RECEPTORS 



Chemoreceptor Mechanisms 



V. G. Dethier 



Department of Biology, The Johns Hopkins University, Baltimore, Maryland 



Introduction 



The following two questions, which were propounded by the originators 

 of this symposium, represent the starting point and the ultimate goal of 

 much of the research which involves stimulating sensitive tissue: How are 

 physical stimuli transduced into nervous excitation? Is the ultimate reaction 

 biochemical or biophysical? Insofar as stimulation by chemicals is concerned 

 there is no tissue more appropriate for investigation than the tissue which is 

 specialized by nature to receive chemical stimuli which play an indispensable 

 role in the daily economy of living, in short, the chemoreceptors. In our igno- 

 rance it is still expedient to refer to the principal chemical senses as taste and 

 olfaction. The following discussion will utilize this distinction; and, since greater 

 attention has been bestowed by experimenters on the sense of taste, the major 

 emphasis here will be placed on that sense. The discussion will, moreover, at- 

 tempt, to adduce from experiments conducted on the two most extensively 

 studied groups of animals, mammals and insects, evidence for a general theory 

 of action of chemical stimuli. 



Taste 



Mammals 



Taste in mammals is subserved by cells within papillae situated principally 

 on the tongue. Within the papillae the receptors are gathered together in groups, 

 the taste buds. Within the buds lie a variable number of cells (Fig. 1). In man it 

 is generally believed that there are four primary taste modalities, sour, salt, 

 bitter, and sweet, and that most other taste sensations are compounded of these. 

 The earliest suggestion that there might be specific receptors for the separate 

 primary tastes derived from the observation that different areas of the tongue 

 were differentially sensitive to the four qualities. Topical application of solutions 



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