Neural control of middle ear aeration.

This study investigates the afferent and efferent pathways by which respiratory neurons in the brain can monitor and regulate middle ear aeration. Experiments were performed on 11 adult cynomolgus monkeys (Macaca fascicularis). The neural tracer, horseradish peroxidase, was placed on the transected nerves of the tympanic plexus in four animals. Horseradish peroxidase-labeled nerve terminal fields were observed in the ipsilateral respiratory subnuclei of the nucleus of the solitary tract. This may represent the sensory pathway by which the degree of middle ear aeration is monitored by the brain. Horseradish peroxidase was injected into the eustachian tube muscles in six of the monkeys, and horseradish peroxidase-labeled motoneurons were observed in the ipsilateral trigeminal motor nucleus (tensor palati muscle) and nucleus ambiguus (levator palati muscle). These brain-stem motor nuclei may represent the efferent pathways by which the degree of middle ear aeration is regulated. The results of these primate experiments confirm our earlier studies on rabbits and cats. A theory for the neural control of middle ear aeration is proposed.