Abstract
Sensory input via the pharyngeal branch of the glossopharyngeal nerve (GPN-ph), which innervates the pharyngeal region and the superior laryngeal nerve (SLN), which innervates the laryngeal region are very important for eliciting reflex swallowing. Our previous study found that nitric oxide (NO) was involved in reflex swallowing from the pharynx. It is known that NO is produced by the activation of NMDA receptor. In this study, we investigated whether NMDA-NO pathways modulate initiation of reflex swallowing from the pharyngo-laryngeal region. Urethan-anesthetized rats were used. To evoke swallowing, the GPN-ph and the SLN were stimulated by repetitive electrical stimulation (10-20 μA, 10-20 Hz, 1.0 ms). The latency for the first swallow and the time interval between swallows were measured. L-NNA, a non-selective inhibitor of NO synthase (NOS), and 7-nitroindazole, a selective inhibitor of neural NOS extremely reduced occurrence of swallowing evoked by the GPN-ph, whereas swallowing evoked by the SLN was little changed. Furthermore, MK-801, an antagonist of NMDA receptor, suppressed reflex swallowing evoked by the GPN-ph and by the SLN. NMDA restored the suppression of reflex swallowing by MK-801. These results suggest that NMDA-NO pathways are involved in the neural mechanism of initiation of reflex swallowing from the pharynx. [Jpn J Physiol 55 Suppl:S172 (2005)]
