Activation of p44/42 mitogen activated protein kinases in thrombin-inducedbrain tolerance

Background: Our recent studies have shown that prior intracerebral injectio n of a low dose of thrombin attenuates the brain edema formation that resul ts from either an intracerebral hematoma, an intracerebral injection of a l arge dose of thrombin or cerebral ischemia. The aim of the current study is to investigate whether thrombin-induced tolerance (thrombin preconditionin g.. TPC) is associated with activation of p44/42 mitogen activated protein (MAP) kinases. Methods: This study contained three parts. In the first, rat s received an intracerebral infusion of either saline or one unit thrombin (the TPC dose) into the right caudate nucleus. After 1, 3 and 7 days, the r ats will be killed and brains used to detect p44/42 MAP kinases activation using Western blot analysis and immunohistochemistry. In the second and thi rd parts, rats received intracerebral infusions of either vehicle, one unit thrombin (TPC) or one unit thrombin and 5 nmol PD 098059. These rats were either killed to detect kinases activation after 24 h or received a second intracerebral infusion of five-unit thrombin 7 days later with brain edema being assessed after a further 24 h. Results: Western blot analysis demonst rated that p44/42 MAP kinases were activated in the ipsilateral basal gangl ia after the intracerebral infusion of thrombin one unit. Cells immunoreact ive for activated p44/42 MAP kinases were found in the ipsilateral basal ga nglia and ipsilateral cortex. PD 098059, a MAP kinase kinase inhibitor, abo lished thrombin-induced activation of p44/42 MAP kinases. TPC suppressed th rombin-induced brain edema while PD 098059 blocked this protective effect. The water contents in the ipsilateral basal ganglia 24 h after infusion of thrombin five units were 82.6 +/-0.8%. 79.2 +/-0.4% and 81.8 +/-1.9% in the control, TPC alone and TPC plus PD 098059 groups, respectively. Conclusion : Thrombin can activate p44/42 MAP kinases within the brain and the protect ive effects of thrombin preconditioning on brain edema formation are relate d to this activation. (C) 2001 Elsevier Science B.V. All rights reserved.