Inhibition to the rod pathway is modulated in lens-induced myopic mice

Abstract

Purpose : Functional rod pathways play an important role in myopia development. However, it is unclear how rod pathway signaling, or inhibition, is affected in myopic eyes. Here, we directly investigated how lens-induced myopia (LIM) modulates evoked and spontaneous inhibition to the rod pathway by performing single-cell recordings in rod pathway neurons from myopic mice.

Methods : LIM was generated in male C57BL/6J mice at 4 weeks of age by covering the right eye with a -10 diopter (D) lens while the left eye was uncovered (n=22). A subset of naïve control mice was not treated with lenses (n=5). Refractive error was measured at baseline and weekly for at least two weeks, before retinas were prepared for single-cell voltage clamp recordings. White, full-field, flash stimuli (0.003 – 300 cd/m², 500 msec duration) were presented to dark-adapted rod bipolar cells (RBCs). Light-evoked inhibitory responses were measured and compared between LIM (n=9 cells) and non-LIM (LIM left eye + naïve, n=8 cells) eyes. Additionally, spontaneous inhibitory currents that occur without a light stimulus were quantified (LIM: n=14 cells, non-LIM: n=8 cells).

Results : LIM mice developed a myopic shift after two weeks of lens treatment (OD minus OS: -4.2±0.5 D, p<0.001, ANOVA) while naïve controls did not. Previously, we found that RBC light-evoked inhibitory responses were modulated by lens treatment across flash intensity (peak amplitude: p=0.007, latency: p=0.022, ANOVAs). When averaged across flash intensity, and compared to non-LIM eyes, LIM inhibitory response magnitude was greater with brighter flashes (response area: 3341±806 vs. 1821±553 pA*ms, p=0.02) while response latency was delayed with dimmer flashes (383±18 vs. 263±27 ms, p<0.001) (Wilcoxon tests). Furthermore, spontaneous inhibitory current frequency (0.95±0.30 vs. 0.22±0.09 Hz, p=0.024), but not amplitude (38.3±6.2 vs. 40.5±9.4 pA, p=0.973), was increased in LIM eyes (Wilcoxon tests).

Conclusions : We show that LIM alters rod pathway signal strength and timing, with light-evoked inhibition differently affected by dim and bright stimulation. Moreover, spontaneous inhibitory current frequency, but not amplitude, increased, suggesting altered amacrine cell signaling. Future directions include isolating GABA and glycine receptor input to RBCs to determine LIM effects. Our results show that myopia alters rod pathway signal balance, suggesting a role for these pathways in myopia development.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.