The role of cell kinematics and the N-methyl D-aspartate receptor in apoptosis and necrosis in the in vitro hippocampus following mechanical injury

There are an estimated 1.4 million cases of traumatic brain injury (TBI) per year in the United States, yet no suitable pharmacological treatment has been developed that provides treatment without undesirable side effects. Through the use of computational models, thresholds have been developed for the forces necessary to induce injury in the brain, but these models have not yet examined the contribution of the cellular components of the tissue to these thresholds. Additionally, there has not been a thorough examination of the relationship between cellular mechanics and the resulting pattern of cell death which is observed following TBI. A more thorough understanding of the correlation of the mechanics of injury to the extent and distribution of apoptotic and necrotic cell death may aid in the understanding of the progression of brain injury and aid in the development of treatments. In this dissertation, organotypic cultures are used to examine both the mechanical response of the tissue to a quasistatic biaxial deformation and the levels of stretch necessary to induce the activation of markers of apoptosis and necrosis. Both the cellular components of the tissue as well as the extracellular matrix are shown to play important roles in the nonlinear behavior of the tissue. Further, with a dynamic stretch injury, there is a transition from apoptotic to necrotic cell death at higher stretch levels. Within the hippocampus, there is a shift in regional susceptibility from the dentate gyrus to the CA3 region with the increase in the level of stretch. Finally, selective inhibition of extrasynaptic N-methyl D-aspartate (NMDA)-NR2B receptors attenuated both caspase-3 activity and calpain-mediated spectrin breakdown product. Alternatively, inhibition of synaptic receptors (NMDA-NR2A containing) resulted in the appearance of activated caspase-3 and enhanced calpain-mediated SBDP following severe stretch. Together, these studies provide further evidence of the correlation between the severity of injury and the cellular response. Further studies into the contribution of cascades associated with the synaptic and extrasynaptic NMDA receptors may lead to the development of pharmacotherapies capable of reducing or redirecting the cellular response to injury and improving the management of TBI