NEURONAL MEDIATORS IN MONOGENEAN PARASITES

In common with other flatworms, monogenean parasites are rich in neuroactive substances. In addition to the classical fast-acting cholinergic and aminergic neuronal components, involved in regulating motor activity and perhaps mediating sensory responses in the worms, are numerous, slow-acting peptidergic elements that possibly mediate much longer term events and behaviours. Using immunochemical procedures, as many as 10 regulatory peptide immunoreactivities have been demonstrated to date in the monogenean, Diclidophora merlangi. Of these peptides, by far the most abundant is neuropeptide F (NPF), a finding which is consistent with the observations in representatives of all major invertebrate phyla investigated. In D. merlangi, NPF occurs extensively throughout central and peripheral nerve elements, including those of the reproductive system. Moreover, in the female reproductive system, the innervation of the duct muscles that are responsible for the highly-ordered series of contractions and relaxations essential in egg assembly, appears to be exclusively peptidergic. While the functional properties of NPF have yet to be determined, its subcellular localisation at neuromuscular junctions in the egg-forming apparatus of D. merlangi supports a peptidergic involvement in reproductive function, perhaps in coordinating the cyclical sequence of muscle contractility involved in egg formation.