Pica caused by emetic drugs in laboratory rats with kaolin, gypsum, and lime as test substances.

Pica refers to eating nonfood substances. The pica behavior has been the focus of attention in physiological and pharmacological studies, because its consumption is a good marker of nausea in laboratory rats, which cannot vomit due to neuroanatomical reasons. Almost all pica studies with rats have used kaolin clay pellets as nonfood substances. The present study primarily aimed to explore an alternative (or more suitable) substance to kaolin for detection of nausea induced by emetic drugs. Two calcium compounds, gypsum and lime, were evaluated in this study. An injection of lithium chloride (LiCl) increased pica behavior not only in the rats given kaolin but also in the rats given gypsum, suggesting that gypsum consumption could be used as an indicator of nausea. However, its sensitivity was no greater than that of kaolin consumption. In addition, lime is not a useful marker for nausea because the size of pica was small in the LiCl-injected rats, and did not differ from the control in the cisplatin-injected rats. In short, the superiority of kaolin as a test substance for nausea could not be overturned. However, the fact that nauseous rats displayed pica behavior with gypsum and lime refutes the claim that aluminosilicate, the main component of kaolin, is the critical determinant of emetic-caused pica in laboratory rats.