SENSORY-MOTOR RESPONSES THAT ASSOCIATE WITH LOSS OF THE VESTIBULAR TYPE I HAIR CELLS IN RATS

The rat tail-lift and air-righting reflexes are anti-gravity responses triggered by the vestibular system. Previous data indicated that diverse populations of vestibular sensory hair cells (HC) may be responsible for these two reflexes. Here, we reassessed the relationship between HC loss and reflex loss in rats with graded lesions in the vestibular organs caused by exposure to several different doses of the ototoxic chemical 3,3’-iminodipropionitrile (IDPN). After exposure, the anti-gravity responses were measured and then the vestibular organs were obtained to assess the loss of type I HC (HCI) and type II HC (HCII) in central and peripheral regions of crista, utricle and saccule. IDPN caused a dose-dependent loss of vestibular function and loss of HCs. Paired histological and functional data from individual animals were fitted by orthogonal distance regression to non-linear models. Regions of the sigmoid with moderate slope (between 10º and 80º) were inferred to reveal a meaningful association of the reflex loss with HC loss. Then, the percentage of cells lost in these moderate slope regions were obtained as an indicator of the strength of the association. For both the tail-lift and air-righting reflexes, higher percentages were obtained for HCI than for HCII, supporting the hypothesis that both reflexes mostly depend on HCI function. The results also supported the hypotheses that the tail-lift response likely depends on the crista or utricle HCIs whereas the air-righting response more likely depends on utricle or saccule function.
Support: ANR-20-NEUR-0005, ANR, France; PCI2020-120681-2, MCIN/AEI/10.13039/501100011033 and NextGenerationEU/PRTR; EU Grant 101120139.