Chorda Tympani Nerve Section Research Articles

BDNF is required for taste axon regeneration following unilateral chorda tympani nerve section

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.

Taste Disorders after Stapedotomy

Objective To asses temporal evolution of taste disorders after stapedotomy and its correlation with chorda tympani nerve (CTN) preservation. Methods A retrospective study was conducted at the Department of Otolaryngology-Head and Neck Surgery of the Hospital Clínico de la Universidad de Chile between 2002 and 2007. Medical records of 141 patients with otosclerosis subject to stapedotomy were analyzed in search for CTN preservation or section during stapedotomy. A survey was applied to evaluate postoperative taste function and its evolution on time. Fisher's test was applied. Results CTN was preserved in 131 patients (93%) and sectioned in 10 patients (7%). The incidence of taste disorder was 7% (10 patients) in the CTN preservation group and 20% (2 patients) in the sectioned group (p> 0.05). All patients had full recovery of taste function before 12 months after surgery, being faster in the CTN preservation group than the sectioned group (6 months vs. 12 months respectively). Patients with section of CTN have an odds ratio of 3 compared with CTN preservation patients. Conclusions Taste disorders are present in patients subjected to stapedotomy even when CTN is preserved, with full recovery 12 months after surgery.

Taste function after section of chorda tympani nerve in middle ear surgery

Objective To investigate prospectively the clinical manifestations and the functional recovery of taste after section of chorda tympani nerve (CTN) during middle ear surgery, the subjective and objective study on the patients was performed. Methods Thirty-five patients underwent surgery with unilateral ( n = 32) or bilateral ( n = 3) section of CTN between January 2000 and April 2002. The patients were asked about taste symptoms before surgery and 2 weeks and 2 years after surgery. The CTN function was also measured with electrogustometry (EGM) at the same time points. Results In unilateral section of CTN, 19/32 (59.4%) complained of taste disorder and 11/32 (34.4%) tongue numbness. Most of these taste symptoms disappeared within 2 years although the EGM threshold did not recover. 16/17 patients (94.1%) who used to cook everyday had little difficulty in flavoring dishes. In bilateral section of CTN, the patients had no problem of taste at 2 years after surgery, either. Conclusion These findings help explain the potential complications to the patients before surgery, although the number of cases was small in this series.

Lipopolysaccharide-induced up-regulation of activated macrophages in the degenerating taste system

Unilateral chorda tympani (CT) nerve section and maintenance on a sodium-restricted diet leads to a rapid decrease in neurophysiological taste responses to sodium in the contralateral, intact CT nerve. Up-regulation of immune function with lipopolysaccharide (LPS; 100 microg i.p.) induces a recovery of normal sodium taste responses, suggesting that the sodium-deficient diet is immunosuppressive. In fact, there is a bilateral increase in the number of lingual, activated macrophages in control-fed rats receiving CT nerve section that does not occur in sodium-deficient rats after sectioning. In the current study, we hypothesized that the LPS-induced recovery of normal taste function in sodium-deficient rats is based on an increase in the activated macrophage response to denervation. Rats receiving a unilateral CT nerve section, a sodium-restricted diet, and/or an injection of LPS (100 microg; i.p.) were overdosed with pentobarbital at day 2 postsectioning, and tongues were rapidly dissected and frozen. Cryosections were then immunohistochemically stained to determine the percentage of ED1 staining for activated macrophages or the number of alphabeta or gammadelta T cells. Activated macrophage levels were significantly increased in sodium-restricted rats that received LPS following unilateral CT nerve section, supporting our hypothesis. These novel findings suggest that LPS overcomes the immunosuppression induced by the sodium-restricted diet and also indicate that the immune system plays a role in regulating taste function after neural injury.

Nerve-Target Interactions in the Gustatory System Following Unilateral Chorda Tympani Nerve Section

Although much effort has been directed at examining the morphological characteristics of denervated and regenerated taste buds, relatively little is known about the physiology of reinnervated taste cells (Vintschgau and Honigschmied, 1876; Guth, 1957; Fujimoto and Murray, 1970; Cheal and Oakley, 1977; Whitehead et al., 1987). Over 25 years ago, Oakley (Cheal et al., 1977) and colleagues found that some chorda tympani fibers reinnervated fungiform papillae on the gerbil’s anterior tongue in <2 weeks post-sectioning. Studies that examined recovery of taste function following nerve damage (Cain et al., 1996; Cheal et al., 1977; Ninomiya, 1998; Yasumatsu et al., 2003) indicate that regenerated taste nerves generally recover normal function after progressing through a transitional period. Only relatively recently has the impact of environment on the adult regenerating taste system been explored. Regenerating taste receptor cells in adult rats are susceptible to dietary influences (Hill and Phillips, 1994). Sectioning the chorda tympani unilaterally in rats fed a sodium-restricted diet at adulthood resulted in a regenerated nerve that had attenuated responses to sodium salts. Responses to other stimuli were unaffected. In addition, there were other, novel effects. In the same rat, the contralateral, uncut nerve was supersensitive to sodium salts. The supersensitivity developed progressively following an initial

Taste function after section of chorda tympani nerve in middle ear surgery

Objectives: We already reported that taste disturbance occurred more frequently after preservation of chorda tympani nerve (CTN) than after section of CTN, especially in cases of otosclorosis, and that younger patients showed higher recovery rate of CTN function than older ones. In the present study, we examined taste function after the section of CTN in middle ear surgery. Methods: Fifty-nine patients were followed up more than 2 years after section of CTN on unilatreral side (42 ears) or on both sides (34 ears) from 1999 to 2002. They aged from 7 to 63 years with a mean of 46.2 years, and they consisted of 63 ears of cholesteatoma, 6 ears of adhesive otitis media and 7 ears of chronic otitis media. Taste function was evaluated by electrogustometry (EGM) and questionnaire. Results: The threshold of EGM was still much elevated 2 years after surgery either in unilatreral or bilateral section of CTN. Interestingly, the area with no response of EGM became smaller in patients below 10 years old with the time, but it was the same in middle and old aged patients. In the questionnaire, symptoms of taste disturbance or tongue numbness ceased 3–12 months (mean, 7.2 months) after unilateral section of CTN and they ceased 1–12 months (mean, 6.7 months) after bilateral section of CTN. Conclusion: These findings suggested that CTN of the opposite side might compensate taste function in case of unilatreral section, and that glossopharyngeal nerve might compensate it in case of bilateral section.

Sympathetic mediation of salivation induced by intracerebroventricular pilocarpine in rats

Central cholinergic activation by pilocarpine induces salivation dependent on the integrity of forebrain areas. The present work investigates the autonomic mediation of this salivation. Pilocarpine (500 nmol/rat) was injected into the lateral ventricle (LV) of tribromoethanol-anesthetized adult male rats. Preweighed cotton balls were inserted into the oral cavity and weighed again 7 min later. α-Adrenoceptor antagonists (3–50 μmol/kg) prazosin (α 1), yohimbine (α 2) or propranolol (β) injected intraperitoneally (i.p.) produced, 80%, 20% and 0% inhibition respectively of the LV pilocarpine-induced salivation. Intracerebroventricular injections (160 nmol) of the antagonists did not alter the effects of pilocarpine injected into the LV. Bilateral section of chorda tympani nerve or bilateral sympathetic cervical ganglionectomy produced 0% and 40% inhibition of pilocarpine-induced salivation, respectively. Ganglionectomy did not alter salivation induced by i.p. injection of pilocarpine (4 μmol/kg). The results indicate that there is a large sympathetic contribution to the salivation induced by central cholinergic activation.

Novel regulation of peripheral gustatory function by the immune system.

Soon after adult rats receive unilateral chorda tympani nerve section in combination with dietary sodium restriction, neural taste responses recorded from the intact, contralateral chorda tympani nerve are substantially reduced. We hypothesized that the immune system is compromised in sodium-restricted rats, which leads to functional alterations in the peripheral taste system after neural injury. Here, immune function was stimulated with a systemic injection of lipopolysaccharide (LPS), and neurophysiological responses were recorded from the uncut chorda tympani 4-10 days after nerve section to determine if normal sodium sensitivity was restored. Rats receiving nerve section, dietary sodium restriction, and LPS exhibited normal sodium responses. In intact rats, injection of LPS alone or LPS injection combined with sodium restriction had no effect on taste responses to sodium stimuli. Surprisingly, combining nerve section, LPS injection, and maintenance of rats on a normal diet induced supersensitive responses to sodium. These findings are the first to demonstrate that the immune system can regulate peripheral gustatory function.

Salt discriminability is related to number of regenerated taste buds after chorda tympani nerve section in rats.

Transection of the chorda tympani nerve (CTX) impairs taste-guided discrimination of NaCl from KCl in rats. We wanted to determine whether this discrimination recovers after chorda tympani regeneration. Experiment 1 showed that few taste buds regenerated 14 days after CTX, whereas substantial regeneration occurred 42 days after surgery. Experiment 2 demonstrated that rats trained before CTX could clearly discriminate the two salts when tested starting 49 days after surgery, whereas rats tested starting 8 days after surgery were severely impaired in this task. Rats tested starting 28 days after CTX were unimpaired, moderately impaired, or severely impaired on the discrimination task. Overall, discrimination performance was significantly related to the number of regenerated taste buds. Unilaterally transected rats tested shortly after surgery were nearly as competent as controls. These results indicate that rats can recover the ability to discriminate NaCl from KCl after regeneration of anterior tongue taste buds.

Parasympathetic-mediated reflex salivation and vasodilatation in the cat submandibular gland

The aim of the present study was to compare and characterize the secretory and vasodilator effects induced by chorda lingual nerve (CLN) stimulation (i.e., direct parasympathetic stimulation) and reflex parasympathetic stimulation in the submandibular gland (SMG) of sympathectomized cats. The increase in blood flow and salivary secretion in response to electrical stimulation of the central cut ends of the vagus and inferior alveolar nerves, as well as to stimulation of the CLN at a site approximately 5 mm distal to the intersection of the CLN and the SMG duct (site D) was completely abolished by section of the chorda tympani nerve (CTN). Neither response to CLN stimulation at a site nearly 5 mm proximal to the intersection of the CLN and the SMG duct (site C) was affected by CTN section. Section of the CLN at a site approximately 5 mm distal to the intersection of the CTN and the CLN abolished the submandibular salivary and vasodilator responses elicited by CLN stimulation at site D but had no effect on the two responses evoked by CLN stimulation at site C. The blood flow increases evoked by electrical stimulation of the CLN at site D were greatly reduced by prior treatment with the autonomic ganglion blocker hexamethonium, but the vasodilator responses evoked from site C were reduced much less. These data suggest that the secretory and vasodilator responses elicited by CLN stimulation at site D and those by vagus and inferior alveolar nerve stimulation are mediated largely via a parasympathetic reflex mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

The contribution of gustatory nerve input to oral motor behavior and intake-based preference. I. Effects of chorda tympani or glossopharyngeal nerve section in the rat

Two-bottle intake tests and taste reactivity (TR) tests were used to reveal whether changes in ingestive behavior would follow bilateral section of either the chorda tympani (CT) or the glossopharyngeal (GP) nerve. Rats received two-bottle intake tests to compare 24-h ingestion of water to that of NaCl, MgCl 2, quinine, or sucrose. Prior to each long-term intake test, rats received a 1 min, 1 ml intraoral infusion of the same chemical stimulus. Ingestive and aversive oral motor responses elicited by these 1 ml infusions were videotaped and subsequently analyzed. GP-section did not alter quinine or sucrose preference; overall, preference of MgCl 2 and NaCl was also similar to controls. In contrast, TR tests in GP-sectioned rats revealed that most quinine, MgCl 2 and NaCl stimuli elecited significantly fewer aversive oral motor responses. In addition, the latency of aversive responses to these 3 chemical stimuli was increased for these rats. Intake-based preference tests failed to show any difference between rats with CT nerve section and controls. In TR tests, however, CT-sectioned rats displayed significantly fewer ingestive oral motor responses to NaCl, MgCl 2, and quinine than controls. Neither sucrose intake nor sucrose-elicited TR were altered by CT or GP nerve section. This report confirms the failure of long-term intake tests to uncover behavioral deficits following the section of gustatory nerves. In contrast, the use of a different behavioral test makes clear for the first time that gustatory nerve section has dramatic consequences on ingestive behavior. The examination of taste elicited oral motor behaviors reveals a coherent and nerve specific pattern of neurological deficit following peripheral nerve section.

Chemospecific deficits in taste detection after selective gustatory deafferentation in rats

Electrophysiological data support the existence of sodium-specific taste receptors that appear to be limited to the anterior tongue. However, previous behavioral findings suggest that bilateral transection of the chorda tympani nerve (CTn) has minimal consequences on NaCl intake and preference. This study employed a conditioned avoidance procedure to measure detection thresholds to NaCl and sucrose both before and after bilateral transection of the CTn. Rats were trained to maintain spout contact in response to water presentations (70 microliters) and to avoid spout contact when a taste solution (70 microliters) was presented. In experiment 1, all rats (n = 3) showed statistically significant impairments in the detectability of NaCl after bilateral section of the CTn. The mean increase in the NaCl detection threshold was 1.41 log units. In contrast, sucrose threshold in these same rats was marginally affected by CTn section (mean increase = 0.22 log units). Experiment 2 (n = 4) replicated the findings of the first experiment. The mean increase in the NaCl detection threshold was 2.23 log units. Sucrose threshold in these rats was, again, only marginally affected by CTn section (mean increase = 0.83 log units). Histological examination of the anterior tongue from the rats in experiment 2 indicated that the CTn transections were complete. These findings reveal that the anterior oral receptive field (innervated by the CTn) containing only 15% of the total taste bud population is critical for the normal detection of NaCl.

Surgery of sialorrhoea.

The drooling that accompanies motor neurone disorders adds to the burden of an individual already severely handicapped socially. Control of this problem can be achieved by a number of measures, such as the surgical repositioning of the salivary gland ducts and by use of medical or surgical means of reducing salivary production. Nineteen patients aged 5 to 9 years, with excessive drooling as a result of perinatal brain damage, have been treated surgically at Groote Schuur Hospital, Cape Town, by bilateral tympanic neurectomies, unilateral chorda tympani nerve section and contralateral submandibular gland excision. In all 19, salivary flow was reduced and the drooling problem significantly improved. No post-operative complications occurred.

Transtympanic Neurectomies for Control of Drooling

Twenty patients of drooling were studied. Of the 20 patients studied, 8 patients underwent bilateral chorda tympani nerve section, and 12 patients underwent bilateral chorda tympani nerve along with bilateral tympanic nerve sections. Bilateral chorda tympani nerve section in combination with bilateral tympanic nerve section is a better and more effective procedure for control of drooling than bilateral tympanic nerve section alone. In both these methods there is immediate stoppage of drooling i.e. on 2nd postoperative day but chances of recurrence of drooling are less in chorda tympani nerve section in combination with tympanic nerve section (17%) than chorda tympani nerve section alone (38%).

Parasympathetic nerve section for control of sialorrhea

• Twenty mentally retarded patients with a considerable drooling problem underwent transtympanic sectioning of selected preganglionic parasympathetic nerve fibers to the major salivary glands. Following surgery, cessation of troublesome sialorrhea occurred in 15 of 20 patients; but by six months postoperatively, only ten patients remained controlled. The best results obtained were in a subgroup of five patients who underwent bilateral Jacobson nerve and chorda tympani nerve section. In four of these patients, sialorrhea was controlled after a minimum follow-up of two years. Parasympathetic denervation of the major salivary glands via a transtympanic approach is offered as a primary modality of therapy in those mentally retarded patients judged to have considerable sialorrhea. Sacrifice of both chorda tympani nerves appears to enhance the surgical results.

Parasympathetic nerve section for control of sialorrhea.

Twenty mentally retarded patients with a considerable drooling problem underwent transtympanic sectioning of selected preganglionic parasympathetic nerve fibers to the major salivary glands. Following surgery, cessation of trouble-some sialorrhea occurred in 15 to 20 patients; but by six months postoperatively, only ten patients remained controlled. The best results obtained were in a subgroup of five patients who underwent bilateral Jacobson nerve and chorda tympani nerve section. In four of these patients, sialorrhea was controlled after a minimum follow-up of two years. Parasympathetic denervation of the major salivary glands via a transtympanic approach is offered as a primary modality of therapy in those mentally retarded patients judged to have considerable sialorrhea. Sacrifice of both chorda tympani nerves appears to enhance the surgical results.

Rôle of nerve and epithelium in the regulation of alkaline phosphatase activity in gustatory papillae

The loss of alkaline phosphatase activity from the gustatory epithelium of the rat's vallate papilla after glossopharyngeal nerve transection indicates that the enzyme is neurally regulated. The absence of this enzyme from the gustatory epithelium of the fungiform papillae innervated by the chorda tympani nerve suggests that these two nerves may differ in their capacity to regulate this enzyme. Since alkaline phosphatase is present throughout all the folds of the foliate papilla and since this papilla is innervated by glossopharyngeal and chorda tympani nerves, selective nerve sections should answer the question as to whether the chorda tympani nerve is capable of maintaining alkaline phosphatase activity. Two weeks after chorda tympani nerve section alone, taste buds and alkaline phosphatase activity were absent from the anterior folds but present posteriorly, while after glossopharyngeal nerve section alone, buds and enzyme were absent in the posterior folds but present anteriorly. It was only after combined chorda tympani and glossopharyngeal nerve transection that all taste buds and alkaline phosphatase disappeared. The only additional change 20 weeks after the respective nerve sections was a greater epithelial atrophy of the denervated folds. The results indicate that the regulation of alkaline phosphatase is not gustatory-nerve specific, but is a property common to both chorda tympani and glossopharyngeal nerves. The relative independence of alkaline phosphatase of the type of gustatory innervation stresses the importance of continued studies of both nerves and epithelium in gustatory function.

Chorda tympan nerve section for postherpetic neuralgia of the tongue.

Herpes zoster is considered at present an acute specific infection caused by a neurotropic and epidermotropic virus with a predilection for the posterior spinal ganglia or the extramedullary ganglia of the cranial nerves. The clinical picture includes an erythematous vesicular eruption in the cutaneous or mucosal distribution of the sensory nerves. In herpes zoster oticus the herpetic eruption occurs in a certain area of the external ear (the "geniculate" zone). Hunt contended, in a report published in 1907, that the primary disorder was in the geniculate ganglion of the facial nerve. He assumed that the infection spreads from the ganglion by means of anastomosis to other cranial nerves, especially the statoacusticus and its ganglia. Later pathoanatomical studies have shown that, in addition to neuritic changes, localized leptomeningitis also occurs in cases of herpes zoster (Denny-Brown and associates). This is easy to understand because the geniculate ganglion, as well as the