Distribution and Origin of VIP‐, SP‐, and Phospholipase Cβ₂‐Immunoreactive Nerves in the Tongue of the Bullfrog, Rana catesbeiana

Abstract

Previous studies have found a few intralingual ganglionic cells that were immunoreactive to vasoactive intestinal polypeptide (VIP) in the frog. A recent study reported a large number of such cells, and the possibility of the release of substance P (SP) from these. The aim of the present study was to investigate the distribution, origin, and colocalization of VIP-and SP-immunoreactive nerves in the tongue of the bullfrog, R. catesbeiana. In addition, the study also examined the colocalization of SP and phospholipase Cb 2 (PLCb 2 ) in the tongue and jugular ganglion. VIP immunoreactivity was seen in unipolar cells that were sparse in nerve bundles in the submucosal and muscle layers. The density of VIP-immunoreactive cells was approximately 4.8 cells/mm 3 . Their fibers terminated in the vicinity of the epithelial basal layer of the fungiform papillae. SP immunoreactivity was not seen in the VIPimmunoreactive cells, but was observed in pseudounipolar cells in the jugular ganglion. The SP fibers terminated close to the free surface, showing spindle-and button-like profiles. Transection of glossopharyngeal nerve resulted in the persistence of VIP-immunoreactive cells and the disappearance of SP-immunoreactive fibers in the tongue. SP immunoreactivity was co-expressed with PLCb 2 in both the tongue and jugular ganglia. No PLCb 2 immunoreactivity was seen in cells comprising the epithelial taste disk. These findings indicate that the origin of VIP nerve fibers are unipolar cells in the tongue, and SP and PLCb 2 fibers Abbreviations used: AChE 5 acetylcholinesterase; DAPI 5 6-diamidino-2-phenylindole, dihydrochloride; NOS 5 nitric oxide synthase; PB 5 phosphate buffer; PBS 5 phosphate buffered saline; SP 5 substance P; VIP 5 vasoactive intestinal polypeptide.Ethical approval: Our research conformed to the guidelines for the care and use of experimental animals established by the Ethical Committee of Animal Experiments of Matsumoto Dental University.Grant sponsor: National Institute for Physiological Sciences.