The metabolism of arachidonic acid, lipoxygenase-reaction products, prostaglandins and phospholipids in rat brain will be investigated during experimentally-induced seizures. Phosphatidylinositol, phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate, which are enriched in arachidonoyl groups, and their metabolites, inositol-1,4,5-trisphosphate and diacylglycerols, will be studied, to test the hypothesis that these particular components of neuronal cell signaling systems are the membrane target affected by convulsions. The accumulation of endogenous arachidonoyldiacylglycerol, known to occur as a result of seizures, is proposed to be a consequence of enhanced breakdown of polyphosphoinositides mediated by phospholipase C. The effects of the muscarinic cholinergic antagonist, atropine, and the inositol phosphatase inhibitor, lithium, on the phosphoinositide cycle, will be evaluated. The hypothesis to be tested also includes convulsion-induced changes in phospholipase A2, resulting in the release of arachidonic acid from synaptic membrane phospholipids, through a receptor-related mobilization of calcium. The role of calcium will be evaluated using calcium channel modulators. As a result of phospholipase A2 activation, subsequent production of oxygenated metabolites of arachidonic acid, particularly hydroxyeicosatetraenoic acids, may be enhanced. Emphasis will be placed on the membrane lipid sources, neuroanatomical and subcellular distribution, and fate of the rapidly released arachidonic acid and arachidonoyl-diacylglycerols that occur in the rat brain during bicuculline-induced status epilepticus and after electroconvulsive shock. Convulsions will be induced in mechanically ventilated, well-oxygenated animals. In some experiments 32P or [14C]arachidonic acid will be injected intraventricularly to follow precursor-product relationships. This proposal will employ in vivo models and subcellular fractions. Very rapid fixation of the tissues within 1 second will be achieved by high-powered, head-focused microwave irradiation. Powerful analytical techniques, such as high performance liquid chromatography, gas-liquid chromatography, and gas chromatography-mass spectrometry, will be used to examine biochemical changes in phospholipids and fatty acids of neuronal membranes. The results of this study will have application in the management of epileptic seizures and will provide data on the use of drugs that are potentially capable of halting or reversing membrane lipid breakdown, consequently preventing or limiting the brain damage caused by epilepsy.
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