Superior laryngeal neurons directly excite cardiac vagal neurons within the nucleus ambiguus

The aim of this study was to test whether superior laryngeal neurons have a xon collaterals that synapse upon cardiac vagal neurons. Superior laryngeal neurons were tested as likely mediators of cardio-respiratory interaction because these neurons are active in post-inspiration, co-localized with car diac vagal neurons, and have many axon collaterals within the nucleus ambig uus. Nontoxic fluorescent tracers were utilized to identify, in vitro, both superior laryngeal neurons that innervated the crico-thyroid muscle, and c ardiac vagal neurons that projected to cardiac ganglia. Co-localization of these two populations of neurons demonstrated that cardiac vagal and superi or laryngeal neurons are both co-localized in the nucleus ambiguus. Simulta neous dual patch clamp recordings were used to either inject depolarizing c urrent and evoke an action potential (current clamp configuration) or contr ol the voltage and depolarize an identified single superior laryngeal neuro n (voltage clamp configuration) while simultaneously recording from a cardi ac vagal neuron. Depolarization of some, but not all, individual superior l aryngeal neurons elicited post-synaptic excitatory currents in cardiac vaga l neurons, indicating that at least some superior laryngeal neurons monosyn aptically synapse upon cardiac vagal neurons within the nucleus ambiguus. ( C) 2000 Elsevier Science Inc.