TUNEL staining and electron microscopy studies of apoptotic changes in the guinea pig vallate taste cells after unilateral glossopharyngeal denervation

Abstract

On the basis of our previous report that unilateral glossopharyngeal neurectomy in the guinea pig resulted in degeneration and disappearance of taste buds in ipsilateral vallate papillae (Huang and Lu 1996), it is reasonable to speculate that gustatory denervation may enhance apoptosis of taste bud cells, with taste buds decreasing in number and ultimately disappearing after neurectomy. We were therefore determined to investigate apoptosis of taste bud cells in guinea pig vallate papillae after unilateral glossopharyngeal neurectomy using both terminal deoxynuleotidyl transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) at the light microscopic level and by conventional electron microscopy. A total of 34 adult guinea pigs were unilaterally glossopharyngeal-neurectomized and sacrificed at 3, 6, 12 h and 1, 3 and 7 days after surgery. The results revealed that only a very few TUNEL-positive nuclei indicating apoptosis were present in normal taste buds, but in surgically denervated papillae, they increased in number from 6 h-12 h after surgery, reached at peak on day 1 and then gradually decreased. In apoptotic cells from normal taste buds, electron microscopy revealed condensation of the chromatin against the nuclear envelope, changes in the nuclear envelope, and fragmentation of the nucleus, but the integrity of the plasma membrane and organelles was maintained. Neurectomized taste cells were also characterized by condensed and fragmentary nuclei, compactness of the cytoplasmic organelles, and the appearance of pedunculated protuberances on the cell surface. From these observations, we conclude that: (1) glossopharyngeal neurectomy enhanced apoptosis of vallate taste bud cells in guinea pig; (2) appropriate gustatory nerve innervation is an essential component for the maintenance of the taste bud, and may play a role in apoptosis of taste cells.

Histochemical changes and apoptosis in degenerating taste buds of the rat circumvallate papilla

“…More recently, we applied immunohistochemistry for ssDNA to demonstrate the presence of apoptotic cells in taste buds of normal rat circumvallate papillae (Ueda et al, 2008). Our present results showed that gustatory denervation causes an increase in the number of ssDNA-immunoreactive cells, which is consistent with the results of previous studies (Takeda et al, 1996;Huang and Lu, 2001). The average number of apoptotic taste bud cells per taste bud in the mouse circumvallate papilla is approximately five times higher on PO1 (Takeda et al, 1996), and approximately 15-times higher in the guinea pig vallate papilla (Huang a n d L u , 2 0 0 1 ) c o m p a r e d w i t h t h a t u n d e r n o r m a l conditions.…”

“…Although there is disagreement on the cell-lineage of taste bud cells, recent studies have shown that taste bud cells die by apoptosis under normal conditions and after denervation (Takeda et al, 1996;Zeng and Oakley, 1999;Zeng et al, 2000;Huang and Lu, 2001). Our previous study (Ueda et al, 2008) showed that apoptosis occurs in type II cells and probably also type I cells under normal conditions, as revealed by single-stranded DNA (ssDNA) immunohistochemistry.…”

“…Taste bud cells are thought to die by apoptosis, as demonstrated by TUNEL staining (Takeda et al, 1996;Huang and Lu, 2001) and immunohistochemistry for apoptosis-related molecules (bax, bcl-2; Zeng and Oakley, 1999;Zeng et al, 2000). More recently, we applied immunohistochemistry for ssDNA to demonstrate the presence of apoptotic cells in taste buds of normal rat circumvallate papillae (Ueda et al, 2008).…”

Taste bud cell dynamics during normal and sodium‐restricted development

“…As the taste bud nears mature size, the requirement for rapid cell addition would abate. Once taste buds mature, maintenance of proper taste bud size would require proliferation rates coordinated with taste bud cell death (Zeng et al, 1999;Haung and Lu, 2001). These coordinated processes might be at equilibrium once taste bud size matches numbers of innervating neurons (Krimm and Hill, 1998).…”

Endothelial Cell Apoptosis during Glomerular Capillary Lumen Formation In Vivo

“…Capillary loops were defined as structures delimited by glomerular basement membrane and abluminal podocytes. Early apoptotic cells were defined as those containing nuclei with condensed chromatin along the nuclear membrane, dense cytoplasm, intracytoplasmic vacuoles, and dense bodies, as described previously by others (10,11) Immunohistochemistry Dual labeling for TUNEL and von Willebrand factor (vWF) was performed on formalin-fixed, paraffin-embedded kidney sections (5 m) from 5-d-old rats. Sections were deparaffinized with xylene followed by rehydration through a graded series of ethanol and double distilled water in a standard manner.…”