Sensitivity of EEG in young rats to toluene exposure

Abstract Effects of toluene on the electroencephalogram (EEG) and its power spectra were measured during a 2-hr exposure in a dynamic inhalational chamber in young rats (30–53 days old) and compared to those in adult rats (63–77 days old). Rats were exposed to one of the three concentrations [low (108–111 ppm), medium (160–163 ppm), and high (407–432 ppm)] of toluene on different days. In tests on sleep-wake cycle, in the young animals the duration of the wake stage (W) was increased with decreases of rapid eye movement (REM) and non-REM (NREM) sleep during hr 1 and hr 2 of exposure to the low concentration. These effects were marked at the medium and the high concentrations. In adult rats, at the low concentration the increase of W and the decrease of REM were observed only at hr 1; however, at medium and high concentrations those changes of W and REM sleep were marked along with a decrease of NREM. Comparison of the changes of duration of different states in rats of two age groups showed that there was a significant difference in the increase of W and the decrease of NREM sleep in young rats at hr 2 of exposure to low concentrations only compared to those in adult rats. Tested on power spectrum in young rats during REM sleep recorded from the visual cortex, the power of δ waves increased at the medium and high concentrations and that of θ wave decreased at the high concentration during hr 2 of exposure compared to the controls. In adult animals the power of θ wave recorded from the visual cortex during REM sleep was also decreased at hr 2 of exposure to the concentration. In both groups no significant change in power spectrum was observed during W and NREM sleep. However, from the effects on sleep-wake cycle at low concentration the young rats appear to be more sensitive to toluene exposure compared to adult rats.