CONVERGENCE OF AFFERENTS FROM THE SLN AND GPN IN CAT MEDULLARY SWALLOWING NEURONS

We demonstrated the convergence of information from the pharyngeal and laryngeal mucosa, transmitted by the glossopharyngeal nerve (GPN) and superior laryngeal nerve (SLN), in the nucleus of the tractus solitar ius (NTS). First, the distribution of terminals of the GPN and SLN in the NTS was examined by an HPR tracing technique in cats, and the syna pse formation of these neurons with NTS neurons was demonstrated by el ectron microscopy. The HRP-labeled SLN and GPN terminals were localize d in a small area of the interstitial subnucleus of the NTS, slightly rostral to the obex, forming synapses with NTS neurons. Next, using ex tracellular recording in anesthetized cats, we determined whether or n ot swallowing-related neurons in the medulla oblongata receive periphe ral inputs. Convergence of peripheral sensory inputs from the SLN and GPN was observed in more than 80% of the NTS cells. These results sugg est that the NTS is not only a sensory-relay nucleus but also integrat es information necessary for eliciting protective reflexes of the uppe r airway, such as swallowing.