Relationship Between Sensory Stimuli-Elicited IPSPs in Motoneurons and PGO Waves During Muscle Atonia Induced by Carbachol Injection into the Nucleus Pontis Oralis Kristi A. Kohlmeier, Faustino L—pez-Rodr’guez, Francisco R. Morales and Michael H. Chase Department of Physiology, and the Brain Research Institute, UCLA School of Medicine, Los Angeles, Ca 90095
APStracts 4:0092N, 1997.
ABSTRACT
Inhibitory postsynaptic potentials (IPSPs) can be produced in masseter motoneurons by sensory stimuli following the injection of carbachol into the nucleus pontis oralis (NPO) of a-chloralose-anesthetized cats (Kohlmeier et al., 1994, 1995). We have postulated previously that these IPSPs which are induced in masseter motoneurons by sensory stimuli, arise as the result of phasic activation of the motor inhibitory system that mediates atonia occurring spontaneously during active sleep (Chase et al., 1989; Kohlmeier et al., 1996, In Press). In the present study we determined that sensory stimuli, which excite different sensory pathways, somatosensory and auditory, also elicit ponto-geniculo-occipital (PGO) waves during the carbachol-induced state. Because the elicitation of PGO waves has been hypothesized to be a central sign of activation of alerting mechanisms, (Morrison and Bowker, 1975), we suggest that these stimuli also excite those central nervous system (CNS) structures which are involved in the alerting network. The temporal association of the sensory stimuli-elicited IPSPs and PGO waves was also examined by correlating the intracellular response of masseter motoneurons and the extracellular response of LGN neurons to somatosensory and auditory stimuli. Sensory stimuli produced an IPSP which had a similar latency from the foot of the elicited PGO wave as that of spontaneously-occurring motoneuron IPSPs and PGO waves that occur during both carbachol-induced muscle atonia (Kohlmeier et al., 1996) and naturally-occurring active sleep (L—pez- Rodr’guez et al., 1992). In addition, the intensity of the stimulus necessary for elicitation of PGO waves was found to be lower than that required for the elicitation of IPSPs in motoneurons. Additionally, evoked responses in masseter motoneurons during the carbachol-induced state were graded in response to increases in stimulus intensity. The preceding data suggest that some type of processing of sensory input occurs such that only those stimuli that are capable of activating alerting mechanisms involved in the generation of PGO waves result in an increase in activity in the motor inhibitory system. We conclude that there may be a functional link between alerting mechanisms involved in the generation of PGO waves and the motor inhibitory system that generates IPSPs in motoneurons. This functional link may serve to preserve atonia, and thus the state of active sleep, from potentially disruptive PGO- related influences that, during other behavioral states, result in motor activation. 

Received 17 December  1996; accepted in final form 5 June  1997.
APS Manuscript Number J0985-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997