Effect of stimulation of the nucleus reticularis gigantocellularis on the membrane potential of cat lumbar motoneurons during sleep and wakefulness

Abstract

The present study was performed in order to determine the effect of electrical stimulation of the medullary nucleus reticularis gigantocellularis (NRGc) on the membrane potential of spinal cord motoneurons during sleep and wakefulness. Accordingly, intracellular recordings were obtained from lumbar motoneurons in unanesthetized normally respiring cats during naturally occurring states of wakefulness, quiet sleep and active sleep. Electrical stimuli applied to the NRGc evoked synaptic potentials which occurred at short latency ( <10ms) and did not exhibit consistent changes in their waveforms during any states of sleep or wakefulness. During wakefulness and quiet sleep, longer latency ( 20ms) low-amplitude hyperpolarizing potentials occasionally followed NRGc stimulation. However, during active sleep, NRGc stimulation produced, in all motoneurons, relatively large hyperpolarizing potentials that were characterized by a mean amplitude of 3.5±0.4mV(mean±S.E.M.), a mean latency-to-peak of 43.0±0.8ms, and an average duration of 34.4±1.7ms. These potentials were capable of blocking the generation of orthodromic spikes elicited by sciatic nerve stimulation. When anodal current or chloride was passed through the recording electrode, the hyperpolarizing potentials decreased in amplitude, and in some cases their polarity was reversed. These results indicate that the active sleep-specific hyperpolarizing potentials were inhibitory postsynaptic potentials. Thus, the NRGc possesses the capability of providing a postsynaptic inhibitory drive that is directed toward lumbar motoneurons which is dependent on the occurrence of the behavioral state of active sleep. These data suggest that the NRGc may be an important link in the brainstem-spinal cord system that is responsible, during active sleep, for the postsynaptic inhibition of lumbar motoneurons.