PGO-related potentials in lumbar motoneurons during active sleep.

1. The present report describes the relationship that occurs during active sleep between ponto-geniculo-occipital (PGO) waves and changes in spinal cord motoneuron membrane potential. 2. These changes were characterized by the appearance of a complex pattern of motoneuron hyperpolarizing potentials, with a duration of approximately 300 ms, that were centered around the PGO wave. The first hyperpolarizing potential began before the onset of the PGO wave. Emerging from this hyperpolarizing potential was a second, larger-amplitude hyperpolarizing potential; it was followed by a succession of smaller-amplitude hyperpolarizations. 3. All potentials were present in conjunction with PGO waves during active sleep, but they were observed only in some motoneurons when PGO waves occurred during the transition period from quiet sleep to active sleep. 4. The potentials were reversed by chloride, demonstrating that they were inhibitory postsynaptic potentials (IPSPs). 5. These data, combined with the fact that these PGO-related IPSPs are blocked by strychnine, support the hypothesis that they are the result of the phasic enhancement of the activity of the same system that inhibits motoneurons during active sleep.