Motion sickness: Multiple linear regression identifies behaviours linked to motion-induced emesis in Suncus murinus (house musk shrew).

Motion sickness (MS) is a complex syndrome characterized by a spectrum of autonomic and behavioural symptoms, often accompanied by emesis. Suncus murinus has become a primary species in which to study the mechanisms of emesis control, yet the behavioural profile associated with motion-induced malaise of this animal has not been thoroughly assessed. In this study, we exposed 129 animals to provocative motion (1 Hz, 4-cm horizontal reciprocating displacement, 30 min) to induce MS and systematically recorded spontaneous behaviours, retching and/or vomiting (R/V), and changes in body surface and tail temperatures. A non-biased MS symptom score was developed based on stepwise multiple linear regression, incorporating nine observable behaviours and physiological variables, namely scratching, stretching, chin on the floor, burrowing, chewing the bedding, micturition, defecation and/or tenesmus, remaining stationary, and body surface and tail temperature changes. Administration of two anti-MS drugs, diphenhydramine (30 mg/kg, s.c.) and scopolamine (10 mg/kg, s.c.), significantly reduced the MS symptom score from 14.25 ± 1.89 to 7.84 ± 0.85 and from 18.11 ± 2.28 to 11.91 ± 0.87 respectively, indicating the validity of the scoring system as a quantitative measure of motion-induced 'sickness', 'malaise', and even 'nausea' in this species. Shapley additive explanation (SHAP) analysis further indicated the contributions of two individual spontaneous behaviours, stationary duration and chin on the floor episode, to MS prediction. Our findings suggest that this behavioural scoring system provides a reliable and translationally relevant tool for studying MS and screening potential anti-emetic treatments for humans.