Minocycline plus N-acetylcysteine improve chronic and progressive structural and functional deficits following a single TBI in male mice

Abstract

Traumatic brain injury (TBI) is the leading cause of death and disability above any other trauma. The high prevalence of later life degenerative outcomes strongly suggests a single TBI can develop into a progressive neurodegenerative disorder. Clinical TBI may produce chronic deficits in limb coordination, and gait that is associated with corpus callosum damage. Detection of chronic motor deficits after TBI may be obscured by effects of aging or the development of compensatory motor strategies. Chronic motor deficits are poorly studied in rodent TBI models. The murine closed head injury (CHI) model produces diffuse, chronic white matter injury that may underlie chronic white matter dysfunction and motor deficits. DeepLabCutTM markerless limb tracking provided the data for novel assessments of limb function on beam walk and simple-complex wheel. Injured mice on beam walk do not differ from sham mice on time to traverse or foot fault number. Novel assay beam walk absition integrates time and extent of all foot faults during a beam walk trial. Injured mice have chronic absition deficits that are blocked by dosing of minocycline and N-acetylcysteine beginning 12 hours post injury (MN12). Absition deficits do not appear until 90 DPI and worsen at 180 DPI suggesting chronic and progressive motor decline. Speed is a standard method to assess performance on simple-complex wheel. Novel assays show that at 14 DPI, MN12 improves limb coordination to prevent an injury dependent decline in running speed. Ex-vivo T2 and diffusion-tensor MRI studies show that MN12 prevents most progressive gray and white matter atrophy in motor structures and improves bilateral white matter integrity. MN12 increases inflammatory cell density in corpus callosum after CHI. This increased inflammatory response is likely beneficial since MN12 improves callosal structure and function. Evoked compound action potentials (CAP) assess corpus callosum function from 3 to 180-days post injury (DPI). CHI acutely decreases CAP amplitudes that recover by 90 DPI and further increase at 180 DPI. Changes in CAP amplitude are blocked by MN12. CHI mice have chronic corpus callosum dysfunction that coincide with motor deficits. Analysis using DeepLabCutTM limb tracking reveals chronic deficits and compensatory motor strategies not seen with standard outcomes. These observations support the central hypothesis of this thesis: MINO plus NAC improves injury-dependent deficits in white matter histology, structure, and function with a favorable therapeutic time window in male mice, as well as the aim to test if MINO plus NAC reduce structural and functional deficits in white matter after a single CHI in male mice. The results of these experiments provide important information about the chronic phase of TBI in addition to developing novel methods to assay the onset, persistence, and progression of injury-dependent changes in the CHI mouse model of TBI.