Phenotypic change in trigeminal ganglion neurons associated with satellite cell activation via extracellular signal-regulated kinase phosphorylation is involved in lingual neuropathic pain.

Iatrogenic trigeminal nerve injuries remain a common and complex clinical problem. Satellite glial cell (SGC) activation, associated phosphorylation of extracellular signal-regulated kinase (ERK), and neuropeptide expression in the trigeminal ganglion (TG) are known to be involved in trigeminal neuropathic pain related to trigeminal nerve injury. However, the involvement of these molecules in orofacial neuropathic pain mechanisms is still unknown. Phosphorylation of ERK1/2 in lingual nerve crush (LNC) rats was observed in SGCs. To evaluate the role of neuron-SGC interactions under neuropathic pain, calcitonin gene-related peptide (CGRP)-immunoreactive (IR), phosphorylated ERK1/2 (pERK1/2)-IR and glial fibrillary acidic protein (GFAP)-IR cells in the TG were studied in LNC rats. The number of CGRP-IR neurons and neurons encircled with pERK1/2-IR SGCs was significantly larger in LNC rats compared with sham rats. The percentage of large-sized CGRP-IR neurons was significantly higher in LNC rats. The number of CGRP-IR neurons, neurons encircled with pERK1/2-IR SGCs, and neurons encircled with GFAP-IR SGCs was decreased following CGRP receptor blocker CGRP8-37 or mitogen-activated protein kinase/ERK kinase 1 inhibitor PD98059 administration into the TG after LNC. Reduced thresholds to mechanical and heat stimulation to the tongue in LNC rats were also significantly recovered following CGRP8-37 or PD98059 administration. The present findings suggest that CGRP released from TG neurons activates SGCs through ERK1/2 phosphorylation and TG neuronal activity is enhanced, resulting in the tongue hypersensitivity associated with lingual nerve injury. The phenotypic switching of large myelinated TG neurons expressing CGRP may account for the pathogenesis of tongue neuropathic pain.

Bilateral sensory deprivation of trigeminal afferent fibres on corticomotor control of human tongue musculature: a preliminary study.

Transcranial magnetic stimulation (TMS) has demonstrated changes in motor evoked potentials (MEPs) in human limb muscles following modulation of sensory afferent inputs. The aim of this study was to determine whether bilateral local anaesthesia (LA) of the lingual nerve affects the excitability of the tongue motor cortex (MI) as measured by TMS. The effect on MEPs after bilateral LA of the lingual nerve was studied, while the first dorsal interosseous (FDI) muscle served as a control in ten healthy participants. MEPs were measured on the right side of the tongue dorsum in four different conditions: (i) immediately prior to anaesthesia (baseline), (ii) during bilateral LA block of the lingual nerve, (iii) after anaesthesia had subjectively subsided (recovery) and (iv) 3 h after bilateral lingual block injection. MEPs were assessed using stimulus-response curves in steps of 10% of motor threshold (T). Eight stimuli were given at each stimulus level. The amplitudes of the tongue MEPs were significantly influenced by the stimulus intensity (P < 0·001) but not by condition (P = 0·186). However, post hoc tests showed that MEPS were statistically significantly higher during bilateral LA block condition compared with baseline at T + 40%, T + 50% and T + 60% (P < 0·028) and also compared with recovery at T + 60% (P = 0·010) as well as at 3 h after injection at T + 50% and T + 60% (P < 0·029). Bilateral LA block of the lingual nerve seems to be associated with a facilitation of the corticomotor pathways related to the tongue musculature.

Differences in control of parasympathetic vasodilation between submandibular and sublingual glands in the rat.

We examined blood flow in the submandibular gland (SMGBF) and sublingual gland (SLGBF) during electrical stimulation of the central cut end of the lingual nerve (LN) in the urethane-anesthetized rats using a laser speckle imaging flow meter. LN stimulation elicited intensity- and frequency-dependent SMGBF and SLGBF increases, and the magnitude of the SMGBF increase was higher than that of the SLGBF increase. The increase in both glands was significantly inhibited by intravenous administration of the autonomic cholinergic ganglion blocker hexamethonium. The antimuscarinic agent atropine markedly inhibited the SMGBF increase and partly inhibited the SLGBF increase. The atropine-resistant SLGBF increase was significantly inhibited by infusion of vasoactive intestinal peptide (VIP) receptor antagonist, although administration of VIP receptor antagonist alone had no effect. The recovery time to the basal blood flow level was shorter after LN stimulation than after administration of VIP. However, the recovery time after LN stimulation was significantly delayed by administration of atropine in a dose-dependent manner to the same level as after administration of VIP. Our results indicate that 1) LN stimulation elicits both a parasympathetic SMGBF increase mainly evoked by cholinergic fibers and a parasympathetic SLGBF increase evoked by cholinergic and noncholinergic fibers, and 2) VIP-ergic mechanisms are involved in the noncholinergic SLGBF increase and are activated when muscarinic mechanisms are deactivated.

Surgical neurolysis for the treatment of neuropathic pain in 2 postmenopausal women with mandibular necrosis resulting from oral bisphosphonates.

We analyze the use of surgical neurolysis for the treatment of neuropathic pain of the inferior alveolar nerve. For that, 3 surgical neurolysis were performed on 2 postmenopausal women experiencing neuropathic pain of the inferior alveolar nerve due to mandibular necrosis resulting from treatment with oral bisphosphonates. Both patients showed sensory impairment of the inferior alveolar nerve. We obtained complete control of neuropathic pain after 6 months of the patients' evolution, preserving the function of the lingual nerve in all 3 neurolysis, without causing any impact as regards to the sensitive situation before treatment. Surgical neurolysis of the inferior alveolar nerve may be considered as the choice therapeutic technique to treat neuropathic pain of this nerve when there is a sensory impairment in patients showing mandibular necrosis resulting from bisphosphonates.

What factors are associated with functional sensory recovery following lingual nerve repair?

PURPOSE: To identify factors associated with functional sensory recovery (FSR) after lingual nerve repair. MATERIALS AND METHODS: This retrospective cohort study was composed of subjects who underwent lingual nerve repair from 2004 through 2010. The predictor variables were demographic, anatomic, and operative measurements. The primary outcome measurement was FSR (ie, FSR achieved, yes or no). The secondary outcome measurements were time to FSR and an improvement of at least 2 levels on the British Medical Research Council scale of neurosensory function. Descriptive, bivariate, and multiple logistic regression statistics were computed to identify associations between the predictor variables and FSR. A Cox proportional hazards model was used to identify associations between the predictors and time to FSR. P ≤ .05 was considered statistically significant. RESULTS: The sample was composed of 55 subjects with a mean age of 30.7 ± 11.2 years. The mean duration from injury to repair was 151.6 days (range, 41 to 384 days). Most patients (74.5%) achieved FSR postoperatively, with a mean time to FSR of 262.8 days (median, 208 days). Eighty-six percent of subjects showed an improvement of at least 2 levels on the British Medical Research Council scale. In multiple regression models, younger subjects were more likely to achieve FSR (odds ratio, 1.10; 95% confidence interval, 1.01 to 1.18; P = .02); subjects with better preoperative neurosensory function achieved FSR faster (hazard ratio, 1.9; 95% confidence interval, 1.2 to 3.1; P = .01). CONCLUSION: Most patients undergoing lingual nerve repair achieved FSR. Younger subjects were more likely to achieve FSR. Subjects with better preoperative neurosensory function achieved FSR faster.

Response latency to lingual taste stimulation distinguishes neuron types within the geniculate ganglion.

The purpose of this study was to investigate the role of response latency in discrimination of chemical stimuli by geniculate ganglion neurons in the rat. Accordingly, we recorded single-cell 5-s responses from geniculate ganglion neurons (n = 47) simultaneously with stimulus-evoked summated potentials (electrogustogram; EGG) from the anterior tongue to signal when the stimulus contacted the lingual epithelium. Artificial saliva served as the rinse solution and solvent for all stimuli [(0.5 M sucrose, 0.03-0.5 M NaCl, 0.01 M citric acid, and 0.02 M quinine hydrochloride (QHCl)], 0.1 M KCl as well as for 0.1 M NaCl +1 µM benzamil. Cluster analysis separated neurons into four groups (sucrose specialists, NaCl specialists, NaCl/QHCl generalists and acid generalists). Artificial saliva elevated spontaneous firing rate and response frequency of all neurons. As a rule, geniculate ganglion neurons responded with the highest frequency and shortest latency to their best stimulus with acid generalist the only exception. For specialist neurons and NaCl/QHCl generalists, the average response latency to the best stimulus was two to four times shorter than the latency to secondary stimuli. For NaCl-specialist neurons, response frequency increased and response latency decreased systematically with increasing NaCl concentration; benzamil significantly decreased NaCl response frequency and increased response latency. Acid-generalist neurons had the highest spontaneous firing rate and were the only group that responded consistently to citric acid and KCl. For many acid generalists, a citric-acid-evoked inhibition preceded robust excitation. We conclude that response latency may be an informative coding signal for peripheral chemosensory neurons.

Ultrasound-Guided Inferior Alveolar Nerve Block in the Horse: Assessment of the Extraoral Approach in Cadavers.

Blinded techniques to desensitize the inferior alveolar nerve (IAN) include intraoral, angled, and vertical extraoral approaches with reported success rates of 100%, 73%, and 59%, respectively. It has not been determined whether an ultrasound-guided extraoral approach is feasible. Further, the fascicular nature of the inferior alveolar and lingual nerves of the horse has not been described. The objectives of this study were to describe a low-volume ultrasound-guided vertical extraoral inferior alveolar nerve block technique and to describe the fascicular nature of these nerves. An ultrasound-guided approach to the IAN was conducted with a microconvex transducer and an 18-G, 15-cm spinal needle using a solution containing iodinated-contrast and methylene blue dye. Accuracy was assessed by contrast visualized at the mandibular foramen on computed tomography (CT) and methylene blue dye staining of the nerves on gross dissection. Sections of inferior alveolar and lingual nerves were submitted for histological analysis. Assessment by CT and dissection determined success rates of 81.3% and 68.8%, respectively; 68.8% of injections had inadvertent methylene blue dye staining of the lingual nerve. Nerve histology revealed both the inferior alveolar and lingual nerves to be multifascicular in nature. Mean fascicle counts for the inferior alveolar and lingual nerves were 29 and 30.8, respectively. The technique is challenging and no more accurate than previously published blinded techniques. Any extraoral approach to the IAN is likely to also desensitize the lingual nerve.

Fungiform taste bud degeneration in C57BL/6J mice following chorda-lingual nerve transection.

Taste buds are dependent on innervation for normal morphology and function. Fungiform taste bud degeneration after chorda tympani nerve injury has been well documented in rats, hamsters, and gerbils. The current study examines fungiform taste bud distribution and structure in adult C57BL/6J mice from both intact taste systems and after unilateral chorda-lingual nerve transection. Fungiform taste buds were visualized and measured with the aid of cytokeratin 8. In control mice, taste buds were smaller and more abundant on the anterior tip (<1 mm) of the tongue. By 5 days after nerve transection taste buds were smaller and fewer on the side of the tongue ipsilateral to the transection and continued to decrease in both size and number until 15 days posttransection. Degenerating fungiform taste buds were smaller due to a loss of taste bud cells rather than changes in taste bud morphology. While almost all taste buds disappeared in more posterior fungiform papillae by 15 days posttransection, the anterior tip of the tongue retained nearly half of its taste buds compared to intact mice. Surviving taste buds could not be explained by an apparent innervation from the remaining intact nerves. Contralateral effects of nerve transection were also observed; taste buds were larger due to an increase in the number of taste bud cells. These data are the first to characterize adult mouse fungiform taste buds and subsequent degeneration after unilateral nerve transection. They provide the basis for more mechanistic studies in which genetically engineered mice can be used.

Functional role of lingual nerve in breastfeeding.

Functional role of lingual nerve in breastfeeding was investigated in rat pups during the suckling period. DiI, a postmortem neuronal tracer, was used to confirm the immature lingual nerve (LN) responsible for tongue sensation and resulted in successful fiber labeling anterogradely to the tongue, which showed different distribution patterns from fiber labeling derived from the hypoglossal nerve. Unilaterally LN-injured pups did not show suckling disturbance with absence of any shortening (P11 pups: 559+/-16s; 105% of the control value) in nipple attachment time and the survival rate remained high (P11: 100%). Bilaterally LN-injured pups showed suckling disturbance with marked shortening (P11 pups: 220+/-54 s; 42% of the control value) in nipple attachment time and a low survival rate (P1: 33%; P11: 41%). Bilaterally infraorbital nerve-injured or bilaterally bulbectomized pups did not show any nipple attachment at all and there were no survivors, confirming the crucial roles of upper lip sensation and olfaction in suckling. Based on these findings, we conclude that tongue sensation is very important, but not essential for suckling.

Extending the enteric nervous system.

The work reviews the evidence suggesting that lingual components of the autonomic system may be considered the most rostral portion of the enteric nervous system (ENS) defining the concept of lingual ENS (LENS). The LENS is not dissimilar from the more distally located portions of the ENS, however, it is characterized by a massive sensory input generated by collaterals of gustatory and trigeminal fibers. The different neuronal subpopulations that compose the LENS operate reflexes involved in regulation of secretion and vasomotility. Systemic reflexes on the digestive and respiratory apparatus are operated by means of neural connections through the pharynx or larynx. The LENS can modulate the activity of distally located organs by means of the annexed glands.The LENS seems therefore to be a "chemical eye" located at the beginning of the digestive apparatus which analyses the foods before their ingestion and diffuses this information distally. The definition of the LENS supports the concept of an elevated degree of autonomy in the ENS and puts in a new light the role of the gustatory system in modulation of the digestive functions. For its characteristics, the LENS appears to be an ideal model to study the elementary connectivity of the ENS.

Acetylcholine synthesis, muscarinic receptor subtypes, neuropeptides and secretion of ferret salivary glands with special reference to the zygomatic gland.

Studies on salivary secretion are usually focused on parotid and submandibular glands. However, the film of mucin, that protects the oral structures and is responsible for the feeling of oral comfort, is produced by the submucosal glands. The submucosal zygomatic and molar glands are particularly large in carnivores such as the ferret. Comparisons between the mucous sublingual, zygomatic and molar glands, serous parotid and sero-mucous submandibular glands showed the acetylcholine synthesis, in terms of concentration, to be three to four times higher in the mucous glands than in the parotid and submandibular glands. Bromoacetylcholine inhibited 95-99% of the synthesis of acetylcholine in the incubates of the five types of glands, showing the acetylcholine synthesis to depend on the activity of choline acetyltransferase. The high acetylcholine synthesis in the zygomatic gland was of nervous origin, since cutting the buccal nerve, aiming at parasympathetic denervation, and allowing time for nerve degeneration, reduced the acetylcholine synthesising capacity of the gland by 95%. A similar reduction (96%) in the parotid gland followed upon the avulsion of the parasympathetic auriculo-temporal nerve. Zygomatic saliva was very viscous. The salivary flow rate in response to electrical stimulation (20 Hz) of the buccal nerve (zygomatic gland), expressed per gland weight, was one-third of that to stimulation of the auriculo-temporal nerve (parotid gland) or the chorda-lingual nerve (submandibular gland). As previously shown for the parotid and submandibular gland, a certain fraction (25%) of the parasympathetic secretory response of the zygomatic gland depended on non-adrenergic, non-cholinergic transmission mechanisms, probably involving substance P and vasoactive intestinal peptide and possibly calcitonin gene-related peptide. Particularly, high concentrations of vasoactive intestinal peptide were found in the sublingual and molar glands, and of substance P in the submandibular, zygomatic and molar glands; notably, the concentration of calcitonin gene-related peptide of the sublingual gland was not detectable. All five muscarinic receptor subtypes were detected in the five glands. The receptor protein profile, as judged by immunoblotting and semi-quantitative estimations, was about the same in the glands: high level of M3, low level of M2 and levels roughly in the same range of M1, M4 and M5. Compared to the parotid and submandibular glands, the M5 receptor level was particularly low in the mucin-secreting glands. The present study points out both similarities and dissimilarities between the five types of glands investigated. The zygomatic gland, in particular, appears to be a suitable model for future studies aiming at causing relief of dry mouth by local pharmacological treatment.

Effects of isoflurane on parasympathetic vasodilatation in the rat submandibular gland.

Volatile anesthetics have been known to suppress parasympathetic reflex vasodilatation in the lower lip and palate. However, in the submandibular gland, little is known about the effects of these anesthetics on the parasympathetic vasodilatation elicited by reflex and direct (i.e., non-reflex) activation of the parasympathetic vasodilator mechanisms. Although both parasympathetic vasodilatations were inhibited by isoflurane in a concentration- and time-dependent manner, the effects of continuous administration of the alpha(1)-adrenoceptor agonist methoxamine were markedly different: The reflex vasodilatation was not affected by methoxamine, while the direct vasodilatation was significantly reduced. Picrotoxin (GABA(A) receptor antagonist) attenuated the inhibitory effect of isoflurane on direct vasodilatation and the systemic arterial blood pressure. These findings suggest that the isoflurane-induced inhibitory effects on direct vasodilatation are produced by a decrease of peripheral vascular tone by GABAergic mechanisms, whereas those on the reflex vasodilatation are produced exclusively by the inhibition of the reflex center.

Developmental time course of peripheral cross-modal sensory interaction of the trigeminal and gustatory systems.

Few sensory modalities appear to engage in cross-modal interactions within the peripheral nervous system, making the integrated relationship between the peripheral gustatory and trigeminal systems an ideal model for investigating cross-sensory support. The present study examined taste system anatomy following unilateral transection of the trigeminal lingual nerve (LX) while leaving the gustatory chorda tympani intact. At 10, 25, or 65 days of age, rats underwent LX with outcomes assessed following various survival times. Fungiform papillae were classified by morphological feature using surface analysis. Taste bud volumes were calculated from histological sections of the anterior tongue. Differences in papillae morphology were evident by 2 days post-transection of P10 rats and by 8 days post in P25 rats. When transected at P65, animals never exhibited statistically significant morphological changes. After LX at P10, fewer taste buds were present on the transected side following 16 and 24 days survival time and remaining taste buds were smaller than on the intact side. In P25 and P65 animals, taste bud volumes were reduced on the denervated side by 8 and 16 days postsurgery, respectively. By 50 days post-transection, taste buds of P10 animals had not recovered in size; however, all observed changes in papillae morphology and taste buds subsided in P25 and P65 rats. Results indicate that LX impacts taste receptor cells and alters epithelial morphology of fungiform papillae, particularly during early development. These findings highlight dual roles for the lingual nerve in the maintenance of both gustatory and non-gustatory tissues on the anterior tongue.

Neurophysiological and biophysical evidence on the mechanism of electric taste.

The phenomenon of electric taste was investigated by recording from the chorda tympani nerve of the rat in response to both electrical and chemical stimulations of the tongue with electrolytes in order to gain some insight into its mechanism on both a neurophysiological and biophysical basis. The maximum neural response levels were identical for an individual salt (LiCl, NaCl, KCl, or CaCl2), whether it was presented as a chemical solution or as an anodal stimulus through a subthreshold solution. These observations support the idea that stimulation occurs by iontophoresis of ions to the receptors at these current densities (less than 100 microA/cm2). Electric responses through dilute HCl were smaller than the chemically applied stimulations, but the integrated anodal responses appeared similar to chemical acid responses, as evidenced by an OFF response to both forms of stimuli. Hydrogen may be more permeant to the lingual epithelium and would thus be shunted away from the taste receptors during anodal stimulation. When the anion of electric taste was varied via subthreshold salt solutions, the response magnitude increased as the mobility of the anion decreased. The transport numbers of the salts involved adequately explains these differences. The physical aspects of ion migration occurring within the adapting fluid on the tongue are also discussed. Direct neural stimulation by the current appears to occur only at higher current densities (greater than 300 microA/cm2). If the taste cells of the tongue were inactivated with either iodoacetic acid (IAA) or N-ethyl maleimide (NEM), or removed with collagenase, then responses from the chorda tympani could be obtained only at these higher current densities. Latency measurements before and after IAA or NEM treatment corroborated these findings. The results are discussed in terms of several proposed mechanisms of electric taste and it is concluded that an ion accumulation mechanism can adequately explain the data.

Selectivity of lingual nerve fibers to chemical stimuli.

The cell bodies of the lingual branch of the trigeminal nerve were localized in the trigeminal ganglion using extracellular recordings together with horseradish peroxidase labeling from the tongue. Individual lingual nerve fibers were characterized with regard to their conduction velocities, receptive fields, and response to thermal, mechanical, and chemical stimuli. Fibers were classified as C, A delta, A beta, cold, and warm. The chemical stimuli included NaCl, KCl, NH4Cl, CaCl2, menthol, nicotine, hexanol, and capsaicin. With increasing salt concentration the latency of the response decreased and the activity increased. The responses elicited by salts (to 2.5 M), but not nonpolar stimuli such as menthol, were reversibly inhibited by 3.5 mM of the tight junction blocker, LaCl3. These data suggest that salts diffuse into stratified squamous epithelia through tight junctions in the stratum corneum and stratum granulosum, whereupon they enter the extracellular space. 11 C fibers were identified and 5 were characterized as polymodal nociceptors. All of the C fibers were activated by one or more of the salts NaCl, KCl, or NH4Cl. Three C fibers were activated by nicotine (1 mM), but none were affected by CaCl2 (1 M), menthol (1 mM), or hexanol (50 mM). However, not all C fibers or even the subpopulation of polymodals were activated by the same salts or by nicotine. Thus, it appears that C fibers display differential responsiveness to chemical stimuli. A delta fibers also showed differential sensitivity to chemicals. Of the 35 characterized A delta mechanoreceptors, 8 responded to NaCl, 9 to KCl, 9 to NH4Cl, 0 to CaCl2, menthol, or hexanol, and 2 to nicotine. 8 of 9 of the cold fibers (characterized as A delta's) responded to menthol, none responded to nicotine, 8 of 16 were inhibited by hexanol, 9 of 19 responded to 2.5 M NH4Cl, 5 of 19 responded to 2.5 M KCl, and 1 of 19 responded to 2.5 M NaCl. In summary, lingual nerve fibers exhibit responsiveness to chemicals introduced onto the tongue. The differential responses of these fibers are potentially capable of transmitting information regarding the quality and quantity of chemical stimuli from the tongue to the central nervous system.

Parasympathetic mediated pupillary dilation elicited by lingual nerve stimulation in cats.

PURPOSE: To determine the autonomic efferent nerve pathways for the reflex pupillary dilation elicited by somatic stimulation in cats. METHODS: Cats anesthetized with a mixture of alpha-chloralose (50 mg/kg) and urethane (100 mg/kg) were intubated and paralyzed by intravenous injection of pancuronium bromide. The central cut end of the lingual nerve (LN) was stimulated electrically to simulate somatic stimulation, and 1 microL of lidocaine (2%) was microinjected into the Vsp or the EW nucleus to determine its effect on the pupillary dilation induced by LN stimulation. The effect of electrically stimulating the Vsp or sectioning the superior cervical sympathetic nerve (CSN) on the pupillary response was also examined. RESULTS: Stimulation of the LN or the trigeminal spinal nucleus (Vsp) evoked pupillary dilation in a frequency- and intensity-dependent manner. These responses were not affected by sectioning the ipsilateral or both CSNs. The pupillary responses were markedly suppressed by microinjecting lidocaine into the ipsilateral Vsp or the Edinger-Westphal (EW) nucleus, but not by injection into the contralateral Vsp. CONCLUSIONS: These results indicate that the Vsp and EW nucleus act as bulbar relay centers for pupillary dilation elicited by LN stimulation and suggest that the efferent arc of the response is a parasympathetic pathway. The contralateral pupillary dilation appears to be mediated, at least in part, by fibers projecting from the Vsp to the contralateral EW nucleus.

The effect of bilateral lingual nerve anesthesia and increased occlusal vertical dimension on the onset of swallowing in adult males.

The present study attempts to determine whether the onset of swallowing is affected by bilateral lingual and inferior alveolar nerve anesthesia and by raising the occlusal vertical dimension by wearing an occlusal bite plate. Twenty young male volunteers were selected and asked to chew and swallow corned beef and a corned beef and liquid mixture in their usual manner before and after modifications were made. Oral and pharyngeal swallowing was investigated using videofluoroscopic examination in the lateral plane. Eight objective indicators, including oral containment time, swallowing threshold, and pharynx-to-swallow intervals were estimated. Oral containment time, total sequence duration, total number of chews, and total number of swallows of the two test foods were significantly different before and after the modifications. Individual pharynx-to-swallow intervals also varied. The results indicate that modification of the masticatory condition affects the onset of swallowing and that changes in the onset varied among the participants.

Nerve fiber analysis on the morphology of the lingual nerve.

The route of fine fascicles of nerve fibers in the lingual nerve was clarified. Contemporary anatomy textbooks describe the lingual nerve as supplying sensory innervation to the mucous membrane of the presulcal part of the tongue, the floor and side wall of the mouth, and the mandibular gums. In addition to receiving the chorda tympani and a branch of the inferior alveolar nerve, the lingual nerve is connected to the submandibular ganglion by a few branches. It carries preganglionic fibers from the chorda tympani and postganglionic fibers from the submandibular ganglion to the submandibular and sublingual glands. The branch from the mylohyoid nerve is described as a sensory nerve. However, we observed that this branch was directly connected to the submandibular ganglion. Furthermore, the branch from the submandibular ganglion innervated thin membranous tissue that originated in the petrous part of the temporal bone and inserted into the lateral surface of the superior constrictor. These branches have not been described in the anatomy textbooks and literature. Therefore, we studied the morphological features of the lingual nerve and discovered the route of fine fascicles of nerve fibers in the lingual nerve. These findings will likely improve the neurological and physiological understanding of the function of the lingual nerve.

Collateral reinnervation of taste buds after chronic sensory denervation: a morphological study.

Peripheral transganglionic transport of horseradish peroxidase (HRP) was used to label afferent fibers in the taste buds and lingual epithelium 2-12 weeks after chronic chorda tympani or combined chorda tympani-lingual nerve lesions. From 4-12 weeks after a chronic chorda tympani lesion, taste buds could be found. These were innervated by fibers from the ipsilateral lingual nerve. From 8-12 weeks after a chronic chorda tympani-lingual nerve lesion, nerve fibers from the contralateral lingual nerve could be found in a few taste buds on the denervated side of the tongue. Thus, collateral sprouting took place over the midline in this instance. These findings indicate that intact gustatory axons do not sprout into denervated taste buds, but trigeminal fibers in the lingual nerve do have this ability.

Central projections of gustatory nerves in the rat.

The central distributions of gustatory and non-gustatory branches of cranial nerves V, VII, IX, and X were examined after application of horseradish peroxidase to the cut nerve. The nerves conveying gustatory information, chorda tympani (CT), greater superficial petrosal (GSP), lingual-tonsilar branch of IX (LT-IX), superior laryngeal branch of X (SL), distributed primarily to the lateral division of the nucleus of the solitary tract (NST) from its rostral pole to the obex. The CT and GSP distributions were coextensive and terminated most densely in the rostral pole of NST. The LT-IX distribution concentrated between this major CT/GSP distribution and the area postrema with a caudal extension into the interstitial nucleus of NST. This nerve also had a substantial projection, not found in other gustatory nerves, into the dorsolateral aspect of the medial NST. The SL distribution overlapped LT-IX in the caudal medulla. The lingual and inferior alveolar nerves, two oral trigeminal branches, projected to regions of NST innervated by the gustatory nerves. The cervical vagus nerve distributed primarily to the medial NST in the caudal half of the nucleus and exhibited only minimal overlap with gustatory nerve distributions. The nucleus of the solitary tract appears to have two major functional divisions--an anterior-lateral oral-gustatory half, and a posterior-medial visceral afferent half.