The serotoninergic, cholinergic and peptidergic components of the nervous system in the monogenean parasite, Diclidophora merlangi: a cytochemical study.

Confocal scanning laser microscopy has been employed with immunocytochemical techniques to map the distribution of serotoninergic and peptidergic components in the nervous system of the monogenean gill-parasite, Diclidophora merlangi; results are compared with the distribution of cholinergic components, following histochemical staining for cholinesterase activity. While all three neurochemical elements are present in the central and peripheral nervous systems, the cholinergic and peptidergic systems dominate the CNS, whereas the PNS has a majority of serotoninergic nerve fibres. The cholinergic and peptidergic neuronal pathways overlap extensively in staining patterns, suggesting possible co-localization of acetylcholine and neuropeptides. Within the peptidergic nervous system, immunoreactivity to the pancreatic polypeptide family of peptides and FMRFamide were the most prevalent. Gastrin/cholecystokinin (CCK)-, neuropeptide Y-, substance P-, neurokinin A- and eledoisin-like immunoreactivities have been demonstrated for the first time in a monogenean parasite. The gastrin/CCK- and tachykinin-like immunoreactivities had an apparently restricted distribution in the worm.