Abstracts

Rationale: The highest incidence of seizures occurs during the neonatal period when immature networks are hyperexcitable and susceptible to synchronized activity. During development, GABA, the primary inhibitory neurotransmitter in adults, excites neurons due to high expression of the Na -K -2Cl^- cotransporter (NKCC1). NKCC1 facilitates seizures because it renders GABA activity excitatory through intracellular Cl^- accumulation, while blocking NKCC1 with bumetanide suppresses seizures. Bumetanide is currently being tested in clinical trials for treatment of neonatal seizures. Methods: Pregnant mice and their postnatal pups were treated with daily intraperitoneal injections of bumetanide at 0.2 mg/kg. We performed whole-cell patch clamp recordings in cortical pyramidal neurons to record miniature postsynaptic current to assess for synaptic connectivity. We studied neuronal morphology by using in utero electroporation of GFP-expressing plasmids and 3D reconstruction of their morphology using confocal microscopy. We also performed a battery of behavioral tests to assess for any developmental and permanent functional deficits in treated mice. Results: By blocking NKCC1 with bumetanide during cortical development, we found a critical period for the development of AMPA synapses. Disruption of GABA signaling during this window resulted in permanent decreases in excitatory synaptic transmission and sensorimotor gating deficits, a common feature in schizophrenia. Conclusions: Our study identifies an essential role for GABA-mediated depolarization in regulating the balance between cortical excitation and inhibition during a critical period and suggests a cautionary approach for using bumetanide in treating neonatal seizures.