Effects of ozone and nitrogen dioxide on drinking and eating behaviors in mice

Male ICR mice were exposed continuously to ozone (O3) and nitrogen dioxide (NO2) for 7 days to examine the effects on drinking and eating behaviors. Ozone at 0.1 ppm did not affect drinking and eating activities, whereas drinking activity decreased in a concentration-dependent manner to 47.7, 12.8, and 3.0% of the control value with 2-day exposures to 0.2, 0.4, and 0.8 ppm O3, respectively, and eating activity decreased to 35.2 and 8.7% of the control value at 0.4 and 0.8 ppm O3, respectively. Body weight also decreased markedly by 2.0, 4.6, and 7.5 g at 0.2, 0.4, and 0.8 ppm O3, respectively. These decrements reached a maximum on the second day of exposure. However, alterations in drinking and eating activities and body weight were transient, leading to recovery during the continuous O3 exposures. The recovery processes were dependent on the concentrations of O3. Nitrogen dioxide at 4 ppm did not affect drinking and eating activities, whereas drinking activity decreased in a concentration-dependent manner to 56.8, 8.3, and 18.7% of the control value with 2-day exposures to 6, 8, and 12 ppm NO2, respectively, and eating activity decreased markedly to 21.8 and 16.4% at 8 and 12 ppm NO2, respectively. Body weight also decreased by 2.5, 5.5, and 6.1 g at 6, 8, and 12 ppm NO2, respectively. These decrements reached a maximum on the second day of exposure. As in the O3 exposures, the decrements in drinking and eating activities and body weight were transient and recovered during the continuous exposures to NO2 depending on the concentrations of NO2. Drinking and eating activities and body weights of mice that had been previously exposed to 12 ppm NO2 for 7 days did not show changes when the mice were exposed to 0.4 ppm O3 9 days after NO2 exposure. The present study demonstrates that photochemical oxidants suppress drinking and eating behaviors in mice and that they recover thereafter under the continuous exposure conditions.