Immunocytochemical Localization of the GABACReceptor ρ Subunits in the Mammalian Retina

Polyclonal antibodies against the N terminus of the rat ρ1 subunit were generated to study the distribution of GABAC receptors in the mammalian retina. The specificity of the antibodies was tested in Western blots and transfected HEK-293 cells. No cross-reactivity with the GABAA receptor subunits α1–3, β1–3, γ2, δ or with the glycine receptor subunits α1 and β could be detected. In contrast, the ρ1, ρ2, and ρ3 subunits were all recognized by the antibodies. In vertical sections of rat, rabbit, cat, and macaque monkey retinae, strong punctate immunoreactivity was present in the inner plexiform layer. Weaker immunoreactivity was also present in the outer plexiform layer, and cell bodies of bipolar cells were faintly labeled. Double immunostaining of vertical sections and immunostaining of dissociated rat retinae showed the punctate immunofluorescence to colocalize with bipolar cell axon terminals. The puncta possibly represent clustering of the ρ subunits at postsynaptic sites.