Fig. 1

Experimental design. a The timeline of this experiment. b The stress regimen during the establishment period: one of the recorded two types of noises was played randomly for 1 min in a loop with random intervals from 1 to 60 s, lasting 8 h every day for totally 30 days. c Sound pressure level (SPL) and sound frequency spectrum analysis in real time of two noises by SPL Spectrum Analyzer Software. The bar charts represent wide spectrum distribution and the green waveform represents the wave crests at around 300 Hz and 3 kHz. Left: noise type 1, the high speed turbine dental drill; Right: noise type 2, the ultrasonic tooth cleaner. d Left: The experimental apparatus used to play the noise to animals. Mice were placed in home cages inside a plexiglass box, 30 cm from sound source on the top. Right: Photos of the real experimental setup