Comparison of unconditioned reflex and conditioned avoidance tests in rats exposed by inhalation to carbon monoxide,...

The sensitivity of unconditioned reflex and conditioned avoidance tests in evaluating behavioral toxicity was compared. Male rats were exposed by inhalation up to four hours to 0, 200, 400, 800 or 1600 ppm carbon monoxide (CO); 0, 1500, 3000, 6000 or 12,000 ppm 1,1,1-trichloroethane; 0, 800, 1600, 3200, or 6400 ppm toluene; or 0, 4000, 8000, 16,000 or 32,000 ppm ethanol. Animals were tested for behavioral changes at one-half, one, two and four hours during exposure and eighteen hours after exposure ended. In unconditioned reflex testing the presence or absence of specific unconditioned reflexes (such as corneal, placing, grasping and righting reflexes) and simple behavior patterns including locomotor activity and coordination were observed. The conditioned reflex task consisted of shock avoidance by lever press following simultaneous light and sound stimuli. Rats began to fail unconditioned reflex tests at 800 ppm CO, 3000 ppm trichloroethane, 800 ppm toluene and 8000 ppm ethanol. Decrements in conditioned avoidance were observed at 800 ppm CO, 6000 ppm trichloroethane, 3200 ppm toluene and 8000 ppm ethanol. Neither test was consistently more sensitive than the other in detecting behavioral changes. For both methods, the concentrations at which changes were detected in rats were two to tenfold higher than those reported for human effects.