Focal brain cooling (FBC) at 15℃ and transient receptor potential vanilloid 4 (TRPV4) deficiency relieve brain infarction. TRPV4 channels are inactivated by cooling (< 27℃), suggesting that the anti-ischemic effects of FBC include those of TRPV4 inactivation. However, the extent to which TRPV4 inactivation contributes to the anti-ischemic, anti- blood-brain barrier (BBB) disruption, and anti-apoptosis effects of FBC on cerebral infarction remains unclear. We investigated the contribution and mechanisms of RN1734, a TRPV4 antagonist, in FBC for cerebral infarction using TRPV4 knockout and wild-type mice. Focal cerebral infarction was induced by photochemically induced thrombosis. Infarct volume, BBB disruption, and number of apoptotic cells were evaluated. The TRPV4 antagonist or deficiency showed similar anti-ischemic and anti-BBB disruptive effects to those of FBC. Intracerebroventricular injection of RN1734 showed a similar reduction in the number of apoptotic cells to that of FBC. These anti-ischemic and -apoptotic effects were completely inhibited with injection of GSK1016790A, a TRPV4 agonist, immediately before FBC. Our results showed that TRPV4 modulation is the primary factor contributing to the antiischemic effects of FBC, and TRPV4 channel inactivation relieve focal ischemic infarction by relieving BBB disruption and preventing apoptosis. Therefore, FBC treatment improves ischemic stroke through the modulation of TRPV4 channels.

Vestibular hair cells are susceptible to damage from various stimuli such as infections, ischemia, and certain therapeutic drugs, including aminoglycoside antibiotics and the antineoplastic agent cisplatin. In mammals, damage to the vestibular hair cells is permanent. This study aimed to evaluate the protective effects of nobiletin (NOB) against aminoglycoside-induced hair cell death using utricles collected from adult mice. The utricles removed from CBA/N mice were assigned to eight groups according to the dose of NOB and the administration or not of neomycin. Hair cells in the utricles were counted by double labeling with calmodulin and calbindin. NOB inhibited hair cell death in utricles exposed to neomycin. The protective effect of NOB on hair cells in the utricles was also suggested to have resulted from the inhibition of the production and accumulation of 4-hydroxy-2-nonenal, the final product of lipid peroxide aldehyde. NOB suppressed neomycin-induced hair cell death. The principle of hair cell protection from aminoglycoside-induced hair cell death suggests that NOB inhibits reactive oxygen species formation in the utricles exposed to neomycin.