Abstract
Purpose :
To evaluate the functional role of various retinal neurotransmitters in temporal resolution since the critical flicker fusion frequency (CFF) has been applied in ophthalmic pathophysiologic research but many aspects are yet unknown.
Methods :
Adult (12-24 weeks of age), healthy, male, and female wild-type C57BL/6J mice were used for electroretinograms (ERG). In dim red illumination, dark-adapted (> 12 hours) mice were first intraperitoneally anesthetized, and then, the right eye of each animal was intravitreally injected with 1 μL of PBS solution containing one of the following drugs, which are agonists or antagonists of retinal neurotransmitters: APB (25 mM), Glutamate (100 mM), GABA (100 mM), DNQX (30 mM), Bicuculline (10 mM), and Glycine (10 mM). Meanwhile, the left eye was injected with 1 μL of PBS solution as a control. The mice were then kept for ten minutes in complete darkness before recording to let drugs work efficiently and preserve the animals' full dark adaptation. After that, the physiological study was conducted on animals in vivo by recording binocular responses of the rod-mediated (scotopic condition, white flash strength of 0.01 cd.s.m-2) and cone-mediated (photopic condition, white flash strength of 15 cd.s.m-2, against a rod saturated background luminance of 32 cd.m-2) signals of flickering frequency for frequencies 3 Hz to 50 Hz. Moreover, the effect of pH buffer HEPES (25 mM) was also studied. The amplitude of flicker response was analyzed in detail.
Results :
APB abolished the rod-mediated but not the cone-mediated flicker responses. All the intravitreal injections of agents severely affected the lower flickering frequency response amplitude, in particular, at 3 Hz. Meanwhile, APB, glycine, and HEPES lowered the threshold of the CFF from 50 Hz to 40 Hz. GABA remarkably enhanced rod-mediated and cone-mediated flicker responses at 3 Hz, while Glutamate and Glutamate/GABA only did in rod-mediated flicker responses.
Conclusions :
Both ON and OFF visual pathways are implied in cone-mediated responses. In contrast, only the ON visual pathway plays a role in rod-mediated flicker responses, which seems to be enhanced by horizontal cells. Therefore, due to its higher sensitivity, in the pathophysiological investigation, applying the low, not the high, flickering frequency is more appropriate.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.