Blocking Early GABA Depolarization with Bumetanide Results in Permanent Alterations in Cortical Circuits and Sensorimotor Gating Deficits

Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California, San Francisco CA 94143, USA.
Cerebral Cortex (Impact Factor: 8.67). 03/2011; 21(3):574-87. DOI: 10.1093/cercor/bhq124
Source: PubMed


A high incidence of seizures occurs during the neonatal period when immature networks are hyperexcitable and susceptible to hypersyncrhonous activity. During development, γ-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in adults, typically 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. By blocking NKCC1 with bumetanide during cortical development, we found a critical period for the development of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate 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. 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.

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Available from: Doris Wang, Dec 05, 2014
    • "If this is the case, disrupting either depolarizing GABA or NMDAR-mediated signaling should prevent the emergence of visually evoked spiking behavior. To determine whether the conversion from non-spiking to spiking requires depolarizing GABAergic inputs, we used bath application of bumetanide (100 mM) to block the Cl À transporter NKCC1 that raises intracellular Cl À in developing neurons (Supplemental Experimental Procedures; Rheims et al., 2008; Wang and Kriegstein, 2011; Yamada et al., 2004). Our loose patch cell-attached recordings confirmed that tectal neurons were still able to generate visually evoked spikes under these conditions (26%; 20/78 neurons). "
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    ABSTRACT: The ability to generate action potentials (spikes) in response to synaptic input determines whether a neuron participates in information processing. How a developing neuron becomes an active participant in a circuit or whether this process is activity dependent is not known, especially as spike-dependent plasticity mechanisms would not be available to non-spiking neurons. Here we use the optic tectum of awake Xenopus laevis tadpoles to determine how a neuron becomes able to generate sensory-driven spikes in vivo. At the onset of vision, many tectal neurons do not exhibit visual spiking behavior, despite being intrinsically excitable and receiving visuotopically organized synaptic inputs. However, a brief period of visual stimulation can drive these neurons to start generating stimulus-driven spikes. This conversion relies upon a selective increase in glutamatergic input and requires depolarizing GABAergic transmission and NMDA receptor activation. This permissive form of experience-dependent plasticity enables a neuron to start contributing to circuit function. Copyright © 2015 Elsevier Inc. All rights reserved.
    No preview · Article · Sep 2015 · Neuron
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    • "In general , the use of BTN in critically ill patients requires caution . Blocking NKCC1 function in the brain during development may interfere with critical circuit formation ( Wang and Kriegstein , 2010 ) . BTN non - specificity as a NKCC1 antagonist and its ability to also block KCC2 at higher doses ( Puskarjov et al . "
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    ABSTRACT: Ischemia in the immature brain is an important cause of neonatal seizures. Temporal evolution of acquired neonatal seizures and their response to anticonvulsants are of great interest, given the unreliability of the clinical correlates and poor efficacy of first-line anti-seizure drugs. The expression and function of the electroneutral chloride co-transporters KCC2 and NKCC1 influence the anti-seizure efficacy of GABA A-agonists. To investigate ischemia-induced seizure susceptibility and efficacy of the GABA A-agonist phenobarbital (PB), with NKCC1 antagonist bumetanide (BTN) as an adjunct treatment, we utilized permanent unilateral carotid-ligation to produce acute ischemic-seizures in post-natal day 7, 10, and 12 CD1 mice. Immediate post-ligation video-electroencephalograms (EEGs) quantitatively evaluated baseline and post-treatment seizure burdens. Brains were examined for stroke-injury and western blot analyses to evaluate the expression of KCC2 and NKCC1. Severity of acute ischemic seizures post-ligation was highest at P7. PB was an efficacious anti-seizure agent at P10 and P12, but not at P7. BTN failed as an adjunct, at all ages tested and significantly blunted PB-efficacy at P10. Significant acute post-ischemic downregulation of KCC2 was detected at all ages. At P7, males displayed higher age-dependent seizure susceptibility, associated with a significant developmental lag in their KCC2 expression. This study established a novel neonatal mouse model of PB-resistant seizures that demonstrates age/sex-dependent susceptibility. The age-dependent profile of KCC2 expression and its post-insult downregulation may underlie the PB-resistance reported in this model. Blocking NKCC1 with low-dose BTN following PB treatment failed to improve PB-efficacy.
    Full-text · Article · Apr 2015 · Frontiers in Cellular Neuroscience
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    • "By facilitating the relief of the voltage-dependent magnesium block, GABA via its depolarizing action renders these receptors conductive. The systemic blockade of early GABA-mediated depolarization during a critical period between E17-P7 in mice with bumetanide, a selective NKCC1 inhibitor, leads to lasting disruption of AMPA receptors-mediated glutamatergic transmission in the adult cortex and to an excitatory/inhibitory imbalance (Wang and Kriegstein, 2011). Morphological analysis of bumetanide-treated mice revealed reduced spines density and dendritic arborization in cortical neurons (Wang and Kriegstein, 2011). "
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    ABSTRACT: Early in development, γ-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in the mature brain, depolarizes and excites targeted neurons by an outwardly directed flux of chloride, resulting from the peculiar balance between the cation-chloride importer NKCC1 and the extruder KCC2. The low expression of KCC2 at birth leads to accumulation of chloride inside the cell and to the equilibrium potential for chloride positive respect to the resting membrane potential. GABA exerts its action via synaptic and extrasynaptic GABAA receptors mediating phasic and tonic inhibition, respectively. Here, recent data on the contribution of "ambient" GABA to the refinement of neuronal circuits in the immature brain have been reviewed. In particular, we focus on the hippocampus, where, prior to the formation of conventional synapses, GABA released from growth cones and astrocytes in a calcium- and SNARE (soluble N-ethylmaleimide-sensitive-factor attachment protein receptor)-independent way, diffuses away to activate in a paracrine fashion extrasynaptic receptors localized on distal neurons. The transient increase in intracellular calcium following the depolarizing action of GABA leads to inhibition of DNA synthesis and cell proliferation. Tonic GABA exerts also a chemotropic action on cell migration. Later on, when synapses are formed, GABA spilled out from neighboring synapses, acting mainly on extrasynaptic α5, β2, β3, and γ containing GABAA receptor subunits, provides the membrane depolarization necessary for principal cells to reach the window where intrinsic bursts are generated. These are instrumental in triggering calcium transients associated with network-driven giant depolarizing potentials which act as coincident detector signals to enhance synaptic efficacy at emerging GABAergic and glutamatergic synapses.
    Full-text · Article · Aug 2013 · Frontiers in Neural Circuits
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