Mammalian CNS barosensitivity: studied by brain-stem auditory-evoked potential in mice

High pressure nervous syndrome (HPNS) is an instinctive response of mammalian high-class nervous functions to increased hydrostatic pressure. Electrophysiological activity of mammalian central nervous system (CNS), including brainstem auditory-evoked potential (BAEP), has characteristic changes under pressure. Here we recorded BAEP of 63 mice exposed to 0-4.0 MPa. The results showed that interpeak latencies between wave I and wave IV (IPL1-4) and their changes under pressures (deltaIPL1-4) responded to increasing pressure in a biphase pattern, shortened under pressure from 0 to 0.7MPa, then prolonged later. There were significantly negative correlations between base IPL1-4s and deltaIPL1-4s (p < 0.01). Individual IPL1-4s were supposed to respond to increasing pressure in a relative steady pattern in accordance with its base IPL1-4s. Those with shorter-base IPL1-4 presented direct increases in IPL1-4. However, those with longer-base IPL1-4 had a decreased IPL1-4 under small to moderate pressure then rebounded later. Our results suggested that mammalian CNS functions were susceptible to small to moderate pressure, as well as a higher pressure than 1.0MPa. Mice, as a statistical mass, had an "optimum" pressure about 0.7MPa, rather than atmospheric pressure, referred as shortest IPL1-4s. An individual's response to high pressure might be relied on his base biological condition. Our results highlighted a new approach to investigate a practical strategy to medical selecting barotolerant candidates for deep divers. Diversity of individual susceptibility to hydrostatic pressure was under discussed. Underlying mechanisms of the "optimum" pressure for CNS function and its significance to neurophysiology remain open to further exploration.