hydroxylase-like material in the nervous system of the leech Hirudo medicinalis.

The central ganglia of the leech, Hirudo medicinalis, were processed for the immunohistochemical localisation of bombesin-, substance P-, cholecystokinin-, vasoactive intestinal polypeptide-, enkephalin-, serotonin- and dopamine-beta-hydroxylase-related substances. To varying extents all of the substances were localised in neuropile processes, and all, with the exception of substance P, were associated with specific perikarya. The most prominent neuropeptides, in terms of the number of immunoreactive neurones, were cholecystokinin and vasoactive intestinal peptide. The dopamine-beta-hydroxylase positive neurones are thought to be octopaminergic, and the serotonin monoclonal antibody revealed positive staining in the Retzius cells. We were unable to demonstrate the coexistence of pairs of substances in any neurones in the leech ganglia.