Taste sensitivity decreases with age. Therefore, we investigated the histological
and immunohistochemical changes in the receptive fields circumvallate papilla
(CvP) and fungiform papilla (FfP) to explore the mechanism underlying agerelated changes in taste sensitivity in 6- to 72-week-old rats. We analyzed papilla
size, the thickness of the keratin layer of the papilla and stratified squamous epithelium, taste bud size, the keratin layer around the taste pores in the CvP and
FfP, and the number and distribution of taste buds in the CvP coronal section. We
further assessed the expression of marker proteins for Type II and III cells, phospholipase C subtype beta 2 (PLCβ2), and synaptosomal-associated protein
25 (SNAP-25). The cellular activity of these taste cells was examined through colocalization with the senescence cell marker protein-30 (SMP30). There were no
differences in the number of taste bud sections in the CvP among the age groups.
However, the size of the CvP increased and the density of the taste bud area in
the CvP area decreased with increasing age. In contrast, the number of cells with
co-expression of SMP30, PLCβ2, and SNAP-25 decreased with age. Furthermore,
the morphological structures of the CvP, FfP, and taste buds in these regions
changed with age, but not the overall taste bud number in the CvP coronal section. The decrease in cell count with co-expression of SMP30 and PLCβ2, or
SNAP-25 may indicate reduced cellular functions of taste cells with aging