Figure 7. Conditioning visual stimulation in peripheral subfields increases RGC spike rates and decreases [Cl−]i by a CB1R-dependent mechanism.
(a) Isolated eye preparation for extracellular retinal recordings, and light stimulation with a changing surround luminance. (b) Conditioning visual stimulation protocol displayed on screen. During the initial test period (100 s), 10 light-OFF stimuli (1 s every 10 s) were presented in the central field with a constant dark periphery (Before). This continued during the conditioning period except that periphery visual fields were illuminated continuously for 100 s (conditioning stimulation). After conditioning another set of 10 test stimuli identical to the first set was presented (After). Representative extracellular multiunit RGC spike recordings are shown, in vehicle (Control) and AM-251 (5 µM) containing external solutions. (c,d) Binned PSTHs of recorded spikes from the examples illustrated in (b) show that the average response was strongly enhanced after conditioning stimulation in vehicle (c) but not with AM-251 treatment (d). (e) Group data showing the increase in spiking rates of RGCs induced by conditioning stimulation (n = 10 animals). (f) This effect is prevented when CB1Rs are blocked with AM-251. (n = 10 animals). (g–k) A similar conditioning protocol reduces intracellular Cl− levels selectively in RGCs. Clomeleon signal was imaged in vivo under the two-photon microscope, and the objective was used to project an eyepiece-mounted OLED video display directly onto the imaged region of the retina. (h) Example of in vivo clomeleon-expressing retinal cells, and schematic of the visual conditioning protocol (CP). (i,j) The decrease in RGC (n = 12 cells) somatic ratios of CFP/YFP after conditioning stimulation (the first time point of the second imaging period compared to the mean of the 5 ratio values during the first imaging period) was blocked in AM-251 (n = 17). (k) Only RGCs (n = 22), but not amacrine cells (n = 19) or bipolar cells (n = 10) exhibited this decrease in intracellular Cl− after conditioning stimulation. (e, f) *p<0.05, paired t-test, (k) **p<0.01, two-way RM ANOVA with Holm-Sidak posttest. RGC, Retinal ganglion cell.