A short duration of ischemia (i.e., ischemic preconditioning) results in significant brain protection to subsequent severe ischemic insult. Because previous studies suggest that tumor necrosis factor-α (TNF-α) plays a role in both promoting ischemic damage and neuroprotection, the present work aimed to evaluate the expression of TNF-α mRNA in an established model of ischemic preconditioning using a transient 10-minute occlusion of the middle cerebral artery. Because the level of TNF-α mRNA expression in the brain was too low to be consistently detected by Northern technique, a real-time polymerase chain reaction method was applied to quantitate the absolute copy number of TNF-α transcript in rat brain after the preconditioning procedure. TNF-α mRNA was induced in the ipsilateral cortex as early as 1 hour (27 ± 1 copies of mRNA per microgram of tissue compared to 11 ± 3 copies in sham-operated samples) after preconditioning, reached a peak level at 6 hours (49 ± 10 copies of transcript, n = 4, P < 0.01), and persisted up to 2 days. These data not only demonstrate the utility of real-time polymerase chain reaction for sensitive and accurate measurement of mRNA expression in normal and injured tissues but also suggest a potential role of TNF-α in the phenomenon of ischemic preconditioning.
Detection of Tumor Necrosis Factor-α mRNA Induction in Ischemic Brain Tolerance by Means of Real-Time Polymerase Chain Reaction