Figure 7. Effects of selective GABA receptor blockers on RGC sensitivity .

A, application of the glycine receptor blocker strychnine had no significant effect on the intensity–response function and calculated threshold of an ON LS RGC. B, effects of the GABA_A‐selective blocker gabazine (SR‐95531) and the GABA_C‐selective blocker 1,2,5,6‐tetrahydropyridin‐4‐yl‐methylphosphinic acid (TPMPA) on an ON HS RGC. Neither SR nor TPMPA had a significant effect on the threshold sensitivity of HS cells. C, data showing that SR had no effect on the sensitivity of an ON IS cell, but application of TPMPA increased the threshold sensitivity by ∼1 log unit to the HS range. D, intensity–response functions for an OFF LS cell, showing that SR had no effect on the sensitivity of LS OFF cells, but TPMPA increased the sensitivity by ∼3 log units. E, summary of the effects of SR and TPMPA on ON LS cells. Application of SR had no effect on the sensitivity of LS ON cells, but increased the sensitivity of 20% of LS ON cells, reflected by a leftward shift of intensity–response functions by 2 log units. In contrast, TPMPA increased the sensitivity of all LS ON cells by ∼3 log units to the HS range. F, summary of effects of SR and TPMPA on OFF LS cells. Application of SR had no effect on the threshold sensitivity of 83% of LS OFF cells, but increased the sensitivity of 17% of LS OFF cells, reflected by a leftward shift of intensity–response curves by an average of only ∼1 log unit. In contrast, TPMPA increased the sensitivity of all LS OFF cells by ∼3 log units to the HS range. [Colour figure can be viewed at wileyonlinelibrary.com]