Cerebral preconditioning using cortical application of hypertonic salt solutions: upregulation of mRNAs encoding inhibitors of inflammation.

Previous studies have demonstrated that local application of hypertonic KCl or NaCl to the cerebral cortex induces tolerance to a subsequent episode of ischemia. The objective of the present study was to determine whether application of these salts increases the levels of mRNAs encoding inhibitors of inflammation. Hypertonic KCl or NaCl was applied for 2 h to the frontal cortex of Sprague-Dawley rats. After recovery periods up to 24 h, levels of selected mRNAs were measured in samples from frontal and parietal cortex using Northern blots. Application of hypertonic KCl caused a rapid and widespread increase in the levels of mRNA coding for tumor necrosis factor (TNF), tristetraprolin (TTP), suppressor of cytokine signaling-3 (SOCS3), and brain-derived neurotrophic factor (BDNF), and a 24-h delayed induction of ciliary neurotrophic factor (CNTF) mRNA. Application of hypertonic NaCl caused alterations in mRNA levels that were restricted to the frontal cortex. In this region, application of NaCl rapidly increased levels of mRNA encoding TNF, TTP, and SOCS3, but not BDNF, and caused a delayed induction of CNTF mRNA. These results raise the possibility that upregulation of inhibitors of inflammation after preconditioning may contribute to the induction of tolerance to ischemia.