The pharynx of the nematode Ascaris suum: structure and function.

The pharyngeal muscle of nematodes consists of a syncytium of radial muscle whereby feeding occurs by the process of pharyngeal pumping. It is believed that the pumping behaviour of the pharynx may be partly controlled by the enteric nervous system (ENS), a component of the nematode nervous system which is associated predominantly with the pharynx. The distribution of serotoninergic and peptidergic (especially SALMF-amide-like) immunostaining is widespread in the ENS of Ascaris, being localized within the lateral and dorsal pharyngeal nerve tracts, the pharyngeal commissures, the nerve plexuses and associated nerve cells and fibres. Immunostaining for serotonin (5-HT) was only localized within the ENS. This paper also describes a method to enable in vitro pharmacological studies on the Ascaris pharynx. The effects of "classical" neurotransmitters and native nematode peptides on pharyngeal pumping behaviour in Ascaris have been investigated. The function of the pharynx in Ascaris is discussed.