Microanalysis of ozone depression of motor activity

Ozone, the principal oxidant in photochemical smog, impairs athletic performance and induces complaints of fatigue and lethargy. It also reduces motor activity in rodents. A detailed analysis of this finding was attempted. Eight male Long-Evans rats were housed in cages attached to running wheels located within a 2-m³ exposure chamber. Each revolution of a wheel closed a switch with the time between switch closures recorded by an attached computer. The rats were exposed for 6-hr periods during the nocturnal phase of their light cycle to ozone concentrations of 0.12, 0.25, 0.50, and 1.0 ppm. Five days or more separated successive exposures. The 3 days preceding an exposure served as control observations. Ozone produced initial decrements in the number of revolutions and a progressively greater decrease with continued exposure. Statistically significant depression took place at 0.12 ppm. Analysis of the individual components of wheel running revealed differential susceptibility to ozone. An increase in the interval between bursts of running was primarily responsible for the decrease in the number of revolutions; this interval was also more sensitive to disruption than either time per revolution or burst length at low concentrations. After termination of exposure to low concentrations of ozone, animals showed increased running. At the higher concentrations, running remained suppressed below control values for several hours. A new multivariate graphical technique, the biplot, is presented as a way to simultaneously display the relationships among many complex variables.