The long-term objective of this proposal continues to be focused on defining the significance of platelet-activating factor (PAF), phospholipases and arachidonic acid as steps in the neurosignaling events in epileptic brain damage and epileptogenesis. Studies during the previous five years have made significant discoveries pertinent to understanding signaling relevant to epileptogenesis and neuroprotection. This includes the construction of new molecular and genetic tools that can be used as probes to test specific steps of our hypotheses about key signals that maintain neuroprotection in the hippocampus and in pathways engaged in epileptogenesis.
The specific aims for the next grant period examine these key pathways using mice deficient in the genes that we have found to be critical in seizures (arachidonoyl-diglyceride-selective diglyceride kinase (DGK) epsilon and PAF receptor) using several approaches including kindling epileptogenesis. The central hypothesis to be tested in this proposal is that the lipid messengers PAF, arachidonic acid (AA), inositol 1,4,5-triphosphate (IP3) and arachidonic acid 1,2-diacylglycerol (AA-DG) mediate the initiation and progression of epileptogenesis. PAF, initially, enhances glutamate release and then activates protein kinases and transcription factors that lead to the activation of cyclooxygenase-2 (COX-2) expression and other genes. AA, AA-DG and IP3 potentiate phospholipase A2 (PLA2) activation and PAF synthesis during epileptogenesis Our specific aims are to 1) test the hypothesis that deficiency in PAF-receptor and/or in arachidonyl-diglyceride-selective diglyceride kinase (DGK)-epsilon result in decreased susceptibility to epileptogenesis, 2) identify upstream signaling modified as a consequence of deficiency in PAF-receptor and in DGK-E in neurons in culture and hippocampal slices; 3) define downstream signaling events in epileptogenesis triggered by synaptic activation that leads to gene transcription modulation by bioactive lipids - these studies will test the hypothesis that COX-2 gene overexpression leads to aberrant synaptic plasticity, and this hypothesis is supported by our finding that COX-2 is overexpressed in a kindling model of epileptogenesis; and 4) use pharmacological agents to clarify the mechanisms of synaptic-triggered lipid signaling in epileptogenesis and to test their potential usefulness as neuroprotectants that selectively block critical events in epileptogenesis. This work is expected to provide new insights into neuronal signaling in epileptogenesis, to uncover novel molecular pathways in seizure-induced neuronal injury and define events for neuroprotective pharmacological interventions.
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