Anatomical stability of human fungiform papillae and relationship with oral perception measured by salivary response and intensity rating

Abstract

Fungiform papillae house taste buds on the anterior dorsal tongue. Literature is inconclusive as to whether taste perception correlates with fungiform papillae density (FPD). Gustatory reflexes modulate the amount and composition of saliva subsequently produced, and thus may be a more physiologically objective measure of tastant-receptor interactions. Taste perception fluctuates with time but the stability of individual fungiform papillae is unclear. This study followed ten healthy volunteers longitudinally at baseline, one and six months. FPD, diameter and position were measured and participants rated intensity perception of sucrose, caffeine, menthol and capsaicin solutions. Salivary flow rate, protein concentration and relative changes in protein composition were measured following each tastant. FPD, diameter and position were unchanged at six months. FPD did not correlate with intensity rating for any taste. FPD did correlate with changes in salivary protein output following sucrose (ρ = 0.72, p = 0.02) and changes in levels of proline-rich protein and mucin 7 following capsaicin (ρ = 0.71, p = 0.02, ρ = 0.68, p = 0.04, respectively). These results suggest that over six months fungiform papillae are anatomically stable, playing a greater role in mediating the physiological salivary response to stimuli rather than determining the perceived intensity of taste.

Figure 1

Mean papillae density (±s.e.m.) based on three counts of the same image by a single operator at one month (3a) and six months (3b) from baseline. The different participant numbers are due to participant drop-out. No significant differences in papillae density were observed at one or six months (Wilcoxon signed-rank test, p = 0.54 and 0.20, respectively). (c,d) Show data for papillae diameter and relative position at baseline and six months for nine individuals, (n = 10 measures per participant at each time point). Two-tailed paired t-test revealed no significant differences in diameter (p-value range 0.32–0.95) or papillae position (p-value range 0.15–0.94).

Figure 2

Selection of participant photographs at baseline (left) and 6 months (right). Distinctively shaped clusters of papillae have been identified at both time points and marked with red and black dots to aid visualisation. The different colours are purely to aid visualisation. No manipulations of photographs have been made apart from cropping.

Figure 3

Effects of tastants on salivary flow rate and protein concentration (bars represent mean ± s.e.m., n = 10). P-values shown are for two-tailed paired t-tests, values in bold reflect significance (p < 0.05). Vehicle controls were either water when comparing caffeine or sucrose, or 0.475% ethanol in water when comparing menthol or capsaicin. (a) Sucrose, caffeine and capsaicin increased flow rate significantly vehicle control solutions. (b) Protein concentration was not significantly different from vehicle control for any tastant rinse.

Figure 4

Mean ± s.e.m. band intensity changes between capsaicin 1 ppm rinses and 0.475% ethanol vehicle control rinses. p-values shown reflect two-tailed paired t-test, n = 10. No significant changes were detected for other tastants. Band intensity, as measured by SDS-PAGE densitometry, is expressed relative to standard reference samples run on every gel.

Figure 5

Correlations between FPD and salivary changes following capsaicin 1ppm and sucrose 0.25 M. Although a somewhat linear relationship appears to exist no lines have been fitted due to the use of Spearman’s rank correlation (n = 10).

Figure 6

Illustration of fungiform papillae counting method. (a) Outlines the process of selecting a standardised point to centre a 3 mm radius circular area. (b) Shows the process of calibrating this area relative to the 6 mm diameter disc in ImageJ and counting papillae.