Experimental Study Of Effects And Related Mechanism Of Infrasound On Rat Hippocampus

Purpose: With SD rats exposed to infrasound of 8Hz, at 90dB or 130dB sound presure level(SPL), to observe the changes in temporal and spacial paterns of some message molecules related to learning and memory in hippocampus and to make sure whether the infrasound would lead to apoptosis of hippocampal cells or not, to reveal the mechanism of effects of infrasound on the learning and memory, and to provide theoretical evidences for infrasound protection guideline.Part oneExperiment one The effect of infrasound on Ca2+ concentration inhippocampal cells of SD ratsMaterials and Methods: With the exposure of 8Hz, 90dB and 130dB infrasound, Ca2+ changes in hippocampal cells were observed under laser confocal microscope(LCM) at different time points.Results: 1) With the exposure of 8Hz, 90dB infrasound, there were no significant changes of intracellular Ca2+concentration ([Ca2+]i) at 1d and 7d groups (P>0.05). The most obvious changes were found in 14d group, which showed significant increase of [Ca2+]j in hippocampal cells (P<0.01). [Ca2+]istill maintains at a high level at 21d group, which returned to normal at 28d group. There were no significant differences of [Ca2+]j in hippocampus between the samples of the same time point treated with buffer contained Ca2+ or buffer without Ca2+. 2) There were no significant differences of [Ca2+]i exposed to 8Hz, 130dB infrasound at 1d and 7d groups (P>0.05). The most obvious changes were found at 14d group, which showed significant increase of [Ca2+]i in hippocampus(P<0.01). [Ca2+]j still maintains at a high level at 21 d group, which returned to normal at 28d group. Changes were more significant in the group treatd with Ca2+-containing buffer than the group treated without Ca2+. [Ca2+]j in groups of infrasonic exposure for Id, 7d, 14d and 28d were significant higher than that of the groups at the same time point but treated without Ca2+. There was no significant difference between the 28d group and the control group. [Ca +]j at 21 d group treated with Ca2+-contained buffer were obviously decreased than that of the group treated without Ca2+, which indicated that the amplitude of its [Ca2+]j from the top to the bottom is much sharper than that of the later group. Accordingly, exposure of 8Hz, 130dB infrasound can enhance the membrane permeability of hippocampal cells to Ca2"1" at all the time points, yet in different degree. 3) Exposure of 130dB infrasound at the same frequency leads to much more significant effect on [Ca2+]i in hippocampal cells compared with 90dB SPL.In the current study, we observed that there was a temporal regularity of [Ca2+]i in hippocampal cells exposed to 8Hz 90dB or 130dB infrasound, of which the injuries in the micro or ultrastructure of brain tissue also showed the same temporal regularity. The consistency of that indicated sustained high level of [Ca 2+]i and [Ca 2+]i overload is one of the key factors for the injuries in neuron structure and/or function resulted from infrasonic exposure.Experiment two The effect of infrasound on expression of RyRs andNMDAR1 in hippocampus of SD ratsMaterials and Methods: with exposure of 8Hz, 90dB or 130dB infrasound, immunohistochemical methods were used to observe the changes of RyRs and NMDAR1 expression in hippocampal cells at different time points.Results: 1) Exposure of 8Hz, 90dB or 130dB infrasound for 14d, 21d and 28d suppressed the RyRs expression in hippocampus, and the inhibited effects of 130dB were earlier than that of the 90dB. Generally, there were similar degrees of decrease in RyRs expression with the two SPL action. 2) There was negative correlation between the changes of RyRs expression and [Ca2+]j in hippocampal cells both at 90dB and 130dB infrasonic exposure.The NMDAR1 expression in hippocampus exposed to 8Hz, 90dB infrasound showed a nonlinear changes. It reached the peak level at 14d group. The changes of NMDAR1 expression in observed regions with different times were positively correlated with the changes of [Ca2+]j exposed to 90dB infrasound. The NMDAR1 expression ex...