Figure 2.

Post-noise hypothermia attenuates early ABR hearing threshold shifts. (A) Experimental protocol for animals used to study of recovery of noise-induced induced injury with TTM. Animals were exposed to 2 h of continuous noise at 105 dB under isoflurane anesthesia before initiating TTM protocols of normothermia and hypothermia. For animals receiving TTM, temperature modulation commenced roughly 15 min post-noise. (B) ABR thresholds were obtained in age-matched female rats at 1, 3, 7, 14 and 28 DPN and compared to combined baseline thresholds (dashed curve). ABRs were obtained for click (Ck) and 2, 4, 8, 16, 24, and 32 kHz pure-tone stimuli. The frequency spectrum of the experimental noise is illustrated by gray vertical bars at 4–8 kHz. Results for post-noise ABR thresholds are shown for animals that recovered from noise exposure in noise only (dark red), normothermia TTM (red), and hypothermia TTM (light blue) conditions. Data presented as mean ± SE of ABR thresholds with between-group comparisons illustrated with colored bars at each stimulus frequency (*p < 0.05, **p < 0.01). (C) To assess hair cell integrity after noise exposure, FITC-Phalloidin labeled hair cell survival was quantified at 28 DPN for apical, middle, and basal cochlear regions in unexposed control (black), noise only (dark red), noise+normothermia (red), and noise+hypothermia animals (blue). Hair cell survival data for respective groups are shown as percent survival (mean ± SE).