Low-threshold neuronal activity of spinal dorsal horn neurons increases during REM sleep in cats: comparison with effects of anesthesia.

1. Cats were prepared for chronic recordings from the lumbar enlargement of the spinal dorsal horn. At the beginning of each recording session, a tungsten microelectrode was advanced through the dura in a physiologically intact, awake, drug-free animal, until amplitude discrimination provided a single neuron with a receptive field on the hindquarters. 2. Extracellular recordings of activity of each neuron were made during receptive field stimulation with tactile and thermal nonnoxious and noxious stimuli. 3. Baseline responses obtained in the awake state were compared with responses of the same neurons during slow-wave or rapid-eye-movement (REM) sleep. In a subpopulation of neurons, the effects of anesthesia (propofol, 7.5 mg/kg iv) were observed after the completion of sleep studies. 4. The low-threshold receptive fields of the seven neurons studied during REM sleep were all increased in size when compared with the baseline value. The average increase was 52.6% (range 26.2-96.7%). 5. The low-threshold receptive fields of the seven neurons studied during REM sleep were reduced by propofol anesthesia by an average of 49.1% (range 29-74%). 6. Neuronal response to receptive field brushing was observed in 15 neurons during REM sleep. The effect of propofol on receptive field brushing was observed in 8 of those neurons. In only one of those eight neurons were the effects of REM sleep and anesthesia in the same direction. 7. Changes in neuronal responses were less consistent during slow-wave sleep but still differed from changes induced by propofol.(ABSTRACT TRUNCATED AT 250 WORDS)