FIGURE 2.

Molecular characterization of phasic and tonic modes of inhibition. Fast inhibitory synaptic transmission, also known as phasic inhibition, is governed by GABA_AR’s with relatively low sensitivity to GABA densely clustered at sites opposing interneuron terminal boutons. Several general factors have been identified that play a role in establishing the contact between pre and post (neurexin-neuroligin2/3; neurexin-dystroglycan), and/or retaining receptors at these sites (gephyrin, collybistin). Phasic GABA_ARs are most commonly composed of 2-α1-3, 2-β, and a γ subunit and are sensitive to benzodiazepines. Tonic inhibition is governed by GABA_AR’s that reside outside of synaptic sites, are highly sensitive to GABA, and are most commonly composed of 2-α4-6, 2-β, and a δ subunit. Much less is known about the mechanisms that localize extrasynaptic GABA_ARs, but radixin is implicated.