Acetazolamide alleviates motion sickness by inhibiting inner ear carbonic anhydrase 2 and reducing endolymph volume.

Motion sickness is common in aerospace, aviation and maritime operations, and travel by vehicles or ships. Existing preventive and therapeutic drugs for motion sickness induce central nervous system (CNS)-related side effects; therefore, there is an urgent need to find new anti-motion sickness targets and to develop novel drugs with reduced adverse effects. In this study, we found that rotational stimulation significantly upregulated carbonic anhydrase 2 (CA2) expression in the inner ears of guinea pigs and mice. Pretreatment with acetazolamide (AZ), an inhibitor of carbonic anhydrase, effectively mitigated motion sickness-related behavioral symptoms in both species and inhibited increase in the inner ear endolymph volume induced by rotational stimulation. Further investigations revealed that AZ mediated its anti-motion sickness effects primarily through mechanisms involving the reduction of intracellular H+ concentrations in vestibular epithelial cells, inhibition of Na+-K+-ATPase activity, and modulation of intracellular Na+ and K+ homeostasis, thereby attenuating endolymph accumulation in the inner ear. This study demonstrated for the first time an involvement of the inner ear CA2 in the induction of motion sickness and an anti-motion sickness effect of its inhibitor AZ, providing a new strategy for developing anti-motion sickness drugs acting on the inner ear.