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 enlargeme nt of the spinal dorsal horn. At the beginning of each a recording ses sion, a tungsten microelectrode was advanced through the dura in a phy siologically intact, awake, drug-free animal, until amplitude discrimi nation provided a single neuron with a receptive field on the hindquar ters. 2. Extracellular recordings of activity of each neuron were made during receptive field stimulation with tactile and thermal nonnoxiou s and noxious stimuli.3. Baseline responses obtained in the awake stat e were compared with responses of the same neurons during slow-wave or rapid-eye-movement (REM) sleep. In a subpopulation of neurons, the ef fects of anesthesia (propofol, 7.5 mg/kg iv) were observed after the c ompletion of sleep studies. 4. The low-threshold receptive fields of t he seven neurons studied during REM sleep were all increased in size w hen 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 b y an average of 49.1% (range 29-74%). 6. Neuronal response to receptiv e field brushing was observed in 15 neurons during REM sleep. The effe ct 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 sl eep and anesthesia in the same direction. 7. Changes in neuronal respo nses were less consistent during slow-wave sleep but still differed fr om changes induced by propofol. 8. These results demonstrate important differences between effects of natural sleep and anesthetic-induced l oss of consciousness on sensory processing in the spinal dorsal horn. They also demonstrate significant disinhibition/excitation during REM sleep resulting in enhanced response of spinal dorsal horn neurons to low-intensity receptive field stimulation.