Laryngeal respiratory motoneurones: morphology and electrophysiological evidence of separate sites for excitatory and inhibitory synaptic inputs.

Activities of respiratory laryngeal motoneurones were recorded intracellularly in the nucleus ambiguus of the cat. Some of them were intracellularly injected with peroxidase for morphological reconstruction. Stimulation of the superior laryngeal nerve (SLN) evoked excitatory responses in both somata and axons of expiratory laryngeal motoneurones. In inspiratory laryngeal motoneurones, the responses induced by the SLN depended on the site of recording: inhibition and decrease of excitatory input in somata, excitation in axons. We conclude that excitatory synaptic effects of SLN stimulation acts mainly on, or close to, the initial segment of inspiratory motoneurones, while inhibition reaches the somato-dendritic region.