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Fig. 3. Loss of Tbx18 causes deafness. (A-C) Analysis of
hearing by ABR (A) and EP (B,C) measurements of Tbx18KO and control
mice. (A) ABR thresholds are significantly increased in Tbx18KO mice
at three weeks (129.3±5.3 dB pe SPL, n=15) and 12 weeks
(130.5±5.8 dB pe SPL, n=10) compared with control animals of
the same age (3 weeks: 54.2±19.2 dB pe SPL, n=18; 12 weeks,
54.9±6.4 dB pe SPL, n=8). (B) Registration of the EP in
Tbx18KO (dashed line) and control mice (solid line) at P21. After
taking the reference DC potential in the fluid meniscus overlying the stria
vascularis (M1), the recording electrode was moved forward. Upon
penetration of the stria vascularis (P), the EP was measured in the scala
media for at least 2 minutes before the animal was sacrificed by the injection
of a barbiturate (T61). Within several minutes of the insult, the EP decreased
to a negative steady-state-potential (SSP) - reaching a minimum after 8-12
minutes. In contrast to the EP, which is given by the steady state of active
and passive ionic current components, the SSP reflects only the passive part
of the ionic conductivities, as long as ion concentrations are minimally
altered after active transport has come to a halt. As a control for baseline
shifts, the reference DC potential was measured after the experiment
(M2) to verify its constancy over the entire time. (C) Disruption
of the EP and SSP in Tbx18KO mice at three weeks of age (control:
EP=102.9±9.1 mV, SSP=-26.4±9.9 mV, n=10;
Tbx18KO: EP=1.3±3.1 mV, SSP=-3.8±3.9 mV,
n=10). The difference in EP and SSP is significant
(P<0.001, Mann-Whitney Rank Sum Test); bars indicate standard
deviation.
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