On the distribution and origins of substance P in the papillae of the rat tongue: An experimental and immunohistochemical study

Abstract The distribution and the orgins of substance P (SP)‐positive fibers in the papillae of the rat tongue were investigated by means of the indirect immunofluorescent method. Three types of papilla contain SP‐positive fibers, though the number ofthese fibers varies from papilla to papilla. The circumvallate papilla contains the greatest number of SP‐positive fibers, followed by the foliate papillae and the fungiform papillae; the filiform papillae lack SP‐positive fibers. The papillar SP‐positive fibers form dense bands in the lamina propria just beneath the epithelium. Some of the fibers enter the epithelium and the taste buds. It should be stressed that not every taste bud is provided with SP‐positive fibers: Only 95% of the taste buds in the foliate papillae, 70% of the taste buds in the fungiform papillae, and 40% of the taste buds in the circumvallate papillae contain detectable SP‐positive fibers. Unilateral section of the glossopharyngeal nerve resulted in a complete disappearance of SP‐positive fibers in the foliate papillae on the operated side, and a slight decrease in the circumvallate papillae on both sides. Bilateral section of the glossopharyngeal nerve resulted in a complete disappearance of SP‐positive fibers in the foliate and circumvallate papillae. Following unilateral section of the chorda tympani, SP‐positive fibers in the tastebuds of the fungiform papillae disappeared completely. In addition, unilateral neurotomy of the mandibular nerve resulted in a complete disappearance of SP‐positive fibers in the epithelium of the fungiform papillae. These facts strongly indicate that SP in the foliate and circumvallate papillae is supplied by the glossopharyngeal nerve, SP in the taste buds of the fungiform papillae by the chorda tympani, and SP in the epithelium of the fungiform papillae by the third division of the trigeminal nerve.