Expression of vasoactive intestinal polypeptide, substance P and neuropeptide Y in jejunal enteric nerves is altered in rabbits suffering from long term <I>Trichinella spiralis</I> infection: an immunohistochemical study

In the early intestinal stage of infection with the nematode <I>Trichinella spiralis</I> alterations in gut motility and chemical code of enteric neurons are observed. The present study was designed to characterize the changes in expression pattern of vasoactive intestinal polypeptide (VIP), substance P (SP) and neuropeptide Y (NPY) in enteric nerves of the rabbit jejunum occurring during long-lasting trichinellosis (35 and 42 days). Sections of the jejunum from healthy and <I>T. spiralis</I>-infected rabbits were processed for double immunocytochemistry in which antibodies against protein gene product 9.5 were used as a pan-neuronal marker and mixed with antisera raised against VIP, SP or NPY. At 35 and 42 days post infection a marked decrease of VIP-, SP- and NPY-immunoreactive (IR) jejunal myenteric neurons was found, whereas the expression of these neuropeptides in submucous neurons was unchanged. In the myenteric plexus and the jejunal circular muscle of <I>T. spiralis</I>-infected rabbits a significant reduction of VIP-IR (but not SP-IR) nerve fibres was noted. In the longitudinal muscle of the jejunum from animals with long-lasting trichinellosis the density of SP-IR nerve terminals was decreased, whereas the number of VIP-containing nerve fibres was unchanged. Long-lasting trichinellosis had no influence on NPY-IR nerve fibres in both circular and longitudinal smooth muscles. The number of NPY-positive (but not VIP- and SP-IR) nerve fibres supplying mucosa and blood vessels was decreased in <I>T. spiralis</I>-infected animals. These data indicate that during long-lasting trichinellosis expression of neuropeptides in jejunal enteric neurons is changed. A possible involvement of VIP and SP in persistent intestinal dysmotility and NPY in altered fluid secretion is discussed.