THE activity of the laryngeal abductor, the posterior cricoarytenoid (PCA) muscles, is diminished with the loss of wakefulness. During sleep, PCA muscles become hypotonic, suggesting that neural mechanisms which control states of consciousness also contribute to state-dependent changes in upper airway patency. The medial pontine reticular formation (mPRF) has long been known to play a key role in sleep control. Microinjection of cholinergic agonists into the mPRF produces a rapid eye movement (REM) sleep-like state and PCA muscle hypotonia, but the neuroanatomical pathways mediating this hypotonia are not clear. Therefore, the present study used retrograde transsynaptic viral labeling to define multisynaptic pathways from the PCA muscles to the mPRF. Pseudorabies virus was injected into the laryngeal PCA muscles of anesthetized rats. The distribution of retrogradely labeled neurons was studied in the brain stem 4 days post-inoculation. The results show that brain stem areas known to be involved in sleep cycle control are part of a multisynaptic pathway providing input to the laryngeal PCA muscles.