OBJECTIVE Many motoneurons and respiratory neurons are demonstrated to receive catecholamine inputs, but the extent and distribution of these inputs to expiratory laryngeal motoneurons (ELM) in the caudal nucleus ambignus (NA) is unknown.In the present study, we aim to: 1) examine whether or not close appositions exist between tyrosine hydroxylase immunoreactive (TH-ir, ie, catecholaminergic) boutons and ELM by using intracellular labelling combined with immunohistochemistry, and, if so, identify the origins of the inputs, and, if yes, 2) identify the potential origins of the catecholamine inputs by using tract-tracing study.METHODS We examined catccholamine inputs to ELM using a combination of intracellular labelling and immunohistochemistry in adult Sprague-Dawley rat.ELM were identified in vivo by their post-inspiratory firing pattern and antidromic responses to electrical stimulation of the recurrent laryngeal nerve.Further tract-tracing study was carried by injecting cholera toxinβ (CTB) into the caudal NA.The retrogradely labelled neurons and the TH-ir structures were revealed by dual fluorescence immunohistochemistry.RESULTS TH-ir close appositions were found on all ELMs, with an average number of 18 ± 5 per neuron (n =7, mean ± SD).Close appositions were commonly observed on the distal dendrites rather than on proximal ones, but none on somata or axons.Further tract-tracing study revealed that a large number of CTB labelled neurons in the ipsilateral nucleus tractus solitarii (NTS) and area postrema (AP) were catecholaminergic, and the highest density appeared at 0.2-0.4 mm caudal to the obex.CONCLUSION We demonstrated for the first time that the ELM receive TH-ir close appositions, suggesting that the catecholamine inputs may play a role in the activity of ELM.The afferents of the superior laryngeal nerve (SLN) project to the NTS neurons at the same longitudinal level, our further tract-tracing study suggests that catecholaminergic neurons located in the NTS at the obex level may play an important role in control of the SLN-mediated airway protective reflexes.