Figure 6. Rod signals in the tertiary rod pathway are weak in primate retina.

(A) Excitatory synaptic input recorded from an On parasol RGC in response to sinusoidally modulated short (rod-preferring; blue traces) and long (cone preferring; red traces) wavelength stimuli. Contrasts were adjusted to produce equal modulation at 2 Hz, and were then held fixed for subsequent recordings from other cell types (e.g. Off parasol RGC). (B) Excitatory synaptic input recorded from an Off parasol RGC from the same retinal mount as A and in response to the same stimuli. (C) Relative weighting of rod and cone signals in excitatory inputs to On and Off RGCs. Mean light levels for A-C were~20R*/rod/s and~200R*/L-cone/s. (D) Schematic of the primary and tertiary rod circuits that influence Off cone bipolar signaling and the actions of the mGluR6 agonist/antagonist mixture LY/APB. (E) Rod-derived excitatory synaptic inputs to an Off parasol cell at 20 R*/rod/s in control conditions and after suppressing activity in all On bipolar cells with an mGluR6 agonist/antagonist cocktail (LY/APB, see Materials and methods). (F) Response ratio (cocktail:control) across cells as a function of mean luminance. Data are plotted as mean ± SEM. (G) Rod-derived excitatory inputs to an Off alpha RGC (mouse; 5 R*/rod/s) in control conditions and after suppressing activity in all On bipolar cells with an mGluR6 agonist/antagonist cocktail (LY/APB, see Materials and methods).

Figure 6—figure supplement 1. Rod, but not cone, signals in excitatory inputs to Off parasol RGCs arise from the primary rod pathway under mesopic conditions.

Example recording of excitatory synaptic input to an Off parasol RGC in response to 2 Hz sine wave modulation of a short (rod-preferring; 100% contrast) or long (cone-preferring; 50% contrast) wavelength LED on a background of ~20 R*/rod/s and ~200 R*/L cone/s. Responses to short, but not long, wavelength light modulations were largely eliminated by a mixture of LY341495 and APB (see Materials and methods).