Effects of nitrous oxide exposure on behavioral changes in mice.

This study was designed to examine the effects of continuous exposure to low levels of nitrous oxide on several behavioral paradigms and the occipital cortex cells of mice. Different groups of mice were exposed to air or two different levels of nitrous oxide (1000 ppm or 2000 ppm) 8 hr/day for eight consecutive days. The exposure to nitrous oxide was achieved by placing animals in a specially designed, enclosed chamber. At the end of the exposure period, all mice were tested for motor coordination, locomotor activity, stereotypic behavior and anxiety level. Cellular examination of the occipital cortex was conducted by counting both the larger neural cells and the smaller neuroglial cells in a specific region. Our results indicated that animals showed no deficit in motor coordination or anxiety level. Histological examination indicated no significant difference in the number of neural cells, neuroglial cells, or total cells counted in the control tissue, as compared to the neural tissue from mice exposed to nitrous oxide. Nitrous oxide-exposed mice showed reduced locomotor activity compared to control animals; however, with the exception of one time period, this decrease was not statistically significant. Animals exposed to nitrous oxide showed a dose-dependent reduction in stereotypic behavior. Our results suggest that short-term exposure to trace levels of nitrous oxide might alter central dopaminergic neuronal activities in striatal and mesolimbic regions. Further research in this area is needed to provide more information regarding the potential effects of repeated exposure to low levels of nitrous oxide. (Pediatr Dent 15:93-98, 1993).