Figure 3.

Regional and cellular expression of the α₅-subunit protein. Selective loss of extrasynaptic α₅GABA_A receptors in α₅(H105R) mice [a, b, c, and d: wild type; a′, b′, c′, d′, and e: α₅(H105R) mutant]. (a and a′) False-color images depicting the regional distribution of the α₅-subunit in parasagital sections of adult mice, as detected by immunoperoxidase staining. Staining in wild type corresponded to that described (11, 31). Note the reduction of staining selectively in the hippocampal formation of mutant mice. (b and b′) Enlargement of the hippocampal formation showing the global reduction of α₅-subunit immunoreactivity in CA1 and CA3 in the mutant compared with control. (c and c′) By comparison, no change in α₅-subunit staining intensity was observed in olfactory bulb granule cells (see Table 1 for quantification). (d and d′) Images from confocal laser scanning microscopy, depicting a double-immunofluorescence staining for the α₅-subunit (red) and gephyrin (green) in the stratum radiatum of CA1. Gephyrin is a postsynaptic marker of GABAergic synapses. The lack of colocalization with the α₅-subunit staining reflects the extrasynaptic distribution of α₅GABA_A receptors. The staining intensity of these receptors is markedly reduced in mutant mice, whereas gephyrin immunoreactivity is unchanged. (e) For comparison, double staining for the α₂ subunit (red) and gephyrin (green) reveals the extensive postsynaptic localization of α₂GABA_A receptors (yellow dots) in α₅ mutant mice. (Scale bars: a, a′, 2.5 mm; b, b′, 0.5 mm; c, c′, 25 μm; d, d′, and e, 10 μm.)