Abstract
Purpose :
Light-evoked responses of neurons in the retina disappear quickly after death. The mechanisms for the postmortem decay of light signals or under what conditions they can be restored ex vivo are not well understood. Here, we elucidate mechanisms leading to a loss of transduction and transmission of light signals and determine conditions that enable restoration of photoreceptor light signaling in the mouse and human retina.
Methods :
We carried out in vivo and ex vivo Electroretinogram (ERG) recordings on mice postmortem (PM). For ex vivo ERGs, retinas were enucleated at several time-points PM. To understand the effects of PM acidosis and hypoxia, media pH or O2 were reduced in some of the experiments. Computational Molecular Phenotyping (CMP) analysis was carried out on mouse retinas fixed at 0 and 45min PM. We obtained research donor human eyes (Lion’s Eye Bank, UT) enucleated and delivered within 2.5-5 hrs PM, and measured light-evoked activity from retina samples using ex vivo ERG.
Results :
Photoreceptor (PR) and bipolar cell (BC) responses were lost within ~10 min after death in vivo. However, rod and cone PR responses could be recorded from eyes enucleated up to 3 or 5-6 hrs PM in mouse and human retinas, respectively. BC component of the ex vivo ERG was observed only in one (out of 17) human donor retinas and decayed faster than the PR response in mouse experiments. CMP showed retinal cells show a loss of glutamate and glutamine within 45 min post mortem. Decrease of pH (to 6.8) caused a decay of BC response amplitudes in ex vivo ERG similar to that observed in in vivo whereas lowering of O2 to ~5-10% did not affect light responses during a ~20 min experiment. The maximal light responses of macular cones (Rmax) were significantly larger in donors who died of stroke compared to those who died due to cardiac arrest, while sepsis as a cause of death predicted the smallest Rmax.
Conclusions :
We demonstrate that photoreceptor light responses that were lost quickly after death in vivo can be restored from mouse and human eyes enucleated several hours post mortem under ex vivo. We show that in addition to post mortem enucleation delay, cause of death should be considered as an important criteria for accepting donors. While research donors will allow studies of photoreceptor physiology, functional studies of the inner retina will probably require a use of eyes enucleated in less than one hour post mortem.
This is a 2020 ARVO Annual Meeting abstract.