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The Rabbit Maxillary Sinus: A Review of the Effects of Innervation on Mucociliary Activity

The stable bone walls of the maxillary sinus of the rabbit permit undisturbed recordings of the mucociliary activity by a photoelectric technique in vivo. The distribution of peptidergic neurotransmittors in the rabbit maxillary sinus was compared with their mucociliary effects on the same preparation. Nerve fibers containing neuropeptide Y were abundant around blood vessels and glands in the lamina propria. A few nerve fibers were seen just beneath the epithelium. Injections with neuropeptide Y decreased mucociliary wave frequency, the maximum decrease was about 15% for the doses 1.0 and 5.0 μg/kg. Vasoactive intestinal polypeptide (VIP) was found in the subepithelial layer and also distributed close to glands and blood vessels in the lamina propria. Administration of VIP alone did not change the mucociliary activity. However, if the rabbits were challenged with threshold doses of the mucociliary stimulant methacholine, the response to the cholinergic agonist was potentiated by VIP. Substance P (SP)-containing nerve fibers were found in the subepithelial layer, with single varicose endings sometimes penetrating into the epithelium. Challenges with SP produced a prompt increase of the mucociliary activity (the maximum increase was about 50% above baseline level), presumably due to increased chloride flux toward the lumen. Similar effects were produced by neurokinin A, which emanates from the same precursor molecule as SP. Another sensory peptide, calcitonin gene-related peptide was without effect on the mucociliary system. Our data indicate that there is a correlation between the occurrence of nerve fibers just beneath the epithelium and mucociliary effects. A localization close to the epithelium seems a logical prerequisite for epithelial effects.