Expression of Distinct α Subunits of GABAAReceptor Regulates Inhibitory Synaptic Strength

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Abstract
Distinct α subunit subtypes in the molecular assembly of GABAAreceptors are a critical determinant of the functional properties of inhibitory synapses and their modulation by a range of pharmacological agents. We investigated the contribution of these subunits to the developmental changes of inhibitory synapses in cerebellar granule neurons in primary cultures from wild-type and α1 subunit −/− mice. The decay time of miniature inhibitory postsynaptic currents (mIPSCs) halved between 6 days in vitro (DIV6) and DIV12. This was paralleled by the decrease of α2 and α3 subunits, the increase of α1 and α6 subunits expression at synapses, and changes in the action of selective α subunit modulators. A small but significant shortening of mIPSCs was observed with development in cells from −/− mice together with a decrease in the expression of α3 subunit. In contrast, the expression of α2 subunit at inhibitory synapses in −/− cells was significantly higher than in +/+ cells at DIV11-12. α5 subunit was not detected, and increased sensitivity to a selective α4/α6 subunit agonist suggests increased expression of extrasynaptic receptors in −/− mice. β2/β3 subunit expression and loreclezole sensitivity increased with development in +/+ but not in −/− cells, supporting the preferential association of the α1 with the β2 subunit. Synaptic charge transfer strongly decreased with development but was not different between cells in the +/+ and −/− groups until DIV11-12. Our results uncover a pattern of sequential expression of α subunits underlying the changes in functional efficacy of GABAergic networks with development.