Combined glossopharyngeal and chorda tympani nerve transection elevates quinine detection thresholds in rats (Rattus norvegicus).

Using a conditioned shock avoidance procedure, behavioral quinine hydrochloride thresholds were measured before and after glossopharyngeal (GLX), chorda tympani (CTX), or combined glossopharyngeal and chorda tympani (GLX?+?CTX) transection, as well as after sham surgery. In Experiment 1, thresholds in the sham, CTX, and GLX rats (Rattus norvegicus) either improved (lowered) or remained the same after surgery. In Experiment 2, GLX?+?CTX caused a pronounced 1.5 log?0 unit increase in presurgically measured thresholds. Neither the glossopharyngeal nor the chorda tympani nerve is necessary for normal sensitivity to low quinine concentrations provided the other is intact. When both of these nerves are transected, however, the remaining afferent input is not sufficient to maintain normal detection performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neural responses of the glossopharyngeal nerve to several bitter stimuli in mice

The neural reaction to bitter stimuli was tested in the glossopharyngeal (GL) and chorda tympani (CT) nerves of mice. Relative responses to several bitter stimuli (quinine, iso-alpha-acids, L-tryptophan and L-phenylalanine) were greater in the GL nerve than in the CT nerve. Strain variability for taste sensitivity to bitter stimuli existed between two strains (C57BL and BALB/C). The GL nerve response to caffeine, iso-alpha-acids and L-phenylalanine in the BALB/C strain was greater than the response in the C57BL strain.     

Effects of Selective Lingual Gustatory Deafferentation on Suprathreshold Taste Intensity Discrimination of NaCl in Rats.

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral discrimination between quinine and KCl is dependent on input from the seventh cranial nerve: implications for the functional roles of the gustatory nerves in rats

The rat glossopharyngeal nerve (GL), which innervates posterior tongue taste buds, contains several physiologically defined taste fiber types; at least one type is primarily responsive to certain alkaloids (such as quinine), and another is primarily responsive to acids and salts. In contrast, the chorda tympani (CT), which innervates anterior tongue taste buds, does not appear to contain fibers that differentially respond to quinine relative to salts and acids. It was therefore predicted that GL transection should disrupt behavioral discriminations between quinine and either acids or salts. Water-restricted rats were trained to press one of two levers if a sampled taste stimulus was quinine (0.1-1.0 mM) and the second lever if the sampled stimulus was KCl (0.1-1.0 M). Sham surgery, GL transection, and sublingual and submaxillary salivary gland extirpation were found to have no effect relative to presurgical performance. Both CT transection and combined GL and CT transection caused a substantial and approximately equal decrement in discrimination performance. Removal of the gustatory branches of the seventh cranial nerve [CT and greater superficial petrosal (GSP)] nearly eliminated the discrimination of the taste stimuli, and combined transection of the CT, GL, and GSP unequivocally reduced performance to chance levels. Although these findings were not presaged by the known electrophysiology, they nonetheless compare favorably with other studies reporting little effect of GL transection on behavioral responses to quinine. These results, in the context of other discrimination studies reported in the literature, suggest that, in rats, the neural coding of taste quality depends primarily on the input of the facial nerve.     

The relative effects of transection of the gustatory branches of the seventh and ninth cranial nerves on NaCl taste detection in rats.

Chorda tympani nerve (CT) transection in rats severely impairs NaCl taste detection. These rats can detect higher concentrations of NaCl, however, suggesting that remaining oral nerves maintain some salt sensibility. Rats were tested in a gustometer with a 2-response operant taste-detection task before and after sham surgery (n = 5), combined transection of the CT and the greater superficial petrosal nerves (GSP; 7x, n = 6), or transection of the glossopharyngeal nerve (GL; 9x, n = 4). Thresholds did not significantly change after sham surgery. Although the GL responds to NaCl and innervates nearly 60% of total taste buds, 9x surgery had no effect. However, 7x surgery increased NaCl detection threshold by ～2.5 log?? units, greater than that reported for CT transection alone. These results suggest that the GSP contributes to NaCl sensitivity in rats and also demonstrate that the GL and perhaps the superior laryngeal and lingual nerve proper can maintain some NaCl detectability at high concentrations. These findings confirm the primacy of the 7th nerve relative to the 9th nerve in sensibility of NaCl in the rat model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The consequences of gustatory nerve transection on taste-guided licking of sucrose and maltose in the rat.

Lick responses to sucrose and maltose (0.01–1.0 M) were measured in nondeprived rats during brief-access taste trials before and after histologically confirmed gustatory neurotomy. Pronounced decreases in sugar responsiveness occurred after combined section of the chorda tympani (CT) and greater superficial petrosal nerves. The additional section of the glossopharyngeal nerve (GL) flattened the sucrose concentration-response function. Extirpation of the sublingual and submaxillary salivary glands also attenuated sugar responsiveness. Section of the CT or GL alone or in combination caused less severe or no decreases in sugar licking. There were signs of licking impairments after some of these neurotomies, but the data suggest that changes in sugar responsiveness were not solely motor in origin. Thus the 7th nerve is necessary and most likely sufficient for the maintenance of normal unconditioned appetitive responsiveness to sucrose and maltose. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amiloride-insensitive units of the chorda tympani nerve are necessary for normal ammonium chloride detectability in the rat.

In spite of its common use as a standard stimulus in peripheral nerve recordings, relatively little is known about the psychophysics of NH?Cl taste. Rats' detection threshold for this salt was tested under a variety of conditions, including amiloride (100 μM) treatment and bilateral chorda tympani (CT) nerve transection. Detectability was measured with a 2-lever operant discrimination procedure used previously to measure detection thresholds for NaCl and KCl. Although NH?Cl and KCl appear to share a common taste quality and transduction mechanism, the logistic function and threshold for NH?Cl were found to be more similar to those of NaCl than to those of KCl. Like that of KCl, however, the detection threshold for NH4Cl increased significantly with CT transection (0.54 log?? units, p     

Chorda tympani nerve transection disrupts taste aversion learning to potassium chloride, but not sodium chloride.

In Experiment 1, rats with chorda tympani nerve transection (CTX) acquired a LiCl-conditioned taste aversion to 0.1 M NaCl at the same rate as controls. After 3 conditioning trials, the aversion generalized to 0.03 and 0.3 M NaCl, but did not generalize to KCl (0.03, 0.1, and 0.3 M), in either the sham or CTX group. In Experiment 2, the sham group, but not the CTX group, formed an aversion to 0.1 M KCl after l trial. The CTX rats did form a moderate aversion after 2 conditioning trials. Following the 3rd trial, the CTX group did not suppress licking to 0.03 or 0.3 M KCl or any concentration of NaCl in relation to controls. Although there is strong evidence that CTX affects NaCl taste perception, these findings indicate that, under certain conditions, rats can nonetheless distinguish NaCl from KCl after such neurotomy. Moreover, CTX appears to have a substantial effect on the perceived intensity of KCl. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Combined, but not single, gustatory nerve transection substantially alters taste-guided licking behavior to quinine in rats.

On the basis of electrophysiological studies, the glossopharyngeal nerve (GL) is far more responsive to quinine than the chorda tympani (CTP) or greater superficial petrosal (GSP) nerves. The licking behavior of 72 male, water-deprived rats to quinine (0.03–3.0 mM) and distilled water (10-sec trials) was tested before and after various nerve transections. GL?+?CTP section caused a substantial reduction in responsiveness. GSP?+?CTP section had a moderate effect, and GL section alone produced only marginal impairments. Control, partially desalivated, and CTP-sectioned rats were unaffected. Thus, the GL is not necessary for normal unconditioned taste-guided appetitive responsiveness to quinine, but the collective input from the GSP and CTP is necessary and most likely sufficient. These data suggest that the quinine-evoked input of the GL and CTP converge centrally. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional recovery of taste sensitivity to sodium chloride depends on regeneration of the chorda tympani nerve after transection in the rat.

Chorda tympani nerve (CT) transection (CTX) raises sodium chloride (NaCl) taste detection threshold, but the effect of CT regeneration on NaCl threshold is unknown. This experiment examined whether CT regeneration supports normal NaCl threshold in the rat. Thresholds were measured with a 2-lever operant procedure. Thresholds increased more than 1 order of magnitude after CTX regardless of recovery period length. Postsurgical thresholds in rats with regenerated CTs did not differ from presurgical values. Stimulus adulteration with amiloride raised thresholds in rats with intact or regenerated CTs by about 1 order of magnitude but did not raise thresholds beyond postsurgical levels in rats with transected CTs. Thus, the regenerated CT supports normal NaCl threshold, which is raised by amiloride. Because thresholds remained elevated 62 days after CTX when regeneration was prevented, compensatory processes alone cannot support normal NaCl threshold. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste responses in the greater superficial petrosal nerve: Substantial sodium salt and amiloride sensitivities demonstrated in two rat strains.

A great quantity of research has focused on neural responses of the chorda tympani nerve (CT) to taste stimuli. This report examined salt and sugar sensitivity of the greater superficial petrosal nerve (GSP) and the effect of amiloride on these neural responses. In addition to Sprague-Dawley (SD) rats that have CT responses typical of most rat strains, we included Fischer 344 (F344) rats whose CT responses to sodium chloride (NaCl) are higher than those of other strains. After a stimulation series in which water served as the rinse, a series of stimuli was presented in 100 μM amiloride. The GSP was highly responsive to NaCl, sodium acetate (NaAc), ammonium chloride, and sucrose; NaCl and NaAc responses were strongly suppressed by amiloride. Relative responses to NaCl were significantly higher in F344 than in SD rats. In summary, the GSP is highly sensitive to salt and sugar stimulation, and palatal taste receptors have a considerable degree of amiloride sensitivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neonatal chorda tympani transection alters adult preference for ammonium chloride in the rat.

The immature gustatory system of the neonatal rat is characterized by sensitivity to disruption by early interventions such as receptor or nerve damage. The present studies examined the effect of chorda tympani transection (neoCTX) of neonates on adult preference for salt and nonsalt stimuli. NeoCTX at 10 days of age led to a striking change in adult rats' preference for NH?C1 solutions but little change in preference for other solutions, including NaC1 and KC1. Permanent anatomical effects of neoCTX included failure of the nerve to regenerate and a loss of all fungiform taste buds. Preference for NH?C1 was not due to an inability to discriminate it from NaC1. Following taste aversion conditioning to NaC1, neoCTX rats clearly distinguished between NaC1 and NH?C1. The effects on NH?C1 preference reflect a sensitive period during development because adult rats receiving similar surgery did not show any change in NH?C1 preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium appetite after transection of the chorda tympani nerve in Wistar and Fischer 344 rats.

Acute sodium depletion in rats leads to dramatic increases in intake of hypertonic NaCl solutions, a behavior known as sodium appetite. The importance of signals conveyed by the chorda tympani (ChT) nerve to the expression of sodium appetite is unclear. The effects of bilateral ChT transection were examined on the short- and long-term response to sodium depletion in Wistar and Fischer 344 (F344) rat strains, because Wistar rats normally display a NaCl preference in the absence of need whereas F344 rats avoid NaCl. In both strains, sodium appetite after ChT transection and treatment with the diuretic furosemide was delayed and blunted or eliminated. The results suggest that signals conveyed by the ChT nerve are important in the expression of a sodium appetite. Effects on F344 rats are particularly interesting because ChT transection surgery appears to have opposite effects on NaCl intake depending on whether F344 rats are sodium replete or deplete. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opponent effects of quinine and sucrose on single fiber taste responses of the chorda tympani nerve

Responses of single chorda tympani fibers to mixtures of taste stimuli were studied in the golden hamster (Mesocricetus auratus). Sucrose-best neurons showed significant suppression to quinine-sucrose mixtures compared to sucrose alone. Quinine may exert its effect as an opponent stimulus in the receptor cells at the second messenger level. This suppression may make bitter quinine more readily detected when embedded in mixtures with sweeteners.     

Effects of chorda tympani nerve anesthesia on taste responses in the NST

Human clinical and psychophysical observations suggest that the taste system is able to compensate for losses in peripheral nerve input, since patients do not commonly report decrements in whole mouth taste following chorda tympani nerve damage or anesthesia. Indeed, neurophysiological data from the rat nucleus of the solitary tract (NST) suggests that a release of inhibition (disinhibition) may occur centrally following chorda tympani nerve anesthesia. Our purpose was to study this possibility further. We recorded from 59 multi- and single-unit taste-responsive sites in the rat NST before, during and after recovery from chorda tympani nerve anesthesia. During anesthesia, average anterior tongue responses were eliminated but no compensatory increases in palatal or posterior tongue responses were observed. However, six individual sites displayed increased taste responsiveness during anesthesia. The average increase was 32.9%. Therefore, disinhibition of taste responses was observed, but infrequently and to a small degree in the NST At a subset of sites, chorda tympani-mediated responses decreased while greater superficial petrosal-mediated responses remained the same during anesthesia. Since this effect was accompanied by a decrease in spontaneous activity, we propose that taste compensation may result in part by a change in signal-to-noise ratio at a subset of sites.     

The relative effectiveness of salt stimuli for the rat.

Determined the relative detectability of 8 salts over a molar concentration range of .0125-.80 in an experiment with 5 male hooded rats. The detectability of those salts, which have a strong sour or bitter quality, is substantially greater when compared with sodium chloride, than their relative effectiveness as determined by the size of the evoked response in the chorda tympani. It is suggested that, like quinine, these salts are more effective on the posterior tongue. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of dietary NaCl deprivation during early development on behavioral and neurophysiological taste responses.

Investigated whether the gustatory system can be modified by restricting dietary NaCl during early development by recording neurophysiological taste responses in Sprague-Dawley rats at various times after deprivation (Exp I), and by measuring behavioral taste preferences in 3 groups of 7 NaCl deprived adult rats (Exp II). Overall findings indicate that Ss deprived of dietary NaCl from the 3rd day of gestation to 12 days postnatally and then placed on a NaCl-replete diet had chorda tympani nerve responses similar to those of nondeprived Ss when recordings were made at 28 days of age and older; however, preferences for NaCl solutions over water were significantly less than those of controls when tested at adulthood. NaCl deprivation in Ss from the 3rd day of gestation to approximately 35 days postnatally resulted in altered chorda tympani nerve responses to NaCl but not to other stimuli such as NH?Cl and KCl. Thus, it is concluded that restriction of dietary NaCl at a period in the rat's development when peripheral and central taste responses are changing results in short-term alterations in peripheral neural responses and in long-term changes in preference behaviors. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anion modulation of taste responses in sodium-sensitive neurons of the hamster chorda tympani nerve

Beidler's work in the 1950s showed that anions can strongly influence gustatory responses to sodium salts. We have demonstrated "anion inhibition" in the hamster by showing that the chorda tympani nerve responds more strongly to NaCl than to Na acetate over a wide range of concentrations. Iontophoretic presentation of Cl- and acetate to the anterior tongue elicited no response in the chorda tympani, suggesting that these anions are not directly stimulatory. Drugs (0.01, 1.0, and 100 microM anthracene-9-carboxylate, diphenylamine-2-carboxylate, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonate, and furosemide) that interfere with movements of Cl- across epithelial cells were ineffective in altering chorda tympani responses to 0.03 M of either NaCl or Na acetate. Anion inhibition related to movements of anions across epithelial membranes therefore seems unlikely. The chorda tympani contains a population of nerve fibers highly selective for Na+ (N fibers) and another population sensitive to Na+ as well as other salts and acids (H fibers). We found that N fibers respond similarly to NaCl and Na acetate, with spiking activity increasing with increasing stimulus concentration (0.01-1.0 M). H fibers, however, respond more strongly to NaCl than to Na acetate. Furthermore, H fibers increase spiking with increases in NaCl concentration, but generally decrease their responses to increasing concentrations of Na acetate. It appears that anion inhibition applies to taste cells innervated by H fibers but not by N fibers. Taste cells innervated by N fibers use an apical Na+ channel, whereas those innervated by H fibers may use a paracellularly mediated, basolateral site of excitation.     

The TMJ-ear connection

This article documents the existence of three structures that traverse through the petrotympanic fissure. These structures are the mandibular malleolar ligament, the chorda tympani nerve and the anterior tympanic artery. The mandibular malleolar ligament or the disk-malleolar ligament originates on the anterior process of the mallous. It traverses through the petro-tympanic fissure and attaches to the posterior portion of the capsule and disk of the temporomandibular joint. The chorda tympani nerve supplies sensory feeling to the posterior two thirds of the tongue. The anterior tympanic artery supplies blood to the area of the tympanic membrane. Clinical experience with implants that impinge or cover ear problems and other symptoms. Removal of these implants and placements with devices that do not cover these structures often relieve these symptoms.     

Chorda tympani transection and selective desalivation differentially disrupt two-lever salt discrimination performance in rats

Water-restricted rats were trained to press 1 of 2 levers if a sampled stimulus was NaCl and the other lever if the stimulus was KCl (0.05, 0.1, or 0.2 M). Responses were reinforced with water. After training, the average rate of correct responses was 90%. Performance was unchanged following sham surgery. Chorda tympani (CT) transection reduced average discrimination performance to 67.7% correct, and extirpation of the sublingual and submaxillary salivary glands reduced average performance to 80% correct. Although selective desalivation moderately reduced discriminability, a disrupted salivary environment does not explain the effects of CT transection. More likely, the discrimination deficit in CT-transected rats reflects a loss of critical taste input conveyed by the CT about salts.