Taste papillae

Fig. 39.—Binding of Sugars to Taste Papillae versus Behavioral Taste-preferences of Bovines. ° ...

The binding specificity of d-[ C]glucose by the taste-papillae membranes, compared to that of control membranes isolated from epithelial tissue, has been confirmed in two studies. One inherent problem in the approach is that the stimuli, primarily carbohydrate sweeteners, are not ideal model compounds to use, as they are not active at low concentrations and do not show sufficiently high binding-constants. The use of other stimulus compounds that are at least several hundred times sweeter than sucrose, such as saccharin, dihydrochalcone sweeteners, dipeptide sweeteners, stevioside, perillartine and other sweet oximes, the 2-substituted 5-nitroanilines, and... 

Fig. 40.—Inactivation of Binding of [ C]Sucrose to Taste Papillae by Heating in Boiling...

FIGURE 50-7 Rattongue, taste papillae and taste buds. (A) Surface of the rat tongue showing location of the taste papillae. (B) Cross-section of the three main types of taste papillae fungiform, foliate and vallate. (C) The taste bud contains 50-100 taste cells, including receptor cells and basal cells. 

PROP status. Individuals classified as tasters of the bitter compound propylthiouracil (PROP) (not found in wine) have been reported to perceive bitterness more intensely and have a higher number of taste pores per taste bud and higher density of fungiform taste papillae on the tongue than non-tasters of PROP (32- 36). Despite this, PROP status has not been demonstrated to affect perception of bitterness or astringency of phenolic compounds in wine (73, 29) or water (75, 77, 79, 30). 

Tastants are detected by specialized structures called taste buds, which contain approximately 150 cells, including sensory neurons Figure 32.12). Fingerlike projections called microvilli, which are rich in taste receptors, project from one end of each sensory neuron to the surface of the tongue. Nerve fibers at the opposite end of each neuron carry electrical impulses to the brain in response to stimultation by tastants. Structures called taste papillae contain numerous taste buds. 

De Strooper B (2007) Loss-of-function presenihn mutations in Alzheimer disease. Talking point on the role of presenihn mutations in Alzheimer disease. EMBO Rep 8 141-146 Dethier VG, Hanson FE (1964) Taste papillae of the blowfly. J Cell Comp Physiol 65 93-100 Dickinson A (2001) Causal leaming-an associative analysis. Q J Exp Psychol 54B 3-25 Dobritsa AA, van der Goes van Naters W, Warr CG, Steinbrecht RA, Carlson JR (2003) Integrating the molecular and cellular basis of odor coding in the Drosophila antenna. Neuron 37 827-841... 

Taste-active chemicals react with receptors on the surface of sensory cells in the papillae causing electrical depolarization, ie, drop in the voltage across the sensory cell membrane. The collection of biochemical events that are involved in this process is called transduction (15,16). Not all the chemical steps involved in transduction are known however, it is clear that different transduction mechanisms are involved in different taste quaUties different transduction mechanisms exist for the same chemical in different species (15). Thus the specificity of chemosensory processes, ie, taste and smell, to different chemicals is caused by differences in the sensory cell membrane, the transduction mechanisms, and the central nervous system (14). 

Lasareff put forward a chemical theory in which each receptor was responsive to only a single taste, and that applied stimuli caused the decomposition of a material within the cell. This decomposition produced ions which then excited the nerve endings in the papillae, the concentration of the ionized products determining the magnitude of the neural activity. 

The importance of lipophilicity to bitterness has been well established, both directly and indirectly. The importance of partitioning effects in bitterness perception has been stressed by Rubin and coworkers, and Gardner demonstrated that the threshold concentration of bitter amino acids and peptides correlates very well with molecular connectivity (which is generally regarded as a steric parameter, but is correlated with the octanol-water partition coefficient ). Studies on the surface pressure in monolayers of lipids from bovine, circumvallate papillae also indicated that there is a very good correlation between the concentration of a bitter compound that is necessary in order to give an increase in the surface pressure with the taste threshold in humans. These results and the observations of others suggested that the ability of bitter compounds to penetrate cell membranes is an important factor in bitterness perception. 

Fig. 2.6 Rostral nasal anatomy of Honey Possum (Tarsipes rostratus) showing (a) section levels and (b) TS at level 4 naso-palatine papilla with taste-buds (TB), gustatory chemoreceptors facing lumen of N-Pd (incisive duct, Id) (from Kratzing, 1987).

In the squamous/stratified epithelium covering, the palatal aperture of the N-P canals and the dorso-lateral surfaces of the papilla, there are occasional clusters of taste buds. These non-olfactory chemosensory elements are positioned at or near to the entrance to the AOS, suggesting that some initial chemosensation may arise from the sampling of material... 

Hofer H.O. (1978). The ductus nasopalatinus and the ductus vomeronasalis, and the occurrence of taste buds in the papilla palatina in Nycticebus coucang (Primates, Prosimiae). VerhAnat Ges 72, 649-650. 

Figure 3. Location of some oral chemosensory receptor systems. Taste buds (schematic upper right) are found on specialized papillae on the tongue and scattered on the palate and posterior oral structures. Free nerve endings are found...

Studies on human taste sensations confirm and extend our understanding of the types of chemical signals measured by these oral chemoreceptor systems. There are, for instance, several distinct sensations elicited by chemical stimulation of fungiform papillae innervated by the geniculate ganglion, indicating that a neural functional complexity similar to that described above for... 

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