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Figure 26. The effects of nitric oxide (NO) upon transfer function and synaptic amplification between cone photoreceptors and L1-type horizontal cells in the turtle eyecup preparation. The transfer function and synaptic amplification were calculated by comparing the mean photoresponses of L1-horizontal cells to those of cones for each recording condition. A. In the dark-adapted state, the transfer function under control conditions is non-linear (open circles) having highest synaptic amplification for small amplitude cone photoresponses, elicited by dim light stimuli. Lowering retinal NO level by adding L-NAME, increased non-linearity (open squares), while raising retinal NO level, by adding L-arginine or sodium nitroprusside (SNP), linearized the transfer function and made synaptic amplification independent of cone response amplitude (triangles and inverted triangles respectively). B. The control light-adapted transfer function is linear having constant synaptic amplification for the entire range of cone photoresponses (open circles). Raising retinal NO level (L-arginine – triangles; SNP – inverted triangles) had no effect, while lowering retinal NO level (adding L-NAME) transformed the transfer function into a non-linear function having highest synaptic amplification for small amplitude cone photoresponses (open squares). The figure is adopted from Levy et al., 2004 (251).