CEREBRAL HYPOXIA-ISCHEMIA STIMULATES CYTOKINE GENE-EXPRESSION IN PERINATAL RATS

Background and Purpose We tested the hypothesis that cerebral hypoxia-ischemia selectively stimulates interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) gene expression in brain regions susceptible to irreversible injury in perinatal rats. Methods To elicit focal hypoxic-ischemic brain injury, 7-day-old perinatal (P7) rats were subjected to right carotid artery ligation followed by 3 hours of 8% O-2 exposure and were killed O to 48 hours after hypoxia. Regional tissue IL-1 beta and TNF-alpha mRNA content were measured by reverse transcription followed by polymerase chain reaction amplification (RT-PCR) in samples prepared from cortex and hippocampus of the lesioned and contralateral hemispheres. cDNAs were amplified with primers specific for IL-1 beta, TNF-alpha, and the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which served as an internal control. The RT-PCR products were subjected to Southern blot analysis and hybridized with P-32-labeled gene-specific probes. Radioactivity was measured in excised bands, and results were normalized on the basis of levels of GAPDH expression. Results In unlesioned P7 brain, IL-1 beta mRNA was barely detectable. In lesioned forebrain, there was a marked, transient stimulation of IL-1 beta mRNA expression, peaking at 4 hours after hypoxia. Hybridization signal was increased 16- to 30-fold over values from contralateral hemisphere samples in three independent assays (P<.05 comparing values in left and right cortex and in left and right hippocampus with the Kruskal-Waillis ranking test); by 24 hours after hypoxia, levels returned to normal. Similar transient increases in TNF-alpha mRNA expression were detected. In a closely related model of perinatal brain injury elicited by focal intracerebral N-methyl-D-aspartate injection, there was a corresponding acute stimulation of IL-1 beta and TNF-alpha mRNA expression at 4 hours after injection. Conclusions These results suggest that IL-1 beta and TNF-alpha may play important roles in the response of the developing brain to acute hypoxic-ischemic injury.