Characteristics of Sustained Blood-Brain Barrier Opening and Tissue Injury in a Model for Focal Trauma in the Rat

Abstract

Minor stab wounding of rodent brain by needle or razor blade is a standard model for immunohistochemical investigations of secondary neuronal degeneration and scarring. Opening of the bloodbrain barrier(BBB) to plasma molecules and inflammatory cells is integral to the secondary injury process. To facilitate quantitative study of these BBB phenomena, we tested the utility of a stereotaxic wire knife as a minimally invasive way for modeling of focal trauma and bleeding in brain parenchyma and substantial, reproducible BBB damage. Adult rats were anesthetized, and through a skull burr hole, the 0.3-mm dia guide cannula housing a laterally extendable tungsten wire (0.13 mm dia) was inserted into the right striatum. A layering of horizontal disk-like cuts (3 mm dia) was made, producing a cylindrical lesion of ∼18 mm³ volume, ∼2.7% of the cerebral hemisphere. Transfer constants (K _i) for blood to brain permeation of [³H]sucrose measured from 30 min to 2 weeks postlesion showed sustained BBB leakiness; for example, mean K _i ± SEM (nL.g^-1.s^-1) for a standard, matrix-dissected forebrain sample enclosing the lesion were 7.2 ± 1.2 (day 1 postlesion), 8.1 ± 1.4 (day 3), 5.4 ± 0.8 (day 14) compared with values for contralateral nonlesioned forebrain ranging from 1.3 ± 0.05 to 1.6 ± 0.3 (n= 3-4 samples per time point). Analysis of the simultaneous transport of [¹⁴C]sucrose (MW = 342 Da) and [³H]inulin (MW ∼5,000) showed significantly larger upward increments inK _i for sucrose than inulin, indicating a pore-like opening mechanism. Significant edema was measured 3 days postlesion. A reactive glial response was indicated by an increase in S100β by 6 h and a glial scar forming around the lesion by 7 days. Secondary brain injury was indicated by a 10% loss of hemisphere mass, measured at 2 months. The wire knife enabled tailoring of interstitial trauma with a minimum of extraneous injury and supported reproducible measurements of sustained BBB injury using relatively few animals.