Emesis in Rodents: Present or Absent? A Critical Review of the Evidence and Implications for the Use of Rodents in Biomedical Research.

Vomiting, a key defence against accidentally ingested toxins, is widely present in mammals. Notably, rodents (e.g., rats, mice) are generally assumed to be unable to vomit, as commonly reported over the last ~100 years, but they are used extensively for biological and particularly biomedical research. However, three recent mouse papers reported 'emetic-like' responses induced by substances that are emetics in humans. Therefore, we critically re-examined the literature underpinning this longstanding view, integrating the recent and largely overlooked historical evidence challenging this consensus. We reappraise the ability of rodents to retch and vomit, concluding that whilst there is some published evidence for retching, the ability to vomit is unproven and for a range of physiological and anatomical reasons (e.g., organisation of the gastroesophageal anti-reflux barrier), it would be problematic. Experimentally testable hypotheses to explain the conflicting findings are proposed, together with criteria that should be fulfilled to define a behaviour as retching or vomiting in rodents. A detailed comparison is made of the physiological and anatomical differences between rodents and species known to vomit. We consider the significance of our conclusions for biomedical research, particularly in relation to the digestive tract and central nervous system, and the wider implications for rodent biology.