PSYCHOMOTOR PERFORMANCE DURING INITIAL STAGE OF EXPOSURE TO HALOTHANE, ENFLURANE, ISOFLURANE AND SEVOFLURANE IN MICE

SUMMARY 1. The dose-response relationship during the pre-anaesthetic and pre-equilibrium state of four inhalation anaesthetics (halothane, enflurane, isoflurane and sevoflurane) on fixed-ratio schedule-controlled behaviour was studied in mice. 2. Animals exposed to halothane, enflurane and isoflurane showed a biphasic pattern (i.e. a significant incremental increase in psychomotor responses at low inspired concentrations (0.1-0.4%) and decrements at greater concentrations) in a dose-dependent manner. Mean peak responses (per cent of control) were 132.3 (P<0.01 vs control), 124.0 (P<0.05) and 116.7% (P<0.05) at 0.1% halothane, 0.3% enflurane and 0.2% isoflurane, respectively. 3. Sevoflurane did not increase schedule-controlled behavioural responses at any concentration. 4. The effect of subanaesthetic concentrations of inhalation anaesthetics on psychomotor performance can be evaluated as changes in the response rate in schedule-controlled behaviour.