276 



BRUCE P. HALPERN 



record was made with a 25// nickle chrome electrode in the rostral medulla 

 oblongata, presumably in the rostral pole of the nucleus of the fasciculus 

 solitarius (see Pfaffmann et a/., 1961). The temporal characteristics of 

 the chorda tympani and the bulbar responses are quite similar. Thus, 

 one can find, at this level of the CNS, well sustained responses to 0.1 m 

 NaCl. 





^?yt 





QJM-HtoCl 



^W\i : 



:Mjcfl^i ---±~ Depth 



: 1.00 mr 



' — — 



Fig. 1. Summated neural responses to chemical stimulation of the anterior 

 portion of the tongue of the rat. Upper record : Response recorded with 

 25/t enamelled nickle chrome electrode 1. 00mm ventral to the dorsal surface 

 of the medulla, 1.9mm lateral to the median dorsal sulcus, and 2.7mm rostral 

 to the obex. Lower record : Response recorded from the entire chorda tympani 

 nerve of another rat. In both cases, downward deflection of the signal lines at 

 the top of the records indicates the duration of chemical flow through the flow 

 system and closed tongue chamber. The signal lines have been retouched. 

 Records read from right to left. 



We will now concentrate on peripheral nerve responses. Are the tem- 

 poral patterns of gustatory responses modified by changes in concentra- 

 tion? Figure 2 compares summated rat chorda tympani responses to 

 0.1 M and 0.01 M NaCl. The figure reads from right to left. The response 

 to 0.01 M NaCl, on the left of the figure, rapidly fell to a very small adapted 

 level. The response decreased to 30 per cent of the peak magnitude within 

 10 sec. Four minutes after stimulus application, this adapted response to 



