High Tolerance and Delayed Elastic Response of Cultured Axons to Dynamic Stretch Injury

Abstract

Although axonal injury is a common feature of brain trauma, little is known of the immediate morphological responses of individual axons to mechanical injury. Here, we developed an in vitro model system that selectively stretches axons bridging two populations of human neurons derived from the cell line N-Tera2. We found that these axons demonstrated a remarkably high tolerance to dynamic stretch injury, with no primary axotomy at strains Ͻ65%. In addition, the axolemma remained impermeable to small molecules after injury unless axotomy had occurred. We also found that injured axons exhibited the behavior of "delayed elasticity" after injury, going from a straight orientation before injury to developing an undulating course as an immediate response to injury, yet gradually recovering their original orientation. Surprisingly, some portions of the axons were found to be up to 60% longer immediately after injury. Subsequent to returning to their original length, injured axons developed swellings of appearance remarkably similar to that found in brain-injured humans. These findings may offer insight into mechanical-loading conditions leading to traumatic axonal injury and into potential mechanisms of axon reassembly after brain trauma.

In vivo imaging of rapid deformation and strain in an animal model of traumatic brain injury

“…However similar levels of strain are believed to cause similar neuropathology (Margulies et al, 1990). This belief is supported by in vitro studies such as those by Smith et al (1999), Morrison et al (2000), and Geddes et al (2003), who investigated the response of cultured axons to stretching. Bain and Meaney (2000) determined thresholds for injury in the guinea pig optic nerve in terms of strain.…”

Mild Traumatic Brain Injury and Diffuse Axonal Injury in Swine

“…Yet even in severe TBI, only a small percentage of axons within a given tract undergo transport interruption resulting in accumulation of transported cargoes in swellings. Unique to traumatic axonal injury, this immediate transport interruption may reflect mechanical disruption of the axonal cytoskeleton, such as breaking of microtubules due the dynamic aspect of the deformation (Smith et al, 1999b;Tang-Schomer et al, 2010). Ultimately, these axons may disconnect at distal points of swellings, which triggers degeneration within days after injury, as characterized by Povlishock and colleagues (Povlishock and Becker, 1985;Grady et al, 1993).…”

Modelos experimentales de traumatismo craneoencefálico

“…Posteriormente, se desarrolló uno de los modelos de TCE focal que más se sigue empleando en la actualidad, conocido como "modelo de percusión lateral por fluido" (lateral fluid percussion, LFP), en el que se aplica una presión directa sobre el cerebro, previamente expuesto, utilizando para ello bien un pulso de aire o uno de agua 31,101,107 . Una técnica más reciente fue reproducir la deformación directa del cerebro con un dispositivo sólido, conocido como "modelo de impacto cortical controlado" (controlled cortical impact, CCI) 68 .…”

“…Una variación posterior del modelo consistió en el estiramiento de las células en cultivo en una sola dirección 87,71 (Figura 6-B). Con el estiramiento de las neuronas que tienen sus prolongaciones alineadas longitudinalmente y paralelas a la dirección de la tensión en cultivo, se trata de reproducir la lesión axonal difusa 101 .…”