Intestinal myoelectric alterations in rats chronically infected with the tapeworm Hymenolepis diminuta

Gastrointestinal Parasites and the Neural Control of Gut Functions

Gastrointestinal motility and transport of water and electrolytes play key roles in the pathophysiology of diarrhea upon exposure to enteric parasites. These processes are actively modulated by the enteric nervous system (ENS), which includes efferent, and afferent neurons, as well as interneurons. ENS integrity is essential to the maintenance of homeostatic gut responses. A number of gastrointestinal parasites are known to cause disease by altering the ENS. The mechanisms remain incompletely understood. Cryptosporidium parvum, Giardia duodenalis (syn. Giardia intestinalis, Giardia lamblia), Trypanosoma cruzi, Schistosoma species and others alter gastrointestinal motility, absorption, or secretion at least in part via effects on the ENS. Recent findings also implicate enteric parasites such as C. parvum and G. duodenalis in the development of post-infectious complications such as irritable bowel syndrome, which further underscores their effects on the gut-brain axis. This article critically reviews recent advances and the current state of knowledge on the impact of enteric parasitism on the neural control of gut functions, and provides insights into mechanisms underlying these abnormalities.

Guanosine 3',5'-cyclic monophosphate: a tapeworm-secreted signal molecule communicating with the rat host's small intestine

Tapeworms alter the physiological environment of the host's small intestinal lumen by contracting the intestinal smooth muscle, thereby slowing the transit of intestinal contents. We hypothesize that parasite-to-host molecular signaling is responsible for the specific patterns of small intestinal smooth muscle contraction observed both during tapeworm infection and after the infusion of tapeworm-secreted molecules into the intestinal lumen of unanesthetized rats. Of the tapeworm-secreted compounds tested, only lumenal infusion of guanosine 3',5'-cyclic monophosphate (cGMP) induced contractile patterns that mimic those observed during tapeworm infection. The response to cGMP occurred in a concentration-dependent fashion. Our study clearly demonstrates that cGMP can serve as an extracellular signal molecule regulating small intestinal motility mechanisms in vivo.

Partial characterization of a tapeworm-secreted signal factor inducing sustained spike potentials in the smooth muscle of the rat small intestine

The rat tapeworm Hymenolepis diminuta alters the myoelectric activity of the small intestine. To determine if secreted factors from the tapeworm are responsible for these alterations of intestinal smooth muscle activity, tapeworm-conditioned medium (TCM) obtained from in vitro culture was infused via an indwelling cannula into the duodenum of an uninfected rat. Myoelectric recordings were analyzed for sustained spike potentials (SSP) and repetitive bursts of action potentials (RBAP), the previously characterized tapeworm modifications of the normal interdigestive myoelectric pattern. Results indicated that TCM initiated SSP, but not RBAP in the intestine of the uninfected rat. The SSP-inducing signal factor activity, present in TCM, was retained after boiling, prolonged freezing, proteinase treatment, and passage through a 10-kDa exclusion filter. The signal factor was soluble in the aqueous phase on lipid extraction. It was concluded that the SSP-inducing signal factor is a nonproteinaceous, heat-resistant, low-molecular weight, water soluble molecule.