Involvement of excitatory amino acids in the activity of swallowing-related neurons of the ventro-lateral medulla

Abstract

Previous studies have shown that swallowing-related (SR) neurons are present in the ventro-lateral medulla (VLM), within and around the nucleus ambiguus. During deglutition, these SR neurons receive an excitatory input from the swallowing network located within the nucleus tractus solitarii and exhibit a swallowing activity, i.e. a burst of spikes occurring in close temporal relationship with the swallowing motor contraction. The present experiments were carried out to evaluate the possible contribution of excitatory amino acids (EAA) receptors to the swallowing activity of VLM neurons. The effects of ionophoretic or pressure applications of EAA agonists and antagonists were investigated on the activity of SR neurons located in the VLM of decerebrate rats. All SR neurons were excited by ionophoretic applications N-methyl- d-aspartate (NMDA) and kainate, a non-NMDA receptor agonist. Furthermore, the swallowing response of the neurons was depressed by ionophoretic applications of both the broad spectrum EAA antagonist, τ d-glutamyl-glycine, and the selective NMDA antagonist, dl-2-amino-5-phosphonovalerate, and by pressure applications of the preferential non-NMDA receptors blocker, 6-cyano-7-nitroquinoxaline-2,3-dione. These results indicate that the swallowing activity of SR neurons located in the VLM depends on the activation of EAA receptors. They moreover suggest that both NMDA and non-NMDA receptor subtypes are involved.