Role of ON and OFF Visual Pathways in Rod- and Cone-Driven Flicker Responses

To evaluate the effects of various retinal neurotransmitters on temporal resolution, particularly, on the Critical Flicker Fusion Frequency (CFF), which has been previously applied in ophthalmic pathophysiologic research.

A binocular physiologic electroretinogram was performed on adult mice. Animals in the control group were injected in the right eye with 1 μL of phosphate-buffered saline (PBS). Animals in the experimental group were injected in the left eye with 1 μL of PBS and in the right eye with 1 μL of PBS to which different molecules were added: 2-amino-4-phosphonobutyric acid (APB), Glutamate, γ-aminobutyric acid (GABA), 6,7-dinitroquinoxaline-2,3-dione (DNQX), Bicuculline, Glycine, and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). Initially, rod response was recorded and later the cone response.

APB suppressed the rod-driven, but not the cone-driven flicker response. The other agents severely affected the lower flickering frequency response amplitude, in particular, at 3 Hz. The threshold of CFF was lowered from 50 Hz to 40 Hz after applying APB, Glycine, and HEPES. GABA remarkably enhanced rod-driven and cone-driven flicker response at 3 Hz, whereas Glutamate and GABA/Glutamate only did in rod-driven flicker response.

Both ON and OFF visual pathways were implied in cone-driven response, but only the ON visual pathway appears to play a relevant role in rod-driven flicker response. Flicker response seems to be enhanced by horizontal cells both in rod-driven and cone-driven response. In addition, due to the greater sensitivity of the flicker at low frequencies, it is suggested that pathophysiological studies should be carried out at said frequencies.