Toluene inhalation exposure for 13 weeks causes persistent changes in electroretinograms of Long–Evans rats

Abstract

Studies of humans chronically exposed to volatile organic solvents have reported impaired visual functions, including low contrast sensitivity and reduced color discrimination. These reports, however, lacked confirmation from controlled laboratory experiments. To address this question experimentally, we examined visual function by recording visual evoked potentials (VEP) and/or electroretinograms (ERG) from four sets of rats exposed repeatedly to toluene. In addition, eyes of the rats were examined with an ophthalmoscope and some of the retinal tissues were evaluated for rod and M-cone photoreceptor immunohistochemistry. The first study examined rats following exposure to 0, 10, 100 or 1000 ppm toluene by inhalation (6 hr/d, 5 d/wk) for 13 weeks. One week after the termination of exposure, the rats were implanted with chronically indwelling electrodes and the following week pattern-elicited VEPs were recorded. VEP amplitudes were not significantly changed by toluene exposure. Four to five weeks after completion of exposure, rats were dark-adapted overnight, anesthetized, and several sets of electroretinograms (ERG) were recorded. In dark-adapted ERGs recorded over a 5-log (cd-s/m2) range of flash luminance, b-wave amplitudes were significantly reduced at high stimulus luminance values in rats previously exposed to 1000 ppm toluene. A second set of rats, exposed concurrently with the first set, was tested approximately one year after the termination of 13 weeks of exposure to toluene. Again, dark-adapted ERG b-wave amplitudes were reduced at high stimulus luminance values in rats previously exposed to 1000 ppm toluene. A third set of rats was exposed to the same concentrations of toluene for only 4 weeks, and a fourth set of rats exposed to 0 or 1000 ppm toluene for 4 weeks were tested approximately 1 year after the completion of exposure. No statistically significant reductions of ERG b-wave amplitude were observed in either set of rats exposed for 4 weeks. No significant changes were observed in ERG a-wave amplitude or latency, b-wave latency, UV- or green-flicker ERGs, or in photopic flash ERGs. There were no changes in the density of rod or M-cone photoreceptors. The ERG b-wave reflects the firing patterns of on-bipolar cells. The reductions of b-wave amplitude after 13 weeks of exposure and persisting for 1 year suggest that alterations may have occurred in the inner nuclear layer of the retina, where the bipolar cells reside, or the outer or inner plexiform layers where the bipolar cells make synaptic connections. These data provide experimental evidence that repeated exposure to toluene may lead to subtle persistent changes in visual function. The fact that toluene affected ERGs, but not VEPs, suggests that elements in the rat retina may be more sensitive to organic solvent exposure than the rat visual cortex.

A Biochemichal and Ultrastructural Study on the Effect of Toluene on the Pars Distalis of Anterior Pituitary Glands of Adult Male Albino Rats

“…Human exposures have the potential to cause significant morbidity and mortality and this explained the high mortality rate (30%), which found in this study during toluene exposure. It was established that the cause of death may be due to cardiopulmonary failure or pulmonary edema (Prayulsatien W, 2013, Mukai M et al, 2014 andWilliam K. et al, 2016 [2,28,29] The endocrine glands; including adrenal, pituitary, thyroid, parathyroid, endocrine part of pancreas, testis and ovary can be affected by various industrial solvents, in human and experimental animals. The pituitary gland hormones are specifically changes after toluene exposure (Yeshvandra et al 2009) [30] .…”

“…It is an aromatic hydrocarbon, lighter than water in its liquid form, but three times heavier than air as a vapor. Also, it is one of the environmental chemical pollutants that are colorless, sweet-smelling liquids, evaporate easily and belong to volatile (becomes vapor at room temperature) organic compounds [1,2] .…”

The neuro-ophthalmological effects related to long-term occupational exposure to organic solvents in painters

“…There is paucity of the clinical studies that demonstrate the effects of organic solvents on the retinal ganglion; however, an experimental animal study was done by Boyes et al (2016) to examine visual function by recording VEP and ERG responses from four groups of rats repetitively exposed to toluene. They found no significant induced change in the VEP amplitudes caused by toluene exposure.…”

Moderate perinatal thyroid hormone insufficiency alters visual system function in adult rats

“…ERGs were recorded using a modified UV-capable Espion E2 Colordome system (Diagnosis, LLC, Lowell, MA) as previously described (Boyes et al, 2014, Boyes et al, 2016. Briefly, three sets of ERGs were recorded including: (1) a dark-adapted (scotopic) flash series, (2) a light-adapted (photopic) UV-flicker series; and (3) a photopic green flicker series.…”

“…Visual evoked potentials were recorded in a Faraday cage from awake rats, restrained in flexible tubes with their heads exposed, and with their eyes approximately 15 cm from the stimulus monitor, as described elsewhere (Hamm et al, 2000, Boyes et al, 2014, Boyes et al, 2016.…”