Search

Introduction: There is a paucity of data reporting the rate of chorda tympani nerve injury during cochlear implantation (CI) surgery. To better provide clarity to patients and surgeons regarding the risk of taste change, we performed a systematic review and meta-analysis of prospective studies examining taste change after CI., Data Sources: PubMed, Embase, and Cochrane Library databases were queried., Methods: Databases were queried according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Search terms included "(chorda tympani OR gustatory OR taste OR chemosensory OR dysgeusia OR nervus intermedius) AND (cochlea OR cochlear implant OR cochlear implantation)." Prospective studies were included and further divided into "objective" and "subjective" assessments of taste dysfunction. A systematic review was performed for all studies. A random-effects model was used to compare studies with similar methods and patient demographics., Results: The initial database query yielded 2,437 articles, which were screened according to inclusion and exclusion criteria. Nine appropriate studies were identified, including 442 total patients-254 with subjective assessment and 271 with objective assessment of gustation. Seventeen of 144 patients (11.8%) reported short-term taste change (incidence = 0.09 [0.02-0.16], 95% confidence interval with pooled data). Twenty-six of 265 patients (9.8%) reported long-term taste change (incidence = 0.07 [0.01-0.13]). Objective results were heterogenous and therefore not amenable to pooled meta-analysis., Conclusions: Taste change from chorda tympani nerve injury is a likely underrecognized complication of CI and may be the most common adverse consequence of CI surgery. Surgeons should counsel prospective patients on this potential complication and that the risk of taste change may persist longer than the immediate postoperative period., Competing Interests: The authors disclose no conflicts of interest., (Copyright © 2023, Otology & Neurotology, Inc.)

Background: The chorda tympani nerve (CTN) is a mixed nerve, which carries sensory and parasympathetic fibres. The sensory component supplies the taste sensation of the anterior two-thirds of the ipsilateral side of the tongue. During middle ear surgery the CTN is exposed and frequently stretched or sacrificed, because it lacks a bony covering as it passes through the middle ear. Injury may cause hypogeusia, ageusia or altered taste sensation of the ipsilateral side of the tongue. To date, there is no consensus regarding which type of CTN injury (sacrificing or stretching), during middle ear surgery, leads to the least burden for the patient., Methods: A double-blind prospective prognostic association study was designed in a single medical centre in the Netherlands to determine the effect of CTN injury on postoperative taste disturbance and quality of life. 154 patients, who will undergo primary stapes surgery or cochlear implantation will be included. The taste sensation, food preferences and quality of life of these patients will be evaluated preoperatively and at one week, six weeks and six months postoperatively using the Taste Strip Test, Electrogustometry, supplementary questionnaire on taste disturbance, Macronutrient and Taste Preference Ranking Task, Appetite, Hunger and Sensory Perception questionnaire and Questionnaire of Olfactory Disorders to assess the association of these outcomes with CTN injury. Evaluation of olfactory function will only take place preoperatively and at one week postoperatively using the Sniffin' Sticks. The patient and outcome assessor are blinded to the presence or absence of CTN injury., Discussion: This study is the first to validate and quantify the effect of chorda tympani nerve injury on taste function. The findings of this study may lead to evidence-based proof of the effect of chorda tympani injury on taste function with consequences for surgical strategies., Trial Registration: Netherlands Trial Register NL9791. Registered on 10 October 2021., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Blijleven et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Experimental or traumatic nerve injury causes the degeneration of associated taste buds. Unlike most sensory systems, the sectioned nerve and associated taste buds can then regenerate, restoring neural responses to tastants. It was previously unknown whether injury-induced immune factors mediate this process. The proinflammatory cytokines, interleukin (IL)-1α and IL-1β, and their requisite receptor are strongly expressed by anterior taste buds innervated by the chorda tympani nerve. We tested taste bud regeneration and functional recovery in mice lacking the IL-1 receptor. After axotomy, the chorda tympani nerve regenerated but was initially unresponsive to tastants in both WT and Il1r KO mice. In the absence of Il1r signaling, however, neural taste responses remained minimal even >8 weeks after injury in both male and female mice, whereas normal taste function recovered by 3 weeks in WT mice. Failed recovery was because of a 57.8% decrease in regenerated taste buds in Il1r KO compared with WT axotomized mice. Il1a gene expression was chronically dysregulated, and the subset of regenerated taste buds were reinnervated more slowly and never reached full volume as progenitor cell proliferation lagged in KO mice. Il1r signaling is thus required for complete taste bud regeneration and the recovery of normal taste transmission, likely by impairing taste progenitor cell proliferation. This is the first identification of a cytokine response that promotes taste recovery. The remarkable plasticity of the taste system makes it ideal for identifying injury-induced mechanisms mediating successful regeneration and recovery. SIGNIFICANCE STATEMENT Taste plays a critical role in nutrition and quality of life. The adult taste system is highly plastic and able to regenerate following the disappearance of most taste buds after experimental nerve injury. Several growth factors needed for taste bud regeneration have been identified, but we demonstrate the first cytokine pathway required for the recovery of taste function. In the absence of IL-1 cytokine signaling, taste bud regeneration is incomplete, preventing the transmission of taste activity to the brain. These results open a new direction in revealing injury-specific mechanisms that could be harnessed to promote the recovery of taste perception after trauma or disease., (Copyright © 2023 the authors.)

Objective: We evaluated chorda tympani nerve (CTN) and postoperative taste dysfunction according to anomaly severity and intraoperative CTN status., Study Design: Prospective observational study., Setting: Tertiary referral center, Samsung medical center hospital., Patients: Thirty-one patients who underwent atresioplasty by a single surgeon in a tertiary referral center were enrolled., Interventions: Therapeutic surgery., Main Outcome Measures: Preoperative Schuknecht type and Jahrsdoerfer score and intraoperative CTN status were recorded, and a postoperative questionnaire was administered to evaluate taste function., Results: A significant difference was found among intact, cut, and unidentified groups in terms of Schuknecht type ( p = 0.000) and Jahrsdoerfer score (9.28 ± 1.11, 8.80 ± 0.83, 8.10 ± 0.93, p = 0.028). CTN was observed in Schuknecht type B, and not in type C ( p = 0.000), and was more likely to be observed as Jahrsdoerfer score increased ( p = 0.012). Taste disturbance tended to last longer in adult patients than in children. A significant difference was observed in the incidence of taste change between cut and intact CTN groups ( p = 0.018)., Conclusion: CTN was not identified during surgery in patients with Schuknecht type C anomalies, and there was no change in taste after surgery. Meanwhile, CTN was observed in all patients with Schuknecht type B anomalies, and CTN injury occurred in 41.67%. Therefore, CTN presence can be predicted by severity of anomaly, and patients with type B anomalies should be informed of the risk of CTN injury before surgery., Competing Interests: Conflict of interest: The authors disclose no conflicts of interest., (Copyright © 2023, Otology & Neurotology, Inc.)

Objectives: The aim of this study was to compare the incidence of chorda tympani nerve (CTN) injury between endoscopic and microscopic stapes surgery., Methods: This randomized controlled clinical trial included 88 patients who were randomly divided into two groups: endoscopic stapedotomy group (n = 44) and microscopic stapedotomy group (n = 44). The incidence of chorda tympani nerve (CTN) injury after surgery was determined by both subjective taste testing and chemical taste tests, before and after surgery. The results were compared between the two groups., Results: The total number of patients who were identified as having CTN affection (based on the chemical testing) was 16 out of 88 (18.2%). The incidence was significantly lower in the endoscopic group (n = 2) than the microscopic group (n = 14) (p = 0.019)., Conclusion: Altered taste as a result of iatrogenic CTN injury can affect the patients' quality of life. Endoscopic ear surgery offers better visualization, less need for extensive manipulation of the chorda tympani, and consequently decreased incidence of CTN injury., (© 2022. The Author(s).)

Introduction: Iatrogenic injury to the chorda tympani (CT) is a well recognized, although potentially underestimated, consequence of stapes surgery. This study aims to review the currently available literature to determine the incidence and prognosis of taste disturbances in these patients., Data Sources: PubMed, Embase, and Cochrane Library databases., Methods: Databases were searched according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Search terms included (chorda tympani OR gustatory OR taste OR chemosensory OR dysgeusia OR nervus intermedius) AND (ear surgery OR middle ear OR stapes OR stapedectomy OR stapedotomy). Patients with prospective data collection including preoperative data were further divided by methodology into "objective" and "subjective" assessments of taste dysfunction. A systematic review was performed for all included studies, with meta-analysis using a random-effects model was used for those with comparable methodology and patient populations., Results: Initial search yielded 2,959 articles that were screened according to inclusion and exclusion criteria. Once duplicates were removed, seven studies were identified, representing 173 patients with subjective testing (all seven studies) and 146 with objective testing (five studies). Eighty of 173 patients (46.2%) noted a disturbance in taste at early follow-up, whereas as 26 of 173 (15.0%) noted long-term problems. Objective methodology and result reporting were heterogenous and not amenable to pooled meta-analysis for all studies included., Conclusion: Changes in taste occur relatively frequently after stapedectomy. Surgeons should continue to counsel prospective patients as to the risks of both short- and long-term taste disturbances., Competing Interests: The authors disclose no conflicts of interest., (Copyright © 2022, Otology & Neurotology, Inc.)

Introduction: Preserving maximal quality of life is an important factor in middle ear surgery according to current standards. Taste disturbance is a common postoperative complication, which can be explained with the risk of injury due to the localisation of chorda tympani. The knowledge about this complication is mandatory for optimal surgical decision-making and for patient education as well. Objective: Investigation of early postoperative taste disturbances, to clarify the differences between the impact of different surgical interventions, and the impact of nerve manipulation. Methods: 15 stapes surgeries and 28 tympanoplasties were investigated. Patients answered subjective questionnaires before surgery and on the first postoperative day. Visual analogue scale (VAS) was used to measure the degree of disturbances (0-10). Degree of nerve manipulation was classified into 5 groups. Results: No significant differences between the impact of stapes surgeries and tympanoplasties could be found (9, 9.1; p = 0.861). In groups '0', '1' and '2', the VAS scores were 10, 9.26, and 8.5. Between the groups no manipulation (0) and significant manipulation without macroscopic injury (2), the difference was significant (10, 8.5; p = 0.039). In the stapes surgery group, no severe taste disturbance (VAS<5) was found. Discussion: In the case of adequate microscopic surgical technique, the rate of postoperative taste disturbances is relatively low. Conclusions: The rate of postoperative taste disturbance could be kept at a low level while the continuity of the chorda tympani could be preserved in the majority of cases. The postoperative morbidity rate is primarily influenced by the degree of nerve manipulation and not by the type of surgery.

The chorda tympani is a gustatory nerve that fails to regenerate if sectioned in rats 10 days of age or younger. This early denervation causes an abnormally high preference for NH 4 Cl in adult rats, but the impact of neonatal chorda tympani transection on the development of the gustatory hindbrain is unclear. Here, we tested the effect of neonatal chorda tympani transection (CTX) on gustatory responses in the parabrachial nucleus (PbN). We recorded in vivo extracellular spikes in single PbN units of urethane-anesthetized adult rats following CTX at P5 (chronic CTX group) or immediately prior to recording (acute CTX group). Thus, all sampled PbN neurons received indirect input from taste nerves other than the CT. Compared to acute CTX rats, chronic CTX animals had significantly higher responses to stimulation with 0.1 and 0.5 M NH 4 Cl, 0.1 and 0.5 M NaCl, and 0.01 M citric acid. Activity to 0.5 M sucrose and 0.01 M quinine stimulation was not significantly different between groups. Neurons from chronic CTX animals also had larger interstimulus correlations and significantly higher entropy, suggesting that neurons in this group were more likely to be activated by stimulation with multiple tastants. Although neural responses were higher in the PbN of chronic CTX rats compared to acute-sectioned controls, taste-evoked activity was much lower than observed in previous reports, suggesting permanent deficits in taste signaling. These findings demonstrate that the developing gustatory hindbrain exhibits high functional plasticity following early nerve injury. NEW & NOTEWORTHY Early and chronic loss of taste input from the chorda tympani is associated with abnormal taste behaviors. We found that compared to when the chorda tympani is sectioned acutely, chronic nerve loss leads to amplification of spared inputs in the gustatory pons, with higher response to salty and sour stimuli. Findings point to plasticity that may compensate for sensory loss, but permanent deficits in taste signaling also occur following early denervation.

Background: The posterior tympanum approach of cochlear implantation is easy to damage the facial nerve and cord tympanic nerve. Therefore, we need to improve the safety of cochlear implantation., Objectives: To discuss the safety and feasibility of active and adequate transparent exposure of the facial nerve and chorda tympani nerve during the surgery., Methods: A retrospective analysis was performed on all 945 patients who underwent cochlear implantation from January 2011 to September 2017. All patients have been followed up for 14 months to 5 years postoperatively and postoperative complications have been observed., Results: All 945 patients received artificial cochlear implantation. The facial nerves of 76 cases were above the horizontal semicircular canal plane, while narrow facial recess was observed in 44 cases. Serious chorda tympani nerve variation was found in 1 case. No facial paralysis and facial nerve irritation and abnormal taste occurred after operation., Conclusions: Cochlear implantation with initiative and adequate exposure of facial nerve and the chorda tympani nerve can improve the safety of the cochlear implant surgery. Our study provide a safe and effective method for clinical cochlear implantation to reduce facial nerve and tympanic cord nerve injury.

Objectives: It is generally thought that the recovery of damaged chorda tympani nerve (CTN) function after middle ear surgery is different in pediatric patients from that in adult patients. The purpose of this study was to investigate the changes and the progress of taste and somatosensory functions of the tongue after middle ear surgery in pediatric patients compared with those of adult patients., Study Design: Prospective study., Methods: Fifty-nine pediatric patients and 106 adult patients underwent middle ear surgery. Taste and somatosensory functions of the anterior tongue, the so-called CTN functions, were assessed using electrogustometry (EGM), a 2-point discriminator, an electrostimulator, and a questionnaire before and 2 weeks and 6 months after surgery., Results: Two weeks after surgery, there was no significant difference in the incidence of dysgeusia and abnormal EGM thresholds between the patient groups. The incidence of tongue numbness was significantly lower in pediatric patients than in adult patients regardless of CTN manipulation. Although the lingual somatosensory thresholds of adult patients were significantly increased, those of pediatric patients were not increased. Six months after surgery, the incidences of dysgeusia and an abnormal EGM threshold were lower in pediatric patients than in adult patients. Tongue numbness disappeared, and the thresholds of lingual somatosensory tests returned to normal in most pediatric patients., Conclusion: Not only taste function but also lingual somatosensory function was damaged after middle ear surgery even in pediatric patients. Pediatric patients complained of tongue numbness less frequently and showed earlier recovery than adult patients., Level of Evidence: 2 Laryngoscope, 130:1016-1022, 2020., (© 2019 The American Laryngological, Rhinological and Otological Society, Inc.)

Neural insult during development results in recovery outcomes that vary dependent upon the system under investigation. Nerve regeneration does not occur if the rat gustatory chorda tympani nerve is sectioned (CTX) during neonatal (≤P10) development. It is unclear how chorda tympani soma and terminal fields are affected after neonatal CTX. The current study determined the impact of neonatal CTX on chorda tympani neurons and brainstem gustatory terminal fields. To assess terminal field volume in the nucleus of the solitary tract (NTS), rats received CTX at P5 or P10 followed by chorda tympani label, or glossopharyngeal (GL) and greater superficial petrosal (GSP) label as adults. In another group of animals, terminal field volumes and numbers of chorda tympani neurons in the geniculate ganglion (GG) were determined by labeling the chorda tympani with DiI at the time of CTX in neonatal (P5) and adult (P50) rats. There was a greater loss of chorda tympani neurons following P5 CTX compared to adult denervation. Chorda tympani terminal field volume was dramatically reduced 50 days after P5 or P10 CTX. Lack of nerve regeneration after neonatal CTX is not caused by ganglion cell death alone, as approximately 30% of chorda tympani neurons survived into adulthood. Although the total field volume of intact gustatory nerves was not altered, the GSP volume and GSP-GL overlap increased in the dorsal NTS after CTX at P5, but not P10, demonstrating age-dependent plasticity. Our findings indicate that the developing gustatory system is highly plastic and simultaneously vulnerable to injury., (Copyright © 2019 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Objective: The objective of our systematic review is to investigate the postoperative gustatory function of the chorda tympani nerve following noninflammatory ear surgery for which the chorda tympani is at risk for iatrogenic injury (stretching, handling, or sacrificing)., Data Sources: PubMed and EMBASE., Review Methods: A PubMed and EMBASE databases search was conducted on November 15, 2016. Study inclusion criteria included: 1) ear surgery performed for noninflammatory ear diseases, and 2) gustatory function of the chorda tympani reported as an outcome. The quality of eligible studies was assessed using the risk of bias assessment tool for nonrandomized studies. Study characteristics and outcome data of the included studies were extracted., Results: In total 1,094 articles were retrieved. Fourteen studies encompassing 1,062 operated ears were included after quality assessment. Stapedectomy was the most frequent surgical procedure performed in 398 ears. The follow-up time varied between 6 weeks and 99 months. Patients with a preserved chorda tympani were less symptomatic (24% was symptomatic) compared to patients with a stretched (53% was symptomatic) or sacrificed chorda tympani (47% was symptomatic). The recovery rate varied from 61% to 79%. The results of the electrogustometry and strip test showed a discrepancy with the subjective complaints of the patients., Conclusion: Patients with a stretched chorda tympani were slightly more symptomatic compared to patients with a sacrificed chorda tympani. Therefore, in cases for which the chorda tympani greatly hinders a proper view of the surgical field, sacrificing the nerve could be considered to maximize surgical performance and have a satisfactory postoperative result. Laryngoscope, 1904-1913, 2018., (© 2017 The American Laryngological, Rhinological and Otological Society, Inc.)

Objectives: The aim of study was to evaluate the subjective changes of taste and salivation after middle ear surgery according to chorda tympani nerve (CTN) injury., Study Design: Prospective cohort study., Setting: Tertiary referral center., Patients: We enrolled 180 patients older than 13 years old who received middle ear surgery., Interventions: The patients were classified into cut, manipulated, and intact groups according to intraoperative assessments of the CTN. The patients responded taste and salivation surveys preoperatively, and 1, 3, and 6 months postoperatively., Main Outcome Measures: We analyzed results of questionnaires including disturbance rates, severity and character to evaluate taste and salivation functions., Results: Taste disturbance rate was significantly improved in all groups during follow-up (p < 0.05). The incidence of taste disturbance did not differ significantly between the three groups at each follow-up (p > 0.05). The taste disturbance score improved gradually in the cut and intact groups (p < 0.001), but not in the manipulated group (p = 0.067). Among the patients with taste disturbance, hypoguesia was most common symptom. Incidence of salivation disturbance did not differ between the three groups (p = 0.298). However, this symptom improved significantly only in the intact group (p < 0.001). The taste and salivation disturbance rate was not different between patients with and without chronic otitis media at 3 and 6 months, and both groups showed significant improvement., Conclusions: Prevalence of taste and salivation disturbance was similar between three groups until 6 months. However, taste disturbance did not improve in the manipulated group and salivation disturbance improved only in the intact group.

Objectives: Patients after middle ear surgery often complain of taste disturbance and a lingual numbness. The purpose of this study was to objectively assess changes in the somatosensation of the tongue and taste function in patients undergoing stapes surgery., Study Design: Prospective study., Methods: Symptoms of taste disturbance and tongue numbness after surgery were investigated before and after surgery in 41 patients (13 males, 28 females; mean age 41.8 years) who underwent stapes surgery. Twenty-eight patients (9 males, 19 females; mean age 43.1 years) underwent sensory and taste function tests before and after surgery. Sensory function of the tongue was measured at the operated side and the nonoperated side using the 2-point discrimination test and an electrostimulator test. Taste function was assessed with electrogustometry (EGM)., Results: The chorda tympani nerve (CTN) was gently touched or stretched in all patients. Postoperative thresholds on the operated side were significantly higher than preoperative thresholds in all tests in the patients who underwent all three kinds of tests. Tongue somatosensory symptoms improved significantly earlier than the taste disturbance postoperatively, and the sensory thresholds returned to the baseline along with recovery of symptoms., Conclusion: These findings suggest that dysfunction of the CTN occurred following surgery even when the CTN was preserved, and that the sensory nerve threshold of the tongue correlated with the symptom of lingual numbness. The CTN may play a role not only in taste function but also in the somatosensory function of the tongue., Level of Evidence: 4. Laryngoscope, 128:701-706, 2018., (© 2017 The American Laryngological, Rhinological and Otological Society, Inc.)

Taste nerves readily regenerate to reinnervate denervated taste buds; however, factors required for regeneration have not yet been identified. When the chorda tympani nerve is sectioned, expression of brain-derived neurotrophic factor (BDNF) remains high in the geniculate ganglion and lingual epithelium, despite the loss of taste buds. These observations suggest that BDNF is present in the taste system after nerve section and may support taste nerve regeneration. To test this hypothesis, we inducibly deleted Bdnf during adulthood in mice. Shortly after Bdnf gene recombination, the chorda tympani nerve was unilaterally sectioned causing a loss of both taste buds and neurons, irrespective of BDNF levels. Eight weeks after nerve section, however, regeneration was differentially affected by Bdnf deletion. In control mice, there was regeneration of the chorda tympani nerve and taste buds reappeared with innervation. In contrast, few taste buds were reinnervated in mice lacking normal Bdnf expression such that taste bud number remained low. In all genotypes, taste buds that were reinnervated were normal-sized, but non-innervated taste buds remained small and atrophic. On the side of the tongue contralateral to the nerve section, taste buds for some genotypes became larger and all taste buds remained innervated. Our findings suggest that BDNF is required for nerve regeneration following gustatory nerve section., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Although the ability to taste is critical for ingestion, nutrition, and quality of life, a clear understanding of the influences of age, sex, and chorda tympani (CT) resection on taste function in different regions of the anterior tongue is generally lacking. In this study we employed criterion-free signal detection analysis to assess electric and chemical taste function on multiple tongue regions in normal individuals varying in age and sex and in patients with unilateral CT resections. The subjects were 33 healthy volunteers, ranging from 18 to 87 years of age, and 9 persons, 27 to 77 years of age, with unilateral CT lesions. The influences of age, sex, tongue region, and chorda tympani resections on signal detection sensitivity (d') and response bias (β) measures was assessed in 16 tongue regions to weak electric currents and solutions of sucrose, sodium chloride, and caffeine. Significant age-related decrements in d' were found for sucrose (p=0.012), sodium chloride (p=0.002), caffeine (p=0.006), and electric current (EC) (p=0.0001). Significant posterior to anterior, and medial to lateral, gradients of increasing performance were present for most stimuli. β was larger on the anterior than the posterior tongue for the electrical stimulus in the youngest subjects, whereas the opposite was true for sucrose in the oldest subjects. No sex differences were apparent. d' was depressed ipsilateral to the CT lesion side to varying degrees in all tongue regions, with the weakest influences occurring on the medial and anterior tongue. CT did not meaningfully influence β. This study is the first to employ signal detection analysis to assess the regional sensitivity of the tongue to chemical and electrical stimuli. It clearly demonstrates that tongue regions differ from one another in terms of their age-related sensitivity and their susceptibility to CT lesions., (Copyright © 2015 Elsevier Inc. All rights reserved.)

We reported differential expression of the transient receptor potential vanilloid 1 (TRPV1), the transient receptor potential ankyrin 1 (TRPA1), and the (TRPM8) in the geniculate ganglions (GGs) of naive rats. In medical practice, the chorda tympani nerve (CTN) is injured in some patients during middle-ear surgery, and results in tongue numbness and taste disorder. We investigated changes in the expression of these receptors in GGs after CTN injury. In naive-rat GGs, 11.4, 11.8, and 0.5% of neurons were found to express the TRPV1, the TRPA1, the TRPM8, respectively. At 3 days after CTN injury, 5.2 and 4.0% of activating transcription factor 3-immunoreactive neurons, considered as injured neurons, were found to express the TRPV1 and the TRPA1, respectively. Among activating transcription factor 3-immunonegative neurons, considered as uninjured neurons, 3.9 and 3.8% were found to express the TRPV1 and the TRPA1, respectively. The TRPM8 was not detected in GGs after CTN injury. We found decreased mRNA levels of the TRPV1 and the TRPA1 in all neurons, as well as in uninjured neurons of ipsilateral GGs after CTN injury. CTN injury changes the gene expression in GGs and may have effects on the tongue.

Taste system is a perfect system to study degeneration and regeneration after nerve injury because the taste system is highly plastic and the regeneration is robust. Besides, degeneration and regeneration can be easily measured since taste buds arise in discrete locations, and nerves that innervate them can be accurately quantified. Neurotrophins are a family of proteins that regulate neural survival, function, and plasticity after nerve injury. Recent studies have shown that neurotrophins play an important role in the developmental and mature taste system, indicating neurtrophin might also regulate taste system following gustatory nerve injury. This review will summarize how taste system degenerates and regenerates after gustatory nerve cut and conclude potential roles of neurotrophin in regulating the process.

Objective: To elucidate the degeneration process of fungiform taste buds after severing the chorda tympani nerve (CTN) by confocal laser scanning microscopy in vivo., Study Design: Prospective study., Setting: University hospital., Patients: Seven consecutive patients whose CTN was severed during tympanoplasty for middle ear cholesteatoma., Intervention: Diagnostic., Main Outcome Measures: Preoperative and postoperative gustatory functions were assessed by electrogustometry (EGM). An average of 10 fungiform papillae (FP) in the midlateral region of the tongue were periodically observed, and the number of taste buds was counted using a confocal laser microscope. Among them, 2 to 3 reference FPs were selected based on the typical form of the FP or characteristic arrangements of taste pores. Observation was performed before surgery, 1 or 2 days after surgery, 2 or 3 times a week until 2 weeks after surgery, once a week between 2 and 4 weeks, and every 2 to 4 weeks thereafter until all taste buds had disappeared., Results: EGM thresholds showed no response within 1 month after surgery in all patients. The initial change in the degeneration process was the disappearance of taste pores. The surface of taste buds became covered with epithelium. Finally, taste buds themselves atrofied and disappeared. The time course of degeneration differed depending upon individuals, each FP, and each taste bud. By employing the generalized linear mixed model under the Poisson distribution, it was calculated that all taste buds would disappear at around 50 days after surgery., Conclusion: Confocal laser scanning microscopy was useful for clarifying the degeneration process of fungiform taste buds.

Astringency is an everyday sensory experience best described as a dry mouthfeel typically elicited by phenol-rich alimentary products like tea and wine. The neural correlates and cellular mechanisms of astringency perception are still not well understood. We explored taste and astringency perception in human subjects to study the contribution of the taste as well as of the trigeminal sensory system to astringency perception. Subjects with either a lesion or lidocaine anesthesia of the Chorda tympani taste nerve showed no impairment of astringency perception. Only anesthesia of both the lingual taste and trigeminal innervation by inferior alveolar nerve block led to a loss of astringency perception. In an in vitro model of trigeminal ganglion neurons of mice, we studied the cellular mechanisms of astringency perception. Primary mouse trigeminal ganglion neurons showed robust responses to 8 out of 19 monomeric phenolic astringent compounds and 8 polymeric red wine polyphenols in Ca(2+) imaging experiments. The activating substances shared one or several galloyl moieties, whereas substances lacking the moiety did not or only weakly stimulate responses. The responses depended on Ca(2+) influx and voltage-gated Ca(2+) channels, but not on transient receptor potential channels. Responses to the phenolic compound epigallocatechin gallate as well as to a polymeric red wine polyphenol were inhibited by the Gαs inactivator suramin, the adenylate cyclase inhibitor SQ, and the cyclic nucleotide-gated channel inhibitor l-cis-diltiazem and displayed sensitivity to blockers of Ca(2+)-activated Cl(-) channels., (© The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Objective: To evaluate whether regenerated fungiform taste buds after severing the chorda tympani nerve can be detected by confocal laser scanning microscopy in vivo., Study Design: Retrospective study., Setting: University hospital., Patients: Six patients with a normal gustatory function (Group 1), 9 patients with taste function recovery after severing the CTN (Group 2), and 5 patients without taste function recovery (Group 3) were included. In Groups 2 and 3, canal wall up (closed) tympanoplasty or canal wall down with canal reconstruction tympanoplasty was performed in all patients., Intervention: Diagnostic., Main Outcome Measures: The severed nerves were readapted or approximated on the temporalis muscle fascia used to reconstruct the eardrum during surgery. Preoperative and postoperative gustatory functions were assessed using electrogustometry. Twelve to 260 months after severing the CTN, the surface of the midlateral region of the tongue was observed with a confocal laser microscope., Results: EGM thresholds showed no response 1 month after surgery in all patients of Groups 2 and 3. In Group 2, EGM thresholds showed recovery 1 to 2 years after surgery and before confocal microscopy (-1.3 ± 6.5 dB). There was a significant difference between Group 1 (-5.7 ± 2.0 dB; p < 0.01) and Group 2. In Group 3, EGM thresholds showed no response for more than 2 years. In the control group (Group 1), 0 to 16 taste buds were observed in each FP, and 55 (79.7%) of 69 FP contained at least 1 taste bud. The mean number of taste bud per papilla was 3.7 ± 3.6. In patients with a recovered taste function (Group 2), 0 to 8 taste buds were observed in each FP. In this group, 54 (56.2%) of 94 FP contained at least 1 taste bud. The mean number of taste bud per papilla was 2.0 ± 2.2 (p < 0.01). In Group 3, without recovery, the FP was atrophied, and no taste bud was observed., Conclusion: Regenerated fungiform taste bud could be observed in vivo using confocal laser scanning microscopy, indicating that regenerated taste bud can be detected without biopsy.

Objective: To establish clinical tests for measurement of trigeminal sensitivity on the human tongue and objectively assess changes in oral trigeminal sensitivity and taste ability after chorda tympani nerve (CTN) injury., Study Design: Prospective study., Setting: University hospital., Patients: One-hundred and twenty-six patients with unilateral middle ear diseases who underwent primary middle ear surgery., Main Outcomes and Measures: Trigeminal sensation was measured each operated side as well as nonoperated side both before and 14 days after surgery using 3 kinds of tests: Semmes-Weinstein sensory test (SW test), 2-point discrimination test, and the electrostimulator test. Taste function was assessed with electrogustometry (EGM) similarly., Results: The patients which the CTN was not touched (n = 6) showed no differences between preoperative and postoperative thresholds in any tests. In the patients with sectioned CTN (n=30), postoperative thresholds on the operated side were significantly higher than preoperative thresholds on the electrostimulator test, 2-point discrimination test, and EGM. In the patients with manipulated but not sectioned CTN (n = 90), postoperative thresholds were significantly higher than preoperative thresholds on the electrostimulator test and EGM. The patients with manipulated but not sectioned CTN and abnormal EGM postoperative thresholds (n = 48) showed that postoperative thresholds were significantly higher than preoperative thresholds in all tests., Conclusion: These findings suggest that the electrostimulator test was most useful to objectively assess small changes of trigeminal sensation among the 3 tests. The finding that trigeminal sensitivity of the tongue deteriorated on the operated side after CTN injury suggests that CTN function affected both taste sensation and trigeminal sensation of the tongue.

Objective: Sensory information plays an important role to determine psycho-emotional behaviours of individuals. Lingual nerve can be damaged by dental surgery or trauma, such as physical irritation, radiation, chemotherapy, or viral infection. This study was conducted to examine the psycho-emotional effects of lingual nerve damage in which oral sensory relay to the brain is disrupted., Design: Male Sprague-Dawley rats were tested for anxiety and depression-related behaviours after bilateral transections of the lingual and chorda tympani nerves (Nx) or sham operation. Tissue contents of serotonin and its metabolite in the hippocampus, hypothalamus, and nucleus accumbens were analyzed by high-performance liquid chromatography., Results: Sucrose preference was reduced in Nx rats compared with sham rats, suggesting the development of anhedonia, decreased pleasure seeking behaviour, by the lingual nerves transection. Ambulatory activity was decreased, anxiety-related behaviours during the activity test increased, time spent in the open arms during elevated plus maze test decreased, and immobility duration during forced swim test increased in Nx rats compared with sham rats. Serotonin level in the hippocampus of Nx rats was decreased significantly compared with sham rats., Conclusions: Results suggest that aberration of oral sensory relay to brain may lead to the development of depression- and anxiety-related disorders, and decreased serotonergic neurotransmission in the hippocampus may play a role in its underlying mechanism., (Copyright © 2013 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Objectives: The chorda tympani nerve (CTN) is at risk of damage during cochlear implantation, especially during posterior tympanotomy. The aim of this study was, therefore, to elicit the risk of taste disorders following cochlear implantation surgery involving a mastoidectomy and a posterior tympanotomy approach., Method: Twenty-six patients underwent a taste test before, 3 days after, and 6 weeks after cochlear implantation surgery. The taste sensations - sweet, sour, salt and bitter - were determined. Patients' self-ratings of taste function were also obtained. In addition, the surgeons provided information concerning the intraoperative status of the CTN., Results: In total, 19.2% (5 of 26) of the patients had postoperative taste dysfunction, as measured either subjectively or objectively or both. One of these five individuals had taste disturbance as assessed by both subjective and objective measures; in another, it was merely reported subjectively. Three patients were subjectively asymptomatic but the postoperative taste test revealed a dysfunction. Sixteen percent of the patients in whom the CTN was reported to be preserved intraoperatively had a postoperative taste dysfunction. Although the CTN was rerouted in five patients, only two of them (40%) had transient gustatory dysfunction. In two of those patients with postoperative taste dysfunction, the CTN was not intraoperatively exposed (being protected by bone) despite these individuals' experiencing postoperative taste problems. The recovery rate was 100% at 6 weeks after surgery., Conclusion: Our study indicates that cochlear implantation entails only a minimal risk of taste dysfunction and that this is chiefly a transient problem.

Purpose: The aim of this study is to call attention to the role that radioactive iodine ((131)I) and stapes surgery may play in causing hyposalivation., Materials and Methods: The manner in which (131)I and stapes surgery can cause salivary damage was reviewed. A case report is presented to illustrate the involved pathophysiology., Results: The case report clearly shows the significant injury to the parotid glands caused by the (131)I. However, subjective symptoms of oral dryness only developed after injury to the chorda tympani nerve (CTN) during stapes surgery., Conclusions: The loss of function of both parotid glands after (131)I therapy for thyroid cancer was initially compensated by the secretions of the more radiation-resistant submandibular and sublingual salivary glands (SMSG/SLSG). Damage to the CTN's secretory fibers in one SMSG/SLSG complex led to subjective oral dryness by accentuating an existing objective hyposalivation., (Copyright © 2013 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)

The loss of taste is a common symptom and may have serious somatic and psychological consequences. Little attention is paid to the condition in doctors' practices, however, and the topic is also hardly mentioned in scientific publications. It is important to distinguish between isolated gustatory loss and gustatory loss in combination with other neurological symptoms. Isolated gustatory loss can be the result of a laesion of the chorda tympani of the facial nerve caused by otitis media or damage to the taste buds, for example. Treatment is aimed at removing the cause, e.g. medication or chronic otitis media, but the treatment options are often limited. Zinc supplementation in patients with zinc deficiency has not been proven to be effective. Gustatory loss in combination with other neurological symptoms is caused by damage to one or more cranial nerves, to the brain stem or cerebral cortex, and is an indication for referral to a neurologist. Early detection of the loss of taste, good patient counselling, diagnostics and possible treatment may limit the negative consequences of this condition.

Objective: To compare the incidence of regeneration of the chorda tympani nerve (CTN) and taste function recovery between pediatric and adult patients after severing the CTN., Study Design: Retrospective study., Setting: University hospital., Patients: Consecutive 31 pediatric patients and 61 adult patients who underwent staged tympanoplasty (86 patients) or reoperation (6 patients) because of chronic otitis media with (89 patients) or without cholesteatoma (3 patients) and whose CTN was severed during primary surgery were included., Intervention: Therapeutic., Main Outcome Measures: The severed nerves were readapted or approximated on the temporalis muscle fascia used to reconstruct the eardrum. During secondary surgery, we tried to detect regenerated CTN. Preoperative and postoperative gustatory function was assessed using electrogustometry., Results: Regenerated CTN was detected during secondary surgery in 58.1% (18/31) of pediatric patients and 31.1% (19/61) of adults (p < 0.05). However, the number of patients with preoperatively elevated electrogustometry threshold was greater in adult patients. When the subjects were limited to those with preoperatively normal taste function, there was no significant difference between the 2 groups. Among patients with CTN regeneration, the incidence of taste function recovery was higher (12/18; 66.7%) in children than that (6/19; 31.6%) in adults (p < 0.05). However, there was no significant difference when the subjects were limited to those with preoperatively normal taste function., Conclusion: Chronic inflammation may not severely affect the CTN in pediatric patients, resulting in higher incidences of CTN regeneration and gustatory function recovery after severing the nerve, compared with those in adult patients.

Sweetness signals the nutritional value of food and may moreover be accompanied by a sensory suppression that leads to higher pain tolerance. This effect is well documented in infant rats and humans. However, it is still debated whether sensory suppression is also present in adult humans. Thus, we investigated the effects of sweet taste on the perception of the painful trigeminal stimulus capsaicin in two groups of healthy adult human subjects. A solution of 100 μM capsaicin was applied to the tip of the subject's tongues in order to stimulate trigeminal Aδ- and C-fiber nociceptors. When swallowed, 1M sucrose reduced the capsaicin-induced burning sensation by 29% (p ≤ 0.05) whereas a solution of similar taste intensity containing 1 μM quinine did not. Similarly, sucrose application to the frontal hemitongue suppressed the perception of the burning sensation induced by contralaterally applied capsaicin by 25% (p ≤ 0.01). We furthermore investigated the effects of documented unilateral transection of the chorda tympani nerve on capsaicin perception. In accordance with the ipsi-to-contralateral effect of sucrose on capsaicin perception in healthy subjects, hemiageusic subjects were more sensitive for capsaicin on the tongue contralateral to the taste nerve lesion (+38%; p ≤ 0.01). Taken together, these results argue I) for the existence of food intake-induced sensory suppression, if not analgesia, in adult humans and II) a centrally mediated suppression of trigeminal sensation by taste inputs that III) becomes disinhibited upon peripheral taste nerve lesion., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The chorda tympani (CT) nerve innervates lingual taste buds and is susceptible to damage during dental and inner ear procedures. Interruption of the CT results in a disappearance of taste buds, which can be accompanied by taste disturbances. Because the CT usually regenerates to reinnervate taste buds successfully within a few weeks, a persistence of taste disturbances may indicate alterations in central nervous function. Peripheral injury to other sensory nerves leads to glial responses at central terminals, which actively contribute to abnormal sensations arising from nerve damage. Therefore, the current study examined microglial and astrocytic responses in the first central gustatory relay, the nucleus of the solitary tract (nTS), after transection of the CT. Damage to the CT resulted in significant microglial responses in terms of morphological reactivity and an increased density of microglial cells from 2 to 20 days after injury. This increased microglial population resulted primarily from microglial proliferation from 1.5 to 3 days, which was supplemented by microglial migration within subdivisions of the nTS between days 2 and 3. Unlike other nerve injuries, CT injury did not result in recruitment of bone marrow-derived precursors. Astrocytes also reacted in the nTS with increased levels of glial fibrillary acidic protein (GFAP) by 3 days, although none showed evidence of cell division. GFAP levels remained increased at 30 days, by which time microglial responses had resolved. These results show that nerve damage to the CT results in central glial responses, which may participate in long-lasting taste alterations following CT lesion., (Copyright © 2012 Wiley Periodicals, Inc.)

Chorda tympani nerve transection (CTX) has been useful to study the relationship between nerve and taste buds in fungiform papillae. This work demonstrated that the morphological integrity of taste buds depends on their innervation. Considerable research focused on the effects of CTX on peripheral gustatory structures, but much less research has focused on the central effects. Here, we explored how CTX affects ganglion cell survival, maintenance of injured peripheral axons, and the chorda tympani nerve terminal field organization in the nucleus of the solitary tract (NTS). After CTX in adult rats, the chorda tympani nerve was labeled with biotinylated dextran amine at 3, 7, 14, 30, and 60 days post-CTX to allow visualization of the terminal field associated with peripheral processes. There was a significant and persistent reduction of the labeled chorda tympani nerve terminal field volume and density in the NTS following CTX. Compared with controls, the volume of the labeled terminal field was not altered at 3 or 7 days post-CTX; however, it was significantly reduced by 44% and by 63% at 30 and 60 days post-CTX, respectively. Changes in the density of labeled terminal field in the NTS paralleled the terminal field volume results. The dramatic decrease in labeled terminal field size post-CTX cannot be explained by a loss of geniculate ganglion neurons or degeneration of central axons. Instead, the function and/or maintenance of the peripheral axonal process appear to be affected. These new results have implications for long-term functional and behavioral alterations., (Copyright © 2012 Wiley Periodicals, Inc.)

The peripheral taste system remains plastic during adulthood. Sectioning the chorda tympani (CT) nerve, which sends sensory information from the anterior tongue to the central nervous system, causes degeneration of distal fibers and target taste buds. However, taste function is restored after about 40 days in young adult rodents. We tested whether aging impacts the reappearance of neural responses after unilateral CT nerve injury. Taste bud regeneration was minimal at day 50-65 after denervation, and most aged animals died before functional recovery could be assessed. A subset (n=3/5) of old rats exhibited normal CT responses at day 85 postsectioning, suggesting the potential for efficient recovery. The aged taste system is fairly resilient to sensory receptor loss and major functional changes in normal aging. However, injury to the taste system reveals a surprising vulnerability in old rodents. The gustatory system provides an excellent model to study mechanisms underlying delayed recovery from peripheral nerve injury. Strategies to accelerate recovery and restore normal function will be of interest, as the elderly population continues to grow., (Copyright © 2012 IBRO. Published by Elsevier Ltd. All rights reserved.)

Objective: We investigated gustatory changes in patients with chronic otitis media, before and after middle-ear surgery., Methods: This prospective study included 38 patients with unilateral chronic otitis media. We used taste testing solutions to evaluate each patient's taste function. Intra-operative assessments of the chorda tympani nerve were also compared and analysed., Results: Patients with chronic otitis media had significantly worse ipsilateral perception of sour, bitter and salty tastes. In patients with good intra-operative preservation of the chorda tympani nerve, there was significant improvement in gustatory function one month post-operatively, compared with the pre-operative baseline. In patients who sustained intra-operative chorda tympani nerve injury, one month post-operative gustatory function was the same as the pre-operative baseline., Conclusion: Middle-ear surgery for chronic otitis media not only treats the ear but also improves gustatory function in the majority of patients. In patients with intra-operative injury to the chorda tympani nerve, post-operative taste decline is only temporary.

Calcium intake depends on orosensory factors, implying the presence of a mechanism for calcium detection in the mouth. To better understand how information about oral calcium is conveyed to the brain, we examined the effects of chorda tympani nerve transection on calcium chloride (CaCl(2)) taste preferences and thresholds in male Wistar rats. The rats were given bilateral transections of the chorda tympani nerve (CTX) or control surgery. After recovery, they received 48-h two-bottle tests with an ascending concentration series of CaCl(2). Whereas control rats avoided CaCl(2) at concentrations of 0.1mM and higher, rats with CTX were indifferent to CaCl(2) concentrations up to 10mM. Rats with CTX had significantly higher preference scores for 0.316 and 3.16 mM CaCl(2) than did control rats. The results imply that the chorda tympani nerve is required for the normal avoidance of CaCl(2) solution., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Objective: To determine the immediate and long-term taste effects of chorda tympani nerve sacrifice in patients undergoing open cavity mastoidectomy., Design, Setting and Participants: A retrospective, questionnaire survey of patients receiving follow up and aural toilet following open cavity mastoidectomy, over a four-month period. The questionnaire assessed taste disturbance, both immediately post-operative and current. Available surgical records were reviewed for chorda tympani references., Results: Of 57 patients, six had undergone surgery to both ears. Of those who could recall (37/57), 24.3 per cent were aware of taste disturbance immediately after surgery, while 8.7 per cent reported current disturbance (median post-operative interval, 28.5 years; range, one month to 67 years). No bilateral surgery patients were aware of taste disturbance., Conclusion: Mastoidectomy consent procedure emphasises the risk of hearing loss and facial nerve injury, yet in open cavity surgery chorda tympani division is almost inevitable. Reassuringly, most post-operative taste disturbance resolves, and most patients are not aware of long-term disturbance. However, a small percentage suffer ongoing taste disturbance; this could be significant for professional chefs and wine-tasters. The risk of taste disturbance should be addressed in the consent procedure.

Objective: To review the currently available literature on iatrogenic injury of the adult chorda tympani., Design: Systematic literature review., Method: Five electronic databases and one search engine were used to access available English language literature on the chorda tympani, focusing on iatrogenic injury., Results: The chorda tympani is most often injured during middle-ear surgery, after which at least 15-22 per cent of patients experience symptoms, mostly changes in taste and dryness of the mouth. Numerous factors influence whether injury to the chorda tympani causes symptoms, including the extent of injury, type of surgery, age of the patient, anatomical variables and subjective adaptation. Although most patients experience gradual symptomatic recovery, complaints can be persistent and troublesome., Conclusion: Care should be taken to preserve the chorda tympani during middle-ear surgery, and to warn patients pre-operatively about this potential complication. This is particularly important if surgery is bilateral.

Objective: The chorda tympani is at risk of iatrogenic injury throughout its course. This paper reviews the clinical anatomy of the nerve in adults., Design: Systematic literature review., Method: Relevant English-language articles were identified using five electronic databases and one search engine. Data from approximately 70 scientific papers were supplemented with information from selected reference texts., Results: The anatomy of the chorda tympani differs from standard descriptions, particularly regarding its exit from the middle ear and area of lingual innervation. Whilst it is known to convey taste sensation from the anterior two-thirds of the tongue and parasympathetic innervation to the submandibular and sublingual salivary glands, the chorda tympani probably has additional sensory and secretomotor functions., Conclusion: A detailed understanding of the anatomy of the chorda tympani may help to reduce the risk of iatrogenic injury during head, neck and middle-ear surgery, and to explain the variable consequences of such injury.

This study was undertaken to assess dysgeusia in patients who have undergone middle ear surgery for chronic suppurative otitis media (CSOM) when the surgeon's practice was to cleanly divide the chorda tympani without prior manipulation, if it in any way hindered operative access or the aims of surgery. We wanted to determine whether lower rates of taste disturbance might be obtained by early, clean division of the nerve. We followed 110 patients prospectively and asked them to complete a postoperative dysgeusia questionnaire 1 year after surgery. The "cut nerve" group included 81 patients, and the "uncut nerve" group included 29 patients. In the uncut group, the nerve was untouched or underwent minimal handling. In the cut nerve group, 68% of patients had no taste disturbance after surgery; 4% of patients in this group had ongoing symptoms at 1 year postoperatively. In the uncut nerve group, 67% were asymptomatic, while 11% had ongoing taste disturbance at 1 year. Statistical analysis of symptoms beyond 1 year showed a mean difference of 7%, but this is not statistically significant (p = 0.38). These results suggest that early division of the chorda tympani without prior manipulation in patients with chronic suppurative otitis media does not result in higher rates of taste disturbance than in patients with uncut nerves. Indeed rates of taste disturbance in our cut group were lower than in the uncut group, and lower than or comparable to those seen in other studies.

Effects of gustatory nerve transection on salt taste have been studied extensively in rats and hamsters but have not been well explored in the mouse. We examined the effects of chorda tympani (CT) nerve transection on NaCl taste preferences and thresholds in outbred CD-1 mice using a high-throughput phenotyping method developed in our laboratory. To measure taste thresholds, mice were conditioned by oral self-administration of LiCl or NaCl and then presented with NaCl concentration series in 2-bottle preference tests. LiCl-conditioned and control NaCl-exposed mice were given bilateral transections of the CT nerve (LiCl-CTX, NaCl-CTX) or were left intact as controls (LiCl-CNT, NaCl-CNT). After recovery from surgery, mice received a concentration series of NaCl (0-300 mM) in 48-h 2-bottle tests. CT transection increased NaCl taste thresholds in LiCl-conditioned mice and eliminated avoidance of concentrated NaCl in control NaCl-exposed mice. This demonstrates that in mice, the CT nerve is important for detection and recognition of NaCl taste and is necessary for the normal avoidance of high concentrations of NaCl. The results of this experiment also show that the method of high-throughput phenotyping of salt taste thresholds is suitable for detecting changes in the taste periphery in mouse genetic studies.

Objective: To evaluate the relationship between the length of nerve gap defects, incidence of nerve regeneration, and recovery of gustatory function after severing the chorda tympani nerve (CTN)., Study Design: Retrospective study., Setting: University hospital., Patients: Eighty-eight consecutive patients whose CTNs were severed during primary surgery and who underwent secondary surgery were included. Proximal and distal stumps of severed nerves were readapted or approximated during surgery., Intervention: Therapeutic., Main Outcome Measures: Before and after surgery, the taste function was periodically evaluated using electrogustometry. Nerve gaps were classified into 4 groups: readaptation (Group 1), 1 to 3 mm (Group 2), 4 to 6 mm (Group 3), and more than 7 mm (Group 4)., Results: Regenerated nerves in the tympanic segment were detected in 36 (41%) of the 88 patients during secondary surgery. The incidence of nerve regeneration was 100% (10/10) in Group 1, 45% (10/22) in Group 2, 47% (9/19) in Group 3, and 19% (7/37) in Group 4. There was a significant difference between the length of nerve gap defects and incidence of nerve regeneration (p < 0.001). In the 36 patients with a regenerated CTN, the incidence of gustatory function recovery was 60% (6/10) in Group 1, 50% (5/10) in Group 2, 56% (5/9) in Group 3, and 43% (3/7) in Group 4. There was no significant difference between the length of nerve gap defects and incidence of taste function recovery., Conclusion: Reconstruction of a severed CTN is very important for regeneration. However, the regenerated CTN in the tympanic segment does not always reinnervate the fungiform papillae.

There is growing evidence of heterogeneity among responses to bitter stimuli at the peripheral, central and behavioral levels. For instance, the glossopharyngeal (GL) nerve and neurons receiving its projections are more responsive to bitter stimuli than the chorda tympani (CT) nerve, and this is particularly true for some bitter stimuli like PROP & cycloheximide that stimulate the GL to a far greater extent. Given this information, we hypothesized that cutting the GL would have a greater effect on behavioral avoidance of cycloheximide and PROP than quinine and denatonium, which also stimulate the CT, albeit to a lesser degree than salts and acids. Forty male SD rats were divided into four surgery groups: bilateral GL transection (GLX), chorda tympani transection (CTX), SHAM surgery, and combined transection (CTX + GLX). Postsurgical avoidance functions were generated for the four bitter stimuli using a brief-access test. GLX significantly compromised avoidance compared to both CTX and SHAM groups for all stimuli (p < .02), while CTX and SHAM groups did not differ. Contrary to our hypothesis, GLX had a greater effect on quinine than cycloheximide (mean shift of 1.02 vs. 0.27 log10 units). Moreover, combined CTX + GLX transection shifted the concentration-response function further than GLX alone for every stimulus except cycloheximide (ps < .03), suggesting that the GSP nerve is capable of maintaining avoidance of this stimulus to a large degree. This hypothesis is supported by reports of cycloheximide-responsive cells with GSP-innervated receptive fields in the NST and PBN., ((PsycINFO Database Record (c) 2011 APA, all rights reserved).)

To investigate the effects of chorda tympani section on submandibular gland size and function in the early (postoperative day 7) and late (postoperative month 6) postoperative period by ultrasonography, scintigraphy, and biochemical analysis of the saliva patients with unilateral chronic otitis media. One-hundred and thirty patients (46 males and 84 females) who were ≥16 years of age and diagnosed with unilateral chronic otitis media and for whom type 1 tympanoplasty was indicated in 1st Outpatient Clinic of Kartal Dr. Lutfi Kirdar Training and Research Hospital between August 2004 and February 2007 were enrolled in the study. Of 130 patients, 102 patients who were eligible and gave written approval were included in the study. However, of these patients 99 underwent type 1 tympanoplasty and 3 had a canal down mastoidectomy. In 99 patients, chorda tympani nerves of 16 were cut, but 3 patients had to be excluded due to allergic reactions. Before the operation, bilateral submandibular gland ultrasonography was performed on all patients and the anterior-posterior length, the frontal lateral-medial width (transverse), and the paramandibular depth of both submandibular glands were measured. In scintigraphic examinations, perfusion index (PI), uptake ratio and excretion fraction were measured. Then, in biochemical analysis of the saliva the levels of sodium, potassium, chloride, calcium, magnesium, amylase, and the values of pH and density were assessed by the saliva collection through Wharton duct. In the statistical comparison of operated and healthy side of the patients with respect to these parameters Mann-Whitney U test, and in intragroup analysis Wilcoxon test was used. The volume of the submandibular gland of the operated side was significantly lower compared to the healthy side in postoperative month 6 (P < 0.05). According to the baseline volume of the submandibular gland of the healthy side, the increase in postoperative day 7 and month 6 were found to be statistically insignificant (P > 0.05). According to the baseline PI value, the decreases in the PI value in the postoperative day 7 and postoperative month 6 were statistically significant (P < 0.01). The uptake ratio of the patients was lower in the postoperative day 7 and month 6 than those at the baseline; however, the difference was statistically insignificant (P > 0.05). The excretion fraction values in the postoperative day 7 were significantly lower than the baseline values (P < 0.05), whereas the decrease in the EF values in the postoperative month 6 were statistically insignificant (P > 0.05). In conclusion, the present study was the first in the literature in which three parameters of assessment, such as ultrasonography, scintigraphy, and biochemical analysis, were used to determine the changes in submandibular gland size and function following the chorda tympani section. After chorda tympani section, the volume of submandibular gland decreased in the late postoperative period. Moreover, chorda tympani section led to decrease in the saliva secretion and the PI value of the patients in the early and late postoperative period.

Objectives: Loss of taste function was studied pre- and postoperatively in patients who underwent myringoplasty., Patients and Methods: Thirty-two patients who were diagnosed with chronic otitis media and underwent myringoplasty between May 2007 and May 2009 were included in the study. Regional taste test was performed preoperatively and two weeks after the operation in all patients planned to undergo myringoplasty. For patients describing disturbance in the postoperative taste test or in the questionnaire form, the taste test was repeated at six months after the operation and the questionnaire form was completed., Results: Chorda tympani was preserved in 18 patients (56.2%), traumatized in nine patients (28.1%), and cut completely in five patients (15.7%). Totally in 10 out of 32 patients (31.2%), an disturbance in the taste test was found at two weeks postoperatively. Sweetness/saltiness, bitterness, and sourness taste disturbances were found in 10, nine, and two patients, respectively. Improvements were identified in two out of 10 patients in the taste test performed at six months. The disturbances in the taste tests of eight patients continued to exist at that time. Sweetness/saltiness, bitterness, and sourness taste disturbances were found in eight, seven and two patients, respectively., Conclusion: The chorda tympani nerve may be traumatized or completely cut as a complication of ear surgery. Sacrificing the nerve, where it is highly traumatized by surgical devices, reduces the duration of postoperative complaints.

Objective: To investigate the effect of sensory or motor nerve damage to the tongue using a mouse model., Study Design: Animal study., Setting: Research laboratory., Subjects and Methods: Adult male and female mice from inbred strains B6 (n = 19) and D2 (n = 25). Following lick training, bilateral lingual-chorda tympani nerve cuts (LX) (n = 6 B6, n = 7 D2), unilateral hypoglossal nerve cuts (HX) (n = 7 B6, n = 9 D2), or sham surgery (n = 6 B6, n = 9 D2) was performed. Mice were lick tested postsurgically with both water and sucrose (4 days total). Following testing, post mortem dissections and microscopic analysis of tongue papillae were performed., Results: In both strains, HX and LX mice demonstrated a significant reduction in volume per lick (VPL) in the surgical groups relative to shams. Neither motor nor sensory nerve transection affected local lick rate. In most LX mice in both strains, taste papillae were reduced compared with HX or sham mice., Conclusion: Mice of either strain with either a sensory or a motor nerve injury have a significant loss of VPL during ingestion of either a neutral (water) or preferred (sucrose) stimulus. This reduction in VPL reflects a deficit in licking. Lick rate was not affected by deafferentation. A reduction in fungiform papillae following LX but not HX mice was noted.

Chorda tympani denervation (CTD) of rats was earlier shown to result in loss of submandibular gland (SMG) weight (at only 1 wk) and in continued reduction in aquaporin 5 (AQP5) protein expression (until 4 wk), without affecting its mRNA synthesis (Li X, Azlina A, Karabasil MR, Purwanti N, Hasegawa T, Yao C, Akamatsu T, Hosoi K. Am J Physiol Gastrointest Liver Physiol 295: G112-G123, 2008). The present study indicated that despite elevation of bax, a proapoptosis protein, by CTD, the operation also increased the level of bcl-2, an antiapoptosis protein, in the SMG. Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL assay) showed no increase in the number of apoptotic cells in the SMG. CTD, however, induced strongly and transiently (at 1-3 days) the protein expression of LC3B-II, a marker protein of autophagosomes, suggesting that the reduction in the gland weight was due to onset of autophagy by CTD. Upon CTD, Lamp2, a lysosomal marker, gradually increased in amount, reaching a peak at the 14th day. Immunohistochemical analysis revealed an increase in the number of lysosome-like structures positive for both AQP5 and Lamp2 in the acinar cells of the SMG after CTD; similar changes were observed also for AQP5 and LC3Bs. These data suggest that AQP5 in the SMG entered autophagosomes and/or lysosomes for degradation upon CTD. In vitro AQP5-degrading activity was found in the SMG extracts, and such activity was shown to be increased by CTD. Inhibitor experiments implied cathepsins B and L to be candidate enzymes for this degradation under normal and CTD conditions, respectively.

Introduction: Chorda tympani injury as a complication of middle-ear surgery has been extensively studied with regard to its effects upon taste. However, the chorda tympani also carries parasympathetic fibres to the salivary glands of the oral cavity. To date, little has been reported about the effect of chorda tympani section upon salivary function., Setting: Tertiary care centre., Material and Methods: We report a case series of three patients with bilateral chorda tympani lesions. Chorda tympani function was assessed using 'taste strips' and unstimulated sialometry. A careful history of oral symptoms was taken., Results: All patients showed transient or permanent bilateral ageusia of the anterior two-thirds of the tongue, and a decreased resting salivary flow rate. In addition, all patients suffered from transient or persistent, distressing xerostomia., Conclusion: Taste disorders may occur after middle-ear surgery but they are mostly transient, even when the chorda tympani nerves are sectioned bilaterally. In contrast, bilateral chorda tympani lesions may lead to severe, persistent and distressing xerostomia. Based on this neglected aspect of chorda tympani function, we emphasise the importance of preserving the chorda tympani whenever possible.

The adult peripheral taste system is capable of extensive functional plasticity after injury. Sectioning the chorda tympani (CT), a primary sensory afferent nerve, elicits transient changes in the uninjured, contralateral population of taste receptor cells. Remarkably, the deficits are specific to the sodium transduction pathway. Normal function is quickly restored in the intact nerve, in parallel with an influx of macrophages to both the denervated and uninjured sides of the tongue. However, changing the dietary environment by restricting sodium blocks the macrophage response and prolongs functional alterations. Since the functional deficits occur before macrophages are present in the peripheral taste system, we hypothesized that neutrophils play a role in modulating neural responses in the intact CT. First, the dynamics of the neutrophil response to nerve injury were analyzed in control-fed and sodium-deficient rats. Nerve sectioning briefly increased the number of neutrophils on both the denervated and uninjured sides of the tongue. The low-sodium diet amplified and extended the bilateral neutrophil response to injury, in parallel with the persistent changes in sodium taste function. To test the impact of neutrophils on taste function, we depleted these cells prior to nerve sectioning and recorded neural responses from the intact CT. This treatment restored normal sodium responses in the uninjured nerve. Moreover, recruiting neutrophils to the tongue induced deficits in sodium taste function in both CT nerves. Neutrophils play a critical role in ongoing inflammatory responses in the oral cavity, and may induce changes in taste perception. We also suggest that balanced neutrophil and macrophage responses enable normal neural responses after neural injury., (Copyright 2010 IBRO. Published by Elsevier Ltd. All rights reserved.)

Background: The anatomical course of the Chorda tympani nerve (CTN) in the middle ear is known to be very variable, which becomes most obvious during middle ear operations. As well, postoperative gustatory dysfunction belongs to the most frequent complications after otosurgical interventions. The aim of this study was to develop a clinical classification of the intraoperatively visible course of the CTN and to demonstrate a possible correlation of its anatomic course with the prevalence of actual postoperative taste disorders., Methods: Only cases of first-time ear surgery all operated by one experienced otosurgeon were assessed. Preoperatively, gustatory testing with standardised chemical solutions (sweet, sour, salty, bitter) was performed. During surgery the course of the CTN was classified at first sight by 3 topografical criteria: The angle (A), the height (H) and the depth (D) of the nerve's emergence from the lateral tympanic wall. In cases of postoperative taste dysfunction the patients were followed-up on a regular basis., Results: 103 patients were included in the study. The angle of the nerve;s emergence from the tympanic bone was below 30 degrees in 59 (A1), between 30 degrees and 60 degrees in 41 (A2) and within 60 degrees and 90 degrees in 3 cases (A3). The height of emergence was 33 times in the superior (H1), 61 times in the middle (H2) and 9 times in the inferior third (H3) of the posterior meatal wall. The depth of emergence lay within the plain of the tympanic sulcus in 26 individuals (D1), 44 times medially to this plain without overlapping bone (D2) and 33 times medially but covered by a bony spur (D3). The CTN was preserved in 92 procedures. Postoperatively, gustatory function was diminished in 7% of the cases., Conclusion: This study confirms the high diversity of the surgical anatomy of the CTN. According to the proposed classification the A1-H1-D2/3-situation belongs to the CTN-constellations observed most frequently. It is this very anatomical situation, that apparently tends to be associated with postoperative taste deficits quite regularly due to inevitable intraoperative manipulations. Taking into account the results of this study an otosurgeon might be able to anticipate the potential risk for the CTN by judging the AHD-status intraoperatively and - therefore - reduce taste disorders postoperatively. Additionally, the probability of a postoperative gustatory dysfunction depends upon the kind of underlying middle ear disease as well., (Georg Thieme Verlag KG Stuttgart * New York.)

The aim of this prospective non-randomized study was to evaluate the alterations in taste sensation after myringoplasty and to investigate the influence of smoking on taste. Ninety-six patients who underwent myringoplasty and 43 healthy controls were examined. Whole-mouth gustatory test solutions were sucrose (sweet); sodium chloride (salty taste); citrate (sour) taste; and quinine hydrochloride (bitter). Sucrose, citric acid, and sodium chloride recognition thresholds were high in the early postoperative period; however, they were regressed to the preoperative status in course of time. No difference was found between preoperative, early/late postoperative taste recognition thresholds of smoker and non-smoker patients. Underlay myringoplasty has little but transient effect on taste recognition in the early postoperative period. This impairment is completely recovered within 6 months. Furthermore, smoking has no effect on the taste recognition of patients with permanent tympanic membrane perforation and has no influence on the alterations in taste recognition thresholds after myringoplasty. We believe that this study will supply some additional aspects in the scope of taste disturbances due to ear surgery and smoking.

Conclusion: Most of the clinical cases experienced taste disturbance after stapes surgery, and in a few cases this disturbance persisted for a long time. The animal experiment suggested the role of geniculate ganglion (GG) cells in nerve generation., Objectives: To clinically examine taste disorder and its recovery after stapes surgery and experimentally demonstrate a role of GG., Patients and Methods: Taste function after preservation of chorda tympani nerve (CTN) in stapes surgery was prospectively investigated with a questionnaire and electrogustometry (EGM). Further, expression of neurotrophic factors in GG after injury of CTN was examined by in situ hybridization histochemistry (ISSH) and RT-PCR., Results: Among the cases, 15/18 (83.3%) were associated with taste disturbance and 6/18 (33.3%) were associated with tongue numbness 2 weeks after surgery; however, the symptoms ceased in 14/18 cases (77.8%). Two weeks after surgery, the EGM threshold was found to be elevated in 15/18 cases (83.3%), while in 10/18 cases (55.6%), it did not decrease until 1 year after surgery. Expression of ISSH and amplified bands of BDNF and GFR increased at 7 and 14 days after nerve injury in ipsilateral GGs and also increased at 7 days on the contralateral side.