Luminance stimulus response and Naka-Rushton parameter changes in rats following ozone exposure

Abstract

Purpose : The impact of the gaseous air pollutant ozone (O₃), a strong oxidant, on the mammalian retina is unknown. This study aims to compare the electroretinogram (ERG) and Naka-Rushton parameters between control and O₃-exposed rats to better understand the effect of O₃ on retinal function.

Methods : Dark-adapted luminance-response functions were obtained from groups of age- and sex-matched Long Evans rats (n=16 rats); eight control (clean air) and eight O₃-exposed (0.4 ppm for 4 hours/day for 7 days). Full-field ERGs were recorded simultaneously from both eyes in each rat. The scotopic ERG was measured and compared between the two groups. Recordings were performed under general anesthesia (ketamine 70 mg/kg, xylazine 2.5 mg/kg, IP). Pupils were dilated with 2.5% phenylephrine and 1% tropicamide eye drops. Naka-Rushton curves were fitted to the dark-adapted ERGs and the V_max, K_m and n parameters compared between the two groups. A repeated measures ANOVA with luminance as the repeated factor was performed.

Results : Experimental data indicates in the scotopic ERG, an acute exposure to O₃ decreased V_max from 1170mV in the control group to 1077mV after a 1-day (4hr) O₃ exposure. A 7- day O₃ exposure further decreased V_max to 811 (p < 0.05). Amplitudes of the a-wave decreased significantly (p < 0.05) from 221 mV in the control group to 145 mV in the 7-day O₃-exposed group. The K_m increased in the 7-day exposed group from 0.0056 to 0.0065 in the control group. The n parameter decreased as a function of O₃ exposure time from 0.49 in the control group, 0.45 in the 1-day exposed group to 0.39 in the 7-day O₃-exposed group. No statistically significant differences in a-wave (F=0.527, p=0.609) and b-wave (F=2.271, p=0.166) implicit time were detected.

Conclusions : This work demonstrates O₃ is a retinal neurotoxin and environmental exposure leads to decreases in retinal responsiveness, changes in retinal sensitivity and homogeneity as indicated by the Naka-Rushton parameters. Results suggest O₃ -exposure contributes to rod system deficits demonstrated by the ERG changes. The current work offers evidence that in sensitive populations living in air-polluted environments, retinal neuron dysfunction may result from O₃–induced oxidative stress.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.