A CHEMOGENETIC EVALUATION OF DELTA SUBUNIT EXCLUSION FROM GABA SYNAPSES

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δ 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 δ-containing receptors from synapses, by virtue of amino acid residues unique to δ, plays a large role in δ’s preferential participation in tonic currents. Here we investigate the alternative hypothesis that weak expression, rather than active exclusion, limits the role of δ containing receptors to tonic influences. The inability to pharmacologically isolate δ receptors is a large reason that conclusions remain elusive. We investigate the role of δ-containing receptors in synaptic and tonic currents using a chemogenetic approach. We isolate δ contributions by expressing a δ subunit harboring a point mutation that renders receptors resistant to the classical non-competitive GABAA receptor antagonist picrotoxin. We thus study δ contributions in isolation from other classes (primarily γ 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 δ 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 δ’s preferential role in tonic currents. We believe it is likely that low-level GABA acting on δ low abundance, high-affinity receptors throughout the cell, are sufficient to account for the preferential role that δ plays in tonic currents.