Systematic evaluation of cerebral injury stimulating by underwater infrasound

Infrasound (<20 Hz) was an inaudible mechanical vibration that threatened public health, especially the central nervous system (CNS) in air environments. In fact, infrasound was also produced by large ships or underwater apparatus, which had potential hazard to underwater operators or divers. However, the propagation characteristics of sound waves in air differed from that in water, and there was no experimental evidence on the potential bioeffects of underwater infrasound. In the present study, we systematically evaluated cerebral injury in Bama mini pigs induced by underwater infrasound.

Forty-two Bama mini pigs (weighing 10-15 kg) were randomly divided into seven groups. After wearing a respiratory mask, the animals were submerged to a depth of 10 meters and exposed to infrasound at frequencies of 8 Hz (145.4 ± 0.2 dB re 1 μPa, 156.2 ± 1.0 dB re 1 μPa), 12 Hz (145.3 ± 0.2 dB re 1 μPa, 161.9 ± 2.4 dB re 1 μPa), and 20 Hz (145.5 ± 0.3 dB re 1 μPa, 165.9 ± 0.3 dB re 1 μPa). Then cerebral function was assessed using electroencephalography (EEG); morphological injuries were evaluated by HE staining, Nissl staining, and immunostaining; oxidative stress and inflammatory cytokines were detected via ELISA assays; and the underlying molecular mechanisms were explored through RNA sequencing and transcriptome analysis.

Compared with the control group, underwater infrasound at 8 Hz led to alterations in EEG in partial brain regions, but with no significant changes in the 12 Hz and 20 Hz groups. In contrast, underwater infrasound at 20 Hz and 12 Hz directly induced histological injury, decreased neuron density, and increased cell apoptosis immediately, but had no impact on histological and neuronal injury induced by 8 Hz exposure. Additionally, there was no significant influence on oxidative stress among all groups. Finally, transcriptome analysis revealed activation of immune and cell apoptosis pathways and key genes. These results provided direct evidence for the adverse effects of underwater infrasound on brains.