The protein MAP-1B links GABAC receptors to the cytoskeleton at retinal synapses

The ionotropic type-A and type-C receptors for the neurotransmitter γ-aminobutyric acid (GABAA and GABAC receptors) are the principal sites of fast synaptic inhibition in the central nervous system1,2,3, but it is not known how these receptors are localized at GABA-dependent synapses. GABAC receptors, which are composed of ρ-subunits3,4,5,6, are expressed almost exclusively inthe retina of adult vertebrates, where they are enriched on bipolar cell axon terminals7,8,9. Here we show that the microtubule-associated protein 1B (MAP-1B) specifically interacts with the GABAC ρ1 subunit but not with GABAA receptor subunits. Furthermore, GABAC receptors and MAP-1B co-localize at postsynaptic sites on bipolar cell axon terminals. Co-expression of MAP-1B and the ρ1 subunit in COS cells results in a dramatic redistribution of the ρ1 subunit. Our observations suggest a novel mechanism for localizing ionotropic GABA receptors to synaptic sites. This mechanism, which is specific for GABAC but not GABAA receptors, may allow these receptor subtypes, which have distinct physiological and pharmacological properties, to be differentially localized at inhibitory synapses.