Fluid Percussion Brain Injury

The fluid-percussion model of brain injury in the rodent is the most commonly used and well-characterized experimental model of TBI. After the skull is exposed and trephination is performed, injury is produced by the impact of a rapid fluid bolus, which strikes the intact dural surface and then moves in the epidural space concentrically from the injection area leading to diffuse loading to the brain. This model subsequently has been used and modified over the past decades to produce injury in a wide range of different animal species. The fluid-percussion technique to produce TBI in the rat was first evaluated with the trephination site placed centrally in the midline. It was subsequently shifted to a lateral location and later modified for use in the mouse. Due to the height of the pendulum, which determines the force of the fluid pressure pulse that is transmitted through a saline-filled reservoir, the injury severity can be varied reproducibly, and studies using this injury model have been conducted over a range of mild to severe experimental TBI.

The fluid-percussion model reproduces contusions as the hallmark of focal (gray matter) damage with accompanying petechial or intraparenchymal and subarachnoid hemorrhages. In fact, central fluid percussion leads to a contusion in the direct vicinity of the site of the maximal fluid impulse, whereas the more pronounced contused area in the lateral fluid-percussion injury tends to be more lateral than the actual trephination and injury site. The extent of this damaged area is associated with injury severity, and a necrotic cavity evolves from the contusion over weeks, which progressively expands due to ongoing cell death up to 1 year postinjury. Injury-induced damage has also been described remote from the injury site. To date, cell damage or cell death has been demonstrated in the thalamus and hippocampus and parallels the cortical cell death up to 1 year postinjury. Although the lateral fluid-percussion model was initially considered to represent a model of unilateral damage, a number of studies have conclusively shown that contralateral damage occurs. Additionally, lateral fluid-percussion injury has been associated with diffuse white matter damage remote from the injury site, reminiscent of human traumatic white matter injury.

Transient impairments in a broad variety of tests for different aspects of neurologic motor function and cognitive deficits have been described. Moreover, long-term investigations have reported persistent cognitive and motor impairments up to 1 year after severe lateral fluid-percussion brain injury.

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