DIFFERENTIAL SUPPRESSION OF UPPER AIRWAY MOTOR-ACTIVITY DURING CARBACHOL-INDUCED, REM SLEEP-LIKE ATONIA

Microinjections of carbachol into the pontine tegmentum of decerebrate cats have been used to study the mechanisms underlying the suppressio n of postural and respiratory motoneuronal activity during the resulti ng rapid eye movement (REM) sleep-like atonia. During REM sleep, disti nct respiratory muscles are differentially affected; e.g., the activit y of the diaphragm shows little suppression, whereas the activity of s ome upper airway muscles is quite strong. To determine the pattern of the carbachol-induced changes in the activity of different groups of u pper airway motoneurons, we simultaneously recorded the efferent activ ity of the recurrent laryngeal nerve (RL), pharyngeal branch of the va gus nerve (Phar), and genioglossal branch of the hypoglossal (XII) and phrenic (Phr) nerves in 12 decerebrate, paralyzed, vagotomized, and a rtificially ventilated cats. Pontine carbachol caused a stereotyped su ppression of the spontaneous activity that was significantly larger in Phar expiratory (to 8.3% of control) and XII inspiratory motoneurons (to 15%) than in Phr inspiratory (to 87%), RL inspiratory (to 79%), or RL expiratory motoneurons (to 72%). The suppression in upper airway m otor output was significantly greater than the depression caused by a level of hypocapnia that reduced Phr activity as much as carbachol. We conclude that pontine carbachol evokes a stereotyped pattern of suppr ession of upper airway motor activity. Because carbachol evokes a stat e having many neurophysiological characteristics similar to those of R EM sleep, it is likely that pontine cholinoceptive neurons have simila r effects on the activity of upper airway motoneurons during both stat es.