O₂ consumption in the outer and inner mouse retina.

Abstract

Purpose : Light stimulation decreases oxygen consumption (QO₂) in the photoreceptors, but there is indirect evidence that it increases QO₂ in proximal retina, at least during flickering light. However, in the intact eye, the presence of the retinal circulation makes it difficult to isolate QO₂ of the inner retina from the O₂ supply. Here vascular interference was eliminated by making microelectrode recordings in the isolated retina, permitting us to test the hypothesis that QO₂ changes during flicker in opposite directions in the outer retina (OR) and inner retina (IR).

Methods : Double-barreled O₂-sensitive microelectrodes were used to measure local PO₂ in isolated mouse (C57Bl/6J) retinae. Simultaneously recorded local ERGs assisted in verifying the electrode position. Steady and diffuse white square wave flickering (1 Hz) light of scotopic and photopic intensities was applied. Previous recordings of retinal electrical activity and light-induced K⁺ changes demonstrated that 1 Hz stimulation is optimal to evoke metabolic changes in the IR.

Results : Spatial profiles of PO₂ across the retina could be fitted with a 5-layer diffusion model in which the OR was represented, as in vivo, by non-consuming layers for the outer segments and outer nuclear layer (1^st and 3^rd layers), and a consuming layer for the inner segments (2^nd layer). The IR is divided into two more layers, in which the 4^th layer represented the OPL through INL and had a QO₂ designated Q4, and a 5^th layer, with a QO₂ of Q5, describing the GCL/NFL. In 75% of the profiles, Q5 was negligible, Q5/Q4 =0. The weighted average of QO₂ across the inner retina (Q_IR) in many cases was comparable or even larger than the weighted average of QO₂ across the outer layers (Q_OR). Flickering light applied while the electrode was stationary at different retinal depths showed that the PO₂ slowly increased over more than 3 min in the OR, reflecting lower Q_OR. However, flicker decreased PO₂ in the IR with a faster time course, stabilizing in less than 40 sec, reflecting an increase in Q_IR.

Conclusions : Retinal QO₂ can be described by a five-layer model that separates QO₂ in the OR and IR. Using microelectrodes allows a spatial analysis that is not possible with Warburg-type measurements, and we show directly the increase in Q_IR underlying neurovascular coupling.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.