The effects of pentobarbital upon auditory and visual thresholds in the baboon

Adult male baboons were trained to perform a reaction time procedure, which required holding a lever depressed for varying time intervals and releasing it during a 1.5 sec test stimulus to receive food. The test stimulus was a 16 kHz tone for auditory threshold testing, and a white light for visual threshold testing. Stimulus intensities were randomly varied to determine detection thresholds, and the latency of each correct lever release was recorded as a measure of reaction time. Acute, IM injections of pentobarbital (1.0 to 17.0 mg/kg) were given at the beginning of 2-hr experimental sessions. Pentobarbital elevated the absolute visual threshold and increased both auditory and visual reaction times in a dose-related manner. Two of three baboons showed reaction time and visual threshold decrements at pentobarbital doses which produced no change in absolute auditory thresholds.