In the United States over 1.7 million cases of traumatic brain injury are reported yearly, but predictive correlation of cellular injury to impact tissue strain is still lacking, particularly for neuronal injury resulting from compression. Given the prevalence of compressive deformations in most blunt head trauma, this information is critically important for the development of future mitigation and diagnosis strategies. Using a 3D in vitro neuronal compression model, we investigated the role of impact strain and strain rate on neuronal lifetime, viability, and pathomorphology. We find that strain magnitude and rate have profound, yet distinctively different effects on the injury pathology. While strain magnitude affects the time of neuronal death, strain rate influences the pathomorphology and extent of population injury. Cellular injury is not initiated through localized deformation of the cytoskeleton but rather driven by excess strain on the entire cell. Furthermore we find that, mechanoporation, one of the key pathological trigger mechanisms in stretch and shear neuronal injuries, was not observed under compression.

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tension)-that this clustering of vesicles is heavily influenced by mechanical tension. Recently, evidence has shown that there is a cortical network of actin, among other things, along the conduit of an axon; its contractility, powered by the acto-myosin machinery, gives rise to the axon's intrinsic tension. Here, we employed transgenic drosophila embryos of stage 16 that have green fluorescence protein tagged to synaptotagmin to track vesicles in neurons. Embryos were dissected such that intact single axons could be visualized in vivo. The axons were then imaged under a time-lapse confocal setup where both spatial and temporal quantification of vesicles could be achieved. We targeted the acto-myosin machinery by performing drug incubations that disrupt the ROCK (and MLCK) pathway, which, after 45 minutes, led to a 35% reduction in fluorescence intensity only at the synaptic region and subsequent washout resulted in a 32% (of the 35%-reduction) recovery after 45 minutes. Another transgenic line with non-muscle myosin II expression reduced was also used for comparison purposes. Furthermore, we aim to establish that vesicle declustering is a direct consequence of the loss of tension, but not the disruption of myosin motors. Towards achieving this goal, we designed a microfluidics platform to perfuse drugs at only the axonal region, but not the synaptic region. We also designed a force sensor to measure the rest tension in an axon before and after pharmaceutical treatment. Preliminary results collectively suggest that axonal tension maintained by the acto-myosin network sustains vesicle clustering. Further experimental evidence is required to understand how such is achieved and the functional role of tension in neurons.