The line of polarity reversalを欠落したGpr156ノックアウトマウスにおける卵形嚢有毛細胞と求心性神経の生理学的または形態学的特性の解析

抄録

In otolith organs, hair bundles of hair cells have varying orientations that reverse along the line of polarity reversal (LPR) located within or at the edge of the central striolar zone. Despite such unique anatomical feature, the significance of simultaneous excitatory and inhibitory inputs upon translational stimuli remains to be understood. GPR156 is a G protein-coupled receptor (GPCR) belonging to metabotropic glutamate receptor subfamily. Recently, Kindt et al. has shown that GPR156 uniformly expressed in the hair cells of five vestibular organs becomes polarized and reverses hair bundle orientation under the control of Emx2, a transcription factor, establishing mirror-image hair cell organization in the otolith organs. (Nat Commun 2021). Gpr156^del/del otolith organs lose the LPR without any other clear anatomical defects. In this study, we examined whether the loss of LPR in Gpr156^del/del mice affects physiological and anatomical properties of hair cells and primary afferent neurons.

We found that the transducer currents of type I and II hair cells in null and het animals had comparable properties (operating range, sensitivity, adaptation time course and extent). 

We also determined whether zone-specific firing pattern is affected by loss of LPR. In wildtype animals, afferent neurons innervating the striola and extrastriola including LES tend to fire in transient and sustained fashion, respectively, in response to depolarizing current steps. Our results show that current steps applied to LES calyces of both Gpr156^del/+ and Gpr156^del/del  utricles elicited multiple spikes (sustained responses), suggesting unaltered firing pattern by loss of Gpr156. 

Together, we conclude that some physiological properties are conserved in hair cells and afferent terminals of the LES in utricles without bundle orientation reversal as a result of deletion of Gpr156.