THE GUSTATORY RELAY IN THE MEDULLA* 



W. Makous,! S. NoRD,j: B. Oakley,§ and C. Pfaffmann 



Brown University 



Prior studies of the gustatory medullary relay by Erickson (1958) and 

 Halpern (1959) have shown that electrophysiological signs of neural 

 activity may be recorded from the anterior solitary tract and nucleus of 

 the rat when the anterior homolateral tongue surface is stimulated with 

 taste solutions. The discharge of impulses resembles very closely that seen 

 in the chorda tympani nerve under the same conditions of stimulation. 

 The response to NaCl is typically an initial transient response followed by 

 a decline to a steady state discharge which lasts for many minutes as long 

 as the stimulus remains on the tongue. The time course of the discharge 

 to sugar is characterized by a slower time rise. The relative effectiveness of 

 different taste stimuli in exciting the medullary taste area is very similar to 

 that seen in the chorda tympani except that in several preparations Halpern 

 observed a relative increase in the magnitude of the response to sugar as 

 the electrode penetrated more ventrally through the active area. The 

 significance of this finding is still to be determined. 



Erickson (1958) showed that some single units in the medulla might 

 respond selectively to only a few of the basic taste stimuli, as, for example, 

 positive to NaCl and HCl but not to quinine or sucrose. But many were 

 sensitive to several of the basic test stimuli, 0-1 m NaCl, 0-1 m KCl, 

 0-005 M HCl, 0-01 M quinine hydrochloride, and 1 -0 m sucrose. Not only 

 did some units respond broadly to most of the taste stimuli, but many 

 were also reactive to cooling and even to mechanical stimulation. Thus, 

 individual second order taste nerve fiber units rarely displayed a narrow 

 specificity to just one stimulus. 



The present paper describes further observations on the topographic 

 relation of the gustatory areas to somesthetic sensitivity of the mouth, 

 head, and body regions in the rat medulla. Further studies of rat single 

 unit activity and additional observations on the solitary nucleus of the 

 cat will also be described. 



* Supported in part by a grant from the National Science Foundation. 



t National Science Foundation Predoctoral Fellow. 



:|: Now at Kenyon College. 



§ Public Health Service Predoctoral Research Fellow. 



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