Effects Of Infrasound On The Proliferation Of Neural Precursor Cells In The Dentate Gyrus Of Adult Rats

0bjective Infrasound is usually defined as sound with frequencies below 20 Hz. It has long wavelength and low frequency. Infrasound exists in various environments and propagates long distances but suffers little or no attenuation. Infrasound with certain frequency and SPL can cause many biological effects on organisms, and the basic mechanism is biological resonance which causes a series of complex physical and chemical reactions in the living body.Infrasound can cause damages in the whole body, especially in the CNS. Previous studies showed that infrasound affected behaviors, memories and cognition of rats, and also caused changes of hippocampal ultrastructures and molecular expressions in brain. It is widely accepted that new neurons can generate in the CNS of adult mammals, and neurogenesis exists in the hippocampal dentate gyrus throughout life. The processes are very complex and are affected by many factors. The hippocampus is one of the important areas of neurogenesis in adult brain. Whether neurogenesis will be affected when the hippocampus is exposed to infrasound has not been reported. Additionally, it is still unclear whether the declined ability of studying and memorizing is associated with the interfered hippocampal neurogenesis by infrasonic exposure.In order to answer these questions, this study was designed to observe BrdU positive cells in the SGZ of hippocampal dentate gyrus of adult rats exposed to infrasound, and to study the effects of infrasound on the proliferation of neural precursor cells in rat brain. All these may help us get a better understanding of the biological mechanisms of infrasound.Methods Adult SD rats were randomly and equally divided into normal control group, sham infrasound group and infrasound group. The rats from infrasound group were exposed to infrasound of 8 Hz at 130 dB for 3, 7, 14 consecutive days (2 h / d), respectively, and were sacrificed at 1, 3, 7 and 14 d after infrasonic exposure. All animals received two intraperitoneal injections (2 h interval) of BrdU before perfusion. The rats from infrasound group were exposed to infrasound of 16 Hz at 130 dB for 7 consecutive days (2 h / d), and were sacrificed at 3, 6, 10, 14 and 18 d after infrasonic exposure. All animals received three intraperitoneal injections (8 h interval) of BrdU before perfusion. The expression of BrdU positive cells in the SGZ of the dentate gyrus was investigated by using immunohistochemistry method for BrdU.Results 1. The number of BrdU positive cells in the SGZ did not revealed a statistical difference between normal control group and sham infrasound group. 2. 3 days'exposure to infrasound of 8 Hz at 130 dB: At 1 and 3 d after infrasonic exposure, the number of BrdU positive cells did not revealed a statistical difference as compared with normal control group; at 7 d, the number of BrdU positive cells decreased as compared with control group (P < 0.05); at 14 d, the number of BrdU positive cells returned to the baseline level. 3. 7 days'exposure to infrasound of 8 Hz at 130 dB: At 1 d after infrasonic exposure, the number of BrdU positive cells did not revealed a statistical difference as compared with normal control group; at 3 and 7 d, the number of BrdU positive cells decreased as compared with normal control group (P < 0.05); at 14 d, the number of BrdU positive cells returned to the baseline level. 4. 14 days'exposure to infrasound of 8 Hz at 130 dB: At 1 and 3 d after infrasonic exposure, the number of BrdU positive cells did not revealed a statistical difference as compared with normal control group; at 7 d, the number of BrdU positive cells decreased as compared with control group (P < 0.05); at 14 d, the number of BrdU positive cells returned to the baseline level. 5. 7 days'exposure to infrasound of 16 Hz at 130 dB: At 3, 6, 10 and 14 d, the number of BrdU positive cells in the SGZ decreased significantly as compared with control group (P < 0.01); at 18 d, the number of BrdU positive cells returned to the baseline level.Conclusions 1. Infrasound of 8 Hz at 130 dB can inhibit the proliferation of neural precursor cells in the SGZ of normal adult rat dentate gyrus, and the inhibition caused by 7 days'infrasonic exposure was stronger than that of 3 and 14 days'exposure. 2. Compared with the results of exposure to infrasound of 8 Hz at 130 dB, the inhibition of the neural precursor cell proliferation in the SGZ after the exposure to infrasound of 16 Hz at 130 dB was much more obvious. 3. After infrasonic exposure, the number of BrdU positive cells in the SGZ returned to the baseline level, which indicated that the inhibited proliferation of neural precursor cells could go back to normal.