LASER-DOPPLER FLOWMETRY MEASUREMENTS OF SUBCORTICAL BLOOD-FLOW CHANGES AFTER FLUID PERCUSSION BRAIN INJURY IN RATS

Laser-Doppler flowmetry (LDF) was used to record subcortical cerebral blood flow in hippocampus and striatum immediately following parasaggi tal fluid percussion brain injuries of mild to moderate severity (2.58 +/- 0.09 atm, 10-11 msec duration) in spontaneously breathing anesthe tized rats. At 5 min postinjury, mean blood flow decreased bilaterally by 20-30% in both brain structures, and remained significantly reduce d during the remainder of the 60 min postinjury recording interval. Bl ood flow did not change in the sham-injured rats. Subsequent beam-walk , beam-balance, and rope-hang assessments revealed significant neurolo gical impairments in the injured rats but not in the sham controls. Th e magnitude of the blood flow changes and the severity of the ensuing neurological impairment were significantly correlated. Histopathologic al assessments revealed hemorrhagic contusions within ipsilateral cort ical regions, occasional neuronal necrosis within underlying thalamus and CA3 and CA4 sectors of the hippocampus, and neuronal cell loss in the hilus of the dentate gyrus. In a second series of experiments, rad iolabeled microspheres were used to validate the LDF blood flow measur ements. The microsphere measurements revealed that the preinjury basel ine and postinjury right hippocampal blood flow changes were not signi ficantly altered by the intrahippocampal presence of an LDF probe, ver ifying that the LDF probe was not by itself an unacceptably disruptive influence on local cerebrovascular reactivity. Moreover, when right h ippocampal blood flow was simultaneously evaluated in injured rats by both techniques, the relative blood flow changes were significantly co rrelated. These results indicate that laser-Doppler flowmetry provides a potentially useful means to appreciate acute regional cerebrovascul ar changes relative to other measures of outcome after brain trauma.