Cellular Reactivity to Mechanical Axonal Injury in an Organotypicin VitroModel of Neurotrauma

Abstract

An in vitro model of traumatic brain injury is described that is based on organotypic cocultures (OTCs) of rat neocortex and thalamus connected by reciprocal axonal projections. Localized mechanical compression of this projection was inflicted with a mechanical device, and the effects on cell viability, axonal morphology, and protein expression levels were analyzed. Within 24 h after insult, major cell damage occurred in infragranular cortical layers containing the corticothalamic projection neurons and in thalamic regions adjacent to the mechanical impact as was assessed through the use of the vital stain Syto 21, and propidium iodide labeling. A small, but significant number of calretinin-positive interneurons in cortical and thalamic areas displayed symptoms of injury. Axonal elements, as revealed by neurofilament (NF-H/M) immunohistochemistry, in the corticothalamic transition zone displayed pathomorphological changes, such as axonal bulbs and swellings, already 4 h after insult. Densitometric analysis revealed that MAP-2a,b expression was not significantly changed within 4 h after injury. A significant reduction in MAP-2a,b amount was evident at 20 h after injury in thalamus (by 31.6%) and cortex (by 30%) maintained for 12 days in vitro (DIV), but not in OTCs aged 20 DIV. The axonally localized form MAP-2c significantly increased in cortex of 12-DIV OTCs at 4 and 20 h after insult (65.6% and 33.4%, respectively). MAP-2c levels in cortex of 20 DIV initially increased by 47.7% and declined below control values 20 h after injury. Thalamic areas revealed a delay in MAP-2c reactivity, in that expression was significantly elevated only at 20 h after injury (by 84.4% in 12-DIV and by 39.6% in 20-DIV OTCs, respectively). These data may reflect the regenerative ability of juvenile, but not of older neurons in response to mechanical axonal injury.