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ELECTRORETINOGRAMS ARE ALTERED BY SUBCHRONIC TOLUENE EXPOSURE TO LONG EVANS RATS: EXPERIMENTAL EVIDENCE SUPPORTING OBSERVATIONS FROM STUDIES OF EXPOSED HUMANS
Citation:
BOYES, W. K., L. DEGN, M. S. BERCEGEAY, J. MWANZA, C. PINCKNEY, T. E. SAMSAM, A. M. GELLER, AND P. J. BUSHNELL. ELECTRORETINOGRAMS ARE ALTERED BY SUBCHRONIC TOLUENE EXPOSURE TO LONG EVANS RATS: EXPERIMENTAL EVIDENCE SUPPORTING OBSERVATIONS FROM STUDIES OF EXPOSED HUMANS. Presented at International Neurotoxicology Association, Pacific Grove, CA, June 10 - 15, 2007.
Description:
Impaired visual functions, including low contrast sensitivity and reduced color discrimination, have been reported in studies of humans chronically exposed to several volatile organic solvents. These reports remain controversial, however, in part due to a lack of confirmation from controlled laboratory experiments, and also the lack of a biological basis for these selective deficits. This study examined rats following exposure to 0, 10, 100 or 1000 ppm toluene by inhalation (6 hr/d, 5 d/wk, 13 wk). The week following exposure, rats (n=l0/dose group) were surgically implanted with indwelling electrodes over visual cortex. The next week, pattern elicited visual evoked potentials (VEP) were recorded over a range of visual pattern contrasts. Four to five weeks after exposure, rats were anesthetized, evaluated with an ophthalmoscope, and electroretinograms (ERG) were recorded. Three sets of ERGS were obtained from each rat, including: (1) a dark-adapted intensity series over a 5-log range of flash luminance values; (2) the response to a 20 Hz flicker of approximately 5 12 nm against a steady 369 nm (W) background, intended to isolate response of m-cones; and (3) the response to a 20 Hz flicker of 369 nm against a steady 5 12 nm background, intended to isolate the response of scones. No significant changes were observed in VEP amplitudes or contrast thresholds derived from VEP contrast-amplitude functions. No dose-related ophthalmoscopic changes were observed. In the ERG dark-adapted intensity series, the latencies of the A- and B-waves were unchanged, but there was a significant dose x intensity interaction for the amplitudes of A- and B-waves. The B-wave amplitudes were reduced only at stimulus luminance values higher than the apparent rod/cone break in rats treated with 1000 ppm toluene. There was no significant reduction in amplitude of the 20 Hz W flicker response. The response to 5 12 nm 20 Hz flicker showed a dose-related trend of amplitude reduction, but was highly variable, and the group differences were not statistically significant. The results of the dark adapted intensity series are suggestive of a deficit in cone photoreceptor function following subchronic toluene exposure. Although not definitive, the results of the 20 Hz 5 12 nm flicker also tend to support a possible cone deficit. These data provide experimental evidence that repeated exposure to toluene may lead to subtle changes in visual function, and suggest a biologically-plausible basis for the visual deficits reported in exposed humans.
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