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ELECTROPHYSIOLOGY AND HISTOLOGY OF AXONAL INJURY IN THE RAT

Departments of Anesthesia and Surgery, St. Michael's Hospital and The University Health Network, Toronto, Ontario

INTRODUCTION

Diffuse axonal injury (DAI) is associated with poor outcome following traumatic brain injury(TBI). In this study, we sought to determine and quantify the functional deterioration of axons following TBI and correlate this with histological markers of injury.

METHODS

Adult male rats underwent fluid percussion-induced TBI. Compound action potentials(CAPs) were recorded in the corpus callosum at 3h, 1d, 3d, 7d, and 14d following injury and compared to shams(n=5/group). Brains were harvested in shams, 3d, 7d and 14d(n=4/group), sectioned, and stained for APP and injured myelin using immunohistochemistry.

RESULTS

Corpus callosum axonal conduction was significantly reduced at 3h(48.8±3.3%), 1d(54.9±3.1%) and 3d(52.9±3.7%) compared to shams(100%). CAP recovered partially at 7d(85.1±4.9%), but deteriorated by 14d(53.2±7.8%). APP expression was significantly increased at 3d(count:1966.3±232.0), 7d(3052.5±265.1), and 14d(1156±218.8) compared to shams(61±13.9). Injured myelin was increased at 3d (count:664.3±194.1), 7d(721±87.8), and 14d(687.8±31.4) compared to shams(52.3±4.4). APP and injured myelin deposition tended to be distributed caudally and laterally.

CONCLUSIONS

This study is the first to report an evaluation of the degree and temporal pattern of axonal dysfunction following TBI. Reversibility was seen between 3d and 7d electrophysiologically but not histologically. This highlights the value and importance of combined functional and morphological approaches in the evaluation of experimental TBI, especially DAI.

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