Induction of interleukin-1 beta mRNA after focal cerebral ischaemia in the rat.

The expression of interleukin-1 beta (IL-1 beta) mRNA in the brain in response to cerebral ischaemia in rats was examined using in situ hybridization histochemistry. Focal cerebral ischaemia was induced in spontaneously hypertensive rats by permanent occlusion of the left middle cerebral artery (MCAO). Whereas no IL-1 beta mRNA could be detected in non-operated and sham-operated rats, middle cerebral artery occlusion induced the expression of IL-1 beta mRNA within 15 min in the ischaemic brain regions prone to become necrotic after 1-2 days. The message appeared as spot-like signals, reached a peak after 3 h and then declined to undetectable levels within 4 days. Additionally, a pronounced but brief induction of IL-1 beta mRNA could be detected 1 h after MCAO in the meninges near the watershed zone. The results demonstrate that the inflammatory cytokine IL-1 beta is induced in a time-dependent way after brain ischaemia.