RESPIRATORY ACTIVITY OF THE RAT POSTERIOR CRICOARYTENOID MUSCLE

An anatomic and electrophysiological study of the rat posterior cricoa rytenoid (PCA) muscle is described. The intramuscular nerve distributi on of the PCA branch of the recurrent laryngeal nerve was demonstrated by a modified Sihler's stain. The nerve to the PCA was found to termi nate in superior and inferior branches with a distribution that appear ed to be confined to the PCA muscle. Electromyography (EMG) recordings of PCA muscle activity in anesthetized rats were obtained under stere otaxic control together with measurement of phrenic nerve discharge. A total of 151 recordings were made in 7 PCA muscles from 4 rats. Phasi c inspiratory activity with a waveform similar to that of phrenic nerv e discharge was found in 134 recordings, while a biphasic pattern with both inspiratory and post-inspiratory peaks was recorded from random sites within the PCA muscle on 17 occasions. The PCA EMG activity comm enced 24.6 +/- 2.2 milliseconds (p <.0001) before phrenic nerve discha rge. The results are in accord with findings of earlier studies that s how that PCA muscle activity commences prior to inspiratory airflow an d diaphragmatic muscle activity. The data suggest that PCA and diaphra gm motoneurons share common or similar medullary pre-motoneurons. The earlier onset of PCA muscle activity may indicate a role for medullary pre-inspiratory neurons in initiating PCA activity.