A New Experimental Framework for the Examination of Acute Dysfunction in Traumatic Neural Injury

The functional consequences of traumatic neural injury are dependent on the mechanical insult and the transfer of force to the cells in the affected tissue, yet these events are not well understood. We have developed a new experimental framework using both in vivo and in vitro models of traumatic brain injury and measurement techniques that span levels of complexity and allow examination of plasma membrane integrity and electrophysiological response in the minutes following the insult. In an in vivo model using a normally cell impermeant dye we found significant uptake in cortical and hippocampal regions ipsilateral to a cortical impact at 10 minute post-insult. In addition, extracellular electrophysiological activity within the same time period was reduced in animals subject to injury. In an in vitro model of injury in which cultured primary neurons were subject to hydrodynamic deformation at comparable rates to the in vivo insult, membrane permeability increased immediately. In addition, custom-made multielectrode arrays were used to measure electrophysiological signals during and immediately following the same insult. Data revealed a reduction in firing frequency, supporting the hypothesis that immediate membrane failure has a disruptive effect on firing and overall network activity. Morphologically, cells that displayed dye uptake in both in vitro and in vivo were elongated and shrunk, suggesting downstream changes in cytoskeletal integrity and/or osmotic balance. A working conceptual model of these acute events includes deformation-induced membrane failure that is rate and magnitude dependent and leads to ionic imbalance. These events may directly alter the ability to fire normally and hence lead to reduced spike amplitude and frequency. Collectively, the acute response leaves the cells vulnerable to energy deficits, abnormal signaling, and, ultimately, cell death