Characterisation of afferent projections to the nucleus ambiguus of the rat by means of fluorescent double labelling.

The rat nucleus ambiguus (Amb nucleus) is composed mainly of laryngeal and pharyngeal motoneurons, and can be differentiated into three main subdivisions with respect to the morphology, distribution and physiological function of their neurons. The medial parabrachial and Kölliker-Fuse nuclei (MPB/KF), and the lateral nucleus of the solitary tract (SolL) play a modulator role over some of the physiological functions assigned to the Amb nucleus. The location and characteristics of labelled neurons in the MPB/KF, SolL and Amb nuclei have been studied following the simultaneous and bilateral injections of True blue and Diamidino yellow in each of the three subdivisions of the Amb nucleus. All of the identified axonal projections were mainly ipsilateral. Some of the described pathways also have collaterals which connect both sides of the Amb complex.