EXPERIMENTAL NEUROLOGY %, 7 14-729 (1987) State-Dependent Respiratory Depression Elicited by Stimulation of the Orbital Frontal Cortex JEREMY D. MARKS, ROBERT C. FBYSINGER, AND RONALD M. HARPER’ Brain Research Institute and Department ofAnatomy, School of Medicine, University of California, Los Angeles, California 90024 Received September IO, 1986; revision received October 21, 1986 The effect of electrical stimulation of the orbital frontal cortex on respiration was studied in unanesthetixed, freely moving cats across sleepwaking states. Single trains of forty 300-PA, OS-ms, constant-current pulses at 60 Hz were delivered to the orbital frontal cortex at four points in the respiratory cycle. Stimuli delivered during expira- tion produced an immediate switch to inspiration. Stimuli delivered during inspira- tion reduced inspiratory EMG slope and peak EMG amplitude, and prolonged inspi- ration. Stimuli delivered during early inspiration produced greater effects than stimuli delivered during late inspiration. Stimulation effects were elicited during quiet waking and quiet sleep but not during rapid-eye-movement sleep. These results suggest that the orbital frontal cortex may contribute to respiratory phase switching, and that its influence on brain stem structures is attenuated during rapid-eye-movement sleep. Q 1987 Academic Preq Inc. INTRODUCTION Different sleep-waking states exhibit characteristic respiratory patterns: breathing in quiet sleep (QS) is more regular than during quiet waking (AW), and inspiratory durations are longer. Rapid-eye-movement sleep (REM), in contrast, is characterized by irregular respiratory patterns with mixtures of long and short inspiratoxy durations (28,30). Respiratory patterning reflects differences in the relative timing of inspiration and expiration in the respira- tory cycle, and depends on the interactions between central neural mecha- Abbreviations: QC-orbital cortex, REM-rapid-eye-movement sleep, QS-quiet sleep, AW-waking, RIMS-root-mean-square. ’ The authors thank Dr. David Megirian and Karen Kluge for valuable assistance. This study was supported by grant HL 224 18-09 from the National Heart, Lung, and Blood Institute. 714 0014-4886/87 $3.00 Copyright 8 1987 by Academic Press, Inc. AU tights of repmduction in any form x-csemd