inositol-1-4-5-trisphosphate and Brain-Injuries

Our previous studies using an in vitro model of traumatic injury have shown that stretch injury of astrocytes causes a rapid elevation in intracellular free calcium ([Ca2+]i), which returns to near normal by 15 min postinjury. We have also shown that after injury astrocyte intracellular calcium stores are no longer able to release Ca2+ in response to signal transduction events mediated by the second messenger inositol (1,4,5)-trisphosphate (IP3, Rzigalinski et al., 1998). Therefore, we tested the hypothesis that in vitro injury perturbs astrocyte IP3 levels. Astrocytes grown on Silastic membranes were labeled with [3H]-myo-inositol and stretch-injured. Cells and media were acid-extracted and inositol phosphates isolated using anion-exchange columns. After injury, inositol polyphosphate (IPx) levels increased up to 10-fold over uninjured controls. Significant injury-induced increases were seen at 5, 15, and 30 min and at 24 and 48 h postinjury. Injury-induced increases in IPx were equivalent to the maximal glutamate and trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid-stimulated IPx production, however injury-induced increases in IPx were sustained through 24 and 48 h postinjury. Injury-induced increases in IPx were attenuated by pretreatment with the phospholipase C inhibitors neomycin (100 microM) or U73122 (1.0 microM). Since we have previously shown that astrocyte [Ca2+]i returns to near basal levels by 15 min postinjury, the current results suggest that IP3-mediated signaling is uncoupled from its target, the intracellular Ca2+ store. Uncoupling of IP3-mediated signaling may contribute to the pathological alterations seen after traumatic brain injury.

Topics: Animals; Animals, Newborn; Astrocytes; Brain Injuries; Cells, Cultured; Cycloleucine; Estrenes; Extracellular Space; Glutamic Acid; Inositol 1,4,5-Trisphosphate; Neomycin; Neuroprotective Agents; Phosphodiesterase Inhibitors; Protein Synthesis Inhibitors; Pyrrolidinones; Rats; Rats, Sprague-Dawley; Signal Transduction; Stress, Mechanical; Type C Phospholipases

Regional levels of lactate and inositol 1,4,5-trisphosphate (IP3), a cellular second messenger of the excitatory neurotransmitter system, were measured after lateral fluid percussion (FP) brain injury in rats. At 5 min postinjury, tissue lactate concentrations were significantly elevated in the cortices and hippocampi of both the ipsilateral and contralateral hemispheres. By 20 min postinjury, lactate concentrations were elevated only in the cortices and hippocampus of the ipsilateral hemisphere. Whereas the IP3 concentrations were elevated in the hippocampi of the ipsilateral and contralateral hemisphere and in the cortex of ipsilateral hemisphere at 5 min postinjury, no elevation in these sites was found at 20 min postinjury. Histologic analysis revealed neuronal damage in the cortex and CA3 regions of hippocampus ipsilateral to the injury at 24 h postinjury. The present results suggest activation of the phosphoinositide signal transduction pathway at the onset of injury and of a possible requirement of early persistent metabolic dysfunction (> 20 min) such as the lactate accumulation in the delayed neuronal damage.

Topics: Animals; Brain Injuries; Cerebral Cortex; Functional Laterality; Hippocampus; Inositol 1,4,5-Trisphosphate; Lactates; Male; Neurons; Phosphatidylinositol Phosphates; Phosphatidylinositols; Rats; Rats, Sprague-Dawley; Reference Values; Signal Transduction; Time Factors