Effects Of Exercise On Neuronal Stress And Neuroinflammation In Mice With Repetitive Mild Traumatic Brain Injury

Traumatic brain injury(TBI)is a serious problem that damages human health and is a major factor in neurological dysfunction.Events such as road traffic accidents,war,falls,sports,and violent conflicts,and are characterized by brain function damage caused by external forces typically causing TBI.When the head is subjected to violent external object impact,it may result in mild,moderate,or severe TBI,causing damage to the brain’s structure and function.Repeated mild traumatic brain injury(rm TBI)can cause varying degrees of physical,mental,emotional,and cognitive impairment,which can affect a person’s life,school,and work.Exercise has a protective effect on the nervous system.This study aims to establish a model of rm TBI and explore the effects of rm TBI and/or exercise on central stress,inflammation,exercise function,memory,emotions,social behavior,and other aspects through exercise intervention.Methods:SPF-grade male C57BL/6J mice were randomly assigned into a sham group(Sham),a repetitive mild traumatic brain injury group(rm TBI),a sham with exercise group(Sham+Exe),and a repetitive mild traumatic brain injury with exercise group(rm TBI+Exe).A hydraulic impact device was used to apply pressure to the right motor-sensory area of the mice to induce rm TBI.From 1 to 7 days after the rm TBI model was established,open field tests and grid foot error tests were conducted to explore the effects of rm TBI and/or exercise on the mice’s exercise function and balance ability;behavioral experiments such as hanging tail test,open field test,social test were used to explore the effects of rm TBI and/or exercise on mood,learning cognition,memory function,and social skills in mice.Starting from the8 th day after the trauma,the exercise group of mice underwent a 4-week exercise training.During the experiment period,neurological severity scores(NSS)were measured every week to explore the effects of rm TBI and/or exercise on their neurological function.A second round of behavioral experiments was performed on the mice at the end of the exercise training.After the behavioral experiments,brain tissue samples were harvested for the evaluation of the neuronal damage in the cortex and the dentate gyrus(DG)of the hippocampus using hematoxylin-eosin staining.The positive cell counts of stress and inflammation-related proteins in brain tissues were detected using immunofluorescence staining,and stress and neural inflammation-related protein expression were determined using Western blotting.The experimental results were semi-quantitatively analyzed with Image J and statistically analyzed with Prism 8.0.Results :The results of the neural and behavioral experiments showed that rm TBI mice showed a significant increase in NSS compared with Sham mice.At the same time,the total distance and the proportion of center distance traveled in the open field were significantly reduced,the number of footstep errors on the grid was significantly increased,the total distance of automatic rotation in the Y-maze was significantly reduced,the social time in the social experiment was significantly reduced,the time to find the platform in the water maze experiment was significantly increased,and the time spent in the original platform area was significantly reduced in rm TBI mice.After exercise training,rm TBI+Exe mice showed significant improvements in the aforementioned neural and behavioral dysfunctions.The HE staining results showed that the neurons were loose and swollen,the cell density was reduced,some cells ruptured,and the tissue structure was disordered around the impact site in the somatosensory cortex of rm TBI mice.The morphological structure of the hippocampus on the injury side was intact,with a few apoptotic cells,and the main changes occurred in DG,the site of important neurogenesis in the brain,manifested as a significant increase in heavily HE-stained cells in the DG granular sublayer,indicating a large portion of neurogenesis.The number of normal neurons in the somatosensory cortex of rm TBI+Exe group mice increased,and the number of neurons with nuclear pyknosis reduced,while the number of deeply HE-stained cells in the DG granular sublayer significantly decreased.The western blotting and immunofluorescence results showed that the expression of stress-related proteins G3BP1 and Caprin1,as well as the levels of neuroinflammationrelated proteins NLRP3,Caspase1,and Iba1,in the brain tissue of rm TBI mice significantly increased compared with Sham mice.The immunofluorescence results also showed coexpression of G3BP1 and Caspase1,Caprin1 and GFAP in brain tissue,indicating the simultaneous presence of sustained stress and neuroinflammation in the chronic phase of rm TBI.The results suggest that the expression level of stress and neuroinflammation-related proteins in the brain tissue of rm TBI mice significantly increased,and exercise training can significantly reduce the expression level.Conclusion:rm TBI induces neuronal damage in mice’s brain tissue and leads to various behavioral and neurological impairments in mice.In the chronic phase of rm TBI,the persistent presence of stress and neuroinflammation in the injured mice’s brain may underpinning of the neuronal damage and various functional impairments.However,4 weeks of comprehensive exercise training can effectively alleviate various neurological and behavioral deficits mentioned above.The neuroprotective effect of exercise training may partly be due to the inhibition of the expression of stress and neuroinflammation-related proteins in the brain..