This research is directed at two conditions in which seizures respond poorly to anticonvulsant therapy: neonatal seizures and intractable temporal lobe epilepsy (TLE). These two conditions share an unusual feature: in both conditions, neurons are excited rather than inhibited by GABA, the principal inhibitory neurotransmitter. GABA is excitatory because neurons in these conditions accumulate intracellular chloride, which reverses GABAA receptor-mediated current flow. NKCC1 is a chloride transporter that imports chloride into neurons, and KCC2 is a chloride transporter that exports chloride. In the proposed research we will test whether NKCC1 activity exceeds KCC2 activity in the neonate and in the kainate model of TLE. Transporter function and expression will be evaluated in the neonatal brain, in the kainate model of TLE, and in adult control animals. We will use whole-cell and gramicidin perforated patch recordings in hippocampal slices to measure the kinetics of these two transporters. We will use western blots and immunocytochemistry to determine the level of expression of the two transporters. The NKCC1 chloride transporter is exquisitely sensitive to the diuretic bumetanide. Using a kainate model of acute neonatal seizures in the rat pup, and the kainate model of chronic TLE in the adult rat, we will test whether blocking NKCC1-mediated chloride accumulation with bumetanide will restore GABAA receptor- mediated inhibition and thereby ameliorate these two types of seizures. To quantify the effects on seizures we will use acute and chronic, radiotelemetric digital EEG recordings and computerized seizure analysis. Bumetanide has already been tested as a diuretic in human neonates at doses that inhibit NKCC1, so bumetanide treatment of neonatal seizures is a new and feasible treatment of a disorder for which there is no effective therapy and a very high risk of lifelong morbidity. Similarly, bumetanide-induced restoration of GABAA receptor-mediated inhibition in intractable TLE could provide a non-surgical therapeutic alternative to patients who are not candidates for epilepsy surgery due to the location of their ictal onset zones.
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