Jaw-opening and -closing premotoneurons in the nucleus of the solitary tract making contacts with laryngeal and pharyngeal afferent terminals in rats

• Distribution of jaw-opening (JO) and -closing (JC) premotoneurons was examined.
• JO and JC premotoneurons were labeled in the nucleus of the solitary tract (Sol).
• The Sol projected to the JO and JC components of the trigeminal motor nucleus.
• Superior laryngeal (SLN) and glossopharyngeal nerves (GpN) terminated in the Sol.
• JO or JC premotomeurons in the Sol made contacts with terminals of SLN and GpN.

This study clarified the neural mechanisms underlying jaw movements in pharyngolaryngeal reflexes such as swallowing in rats. After retrograde tracer injections into the ventromedial division (Vmovm) of the trigeminal motor nucleus (Vmo) containing jaw-opening (JO) motoneurons or into the dorsolateral division (Vmodl) of Vmo containing jaw-closing (JC) motoneurons, JO and JC premotoneurons were labeled with an ipsilateral predominance in the medial and intermediate subnuclei of the rostrocaudal middle two-thirds of the nucleus of the solitary tract (Sol); JC premotoneurons were also in the lateral subnucleus of Sol. After anterograde tracer injections into the Sol, axons were labeled with an ipsilateral predominance in the Vmovm and Vmodl, prominently in the ipsilateral Vmovm. After transganglionic tracer applications to the superior laryngeal nerve (SLN) or the cervical trunk of the glossopharyngeal nerve (GpN-ct), labeled afferents were seen in the medial, intermediate, lateral and interstitial subnuclei of Sol at the rostral three-fourths of Sol, indicating considerable overlap with the JO and JC premotoneurons in the Sol. Double labeling experiments demonstrated contacts between the afferent terminals and the JO and JC premotoneurons. The present study has for the first time revealed the differential distribution of JO and JC premotoneurons in the Sol and features of their projections from the Sol, as well as their connections with SLN and GpN-ct afferent inputs. The JO and JC premotoneurons in the Sol may play an important role in generation and organization of jaw movements in pharyngolaryngeal reflexes evoked by SLN and GpN-ct inputs, such as swallowing.