Pica--a model of nausea? Species differences in response to cisplatin

Rats lack the emetic reflex but exhibit pica in response to stimuli that induce emesis in species with an emetic reflex, hence it has been proposed that pica may be analogous to emesis in species lacking the reflex. In the present study, we investigated whether pica was present in Suncus murinus (with an emetic reflex) as well as in rats and mice (without emetic reflex) to provide a further insight to the validity of pica as a model for nausea/vomiting. Cisplatin (6 mg/kg, i.p.) induced pica in rats, indicated by a significant increase in kaolin consumption at 24 h (but not 48 h) post-treatment whereas we failed to demonstrate this effect in mice (inbred or outbred strain, 6 or 20 mg/kg i.p.) and whilst cisplatin (20 mg/kg, i.p.) induced emesis in Suncus, kaolin intake was not significantly affected. Furthermore, cisplatin significantly increased the weight of gastric contents at 48 h post-injection in rats and mice indicating delayed gastric emptying whereas this effect was not present in Suncus. These results show that Suncus and two strains of mice, unlike rats, do not develop pica in response to cisplatin which suggests that the consumption of kaolin induced by cisplatin may not be associated with whether or not an emetic reflex is present. The differences in ingestive behaviour and gastric response between species with and without an emetic reflex in response to cisplatin treatment as well as the difference between mice and rats, is discussed in relation to the selection of models for the study of nausea and vomiting.