There are two obvious ways in which different GABAAR subtypes could become clustered at different types of synapse: they could be selectively inserted at a particular postsynaptic site, in a highly specific way, or they could be inserted into the plasma membrane relatively randomly and find their way to an appropriate synapse by lateral diffusion,

becoming stabilised there by a synapse class-specific assembly of proteins. The next section summarises some of what we know of GABAAR trafficking in this selleck products context. Several recent studies describe the trafficking, transport to the plasma membrane and subsequent fate of receptors. GABAARs containing a γ2-subunit appear destined for synapses; their surface expression is prolonged and internalization delayed by apposition to a GABAergic bouton. While surface clusters of GABAARs form in cultured neurones without GABAergic input (even apposed to glutamatergic terminals: Studler et al.,

2005), clusters apposed to GAD (glutamic acid decarboxylase)-positive GABAergic terminals are larger, more stable and able (unlike inappropriately located clusters) to recruit postsynaptic density selleck chemicals proteins such as gephyrin (Jacob et al., 2005). Could this property arise from specific “delivery” of GABAARs to postsynaptic plasma membranes by γ2-subunit binding partners? There are at least a few well characterized proteins that interact with this subunit, but the evidence for any of these proteins playing Thalidomide a role in targeting or insertion of GABAARs

at the synapse is sparse. Not only are these proteins largely involved in the intracellular trafficking of GABAARs through secretory pathways, they localize away from the postsynaptic membrane and are often found to be associated with intracellular membranes. One such example is GABARAP, a member of the family of small microtubule-binding proteins, which was initially discovered as an interacting protein of the γ-subunits (Wang et al., 1999). GABARAP was shown to influence the levels of GABAARs expressed at the cell surface, as well as their channel properties (Leil et al., 2004; Chen et al., 2005; Chen & Olsen, 2007; Kawaguchi & Hirano, 2007), yet this protein co-localizes only with intracellular pools of GABAARs, within the Golgi apparatus and other associated intracellular membranes (Kittler et al., 2001). Within these same intracellular compartments GABARAP, and perhaps even GABAARs themselves, interact with NSF (N-ethylmaleimide-sensitive factor), a ubiquitous regulator of membrane fusion and trafficking (Kittler et al., 2001; Goto et al., 2005), as well as with the PRIP proteins (phospholipase-C related catalytically inactive proteins; Kanematsu et al., 2002), with gephyrin (Kneussel et al., 2000), and with proteins involved in vesicular transport and apoptosis. PRIP proteins are unlikely to play a role in synaptic targeting of GABAARs even though they can interact directly with γ-subunits (Kanematsu et al.