Acute axonal shear and stretch in the brain induces an evolving form of axonopathy and is a major cause of ongoing motor, cognitive and emotional dysfunction. We have utilized an in vitro model of mild axon bundle stretch injury, in cultured primary cortical neurons, to determine potential early critical cellular alterations leading to secondary axonal degeneration. We determined that transient axonal stretch injury induced an initial acute increase in intracellular
calcium, principally derived from intracellular stores, which was followed by a delayed increase in
calcium over 48 h post-injury (PI). This progressive and persistent increase in intracellular
calcium was also associated with increased frequency of spontaneous
calcium fluxes as well as cytoskeletal abnormalities. Additionally, at 48 h post-injury, stretch-injured axon bundles demonstrated filopodia-like sprout formation that preceded secondary
axotomy and degeneration. Pharmacological inhibition of the
calcium-activated
phosphatase,
calcineurin, resulted in reduced secondary
axotomy (p < 0.05) and increased filopodial sprout length. In summary, these results demonstrate that stretch injury of axons induced an initial substantial release of
calcium from intracellular stores with elevated intracellular
calcium persisting over 2 days. These long-lasting
calcium alterations may provide new insight into the earliest neuronal abnormalities that follow
traumatic brain injury as well as the key cellular changes that lead to the development of
diffuse axonal injury and secondary degeneration.