NpgRJ_NM_1301 1..9

During development, activation of Cl -permeable GABAA receptors (GABAA-R) excites neurons as a result of elevated intracellular Cl levels and a depolarized Cl equilibrium potential (ECl). GABA becomes inhibitory as net outward neuronal transport of Cl develops in a caudal-rostral progression. In line with this caudal-rostral developmental pattern, GABAergic anticonvulsant compounds inhibit motor manifestations of neonatal seizures but not cortical seizure activity. The Na+-K+-2Cl cotransporter (NKCC1) facilitates the accumulation of Cl in neurons. The NKCC1 blocker bumetanide shifted ECl negative in immature neurons, suppressed epileptiform activity in hippocampal slices in vitro and attenuated electrographic seizures in neonatal rats in vivo. Bumetanide had no effect in the presence of the GABAA-R antagonist bicuculline, nor in brain slices from NKCC1knockout mice. NKCC1 expression level versus expression of the Cl -extruding transporter (KCC2) in human and rat cortex showed that Cl transport in perinatal human cortex is as immature as in the rat. Our results provide evidence that NKCC1 facilitates seizures in the developing brain and indicate that bumetanide should be useful in the treatment of neonatal seizures.