Fig. 1. Protocols. Protocol 1: Acute experiments. In a randomized crossover study, rats were instrumented during isoflurane anesthesia. Subsequently, median effective dose values were calculated individually (Dixon's up and down method), and measurements of breathing, blood pressure, electrocardiogram, pharyngeal pressure, and genioglossus electromyogram were taken at three different effective doses of ketamine and propofol. Protocol 2: Experiments in chronically instrumented rats. After instrumentation with genioglossus muscle, neck muscle, and epidural electroencephalography electrodes, rats were allowed to recover for 7 days. Subsequently, measurements of breathing, electroencephalogram, and muscle activity were made in a plethysmography chamber during wakefulness, sleep, and ketamine anesthesia (two different doses). EEG = electroencephalogram; EMG = electromyogram; GG = genioglossus.