DYNAMICS OF TASTE CELLS 143 



tongue, and no steady state of stimulus concentration is available to the 

 receptor. 



Temperature Dependency 



Since adsorption is little influenced by small temperature changes, little 

 change in magnitude of taste response to a given substance at various 

 temperatures is expected. This is consistent with experimental results with 

 the rat if the taste stimulus is appHed quickly and the response measured. If, 

 however, the temperature change is maintained over a period of a minute 

 or longer, then the metabolism of the taste bud changes as well as the 

 local blood supply and the magnitude of taste response is expected to be 

 very temperature dependent. This is particularly true for cold blooded 

 animals or those taste preparations where the blood supply is not intact 

 and where the whole tongue quickly reaches equilibrium with the tempera- 

 ture of any solution applied to its surface. The difficulties in electro- 

 physiological taste experiments where the temperature varies are com- 

 pounded by the fact that the chorda tympani nerve bundle contains some 

 temperature fibers. Also, the taste nerves are stimulated directly at 

 temperatures of 7 C or below (Fishman, 1957). 



Species Dependency 



The first definitive taste experiments on different species using electro- 

 physiological techniques were undertaken independently by Pfaflfmann 

 (1955) and Beidler (Beidler et al., 1955). They showed large dilTerences 

 in relative responses to sweet, bitter and sour stimuli as well as to various 

 salts. The hamster responds better to sugars, than does the rat, and the 

 cat responds very poorly. The rat responds well to NaCl compared to 

 KCl whereas the reverse is the case for the cat. An abundance of additional 

 evidence on many other species has been accumulated by other laboratories. 

 It is interesting to note that although most rat taste fibers respond best 

 to NaCl and not as well to KCl, there are some single fibers that respond 

 to KCl better than to NaCl. This suggests that differences in overall taste 

 response from one species to another represents merely a different distri- 

 bution in the number of receptors responding best to any one chemical 

 stimulus. 



Stability of Response 



If the taste cells are quick to age and if this results in changes in functional 

 characteristics of the individual taste cells,, how stable are the fiber types ? 

 No change would be expected since one fiber represents taste cells of the 

 same age group. Since the taste buds degenerate upon cutting the nerve 

 supply, would this change the fiber type ? No direct evidence is available 

 but some observations suggest such changes. For example, the magnitude 



