FIG. 4.

Cochlear thresholds are elevated, and response amplitudes are reduced in GABA_B1 nulls, as measured by either ABRs (A, B) or DPOAEs (C, D, E). A,C Mean thresholds (±SEM) for wild-type (+/+) vs. GABA_B1-null (−/−) ears. ABR thresholds were identified by visual inspection of the stacked level-series waveforms. DPOAE threshold was defined by interpolation as the sound pressure of the f₂ primary required to evoke a DPOAE of 0 dB SPL. B, D Mean amplitude vs. level functions (±SEM) for responses evoked by 22.6 kHz tone pips (B) or primaries with f₂ at 22.6 kHz (D). ABR amplitudes are for Wave 1 (i.e., cochlear nerve response). E Distributions of DPOAE thresholds at 22.6 kHz for wild-type (left) and GABA_B1 nulls (right). A–D Data from the right ears of 28 animals of each genotype. E DPOAE data from both ears of these 56 animals, plus from an additional nine GABA_B1-null ears from nine animals studied with strychnine injection.