Ambiguus motoneurons discharging closely associated with ultrasonic vocalization in rats.

Unitary discharges closely associated with ultrasound were recorded from the nucleus ambiguus (NA) and adjacent medullary regions in rats. Two main types of units were distinguished: one firing in tonic bursts against little or no background activity prior to ultrasound emission, and the other remaining silent during ultrasound. Tonic burst units in NA are considered as motoneurons which are essential for ultrasound vocalization since lesions including NA completely abolished its production.