Retinal omega–3 Deficiency Slows Rod Dark Adaptation

Abstract

Abstract: : Purpose: Omega–3 deficiency has been reported to delay the rate of rod deactivation in primates. It could be expected that omega–3 deficiency would also delay photopigment regeneration, or dark adaptation. This study considers the effect of retinal omega–3 fatty acid deficiency on the recovery of the dark current in rats following pigment bleaching. Methods: Sprague–Dawley rats were raised on either omega–3 sufficient (Suf) or deficient (Def) diets from conception (n = 16/diet). Rod electroretinograms were obtained from anaesthetised animals (ketamine : xylazine, 35:5 mg/kg im) at 5, 10 and 20 weeks. Rod deactivation was assessed using a twin flash paradigm (1.9 log cd.s.m^–2, bleach ∼0.1%), with the interstimulus interval (ISI) varied between 1 and 128 s. Amplitude recovery for each ISI was measured at a fixed criterion (t_det) of 6 ms, and described with an exponential based on the decay of activated rhodopsin (MII). Dark adaptation was sampled at 90 second intervals for 30 minutes after a photopigment bleach of ∼20%. The kinetics of rod amplitude recovery during dark adaptation (t_det = 6 ms) were modelled with a double exponential. Results: A significant difference in omega–3 proportions in retinal phospholipids was observed at all ages (p < 0.01). Omega–3 deficiency delayed the rate of rod deactivation following minimal bleach τ_Suf 3.13 ± 0.12 s vs. τ_Def 5.06 ± 0.45 s, p < 0.01), with no delay in onset of this process (T_{C Suf} 1.70 ± 0.05 s vs. T_{C Def} 1.53 ± 0.22 s). Consistent with the deactivation delay, the rate of photopigment regeneration was significantly slower in omega–3 deficient animals, as indicated by the smaller exponential rate constants (p < 0.01), particularly in the initial phase of dark adaptation. This effect manifested in young animals (5 weeks, p < 0.01) and persisted through to 20 weeks (p < 0.01), with no diet and age interaction effects. Conclusions: Retinal omega–3 fatty acid deficiency slowed rod deactivation in rodents, as reported in primates. In addition, omega–3 deficiency reduced the rate of dark adaptation. That omega–3 deficiency impairs both rod deactivation and the early phases of dark adaptation suggests a common lesion in the visual cycle.

Keywords: electroretinography: non-clinical • photoreceptors • lipids