A CHEMOGENETIC EVALUATION OF DELTA SUBUNIT EXCLUSION FROM GABA SYNAPSES

Washington University, Saint Louis MO

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Abstract

? subunits are subunits of GABAA receptors that are found in receptors that mediate tonic inhibition in several neuronal types. It has been suggested that active exclusion of ?-containing receptors from synapses, by virtue of amino acid residues unique to ?, plays a large role in ??s preferential participation in tonic currents. Here we investigate the alternative hypothesis that weak expression, rather than active exclusion, limits the role of ? containing receptors to tonic influences. The inability to pharmacologically isolate ? receptors is a large reason that conclusions remain elusive. We investigate the role of ?-containing receptors in synaptic and tonic currents using a chemogenetic approach. We isolate ? contributions by expressing a ? subunit harboring a point mutation that renders receptors resistant to the classical non-competitive GABAA receptor antagonist picrotoxin. We thus study ? contributions in isolation from other classes (primarily ? containing). Preliminary data utilize a heterologous expression model in primary neurons in the context of endogenous subunits. Proposed experiments extend the work to knock-in animals harboring the mutated subunit under the control of endogenous regulators of expression. Results to date support the idea that ? is not actively excluded from synapses. Continued support for this idea would cause the field to re-think active extracellular localization as an explanation for ??s preferential role in tonic currents. We believe it is likely that low-level GABA acting on ? low abundance, high-affinity receptors throughout the cell, are sufficient to account for the preferential role that ? plays in tonic currents.