%0 Journal Article %A Colin J. Akerman %A Hollis T. Cline %T Depolarizing GABAergic Conductances Regulate the Balance of Excitation to Inhibition in the Developing Retinotectal Circuit In Vivo %D 2006 %R 10.1523/JNEUROSCI.0319-06.2006 %J The Journal of Neuroscience %P 5117-5130 %V 26 %N 19 %X Neurotransmission during development regulates synaptic maturation in neural circuits, but the contribution of different neurotransmitter systems is unclear. We investigated the role of GABAA receptor-mediated Cl− conductances in the development of synaptic responses in the Xenopus visual system. Intracellular Cl− concentration ([Cl−]i) was found to be high in immature tectal neurons and then falls over a period of several weeks. GABAergic synapses are present at early stages of tectal development and, when activated by optic nerve stimulation or visual stimuli, induce sustained depolarizing Cl− conductances that facilitate retinotectal transmission by NMDA receptors. To test whether depolarizing GABAergic inputs cooperate with NMDA receptors during activity-dependent maturation of glutamatergic synapses, we prematurely reduced [Cl−]i in tectal neurons in vivo by expressing the Cl− transporter KCC2. This blocked the normal developmental increase in AMPA receptor-mediated retinotectal transmission and increased GABAergic synaptic input to tectal neurons. Therefore, depolarizing GABAergic transmission plays a pivotal role in the maturation of excitatory transmission and controls the balance of excitation and inhibition in the developing retinotectal circuit. %U https://www.jneurosci.org/content/jneuro/26/19/5117.full.pdf