Excitation of medullary respiratory neurons in REM sleep

Study Objective: To study tonic inputs to medullary respiratory neurons during rapid eye movement (REM) sleep. Design: Single medullary-respiratory-neuron recordings during sleep with spontaneous breathing and during apnea caused by mechanical hyperventilation. Setting: Academic laboratory. Subjects: Three tracheostomized adult cats implanted for polysomnography and extracellular microelectrode recordings. Intervention: Single medullary-respiratory-neuron recordings during spontaneous breathing and mechanical hyperventilation to apnea during non-REM (NREM) and REM sleep. Results: Most but not all respiratory cells of all types (pre-inspiratory, decrementing, augmenting and late inspiratory, phase-spanning, and expiratory) were more active in REM sleep than in NREM sleep during both spontaneous breathing and apnea induced by mechanical hyperventilation. The mean discharge rate of the cells during spontaneous breathing in NREM sleep was 16.7 impulses per second and in REM sleep was 26.5 impulses per second. During ventilator-induced apnea, the mean rates were 10 impulses per second in NREM sleep and 17.5 per second during REM sleep. The increase in activity in REM sleep occurred after a delay of several seconds from the onset of REM sleep. Respiratory cells were excited at times individually and at other times simultaneously in either a reciprocal or nonreciprocal pattern. The degree of excitation of a neuron in REM sleep during ventilator-induced apnea was proportional to the degree of excitation of the neuron in REM sleep during spontaneous breathing. Conclusion: Medullary respiratory neurons are excited individually and collectively in REM sleep. The excitation occurs with a delay after the onset of the state and can stimulate and/or disorganize breathing.