All animals were treated in accordance with the Guide for the Care and Use of Laboratory Animals as adopted by the U.S. National Institutes of Health and approval was granted by the Ethics Committee of the University Medical Center Mainz and the Landesuntersuchungsamt Rheinland-Pfalz (Koblenz, Germany; permit number: 23 177-07/G 12-1-021 E3 and 23 177-07/G 15-1-094). Noise exposure consisted of repetitive playbacks of a 2 hour long noise pattern of 69 aircraft noise events with a duration of 43 s and a maximum sound pressure level of 85 dB(A) and a mean sound pressure level of 72 dB(A), which does not lead to hearing loss.24 (link) Noise events were separated by silent periods with irregular distribution to prevent early adaptation. The noise pattern was played back from downward facing loudspeakers mounted approximately 30 cm above the mouse cages with a Grundig MS 540 compact sound system with a total output of 65 W. Loudness and corresponding sound pressure levels were calibrated with a Class II Sound level meter (Casella CEL-246) within one the cages at initial setup. Actual SPLs during exposure was continuously recorded during the study period with the same device placed between cages with upward facing microphone. The average SPL (Leq3) is 72 dB(A) at a usual background noise level of 48 dB(A) in the animal facility. In control experiments, mice were exposed to ‘white noise’ (this is a random noise with constant spectral density within the range of human hearing from 20 Hz to 20 kHz) using exactly the same average SPL as for aircraft noise. All SPL and maximum sound pressure levels were measured within the mouse cages.
For further information of the methodology employed for determination of blood pressure, stress hormones, vascular function, nitric oxide quantification, oxidative stress parameters, inflammatory pathways, gene and protein expression, next generation sequencing see the Supplementary material online.