Abstracts

Rationale: Traumatic brain injury (TBI) disrupts neuronal circuitry in the cerebral cortex, leading to motor dysfunction, cognitive losses, and, in some cases, post-traumatic epilepsy (PTE). Following TBI, 5-40% of patients progress to develop spontaneous recurrent seizures, or PTE, after a latent period ranging from months to years. The likelihood that TBI leads to PTE is influenced by injury heterogeneity, injury severity, and patient age. Recent studies suggest that early epileptiform activity is associated with increased risk of PTE, but the neuronal circuits dynamics that mediate these EEG signals are unknown. Here, I aim to use in vivo glutamate and calcium widefield mesoscale imaging and micro-electrode array (MEA) recording in the controlled cortical impact (CCI) model of TBI to quantify abnormal network activity that occurs following injury. Methods: We performed CCI in adult male and female CamKIICre mice and implanted cortical windows for mesoscale imaging and/or transparent, flexible nanomesh MEAs on the cortical surface for recording electrical activity. Prior to CCI, animals were injected via tail vein with PHP.eB.SynFLEX.GCaMP7f to broadly express GCaMP7f in neurons. We have optimized mesoscale imaging and MEA recording in sham injured cortex and have begun to implement these approaches following CCI. Mesoscale imaging and MEA data will be collected in head fixed animals for 30 minutes a day, every day, for 7 days beginning 3 days post-surgery. During mesoscale imaging experiments, 470 nm light was used to excite GCaMP7f and 530 nm light was used to capture reflectance signals. This LED system serially illuminates the exposed cortex with 470 nm and 530 nm light to account for changes in absorption due to hemodynamics. Results: We have established a combined surgical protocol for CCI and implantation of the MEA and cortical window. We have also successfully solved several technical and engineering-based challenges. First, we determined that a square is the most effective MEA shape because it allows implantation with the least brain tissue damage. Next, we solved animal destruction of the MEA device by implementing a novel head bar that protects the MEA interconnect carrying the device output signals. MEA-related issues that remain include reducing damage to devices during implantation and ensuring stability of MEA recording over time. Additionally, we have addressed issues related to mesoscale imaging. First, we ensured broad and stable expression of GCaMP7f throughout excitatory neurons by using a CamKIICre and AAV.phpB viral approach. Second, we implemented a head fixation bar that enables both MEA protection and visual access to the cortical surface. Finally, our experiments require implementing these novel approaches for chronic in vivo recording. Thus, we solved challenges related to handling and habituating animals to enter a plexiglass tube and remain head fixed during wakefulness. Currently, we are utilizing these approaches to perform GCaMP7f-based mesoscale imaging and MEA recording in sham and injured cortex. Preliminary data suggests that CCI significantly alters cortical network activity based on both measures. Conclusions: Using these measures, we predict that excitatory signaling and electrical activity are altered in the cortex following CCI. No biomarkers for identifying patients with a high likelihood of developing PTE have been found and proven clinically useful. We hope our work in the present study will lead to clinically useful activity-based predictive biomarkers of PTE. Funding: DOD W81XWH-18-1-0699