Figure 4. Both GABA_A and GABA_C receptors are involved in inhibitory circuits responsible for masking of the ON responses of OFF α-GCs.

A, response of an OFF α-GC in the rabbit retina under control conditions. Trace at bottom indicates onset and offset of the light stimulus. Neither the blockade of GABA_A receptors using SR-95531 (B, 5 μm), nor the blockade of GABA_C receptors using TPMPA (C, 50 μm) alone unmasks an ON response in the OFF α-GC. D, however, the simultaneous blockade of both receptors unmasks the ON response. E, the effects of the selective GABA receptor blockers were reversible after wash. F, response of another OFF α-GC under control conditions. Neither the GABA_B receptor agonist baclofen (G, 100 μm), nor the GABA_B receptor antagonist CGP-55845 (H, 50 μm) unmasks an ON response and neither has a significant effect on the OFF light response of the OFF α-GC. I, response of another OFF α-GC under control conditions. J, blockade of glycine receptors using strychnine (1 μm) increased spontaneous burst activity of the OFF α-GC, but failed to unmask an ON response at stimulus onset. Light intensity of green stimulus = 0.21 Rh* rod⁻¹ s⁻¹.