388 



W. MAKOUS AND OTHERS 



the solitary tract and nucleus seem implicated in anterior tongue taste 

 sensitivity. No gustatory responses were observed either from the medial 

 subnucleus or other medullary structures. 



SINGLE UNIT ACTIVITY IN RAT MEDULLA 



Further study of the activity of single second order taste units in the rat 

 is continuing to produce interesting results. The activity of these units 

 was recorded by a platinum-plated indium microelectrode which " floated " 

 on a spring mounting (modified after Burns and Robson, 1960). This 



WATER TEMP. ''C. 

 10 20 



-3.0 



-2.0 -1.0 



LOG M CONG. 



0.0 



Fig. 6. The action potential frequency of a single taste unit to chemical and 



thermal stimulation of the tongue. The axis, " Water Temp. °C ", refers only 



to the curve labelled " Water ". The average level of activity to distilled water 



is plotted as a horizontal dashed line parallel to the x-axis. 



eliminated sudden injury to the cell membrane as a result of the medulla's 

 periodic pulsations and permitted recording from the same single neuron 

 for periods of four or more hours. The chemical solutions, held in a 

 container above the animal, flowed down through a tube to stimulate the 

 rat's exposed tongue with a fine stream of fluid. Distilled water was 

 always used to rinse the chemical solutions from the tongue. Tactile 

 stimulation with fine monofilament hairs and thermal stimulation with 



