The mechanisms associated with
edema formation after
traumatic brain injury (TBI) have not been fully elucidated. In peripheral tissue injury, the neurogenic component of
inflammation plays a significant role in increased vascular permeability and
edema formation. However, few studies have examined the role of
neuropeptide induced
neurogenic inflammation following TBI. Adult male Sprague-Dawley rats were either left untreated, or pre-treated with
capsaicin (125 mg/kg s.c.) or equal volume vehicle, and injured 14 days later using the 2-meter impact-acceleration model. Subgroups of animals were assessed for blood brain barrier (BBB) permeability (
Evans Blue),
brain edema (wet weight/dry weight) and functional outcome (Barnes maze and Rotarod) for up to 2 weeks post-
trauma. Increased BBB permeability was present in untreated animals between 3 and 6 h after injury but not at later time-points.
Edema was maximal at 5 h after
trauma, declined and then significantly increased over the 5 days post-
trauma. In contrast,
capsaicin pre-treated,
neuropeptide-depleted animals exhibited no significant increase in BBB permeability or
edema compared to vehicle treated animals after injury. Notably, motor and
cognitive impairments were significantly reduced in the
capsaicin-pretreated animals. We conclude that
neurogenic inflammation contributes to the development of
edema and posttraumatic deficits after diffuse TBI.