Immunocytochemical detection of vasoactive intestinal peptide-like and peptide histidine isoleucine-like peptides in the nervous system and the excretory system of adult Nippostrongylus brasiliensis.

Vasoactive intestinal peptide-like and peptide histidine isoleucine-like immunoreactivities were detected in the excretory duct of adult male and female Nippostrongylus brasiliensis, thus indicating the source of these two physiologically active peptides previously isolated from the excretory/secretory products of adult N. brasiliensis. In the nervous system immunoreactivity to both these peptides was confined to females and was found in the neurons of the ovijector associated ganglion. This is consistent with co-synthesis of vasoactive intestinal peptide-like and peptide histidine isoleucine-like peptides which has also been shown to occur in all mammalian vasoactive intestinal peptid-ergic neurons studied to date. However, in addition to this, and in common to some previous studies on helminth vasoactive intestinal peptide and peptide histidine isoleucine immunoreactivities, co-synthesis of the peptides was not indicated in a pair of branched neurons which projected posteriorly and peripherally from the ganglion associated with the ovijector of females and which terminated in two pairs of ganglia also exhibiting vasoactive intestinal peptide-like immunoreactivity only. The position of these ganglia indicated that they innervate muscles close to the body wall and may be responsible for the muscular contractions required for expulsion of eggs from female Nippostrongylus brasiliensis. This is also the first study to successfully detect these peptides in the excretory system of gastrointestinal nematodes.