Date of Degree

5-2019

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biology

Advisor

Carlos Garcia

Advisor

Philip Aitsebaomo

Advisor

Russell Raymond

Abstract

Research Focus. Millions of people who suffer from retinal disease live in air-polluted environments. The impact of the gaseous air pollutant ozone (O3), a strong oxidant, on the retina is unknown. The aim of the present study is to compare the electroretinographic responses between control (no O3 exposure) and O3 -exposed rats and to better understand the effects of O3 on retinal function.

Materials and Methods. Age-matched adult female rats were separated into two groups (N = 6), 3 control and 3 experimental. The experimental group was exposed to 0.4 ppm O3 for 4 hours a day for 7 days in an environmental chamber. Control rats were not exposed to O3. Rats were dark-adapted for a minimum of one hour. ERG recordings were performed under general anesthesia (ketamine 70 mg/kg, xylazine 2.5 kg/mg IP). Active electrodes, which are designed to be used in rats, were placed on each cornea. Reference and ground electrodes were placed subcutaneously in the rat’s forehead and scruff, respectively. Pupils were dilated and a topical anesthetic applied to each eye (2.5% phenylephrine and 1% tropicamide). Lubrication and proper conductance of the active electrodes were maintained with lubricating eye drops (Refresh). Atipamezole 0.8 mg/kg was administered to reverse the effects of the xylazine.

Research Results/Findings. Experimental data indicates, in the scotopic ERG, a sub-chronic exposure to O3 significantly (p < 0.05) decreased Vmax from 361.2 mV in the control group to 323.6 mV after an acute O3 exposure. A 7-day O3 exposure further decreased Vmax to 224 mV (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.

Conclusions from Research. This present study has demonstrated that an acute and sub-chronic exposure to the air pollutant, O3, disrupts retinal function as demonstrated by changes in the ERG response. The rod dominated dark-adapted system appears to be altered as evidenced by the reduced a-wave and b-wave ERG amplitudes. The peak a-wave amplitude mostly reflects rod photocurrents plus postreceptoral contributions, thus O3 exposure appears to decrease rod function. The decreased peak of the b-wave amplitude suggests ozone lowers the currents from depolarizing rod bipolar cells. This clinically significant work demonstrates O3-induced oxidative stress aggravates retinopathies and contributes to vision deficits in sensitive populations living in air-polluted environments.

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