The effects of repeated linear acceleration training and the antimotion sickness
drug,
promethazine, on hypergravity-induced
motion sickness were examined in
musk shrew (Suncus murinus), which is known to show a
vomiting response to motion stimulation. Animals were assigned into five groups: vestibular intact, untreated animals (
Sham), vestibular lesioned (VL) animals, vestibular intact animals with
promethazine hydrochloride administered as daily
drinking water (Prom), vestibular intact animals who underwent horizontal
linear accelerator motion training (Train), and vestibular intact animals treated with both
promethazine hydrochloride and linear acceleration training (Prom+Train). In
Sham animals, the number of
vomiting episodes was 14±2 during 2 G exposure for 10min, and was accompanied by intense Fos expression in the medial vestibular nucleus (MVe), the nucleus of the solitary tract (NTS), the area postrema (AP), and the paraventricular hypothalamic nucleus (PVN). The
vomiting response and Fos expression were completely abolished in VL animals, indicating that these responses are mediated via the vestibular system. Although Train and Prom animals experienced a significantly reduced number of hypergravity-induced
vomiting episodes compared with
Sham animals, the effect was significantly greater in Train animals than in Prom animals. Fos expression in the NTS, AP, and PVN were significantly more reduced in Train animals than in Prom animals. Higher dose of bolus injection of
promethazine (50mg/kg, i.p.) completely abolished the
vomiting episodes, although the animals were drowsy and sedated due to side effects. In conclusion, daily linear acceleration training and
promethazine could prevent the hypergravity-induced
vomiting episodes.