Effects Of Transcranial Magnetic Stimulation On Endogenous Neural Stem Cells In Rats With Traumatic Brain Injury

Backround and ObjectiveTraumatic brain injury (TBI) has a high incidence in all populations. Traffic accident is the major cause of TBI. As the number of vehicle increasing, TBI will be a more and more serious public health problem in China. A prominent obstacle of functional recovery after TBI, especially the old TBI patient, is the loss of cerebral parenchyma. Although endogenous neuronal stem cells (NSCs) can proliferate limitedly after injury, survival rate of new cell is very low. Promoting proliferation and survival of NSC s may be a potential therapy strategy for TBI.As a sort of noninvasive brain stimulation (NBS), transcranial magnetic stimulation (TMS) exerts neuromodulation by activating neurons or changing excitability of a certain brain area. With proper parameters, TMS can effect regional cerebral blood flow and oxidative stess, and modulate neuroplasticity. Besides, results of some studies suggest TMS has the potential of promoting neurogenesis. Based on known effects of TMS and pathophysiology of TBI, scientists inferred that TMS has the potential to treat TBI. However, there is no study that use TMS to treat TBI has been published, as well as study about TMS’s effect on endogenous NSC during post-TBI period.In this study, repetitive TMS was used to treat TBI rat models, and proliferation of endogenous NSC will be carefully observed.MethodsExperimental moderate TBI was made in adult male Sprague-Dawley rats with Feeney’s method. Modified neurological severity scores (mNSS) was performed to assess behavior in postoperative (PO) day1,7,14and28. According to mNSS of PO1, with stratified random grouping, rats were divided into TBI group and TBI+TMS group. TMS was given from PO2with these parameters:voltage of700V, frequency of5Hz, and900stimuli was given daily to rats of TBI+TMS group. In PO7,14and28, some rats in each group were anesthesized, then intracardially perfused with chilled saline then4%paraformaldehyde. Harbored the brains and set to paraffin embedding and sectioning. The majority was used for HE staining and immunohistochemical staining for BrdU, musashil, NeuN and caspase-3. Five brains that harbored in PO14was set for isolation of SVZs, with which immunofluorescence staining for BrdU, DCX, laminin and DAPI was done. Some rats underwent18F-FDG micro-PET scanning in PO2and PO13.ResultsThere is a trend that unexpected death rate of TB1+TMS group was significantly lower than TBI group(15.79%vs37.14%,p=0.09)。From PO1to PO14, mNSS of TBI rats improved gradually. In PO7, TBI group and TBI+TMS group have similar mNSS (7.00±1.27vs6.20±1.92). In PO14, there was a trend that mNSS of TBI+TMS group is significantly lower than TBI group.From PO7to PO28, the relative cerebral parenchyma loss rate increased gradually. And there is a trend that the relative cerebral parenchyma loss rate of TBI+TMS group was significantly lower than TBI group (32.80±3.0%vs38.59+3.2%,p=0.083).In PO2, metabolism level of perilesional cortex and striatum of both groups decreased compared to those sites of healthy hemisphere. In PO13, compared with healthy hemisphere, metabolism level of perilesional cortex of both groups were similar, while that of striatum of both groups were higher. However, there is no significant difference between these two groups in both sites.In immunohistochemical staining, BrdU positive cells density in dorsolateral SVZ were similar between both groups in all three time points, so were NeuN positive cells in perilesional zone. Proportion of musashil positive area in dorsolateral SVZ decreased gradually from PO7to PO28in both group. For caspase-3positive cells density in perilesional zone, TBI group were higher than TBI+TMS group in all time points, and there is a trend that the difference in PO14was statistically significant (p=0.062).For immunofluorescence staining in PO14, both BrdU and DCX positive cells density of TBI group were lower than TBI+TMS group, however, the differences were not significcant.ConclusionFor moderate TBI rats, TMS showed these trends of benefit in post-TBI period in our study: (1) lowered the death rate,(2) accerlerated behavior recovery,(3) and decreased cerebral parenchyma loss. These benefits are in accord with theoretical inference mentioned. However, our results can not support the inference that TMS can promote endogenous NSC proliferation after TBI. Our results also suggested that TMS can not affect regional cerebral metabolism in24h after last stimulation.