Figure 5.

The Effect of Olfactory Stimulation Is Mirrored by a D₁ but Not a D₂ Dopamine Receptor Antagonist

(A) Averaged responses of 17 OFF bipolar cell terminals from three fish injected intraocularly with the dopamine D₁ receptor antagonist SCH 23390 (100 nM; light red). The stimuli are a series of light steps of increasing intensity, as in Figure 1. Control responses are from Figure 1D (dark red). SEM is shown in gray.

(B) Plot of intensity versus response amplitude averaged from the same population of OFF terminals shown in (A). Antagonizing D₁ receptors profoundly suppressed transmission of visual signals through synapses of OFF bipolar cells.

(C) Averaged responses of 20 ON bipolar cell terminals from three fish collected simultaneously with results shown in (A). Control responses (dark green) correspond to traces in Figure 1H. The light green traces show responses measured after SCH 23390 100 nM injection.

(D) Plot of intensity versus response amplitude averaged from the same populations of ON terminals shown in (C). Dotted lines are fits of the Hill function with h = 0.93 and I_1/2 = 0.84 nW/mm² in control and h = 0.62 and I_1/2 = 0.19 nW/mm² in SCH 23390 100 nM. SCH 23390 increased luminance sensitivity by 0.65 log units without significantly altering the amplitude of responses to the brightest lights.

(E) Averaged responses of 45 OFF bipolar cell terminals from three fish injected intraocularly with the dopamine D₂ receptor antagonist sulpiride (2 μM), before (light red) and after (orange) bath administration of methionine 1 mM. The stimuli are a series of light steps of increasing intensity, as in Figure 1. Control responses are from Figure 1D (dark red). SEM is shown in gray.

(F and G) Plot of intensity versus response amplitude averaged from the same population of OFF terminals shown in (E). Control responses (dark red) are from Figure 1D. Please note how sulpiride injection altered the shape of the sensitivity curve of OFF terminals (F), without interfering with the effect of methionine administration (cf. E and G with Figures 1D and 1G).

(H) Averaged responses of 84 ON bipolar cell terminals from three fish after intraocular injection of 2 μM sulpiride, before (light green) and after (light blue) bath administration of methionine. Control responses (dark green) correspond to traces in Figure 1H.

(I and J) Plot of intensity versus response amplitude averaged from the same populations of ON terminals shown in (H). Dotted lines are fits of the Hill function with h = 0.93 and I_1/2 = 0.84 nW/mm² in control, h = 0.87 and I_1/2 = 0.15 nW/mm² in sulpiride, and h = 0.74 and I_1/2 = 0.12 nW/mm² in sulpiride and methionine. Sulpiride increased luminance sensitivity by 0.85 log units as compared to the control trace without significantly altering the amplitude of responses to the brightest lights. No significant effect of methionine administration was observable in this condition.