Traumatic brain injury (TBI) is a pernicious event that destroys many lives. Currently, there are no effective pharmacological treatments for TBI . Treatments once thought promising such as the use of corticosteriods have been determined not to have any neuroprotective qualities [2, 3].
PEG has been used subsequent to a standardized TBI in the rat to reduce cellular damage in brain in various regions, particularly the white matter of the corpus callosum . Additionally, immunohistochemical staining for β-Amyloid Precursor Protein, a protein that aggregates in the axon terminal associated with progressive secondary axotomy, has been significantly reduced by PEG treatment after injury . The salutary effects of PEG have likewise been seen in the injured spinal cord. The mechanical interaction of the polymer with only damaged membranes leads to rapid (minutes to hours) improvements in physiological function, permanent repair of the membrane damage, inhibition of free radical production, and reduction in the size of progressive cavitation [6–8]. These actions result in an improved behavioral recovery after laboratory spinal cord injury (SCI) in guinea pigs and rats, and in clinical cases of paraplegia in dogs .
PEG's membrane sealing and reassembly properties were originally utilized for vesicle fusion and hybridoma formation [10, 9, 11]. PEG molecular weights < 4 kD are sufficient to produce cell and axon fusion [12, 7], recovery of conduction in white matter tracts after crush injury , and a reduction in the destruction of axons after spinal cord crush injury [6, 14].
The studies describing the neuroprotective properties of PEG after brain injury persuaded us to test the effect of PEG injection on rat behavior after TBI. In the rat, the same Impact Acceleration injury model as used in the present investigations produced significant behavioral impairment [15, 1]. Brain-injured animals are impaired in "open-field" evaluations, the "rotorod" behavioral evaluation, and on the beam walk [16, 15]. Open-field exploratory behavior is the most ideal preliminary test to apply to injured animals because this evaluation does not require "blinding" of the investigator, as this person is not involved with the taking, or generating of the data. Furthermore, the natural exploratory behavior of the rat provides the baseline function which also does not require training but does require cognitive, motivational, and motor performance capabilities of the study animals.