An Immunohistochemical Study of Cellular and Nervous Elements in the Taste Organ of the Bullfrog, Rana catesbeiana

Abstract

The cellular and nervous elements of the bullfrog taste organ were examined by immunhisto-chemical methods using various antibodies. The immunoreactivity for spot 35 protein, a soluble protein isolated from bovine cerebellum, was found in numerous taste cells located at the middle or slightly lower levels within the gustatory cell layer. The immunoreactive cells possessed cytoplasmic processes rising upward the free surface and also issued branched processes to the base of the epithelium. The immuno-reaction for spot 35 protein was found diffusely throughout the cytoplasm from the apical to the basal parts of the taste cells. NSE-immunoreactive taste cells were located at the upper or middle levels within the gustatory cell layer in the taste organ. The fact that the cells were smaller in number and size than spot 35 protein-reactive cells and further differed in localization distinguished the NSE-taste cells from the spot 35 protein cells. Serotonin-like immunoreactivity was detectable in the basal cells localized at the base of the taste epithelium. The immunoreactive cells were arranged in a circle at the periphery of the taste organ, each extending a slender process toward the center. The terminal portion of this process spread leaf-like; numerous fine projections protruded from its margin. The serotonin-immunoreactive cells appear to coincide with the mono-amine-containing basal cells, which have been previously reported. Substance P-, calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, peptide HI (PHI)-or gastrin releasing peptide (GRP)-immunoreactive nerve fibers with varicosities were demonstrated within the taste organ. Some substance P-fibers ran along the bottom of the taste organ epithelium. A few thinner substance P-fibers ascended among the epithelial cells of the organ and terminated closely below the free surface. CGRP-fibers were found to correspond to substance P-fibers from their evidencing a double immunostaining. VIP-and PHI-fibers formed a meshwork in the basal area of the taste epithelium. Abundant substance P-and/or CGRP-fibers formed a meshwork among the ciliated cells located at the periphery of the taste organ. However, PHI-and GRP-fibers were detected less than substance P-and/or CGRP-fibers, though VIP-fibers were rarely present in the same region. Neurofilament protein-or tyrosine hydroxylase-like immunoreactivities were found in thick nerve fibers in the taste organ, whereas no immunoreactivities were present in cellular elements within the taste organ. The relationship between cellular and nervous elements in the taste organ was examined by double im-munostainings. The substance P-fibers were closely related with both spot 35 protein-and serotonin-immuno-reactive cells. In addition, VIP-fibers were found in connection with serotonin-immunoreactive cells. From the present study, it is concluded that the bullfrog taste organ might be a chemo-mechanoreceptive sensory organ. © 1988, The Japanese Pharmacological Society. All rights reserved. © 1988, International Society of Histology and Cytology. All rights reserved.