Abstracts

The omega-3 fatty acid docosahexaenoic acid (22:6, n-3, DHA) is highly concentrated in synapses and is required during development, synaptic plasticity and participates in neuroprotection. Free DHA is released through phospholipases from membrane phospholipids in response to seizures. Recently we have elucidated the structure and bioactivity of neuroprotectin D1 a potent DHA-derived mediator in brain ischemia-reperfusion and in oxidative stress (VL Marcheselli, et al., [italic]J Biol Chem[/italic] 278:43807, 2003; PK Mukherjee et al., [italic]Proc Natl Acad Sci, USA[/italic] 101:8491, 2004). Here we have explored the idea that DHA may activate neuroprotective signaling in the rapid kindling model of epileptogenesis. Male mice (C57BL/6; 20-25 g) were used. Tripolar electrode units (Plastic One Inc., Roanoke, VA) were implanted in the right dorsal hippocampus. After 10 days post surgery, the mice were separate randomly in two groups and mini osmotic pumps (Alzet-model 1007D), prepared and filled with DHA/ human serum albumin (HSA) or only with HSA were inserted in the intraperitoneal cavity of each one in order to attain an infusion rate of [italic]6.72 ug/kg/day[/italic] during kindling procedure. Next day kindling was achieved by stimulating 6 times daily for 4 days with a subconvulsive electrical stimulation (a 10-s train containing 50-Hz biphasic pulses of 75-100-[mu]A amplitude) at 30-min intervals. After 1 week another session of stimulation (rekindling) was given. Seizures were graded according to Racine[apos]s Scale and the EEG was recorded through electrodes using Enhanced Graphics Acquisition for Analysis (Version 3.63 RS Electronics Inc. Santa Barbara, CA.) and the EEG was analyzed using Neuroexplorer Software (Next Technology). The DHA-HSA treated group displayed significant fewer stimulus-evoked motor seizures and a limitation of the progression of the severity of the seizures during kindling compared with the HSA treated group. These observations were correlated with a continuous diminution of the numbers of spikes until the inhibition of the after discharge at the end of the kindling. Since excitatory synaptic transmission is enhanced during kindling we also use primary neurons in culture in the presence of NMDA, to activate NMDA glutamate receptors. By tandem LC-PDA-ESI-tandem MS-based lipidomic analysis we isolated and characterized enhanced 10,17S-docosatriene (neuroprotectin D1) synthesis in these cells. The infusion of DHA HSA has an inhibitory effect on the progression of kindling epileptogenesis. We suggest that excitatory synaptic transmission during kindling upregulates NPD1 synthesis from DHA, which in turn modulate excitability-induced changes. The cellular target and molecular pathways involved in DHA action may allow to design novel neuroprotective therapeutic approaches in epileptogenesis. (Supported by NIH NS23002.)