Effect of age on electroretinographic responses in dark agouti rats

Abstract

Introduction: Scotopic threshold response (STR) and photopic negative response (PhNR) are important components of flash electroretinography (ERG) in the assessment of retinal ganglion cell (RGC) function in animal glaucoma models. The amplitude and implicit time (IT) of these parameters can be affected by factors including rat species, age and gender. Here the ERG responses of two different age groups of Dark Agouti (DA) rats are compared. Methodology: Animals were divided into two groups: young adult DA rats 10-12 weeks (n=8) and old adult DA rats 17-19 weeks (n=8). Full field ERG was recorded simultaneously from both eyes after dark adaption and light adaption and parameters were compared between groups. Results: Positive STR recordings were more frequent and of higher amplitudes with shorter implicit times in old adult rats. Furthermore old adult rats achieved higher scotopic a and b wave, photopic b wave and PhNR amplitudes with shorter implicit times. Photopic a-wave amplitudes were however higher in young adult rats. Hence for the rod system, photoreceptor and bipolar cell activity is enhanced in old adult rats, while RGC activity remains similar between groups. For the cone system, RGC and bipolar cell activity is enhanced, while photoreceptor activity is depressed in old adult rats. Conclusion: There are significant differences in electroretinographic responses between young and old adult rats, which may point to age-related changes to the cellular composition of the retina. Such differences need to be considered when conducting glaucoma research in DA rats.