Most fast inhibitory neurotransmission in the brain is mediated by GABAA receptors, which are mainly postsynaptic and consist of diverse alpha and beta subunits together with the gamma 2 subunit. Although the gamma 2 subunit is not necessary for receptor assembly and translocation to the cell surface, we show here that it is required for clustering of major postsynaptic GABAA receptor subtypes. Loss of GABAA receptor clusters in mice deficient in the gamma 2 subunit, and in cultured cortical neurons from these mice, is paralleled by loss of the synaptic clustering molecule gephyrin and synaptic GABAergic function. Conversely, inhibiting gephyrin expression causes loss of GABAA receptor clusters. The gamma 2 subunit and gephyrin are thus interdependent components of the same synaptic complex that is critical for postsynaptic clustering of abundant subtypes of GABAA receptors in vivo.

Patients with panic disorders show a deficit of GABAA receptors in the hippocampus, parahippocampus and orbitofrontal cortex. Synaptic clustering of GABAA receptors in mice heterozygous for the gamma2 subunit was reduced, mainly in hippocampus and cerebral cortex. The gamma2 +/- mice showed enhanced behavioral inhibition toward natural aversive stimuli and heightened responsiveness in trace fear conditioning and ambiguous cue discrimination learning. Implicit and spatial memory as well as long-term potentiation in hippocampus were unchanged. Thus gamma2 +/- mice represent a model of anxiety characterized by harm avoidance behavior and an explicit memory bias for threat cues, resulting in heightened sensitivity to negative associations. This model implicates GABAA-receptor dysfunction in patients as a causal predisposition to anxiety disorders.

No abstract