Miniscope in vivo imaging of cumulative traumatic brain injury

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Project Summary/Abstract In the United States, millions of people sustain a traumatic brain injury (TBI) each year carrying individual, healthcare, and societal costs greater than $45 billion annually. Mild TBI (mTBI) accounts for more than 75% of all TBIs, with many individuals sustaining more than one. mTBI patients report post-concussion syndrome (PCS) symptoms that include sleep disorders (insomnia, daytime sleepiness), somatic symptoms (dizziness, headache, blurred vision), cognitive complaints (memory, executive function), and emotional problems (anxiety, depression, irritability, disinhibition). For many, PCS is transient, and still 10-25% report persistent PCS symptoms. The enigmatic PCS symptom presentation and persistence after mTBI urges investigation into dynamic responses in the brain that tie acute neurophysiology to behavioral function. The investigative team has refined in vivo imaging methods of miniaturized microscopes (miniscopes) to evaluate cerebral blood flow (CBF) and blood brain barrier (BBB) permeability in the unrestrained, behaving mouse. New preliminary data leverage the miniscope headcap to induce impact acceleration (weight drop) closed head injury. The data driving this proposal show immediate accumulation of fluorescent dextrans in the parenchyma within the field of view. The strength of this approach eliminates anesthesia during long-duration imaging, permits naturalistic behavior without head restraint, and locks into a baseplate for repeated imaging of single channel, wide-field, fluorescence. For the first time, the cumulative effects of TBI on neurophysiology (CBF, BBB permeability, sleep) can be regressed toward neurobehavioral impairments. The present proposal tests the hypothesis that the cumulative effects of mTBI on CBF and BBB permeability promote post-traumatic sleep and predict neurological impairments. Male and female mice are prepared for miniscope imaging through a cranial window and attached baseplate. The baseplate headcap substitutes for a helmet in closed-head impact acceleration TBI. With a 15 sec transition, miniscopes visualize CBF and BBB permeability with intraperitoneal dextrans (40-2000 kDa) in vasculature and parenchyma, respectively. The cumulative effects of mTBI are assessed with impacts delivered twice daily, daily, or every other day for a week. Aim 1 monitors the cumulative effects of mTBI with varying temporal spacing on CBF concurrent with post-traumatic sleep and subacute behavioral performance. Aim 2 quantifies the extent of dextran extravasation with post-traumatic sleep and subacute neurological performance. Neurological outcomes include anxiety (open field), spatial memory (novel object location), and somatosensory pain (mechanical hyperalgesia). Twice daily injuries likely show temporal summation of CBF, BBB permeability, and sleep effects, which are recovered with longer recovery times between injuries. The integration of miniscope imaging and closed head injury can propel future studies on physiological perturbations and clinical management of TBI.