Neurophysiological Evidence of Preservation of Brain Stem Function in Experimental Closed Head Injury in the Rat

Abstract

The use of animal models of head injury have contributed substantially to the understanding of the pathophysiology, neuropathology, and underlying mechanisms of traumatic brain injury. Despite this progress, a reproducible model of severe closed head injury (CHI) without substantial brain stem damage was not yet available. This fact has been emphasized by Shima and Marmarou [5]. In the cat model of fluid percussion, using brain stem auditory evoked potentials (BAEP), these workers found a severe impairment of the neurophysiological function of the brain stem. Similar findings were observed in the rat model of FPI [1]. In contrast, our studies of CHI, using a simple weight drop model, shows a markedly different response from the fluid percussion injury (FPI) model. The CHI model is characterized by impact, which causes the compression and acceleration of the partially restrained skull. This mechanism is similar to many high velocity impact injuries seen in humans. However, it is unclear if similar brain stem disturbances seen in FPI would occur in closed head injury. The objective of this study was to investigate the functional integrity of the brain stem in response to CHI. This was accomplished utilizing BAEP’s. Somatosensory evoked potentials (SSEP) were used to evaluate the cervical and cortical neuronal function.