We have developed and tested a rat (Wistar) model of moderate concussion. Concussion is produced by controlled and repeatable mechanical fixed, closed-head injury. Moderate concussion in this model is characterized by 4 to 10 minutes of unconsciousness, absence of skull fractures or brain contusions, and few, if any, acute neurologic symptoms. By 2 hours postinjury, the subsequent trauma is further characterized by regional and global increases in cerebrovascular permeability and decreases in cerebral blood flow. Such changes are accompanied by brain swelling and two phases of elevated intracranial pressure; one lasting about 5 hours with a peak of about 10 mmHg, the other lasting more than 3 days postinjury with a peak of about 30 mmHg. Regional neurohistologic damage detected between 3 and 4 days postinjury correlates for the most part with earlier changes in regional permeability and blood flow. Significant morphologic changes which are characterized by patchy neuronal degeneration can be found in numerous forebrain locations, particularly in the frontal (coup) and entorhinal (contre coup) cortices. These observations have important parallels in human head trauma and suggest that this reliable physiological model may be a useful, relatively simple and inexpensive tool for investigating the mechanisms and therapeutics of head trauma.

Although duration of unconsciousness is commonly used as a prognostic index following traumatic brain injury (TBI), few controlled studies have statistically evaluated the relationship between unconsciousness and histologic pathology, particularly after moderate head injury. Using a pendulum-striker concussive device, a reproducible model of TBI in rats was developed. This model is uncomplicated by skull fractures, contusions, or experimenter-induced craniotomies. In the present study, the severity of the histopathology observed in this model of moderate closed-head injury at 48 h posttrauma is linearly related to the duration of unconsciousness (p < 0.0001). The pathology, assessed with a silver stain for neurodegeneration, is particularly striking if unconsciousness persists for 4 minutes or more. These data suggest that the initial period of unconsciousness may be a useful predictor of clinical brain histopathology associated with moderate closed-head injury, predicting either the degree of pathology and/or the rate it progresses if left untreated.

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