In rats, chorda tympani nerve transection (CTX) greatly increases the detection threshold of sodium chloride (NaCl) and severely disrupts salt discriminability. Here it is shown that CTX has surprisingly little effect, if any, on suprathreshold intensity discrimination. Glossopharyngeal nerve transection (GLX), which has no reported effect on salt sensibility, also did not affect performance. Rats were tested in a 2-response, operant taste intensity discrimination task. Difference thresholds for CTX rats were only slightly higher (-0.15 log/10 unit) than those for GLX and sham-transected rats, when 0.05 M served as the standard, and did not significantly differ when 0.1 M NaCl was the standard. Although the perceived intensity of NaCl might be reduced by CTX, input from remaining taste nerves sufficiently maintains the relative discriminability of suprathreshold NaCl concentrations.

Dotson CD, Colbert CL, Garcea M, Smith JC, Spector AC. The consequences of gustatory deafferentation on body mass and feeding patterns in the rat. Am J Physiol Regul Integr Comp Physiol 303: R611-R623, 2012. First published July 11, 2012 doi:10.1152/ajpregu.00633.2011.-The contribution of orosensory signals, especially taste, on body mass, and feeding and drinking patterns in the rat was examined. Gustatory deafferentation was produced by bilateral transection of the chorda tympani, glossopharyngeal, and greater superficial petrosal nerves. Total calories consumed from sweetened-milk diet and oil-chow mash by the nerve-transected rats significantly decreased relative to shamoperated controls, mostly attributable to decreases in bout number, but not size. Nevertheless, caloric intake steadily increased over the postsurgical observation period, but body mass remained below both presurgical baseline and control levels and did not significantly increase over this time. After the sweetened-milk diet/oil-chow mash phase, rats received a series of sucrose preference tests. Interestingly, the nerve-transected rats preferred sucrose, and intake did not differ from controls, likely due to the stimulus sharing some nontaste chemosensory properties with the sweetened-milk diet. The neurotomized rats initiated a greater number of sucrose-licking bouts that were smaller in size and slower in licking rate, compared with control rats, and, unlike in control rats, the latter two bout parameters did not vary across concentration. Thus, in the absence of gustatory neural input, body mass is more stable compared with the progressive trajectory of weight gain seen in intact rats, and caloric intake initially decreases but recovers. The consequences of gustatory neurotomy on processes that determine meal initiation (bout number) and meal termination (bout size) are not fixed and appear to be influenced by presurgical experience with food stimuli coupled with its nongustatory chemosensory properties. ageusia; body mass regulation; taste loss; taste nerves DECADES OF RESEARCH HAVE SHOWN that nutritional intake contributes to the development of human disease mainly by influencing the development of obesity and its associated conditions (e.g., cardiovascular disease, hypertension, Type 2 diabetes mellitus) [e.g., (8,28,35)]. Collectively, these studies suggest that a majority of obesity-related diseases could be prevented by the adoption of healthier eating habits. In the act of feeding, specialized chemosensory, thermosensory, and mechanosensory receptors, positioned in the nasal and oropharyngeal cavities, provide information to the brain related to the macronutrient composition, caloric density, osmolarity, and potential toxicity of food ingested (1,43,49,76). Chief among these neural signals are those provided by the gustatory system, which is the final guardian of the alimentary tract and provides a chemical analysis of stimulus components that do not typically have sufficiently high vapor pressures to effectively stimulate olfacto...

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