EFFECTS OF TOLUENE INHALATION ON DETECTION OF AUDITORY SIGNALS IN RATS

Inhalation of organic solvents can affect vigilance and reaction time in humans. An animal model of vigilance was designed to assess the eff ects of toluene on these processes. Adult male Long-Evans rats were tr ained to detect auditory signals (20-msec increases in the intensity o f white noise). Two to 4 s after each signal (or blank period), two re tractable levers were inserted into the test chamber. A press on one l ever after a signal and on the other lever after a blank resulted in t he delivery of food. Signal detection analysis showed that sensitivity (Sensitivity Index, SI) and response bias (Responsivity Index, RI) in creased with signal intensity, indicating that loud signals were more detectable than soft signals and that the animals' criterion for respo nding ''signal'' increased with signal intensity. Response latency for correct choices was faster for signal trials than for blank trials. T oluene vapor was added to the airstream of these chambers at concentra tions of 0, 1000, 1500, or 2000 ppm, either 10 or 30 min before testin g and for the duration of each 1-h test. In air, SI increased across t he duration of the test; this within-session improvement was reversed by toluene. RI did not change in air; it was decreased by toluene at t he beginning of each exposure session, returned to the control level d uring exposure to 1000 and 1500 ppm toluene and exceeded air control a fter 40 min exposure to 2000 ppm toluene. Latency increased monotonica lly across toluene concentrations and time on test. Neither signal int ensity nor the duration of toluene exposure before testing altered the se effects of toluene. SI, RI, and latency baselines were recovered af ter toluene exposure indicating that no persistent effects of toluene were detectable. This conclusion was supported by data from other rats showing that toluene exposure (2000 ppm for 2 h/day for 4 consecutive days) did not affect auditory thresholds, as determined by reflex mod ification of an acoustic startle response using a 16 kHz tone as a pre pulse stimulus, 7 or 17 days after exposure to toluene. Finally, rats tested immediately or 20 min after exposure to 0, 1000, 1500, or 2000 ppm toluene were not affected by the vapor, indicating that the impair ment observed during toluene inhalation did not persist beyond the per iod of exposure.