The blood-brain barrier disruption to circulating proteins in the early period after fluid percussion brain injury in rats.

Abstract

Breakdown of the blood-brain barrier (BBB) immediately after traumatic brain injury is not clearly understood. In the present study we focused on the integrity of the BBB to circulating proteins within the first hour after injury. For this purpose, vascular permeability to endogenous albumin and to the exogenous protein tracer horseradish peroxidase (HRP) was examined after a lateral fluid percussion brain injury in rats. Albumin was immunolocalized in brain sections at 3 and 60 min after impact. This distribution was compared with the histochemical localization of HRP given before impact at the same time points. In a separate experiment HRP was given prior to sacrifice to determine the time course for the barrier disruption. Permeability to this protein was assessed at 13, 30, and 60 min after impact. Prominent extravasation of albumin occurred within 3 min of injury and was present in multiple foci within the injured hemisphere. At 60 min the extravasated albumin was present in the same sites, where it was widely distributed. Throughout the related brain parenchyma, little difference was found between the extravascular distribution of albumin and HRP. In the delayed administration paradigm breakdown of the BBB was noted in the impact site, hemorrhagic site in the deep cortical layer, hippocampus, thalamus, and midbrain at 13 min after injury. This injured barrier was restored in most regions by 30 min. However, the impact site and hemorrhagic site remained permeable up to 60 min postinjury. In addition, newly developed barrier disruption to HRP occurred in the parasagittal cortex at 30 and 60 min. In conclusion, widespread breakdown of the BBB to circulating proteins occurred within a few minutes after traumatic brain injury. The time course for this barrier disruption is characterized by three different patterns: (1) transient, (2) prolonged, and (3) delayed opening. This variation in the development of barrier disruption may be related to the secondary barrier failure as well as the primary opening after injury.