IN-SITU HYBRIDIZATION OF MESSENGER-RNA EXPRESSION FOR IP3 RECEPTOR AND IP3-3-KINASE IN RAT-BRAIN AFTER TRANSIENT FOCAL CEREBRAL-ISCHEMIA

Loss of intracellular calcium homeostasis has been regarded an important factor underlying neuron cell death after cerebral ischemic insult. In the brain, a major mechanism for regulation of intracellular calcium is through the signal transduction pathway involving hydrolysis of poly-phosphoinositides and release of the second messenger, inositol 1,4,5-trisphosphate (IP3). IP3 mobilizes calcium by interacting with an intracellular receptor. Upon its release after agonist stimulation, this second messenger is catabolized by a 3-kinase and a 5-phosphatase. In this study, in situ hybridization was carried out to examine the mRNA expression of IP3 receptor (IP(3)R) and IP3 3-kinase (IP3K) in rat brain cortex after transient focal cerebral ischemia induced by temporary occlusion of the middle cerebral artery (MCA) and the common carotid arteries (CCAs). Results indicate a large decrease (52%) in IP(3)R mRNA levels in the ischemic cortex as compared to that in the contralateral side at 4 h after a 45 min ischemic insult. By 16 h, practically no IP(3)R mRNA could be detected in the ischemic cortex. On the other hand, IP3K mRNA levels remained unaltered until 16 h after reperfusion, during which time, expression in the infarct core decreased but that surrounding the core area increased instead. Hybridization of adjacent brain sections with probes for neuron specific enolase (NSE) and beta-actin indicated also a time-dependent decrease in mRNA levels after ischemia, but these changes were less dramatic as compared to IP(3)R. At 16 and 24 h after reperfusion, there was an increase in beta-actin mRNA in cortical areas outside the MCA cortex, suggesting of reactive gliosis. The exquisite sensitivity of IP(3)R gene expression to focal cerebral ischemic insult and its perturbation during the early reperfusion period suggests an important role of the IP(3)R in cerebral ischemic injury.