Intracellular analysis of synaptic potentials induced in trigeminal jaw-closer motoneurons by pontomesencephalic reticular stimulation during sleep and wakefulness.

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Abstract
The chronic intracellular recording technique in unanesthetized but head-restrained cats was utilized to analyze the effects of pontomesencephalic reticular formation (PMRF) stimulation on trigeminal jaw-closer motoneurons during naturally occurring states of sleep and wakefulness. During wakefulness and quiet sleep, short pulse-train PMRF stimulation induced a polysynaptic depolarizing potential of long duration (20-80 ms) in jaw-closer motoneurons. During active sleep, the identical stimulation of the PMRF that was used during wakefulness and quiet sleep produced a polysynaptic hyperpolarizing potential in the same cells. The membrane potential of the cells was altered by current injection during PMRF stimulation to determine the nature of the induced potentials. The depolarizing potential of wakefulness and quiet sleep was characterized as an excitatory postsynaptic potential (EPSP), while the hyperpolarizing potential of active sleep was characterized as an inhibitory postsynaptic potential (IPSP). The IPSP induced in jaw-closer motoneurons by PMRF stimulation during active sleep was compared to the IPSP induced by inhibitory inputs from the intraoral region with respect to their sensitivities to polarizing current and Cl- diffusion from the recording micropipette. The inhibitory pathway for the PMRF-induced IPSP of active sleep is independent of the peripheral inhibitory reflex pathway from intraoral structures to jaw-closer motoneurons. It was suggested that the IPSP Induced in jaw-closer motoneurons during active sleep by PMRF stimulation is generated predominantly onto dendritic compartments of the motoneurons. Similarities between the PMRF-induced IPSP and the spontaneously occurring hyperpolarization of active sleep are discussed.

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