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Functional morphology of the platyhelminth nervous system

Published online by Cambridge University Press:  06 April 2009

D. W. Halton  and
M. K. S. Gustafsson
D. W. Halton*
Affiliation:
Comparative Neuroendocrinology Research Group, School of Biology and Biochemistry, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland, UK
M. K. S. Gustafsson
Affiliation:
Department of Biology, Åbo Akademi University, Biocity, Artillerigatan SF-20500, Åbo, Finland
*
*Corresponding author.
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Summary

As the most primitive metazoan phylum, the Platyhelminthes occupies a unique position in nervous system evolution. Centrally, their nervous system consists of an archaic brain from which emanate one or more pairs of longitudinal nerve cords connected by commissures; peripherally, a diverse arrangement of nerve plexuses of varying complexity innervate the subsurface epithelial and muscle layers, and in the parasitic taxa they are most prominent in the musculature of the attachment organs and egg-forming apparatus. There is a range of neuronal-cell types, the majority being multi- and bipolar. The flatworm neuron is highly secretory and contains a heterogeneity of vesicular inclusions, dominated by densecored vesicles, whose contents may be released synaptically or by paracrine secretion for presumed delivery to target cells via the extracellular matrix. A wide range of sense organ types is present in flatworms, irrespective of life-styles. The repertoire of neuronal substances identified cytochemically includes all of the major candidate transmitters known in vertebrates. Two groups of native flatworm neuropeptides have been sequenced, neuropeptide F and FMRFamide-related peptides (FaRPs), and immunoreactivities for these have been localised in dense-cored neuronal vesicles in representatives of all major fiatworm groups. There is evidence of co-localisation of peptidergic and cholinergic elements; serotoninergic components generally occupy a separate set of neurons. The actions of neuronal substances in flatworms are largely undetermined, but FaRPs and 5-HT are known to be myoactive in all of the major groups, and there is immuno-cytochemical evidence that they have a role in the mechanism of egg assembly.

Keywords

Turbellariansmonogeneanstrematodescestodesnervous systemneuronssynapsesneurotransmittersneuropeptides
Type
Research Article
Information
Parasitology , Volume 113 , supplement S1: Molecular biochemistry and physiology of helminth neuromuscular systems , January 1996 , pp. S47 - S72
Copyright
Copyright © Cambridge University Press 1996

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