Nerves chorda tympani

A century ago, Fick proposed the concept of four primary tastes, namely, sweet, salty, sour, and bitter. It has since been found that taste sensations are not describable by a single collection of discrete primaries. Electrophysiological studies of afierent taste-units in the chorda tympani and glossophyrangeal nerves have revealed that a continuous spectrum of gustation may be based on these four taste elements. Furthermore, the intensities of the tastes that we commonly experience are due not only to gustatory sensations but also to tactile, hot and cold, and, above all, olfactory sensations. The complexities of taste studies are such that, unless one of the taste modalities is singled out for study, there is very little hope of success. 

Figure 2. Integrated neural discharge from the gerbil s chorda tympani nerve in response to a series of increasing concentrations of sucrose applied to the tongue. The solid bars under the records indicate stimulus duration, R is the measure of...

Figure 4. Mean integrated response of the chorda tympani nerve discharge in the gerbil to sucrose (A), methyl a-o-glucopyranoside (A), methyl (S-o-glucopy-ranoside ( ), methyl f -o-fructofuranoside ( ), methyl a-o-fructofuranoside (O), methyl a-o-fructopyranoside ( ), methyl p-n-fructopyranoside (Y), 1,5-anhydro-o-mannitol (Q), fructose (equilibrium mixture, 25°C) (V) Responses are relative to the maximum sucrose response.

Figure 7. (A) Comparison of integrated chorda tympani nerve responses to methyl a-n-glucopyranoside (0)N — 15, methyl a-D-xylopyranoside (A) N — 5, and methyl 2-deoxy-a-D-arabino-hexopy-ranoside ( ) N = 5 solutions flowed over the tongue. Bars represent 95% confidence intervals. (B) Taste responses to methul a-D-glucopyranoside (0) N — 15, methyl a-v-mannopyranoside (O) N = 6, ana methyl a-D-galactopyranoside (A) N = 5. Responses relative to sucrose response of 100% (13).

G. Hellekant, V. Danilova, Y. Ninomiya. Primate sense of taste behavioral and single chorda tympani and glossopharyngeal nerve fiber recordings in the rhesus monkey, Macaca mulatto. J Neuropihysial, Tl (2), 978-993, 1997. 

Shigemura N, Islam AA, Sadamitsu C, Yoshida R, Yasumatsu K, Ninomiya Y. Expression of amiloride-sensitive epithelial sodium channels in mouse taste cells after chorda tympani nerve crush. Chem. Senses 2005 30 531-538. 

Ogiso K, Shimizu Y, Watanabe K, Tonosaki K. Possible involvement of undissociated acid molecules in the acid response of the chorda tympani nerve of the rat. J. Neurophysiol. 2000 83 2776— 2779. 

Its influence on the secretion of the submaxillary glands has been fully worked out. This gland receives branches from the chorda tympani nerve which is endowed with two sets of fibres, one acting immediately on the cells, the other causing the blood-vessels to dilate, being vaso-lnhlbltory. 

The author postulated this to be due to block of the chorda tympani, which runs with cranial nerve VII close to the site of the Nadbath Rehman block. 

Danilova V, Hellekant G (2003) Comparison of the responses of the chorda tympani and glossopharyngeal nerves to taste stimuli in C57BL/6J mice. BMC Neurosci 4 5 Dellisanti CD, Yao Y, Stroud JC, Wang ZZ, Chen L (2007) Crystal structure of the extracellular domain of nAChR alpha 1 bound to alpha-bungarotoxin at 1.94 A resolution. Nat Neurosci 10 953-962... 

Abbreviations CT, Chorda tympani CTX, Bilateral transection of the chorda tympani nerve DRK, Delayed-rectifying potassium FFA, Free fatty acid GL, Glossopharyngeal GLX, Bilateral transection of the glossopharyngeal nerve GPCR, G-protein-coupled receptor LCFA, Long-chain fatty acid PROP, 6-n-Propylthiouracil PTK, Protein tyrosine kinase PUFA, Polyunsaturated fatty acid NST, Nucleus of the solitary tract TG, Triglyceride TRC, Taste receptor cells TRPM5, Transient receptor potential protein 5... 

TRC from fungiform papillae and some of the anterior foliate papillae establish synaptic contacts with the chorda tympani (CT) nerve, whereas the posterior parts of the foliate and circumvallate papillae are innervated by the glossopharyngeal (GL) nerve. The possible involvement of gustatory nerves in the LCFA-mediated fat preference has recently been explored in rodents, by studying the impact of bilateral transection of the CT nerve (CTX) and/or bilateral transection of the GL nerve (GLX). 

Oquendo P, Hundt E, Lawler J, Seed B (1989) CD36 directly mediates cytoadherence of Plasmodium falciparum parasitized erythrocytes. Cell 58 95-101 Pittman DW, Labban CE, Anderson AA, O Connor HE (2006) Linoleic and oleic acids alter the licking responses to sweet, salt, sour, and bitter tastants in rats. Chem Senses 31 835-843 Pittman D, Crawley ME, Corbin CH, Smith KR (2007) Chorda tympani nerve transection impairs the gustatory detection of free fatty acids in male and female rats. Brain Res 1151 74-83... 

Stratford JM, Curtis KS, Contreras RJ (2006) Chorda tympani nerve transection alters linoleic acid taste discrimination by male and female rats. Physiol Behav 89 311-319... 

Frank ME, Bieber SL, Smith DV. 1988. The organization of taste sensibilities in hamster chorda tympani nerve fibers. J Gen Physiol 91 861-896. 

Green, B.G. Schullery, M.T. Stimulation of bitterness by capsaicin and menthol differences between lingual areas innervated by the glossopharyngeal and chorda tympani nerves. Chem. Senses 2003, 28 45-55. 

Adaptation can be defined as a reduction in sensitivity following stimulation and is common to all senses. It is thought that adaptation is due to processes occurring at the receptor level. For example, in response to a steady-state stimulus, the neural discharge of the chorda tympani (the main nerve involved in gustatory perception) progressively declines until zero is reached [13]. The extent of adaptation to taste and aroma stimuli depends not only on the particular compound but also on the strength of stimulus [14-16], the duration of stimulation [17], the method of stimulation [15,18], and prior beliefs about the stimulus [19]. 

Probably the most interesting study showing altered taste thresholds as a function of body state is that of Bradley (13). Perfusing the head of the rat with an artificial blood and simultaneously recording from the chorda tympani nerve, Bradley studied the interaction of the state of the body as reflected by the blood and the electrical response in the taste nerve. He concluded that the taste nerve has a dual nature, responding in different ways to chemicals applied on the tongue and to the composition of the blood, monitored by the intero-receptors. 

---