EFFECTS OF COOLING THE VENTROLATERAL MEDULLA ON DIAPHRAGM ACTIVITY DURING NREM SLEEP

Dysfunction through cooling of neurons near the ventrolateral medullar y (VLM) surface results in apnea in the anesthetized state, whereas si milar neuronal dysfunction in the awake state only modestly decreases breathing. The purpose of this study was to investigate effects on bre athing, as measured by diaphragm electromyogram (EMG(di)), of VLM neur onal dysfunction during NREM sleep, a naturally occurring change in st ate. In six goats, thermodes for cooling were chronically implanted be tween the first hypoglossal rootlet and the pontomedullary junction (a rea M and area S). During wakefulness and NREM sleep, bilateral VLM co oling (thermode temp = 20 degrees C) for 30 sec decreased EMG(di) mean activity and minute EMG(di) (p < 0.05) and lengthened the time betwee n diaphragm contractions. During NREM sleep, reductions in mean and mi nute EMG(di) during cooling tended to be greater than during waking, b ut not significantly. However, following carotid body denervation, VLM cooling caused prolonged apnea during NREM sleep but only a brief apn ea in the awake state. The data suggest that either intact VLM neurona l mechanisms or intact carotid afferents are necessary for sustained E MG(di) activity during NREM sleep.