Morphological observations of diarrhea in mice caused by experimental ciguatoxicosis

Diarrhea and morphological influences on digestive tracts caused by ciguatoxin (CTX) were observed in mice microscopically. The lethal doses and clinical symptoms caused by i.p. administration were almost the same as those by p.o., the prominent difference being diarrhea that was caused only by i.p. route. The diarrhea was caused by a dose from 1/7 MU to 1 MU of CTX (MU: mouse unit, to kill a mouse of 15 g in 24 hr, corresponding to 7 ng of pure CTX), but not at lower or higher doses. In this study, we used an i.p. dose of 4/5 MU (10.4 ng/28 g). Diarrhea started within 10 min after administration and lasted until 30 min. The changes were observed in the large intestine; namely, CTX accelerated mucus secretion and peristalsis in the colon and stimulated defecation at the rectum, resulting in prominent diarrhea. In the colon, a large quantity of mucus was secreted from even immature goblet cells, and epithelial cell damages were observed in the upper portion of the large intestine but not in the latter half. The morphological changes caused by CTX in the upper portion of the large intestine were similar to those seen with cholera toxin.