Title: The electrophysiology of mechanical brain injury in rats
Description: Brain injury resulting from mechanical trauma can cause a variety of adverse functional and biochemical sequelae. The subsequent appearance of seizures, migraines, and other neurological pathophysiologies suggests an alteration in neural excitability associated with a disruption in the balance between neuronal excitation and inhibition. The process by which this occurs has yet to be fully elucidated and the specific nature of the changes in excitation and inhibition is still unclear. We investigated the effects of focal cortical compression on electrically-induced localized seizure threshold and in vivo neural electrophysiology. To establish global changes in excitation and inhibition following cortical deformation, male Long Evans rats were implanted with stimulating screw electrodes in their motor cortices above the regions controlling forelimb movement. Locally induced seizure threshold evolution was monitored over a period of 2 days with repeated trials of ramped electrical stimulation both in the setting of focal cortical compression and non-injury. Localized seizure threshold was significantly lowered following sustained cortical compression as compared to control cases. Electrophysiology was performed utilizing 8x8 microelectrode grid arrays, allowing for simultaneous recordings from large portions of the rat barrel cortex. Paired-pulse whisker deflection was utilized to quantify fine changes in excitation and inhibition in the barrel cortex following focal cortical compression. It was found that focal compression appears to cause an early period of increased inhibition, which is then followed by a prolonged period of hyperexcitation.