Study Of Neural Mechanism Underlying The Adaptation Of Hipposideros Pratti To High Intensity Noise Environment

Noise exposure can damage the auditory system of most animals,including humans,which leads to the noise-induced hearing loss(NIHL),and further impacts behaviors and physiological functions of animals.Although the echolocating bats live in high-intensity noise environment,they still can forage and navigate in groups quite successfully relying on auditory system,which suggests that echolocating bats are adapted to high-intensity noise environments.However,the neural mechanism underlying this adaptation is still unclear.In the present study,we firstly recorded the echolocation calls of Hipposideros pratti,and then,we studied auditory threshold and neural responses before and after 120 dB SPL high-intensity noise exposure and sham exposure using auditory brainstem response(ABR)and obtained the results as following:1.The recorded echolocation calls of H.pratti were constant frequency-frequency modulation(CF-FM)signal,which contains 3 harmonics.the dominant frequency of H.pratti was 59.3±0.5kHz.2.The latency of ABR of H.pratti was less than 7 ms,and there were three positive waves,namely wave Ⅰ,wave Ⅲ and wave Ⅳ/Ⅴ.Latency and amplitude were measured for each wave.The latency decreased with the increase of stimulus intensity;the slope was-0.13±0.05 ms/10 dB.The amplitude increased with the increase of stimulus intensity;the slope was 0.53±0.13 μV/10 dB.The ABR audiogram of H.pratti have two asymmetrical sensitive areas,the best frequencies were 14.1±3.9 kHz and 54.4±2.9 kHz.The slope of the descending branch in the first sensitive area was-3.1±1.0 dB/kHz,the slope of the rising branch was 1.5±0.5 dB/kHz.The slope of the descending branch in the second sensitive area was-1.2±0.5 dB/kHz,the slope of the rising branch was 2.8±0.7 dB/kHz.The two sensitive areas possibly related to the frequencies of social and echolocation calls,respectively.The insensitive frequency before the dominant frequency may be related to doppler shift compensation behavior.3.The threshold shifts of dominant frequency sounds after both noise and sham exposure were less than 5 dB.And the ABR amplitude and latency to 90 dB SPL and 80 dB SPL dominant frequency sounds after noise exposure had no significant difference to those after sham exposure.It indicated that high-intensity noise exposure does not affect the auditory sensitivity and the neural response of dominant frequency.The threshold shifts of insensitive frequency sounds at 2 min after noise exposure was significantly difference to the sham exposure(7.6±6.04 vs.-1.8±6.31 dB,p<0.05),the threshold shifts was recovered in 10 min after the noise.Indicated that high-intensity noise exposure caused temporary threshold shift(TTS)of this frequency.The threshold shifts of social frequency sounds were less than 4 dB after both noise and sham exposure,the amplitude and latency of ABR to 90 dB SPL and 80 dB SPL social frequency sounds were also not significantly difference after noise and sham exposure.4.The threshold shifts of 20 kHz sounds of C57BL/6 mice was 41.5±6.33 dB at 2 min after 110 dB SPL high-intensity noise exposure,and it did not recover after 1 week.The amplitude of ABR had significantly decreased compared to sham exposure,indicated that high-intensity noise exposure caused NIHL in C57BL/6 mice.Taking together,there was no NIHL in H.pratti after noise exposure.These results suggest that the neural responses of the auditory system enable the H.pratti to adapt to the high-intensity noise environment,and the adaptation is potentially related to structural and functional specialization of the inner ear in echolocating bats.