Scanning electron microscopy of denervated taste buds in hamster: Morphology of fungiform taste pores

Abstract

Background: Taste pores of fungiform papillae are critical for taste function. Taste nerve injury affects the pore, rendering it refractory to staining with vital dyes. Whether pores of denervated fungiform papillae disappear or undergo more modest structural changes to account for diminished staining was the subject of the present study.Methods: The chorda tympani in the hamster was severed unilaterally and the anterior tongue prepared for scanning electron microscopy after 31 days of survival.Results: Taste pores were found on 92% of control fungiform papillae. They were round openings formed by the free margins of keratinocytes, and centered in hillock-shaped elevations of the papillary surface. Hillocks were encircled by an indentation which, in turn, was surrounded by a circular epithelial rim. These structures associated with fungiform pores distinguish pores on the anterior tongue from those on the posterior tongue. The pores led to a channel that penetrated into the papilla. The experimental side of the tongue had markedly fewer pores. Definitive pores were present on only 53% of denervated papillae. The papillae that lacked pores either exhibited a small hillock and a subtle depression in place of the pore, or had entirely flat apical surfaces. The denervated papillae that retained pores exhibited structural changes. The pores had smaller diameters and led to shallower channels than control pores. Moreover, these persistent pores were associated with hillocks, indentations and rims that were more variable and less distinct than those of control papillae.Conclusion: Pores of fungiform papillae in hamster are associated with specialized surface features of the papillary epithelium. Denervation results in changes that range from disappearance of the pores to their shrinkage and the atrophy of pore-associated epithelial structures. Anat.

Effect of Chorda Tympani Nerve Transection on Salt Taste Perception in Mice

“…This discrepancy can be attributed to different species and strains of animals and different staining techniques used. For example, mouse strains differ in effects of taste nerve section on taste papillae numbers (St John and Boughter 2004), and the methylene blue staining method employed in our study was shown to have a small false-positive rate (St John et al 1995; Parks and Whitehead 1998). The smaller reduction in percentage of taste buds without taste pores could also be due to incomplete sectioning of the CT, but this is unlikely given that we have observed a clear effect of CTX on taste responses.…”

Glossopharyngeal nerve transection impairs unconditioned avoidance of diverse bitter stimuli in rats.

“…Tongues were kept in formalin until the tissue could be processed and the taste pores, taste buds and fungiform papillae counted to confirm transection. Taste pores in fungiform papillae were stained with methylene blue and counted under a light microscope to confirm CTX (see Parks & Whitehead, 1998; Spector, Schwartz, & Grill, 1990) while circumvallate tissue was embedded in paraffin, cut into 5 −10 um sections, mounted and stained using a hemoxylin/eosin procedure to confirm GLX (Guth, 1957; Spector & Grill, 1992). A taste bud was counted in the circumvallate papilla if there was a visible taste pore or a group of well-organized elongated cells very close to the trench, suggesting the apical taste pore was just out of the plane of section (Geran, Garcea, & Spector, 2004).…”

Time course of morphological alterations of fungiform papillae and taste buds following chorda tympani transection in neonatal rats

“…Taste pores appeared as small, distinct circular concavities on the surface of the papillae. Previous reports using the dorsal structure of fungiform papillae to quantify pores have indicated that taste pores stained with methylene blue are darker than the surrounding epithelium (Miller and Reedy, 1990;Parks and Whitehead, 1998). Those articles used a different methodology for preparing the tongue and used standard transmitted light microscopy to visualize the tissue.…”

“…However, our criteria for defining the pore are based on morphological analysis instead of color variation. Using the terminology established in a recent article that examined tongue mor-phology of hamsters (Parks and Whitehead, 1998), a fungiform papilla with a pore was defined as containing three distinct morphological characteristics: a rim that separated the large border of the papilla from the taste pore region, an indentation just inside the rim, and a hillock that protruded slightly from the indentation and contained the pore [see Figs. 1(A,B) and 2(A)].…”