Anatomical Relationship Between the Lingual Nerve and Submandibular Duct.

ABSTRACT: The purpose of this study was to investigate the anatomical relationship between the lingual nerve and submandibular duct. This study included 1403 patients with submandibular or sublingual gland diseases who underwent intraoral removal of submandibular gland sialoliths, submandibular glands, or sublingual glands. Of all patients, 33 patients underwent bilateral surgeries. All surgeries were performed a single surgeon, and the anatomical relationship between the lingual nerve and submandibular duct was always identified intraoperatively and recorded in the operation recorded. The anatomical relationship was investigated based on the intraoperative findings. The lingual nerve which crosses above the submandibular duct was detected in 8 of 1436 sides (0.6%). There were 4 in the right sides and 4 in the left sides. The lingual nerve below the submandibular gland was seen in 99.4%. Although the lingual nerve crosses above the submandibular duct with a rarer incidence, surgeons should beware of injuring the lingual nerve during intraoral salivary gland surgery.

Parasympathectomy increases resting secretion of the submandibular gland in minipigs in the long term.

Parasympathectomy leads to retrogressive alteration and dysfunction of the submandibular gland (SMG) within 1 month, but its long-term effect is unclear. Excessive secretion is observed in half of the patients 4-6 months after SMG transplantation, which completely denervates the gland. Here, we investigated the long-term effect of parasympathectomy on the secretion of SMGs in minipigs. The results showed that the resting salivary secretion of SMGs decreased by 82.9% of that in control at 2 months after denervation, but increased by 156% at 6 months. Although experiencing an atrophic period, the denervated glands regained their normal morphology by 6 months. The expression of the function-related proteins, including muscarinic acetylcholine receptor (mAChR) 3, aquaporin 5 (AQP5), tight junction protein claudin-3, and claudin-4 was decreased at 2 months after denervation. Meanwhile, the protein expression of stem cell markers, including sex-determining region Y-box 2 and octamer-binding transcription factor 4, and the number of Ki67+ cells were significantly increased. However, at 6 months after denervation, the expression of mAChR3, AQP5, claudin-1, claudin-3, and claudin-4 was significantly raised, and the membrane distribution of these proteins was increased accordingly. The autonomic axonal area of the glands was reduced at 2 months after denervation but returned to the control level at 6 months, suggesting that reinnervation took place in the long term. In summary, parasympathectomy increases resting secretion of the SMGs in the long term with a possible mechanism involving improved transepithelial fluid transport. This finding may provide a new strategy for xerostomia treatment.

Accessory Submandibular Salivary Gland Forming a "Horseshoe" With the Main Submandibular Salivary Gland: A Unique Variation.

Presence of accessory submandibular salivary gland (ASSG) is an extremely rare variation. Knowledge of its relations could be very useful to oral and maxillofacial surgeons, head and neck surgeons, and radiologists. During dissection classes, an ASSG was noted between the mylohyoid and hyoglossus muscles. The main submandibular salivary gland had superficial and deep parts. The deep part was narrow and measured about 5 cm. The lingual nerve passed between the superficial and deep parts. The accessory submandibular gland was situated below and parallel to the deep part of SSG. It also measured 5 cm. The ASSG had its own duct, which joined the duct of main gland. The ASSG and the deep part of the SSG were united at the lateral border of geniohyoid muscle to give a characteristic "horseshoe" appearance. The ASSG overlapped both lingual and hypoglossal nerves.

Parasympathectomy increases resting salivary secretion in normal and irradiated submandibular glands of rats.

Fluid and ion secretion from the submandibular gland (SMG) is mainly regulated by parasympathetic nerves. This study evaluated the effect of parasympathectomy on salivary secretion from normal and irradiated rat SMGs from 1 to 24 wk after denervation. Although stimulated salivary secretion was significantly lower in denervated SMGs compared with contralateral self-controls, the resting salivary flow rates were markedly higher in the denervated SMGs at 1, 12, and 24 wk after denervation. The levels of muscarinic acetylcholine M1 and M3 receptors, as well as of aquaporin 5, were up-regulated. Notably, although irradiated SMGs showed significantly lower resting and stimulated salivary secretion rates than non-irradiated SMGs, the resting salivary secretion rates of the irradiated and denervated SMGs were markedly higher than seen in the irradiated self-control SMGs at 1, 12, and 24 wk after parasympathectomy, and were even higher than seen in the non-irradiated sham-operated rats. The expression of M1 and M3 receptors was similarly elevated. Taken together, our results suggest that parasympathetic denervation increases resting salivary secretion of both normal and irradiated SMGs. This approach might provide a potential modality for relieving radiation-induced xerostomia, which is a common complication following treatment of head and neck cancer.

In vivo imaging of alphaherpesvirus infection reveals synchronized activity dependent on axonal sorting of viral proteins.

A clinical hallmark of human alphaherpesvirus infections is peripheral pain or itching. Pseudorabies virus (PRV), a broad host range alphaherpesvirus, causes violent pruritus in many different animals, but the mechanism is unknown. Previous in vitro studies have shown that infected, cultured peripheral nervous system (PNS) neurons exhibited aberrant electrical activity after PRV infection due to the action of viral membrane fusion proteins, yet it is unclear if such activity occurs in infected PNS ganglia in living animals and if it correlates with disease symptoms. Using two-photon microscopy, we imaged autonomic ganglia in living mice infected with PRV strains expressing GCaMP3, a genetically encoded calcium indicator, and used the changes in calcium flux to monitor the activity of many neurons simultaneously with single-cell resolution. Infection with virulent PRV caused these PNS neurons to fire synchronously and cyclically in highly correlated patterns among infected neurons. This activity persisted even when we severed the presynaptic axons, showing that infection-induced firing is independent of input from presynaptic brainstem neurons. This activity was not observed after infections with an attenuated PRV recombinant used for circuit tracing or with PRV mutants lacking either viral glycoprotein B, required for membrane fusion, or viral membrane protein Us9, required for sorting virions and viral glycoproteins into axons. We propose that the viral fusion proteins produced by virulent PRV infection induce electrical coupling in unmyelinated axons in vivo. This action would then give rise to the synchronous and cyclical activity in the ganglia and contribute to the characteristic peripheral neuropathy.

[Topographic features of lingual nerve and its relationship with other anatomical structures in maxillolingual groove].

By surgical interventions in maxillolingual groove area one should consider anatomical variations and topography of vessels, glands ducts and lingual nerve to prevent their injury. At the Department of Operative Surgery and Topographic Anatomy of the First Moscow State Medical University named after I.M. Sechenov we carried out anatomical study on cadavers (men and women, n=30).The study revealed topographical features of the lingual nerve and its relationship to other anatomical structures in the maxillolingual groove. It was found out that at the level of the second molar (96%) lingual nerve "crosses" duct of submandibular salivary gland, at the level of the third molar lingual nerve is located under the duct and lateral to it, closer to the inner surface of the body of the mandible. At the level of the first molar lingual nerve is located above and medial to Wharton duct and passes along sublingual-lingual muscles (m.hyoglossus).

DLK1 regulates branching morphogenesis and parasympathetic innervation of salivary glands through inhibition of NOTCH signalling.

BACKGROUND INFORMATION: Delta-like proteins 1 and 2 (DLK1, 2) are NOTCH receptor ligands containing epidermal growth factor-like repeats, which regulate NOTCH signalling. We investigated the role of DLK and the NOTCH pathway in the morphogenesis of the submandibular salivary glands (SMGs), using in vitro organotypic cultures. RESULTS: DLK1 and 2 were present in all stages of SMG morphogenesis, where DLK1 inhibited both NOTCH activity and SMG branching. The addition of NOTCH inhibitory agents, either soluble DLK1 (sDLK1) or N-[N-(3, 5-difluorophenacetyl-L-alanyl]-S-phenylglycine t-buthyl ester (DAPT), to the SMG culture medium did not affect the rate of cell proliferation, but induced a strong reduction in SMG branching, increased epithelial apoptosis, and impaired innervation of the epithelial end buds by local parasympathetic ganglion neurons. SMG innervation could be restored by the acetylcholine analog carbachol (CCh), which also rescued cytokeratin 5 (CK5(+))-expressing epithelial progenitor cells. Despite this, CCh failed to restore normal branching morphogenesis in the presence of either sDLK1 or DAPT. However, it improved recovery of branching morphogenesis in SMGs, once DLK1 or DAPT were removed from the medium. CONCLUSIONS: Our data suggest that DLK1 regulates SMGs morphogenesis and parasympathetic nerve fibre outgrowth through inhibition of NOTCH signalling.

Transoral submandibular ganglion neurectomy: an anatomical feasibility study.

BACKGROUND: The management of sialorrhea can be difficult for both the patient and the clinician. Current management includes behavioral modification, anticholinergics, botulinum injections, and a variety of surgical options, which all have demonstrated some efficacy. As minimally invasive procedures flourish, we explore the feasibility of highly selective transoral submandibular neurectomy (TOSN) for the management of sialorrhea. METHODS: Ten human cadaver dissections of the floor of mouth were performed bilaterally, for a total of 20 separate cases. An intraoral technique for highly selective, submandibular ganglion neurectomy is demonstrated. RESULTS: A transoral submandibular ganglion neurectomy was performed in 10 cadavers (20 neurectomies) easily and reliably, without injury to the submandibular duct or the main trunk of the lingual nerve. CONCLUSION: Transoral submandibular neurectomy is an attractive addition to the armamentarium of surgical options for the treatment of medically intractable sialorrhea. Further study in selected patients would need to be performed to demonstrate clinical feasibility.

Reinnervated nerves contribute to the secretion function and regeneration of denervated submandibular glands in rabbits.

This study aimed to investigate the contribution of redistributed nerves in the secretory function and regeneration of a denervated submandibular gland (SMG). The postganglionic parasympathetic and sympathetic denervated SMGs of rabbits were wrapped in polyester or acellular dermal matrices to block nerve regeneration either partially or completely. Submandibular glands were removed 4, 8, 16, and 24 wk after the operation and examined histologically. Furthermore, the aquaporin-5 (AQP5), muscarinic-3 (M3), and ß1-adrenergic receptors were evaluated by immunofluorescence and western blot analysis. After denervation, salivary flow was decreased and acinar cells were atrophic, and the expression levels of the M3, ß1-adrenergic, and AQP5 receptors were decreased. However, both impaired secretion function and atrophic parenchyma were gradually ameliorated with the growing redistribution of parasympathetic and sympathetic nerves. Apoptosis was markedly inhibited and expression of the M3, ß1-adrenergic, and AQP5 receptors was increased after reinnervation. In contrast, SMGs without reinnervated nerves maintained hyposecretion and atrophic parenchyma. In conclusion, reinnervated nerves in a rabbit's denervated SMG played an important role in the secretion function and regeneration of SMGs via up-regulation of the expression of neurotransmitter receptors and AQP5.

Atypical antipsychotics--effects of amisulpride on salivary secretion and on clozapine-induced sialorrhea.

OBJECTIVE: Amisulpride is suggested for treatment of clozapine-induced sialorrhea. However, objective measurements of its effectiveness are lacking and, preclinically, amisulpride has no effect. We currently hypothesise that amisulpride acts by reducing the nervous- rather than the clozapine-driven salivary secretion. MATERIAL AND METHODS: Effects of intravenous amisulpride (as well as of clozapine and raclopride, a dopamine D2/D3 antagonist) were investigated in rats, including those subjected to chronic preganglionic parasympathetic denervation (submandibular glands) or combined postganglionic parasympathetic and sympathetic denervation (parotid glands). In duct-cannulated glands, secretion was evoked reflexly, at low and maximum flow rates, and by electrical stimulation of the parasympathetic and sympathetic innervations, and administration of autonomimetics (including substance P). RESULTS: Unlike clozapine, amisulpride had no effect on the reflexly evoked secretion at maximum rate. With respect to reflex secretion at low rate and to the secretion evoked by muscarinic, α-adrenergic, ß-adrenergic and substance P receptors, amisulpride (in contrast to raclopride) dose dependently potentiated the responses. Amisulpride had no effect on gland blood flow. CONCLUSIONS: No support for any inhibitory influence of amisulpride was found. Conversely, amisulpride universally enhanced secretion, suggesting that amisulpride is a potential drug for dry-mouth treatment. The mechanism behind the potentiation is currently unknown.

Clozapine-induced salivation: interaction with N-desmethylclozapine and amisulpride in an experimental rat model.

Many drugs (e.g. amisulpride) have been used to treat troublesome clozapine-induced salivation; however, varying success has been achieved in this respect, probably because, until recently, the salivatory action of clozapine has been largely unexplained. In the rat, clozapine and its main metabolite, N-desmethylclozapine, were found to exert mixed secretory actions: excitatory, through muscarinic acetylcholine M1-receptors giving rise to a long-lasting, low-level flow of saliva; and inhibitory, through muscarinic M3-receptors and α(1) -adrenoceptors reducing the parasympathetically and sympathetically nerve-evoked flow of saliva. The aim of the present study was to define the interactions between clozapine and N-desmethylclozapine, and clozapine and amisulpride, with respect to the excitatory response. Submandibular glands, sensitized by chronic parasympathetic preganglionic denervation, were studied in pentobarbitone-anaesthetized rats. To prevent clozapine from being metabolized to N-desmethylclozapine by hepatic enzymes, the liver was, under terminal anaesthesia, excluded from the circulation. The weak receptor-stimulating clozapine prevented the strong receptor-stimulating N-desmethylclozapine, at specific ratios in humans and in rats, from exerting its full agonistic action. In conclusion, the contribution of N-desmethylclozapine to the clozapine-induced sialorrhoea was, at most, only partly additive. Furthermore, the present experimental set-up failed to demonstrate any anti-salivatory action of amisulpride on the clozapine-induced flow of saliva.

Salivary gland progenitor cell biology provides a rationale for therapeutic salivary gland regeneration.

An irreversible loss of salivary gland function often occurs in humans after removal of salivary tumors, after therapeutic radiation of head and neck tumors, as a result of Sjögren's syndrome and in genetic syndromes affecting gland development. The permanent loss of gland function impairs the oral health of these patients and broadly affects their quality of life. The regeneration of functional salivary gland tissue is thus an important therapeutic goal for the field of regenerative medicine and will likely involve stem/progenitor cell biology and/or tissue engineering approaches. Recent reports demonstrate how both innervation of the salivary gland epithelium and certain growth factors influence progenitor cell growth during mouse salivary gland development. These advances in our understanding suggest that developmental mechanisms of mouse salivary gland development may provide a paradigm for postnatal regeneration of both mice and human salivary glands. Herein, we will discuss the developmental mechanisms that influence progenitor cell biology and the implications for salivary gland regeneration.

The changes in submandibular gland size and function following chorda tympani section.

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.

Botox(®) to reduce drooling in a paediatric population with neurological impairments: a Phase I study.

BACKGROUND: The treatment of drooling in a paediatric population with neurological impairments is clinically challenging. Surgery is considered invasive, while behaviour modification techniques, correction of situational factors and oral-motor therapy do not always produce sustained improvement. In recent years the use of Botox® to decrease drooling has been investigated. AIMS: To review the clinical data from a Drooling Treatment Project for children with neurological impairments and to establish the validity of the drooling severity and frequency rating scales, establishing Phase I-level information about the therapeutic use of submandibular salivary gland injections of Botox® in various contexts. METHOD & PROCEDURES: A retrospective, explanatory design was used to review the data. Nine children, seven with cerebral palsy and two with operculum syndrome, ranging in age from 5 to 17 years (mean = 9;3 years) were included. Drooling was assessed by qualified speech-language therapists using drooling rating scales, in five different situations and at different time points pre- and post-Botox® injection up to 6 months. Quantitative and qualitative analyses were computed. Parents'/primary caregivers' perceptions of drooling and treatment with Botox® were also considered using an interview form and a quality of life questionnaire. OUTCOMES & RESULTS: Statistically significant reductions in drooling with large effect sizes were obtained in the communicating and general appearance situations. There was a difference in the pattern of response between the children with cerebral palsy and those with operculum syndrome. Discrepancies between the parents and the speech-language therapists regarding the context of drooling reduction were found. Most parents/primary caregivers felt their children's lives and their own had improved following the Botox® injection and would repeat the treatment. The drooling rating scales were a valid method to assess drooling in a clinical situation. CONCLUSIONS & IMPLICATIONS: In the clinical setting of the Drooling Treatment Project, the results indicated that the context in which drooling occurs is an important factor and suggested the value of considering the situational context when making drooling judgments. Further, there was a difference in the pattern of response between the children with cerebral palsy and those with operculum syndrome, suggesting that aetiology may be involved in the response to Botox®.

Effect of High Fat and Fructo-Oligosaccharide Consumption on Immunoglobulin A in Saliva and Salivary Glands in Rats.

Consumption of indigestible dietary fiber increases immunoglobulin A (IgA) levels in saliva. The purpose of this study is to clarify the synergistic effect of the intake of a high amount of fats and indigestible dietary fiber on IgA levels in saliva and submandibular glands (SMG). Seven-week-old Wistar rats were fed a low-fat (60 g/kg) fiberless diet, low-fat fructo-oligosaccharide (FOS, 30 g/kg) diet, high-fat (220 g/kg) fiberless diet, or high-fat FOS diet for 70 days. The IgA flow rate of saliva (IgA FR-saliva) was higher in the low-fat FOS group than in the other groups (p < 0.05). Furthermore, the concentration of tyrosine hydroxylase (a marker of sympathetic nerve activation) in the SMG was higher in the low-fat FOS group (p < 0.05) and positively correlated with the IgA FR-saliva (rs = 0.68. p < 0.0001. n = 32) in comparison to that in the other groups. These findings suggest that during low-fat FOS intake, salivary IgA levels may increase through sympathetic nerve activation.

Roles of lysosomal proteolytic systems in AQP5 degradation in the submandibular gland of rats following chorda tympani parasympathetic denervation.

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.

Orexin A and B in the rat superior salivatory nucleus.

Orexin (OX), which regulates sleep and wakefulness and feeding behaviors has 2 isoforms, orexin-A and -B (OXA and OXB). In this study, the distribution of OXA and OXB was examined in the rat superior salivatory nucleus (SSN) using retrograde tracing and immunohistochemical and methods. OXA- and OXB-immunoreactive (-ir) nerve fibers were seen throughout the SSN. These nerve fibers surrounded SSN neurons retrogradely labeled with Fast blue (FB) from the corda-lingual nerve. FB-positive neurons had pericellular OXA- (47.5%) and OXB-ir (49.0%) nerve fibers. Immunohistochemistry for OX receptors also demonstrated the presence of OX1R and OX2R in FB-positive SSN neurons. The majority of FB-positive SSN neurons contained OX1R- (69.7%) or OX2R-immunoreactivity (57.8%). These neurons had small and medium-sized cell bodies. In addition, half of FB-positive SSN neurons which were immunoreactive for OX1R (47.0%) and OX2R (52.2%) had pericellular OXA- and OXB-ir nerve fibers, respectively. Co-expression of OX1R- and OX2R was common in FB-positive SSN neurons. The present study suggests a possibility that OXs regulate the activity of SSN neurons through OX receptors.

Altered plasticity of the parasympathetic innervation in the recovering rat submandibular gland following extensive atrophy.

Adult rat submandibular glands have a rich autonomic innervation, with parasympathetic and sympathetic nerves working in synergy rather than antagonistically. Ligation of the secretory duct rapidly causes atrophy and the loss of most acini, which are the main target cell for parasympathetic nerves. Following deligation, there is a recovery of gland structure and function, as assessed by autonomimetic stimulation. This study examines whether the parasympathetic nerves reattach to new target cells to form functional neuro-effector junctions. Under recovery anaesthesia, the submandibular duct of adult male rats was ligated via an intra-oral approach to avoid damaging the chorda-lingual nerve. Four weeks later, rats were either killed or anaesthetized and the ligation clip removed. Following a further 8 weeks, both submandibular ducts were cannulated under terminal anaesthesia. Salivary flows were then stimulated electrically (chorda-lingual nerve at 2, 5 and 10 Hz) and subsequently by methacholine (whole-body infusion at two doses). Glands were excised, weighed and divided for further in vitro studies or fixed for histological examination. Ligation of ducts caused 75% loss of gland weight, with the loss of most acinar cells. Of the remaining acini, only 50% were innervated despite unchanged choline acetyltransferase activity, suggesting few parasympathetic nerves had died. Following deligation, submandibular glands recovered half their weight and had normal morphology. Salivary flows from both glands (per unit of gland tissue) were similar when evoked by methacholine but greater from the deligated glands when evoked by nerve stimulation. This suggests that parasympathetic nerves had reattached to new target cells in the recovered glands at a greater ratio than normal, confirming reinnervation of the regenerating gland.

Perineural Invasion and Perineural Tumor Spread in Head and Neck Cancer.

Perineural invasion (PNI), the neoplastic invasion of nerves, is a common pathologic finding in head and neck cancer that is associated with poor clinical outcomes. PNI is a histologic finding of tumor cell infiltration and is distinct from perineural tumor spread (PNTS), which is macroscopic tumor involvement along a nerve extending from the primary tumor that is by definition more advanced, being radiologically or clinically apparent. Despite widespread acknowledgment of the prognostic significance of PNI and PNTS, the mechanisms underlying its pathogenesis remain largely unknown, and specific therapies targeting nerve invasion are lacking. The use of radiation therapy for PNI and PNTS can improve local control and reduce devastating failures at the skull base. However, the optimal volumes to be delineated with respect to targeting cranial nerve pathways are not well defined, and radiation can carry risks of major toxicity secondary to the location of adjacent critical structures. Here we examine the pathogenesis of these phenomena, analyze the role of radiation in PNI and PNTS, and propose guidelines for radiation treatment design based on the best available evidence and the authors' collective experience to advance understanding and therapy of this ominous cancer phenotype.

Expression of NGF in sympathetic neurons leads to excessive axon outgrowth from ganglia but decreased terminal innervation within tissues.

The effects of nerve growth factor (NGF) on sympathetic axon growth were investigated by generating transgenic mice in which the beta subunit of NGF was expressed in sympathetic neurons using the human dopamine beta-hydroxylase (DBH) promoter. In DBH-NGF mice, the sympathetic trunk and nerves growing to peripheral tissues were enlarged and contained an increased number of sympathetic fibers. Although sympathetic axons reached peripheral tissues, terminal sympathetic innervation within tissues was decreased in DBH-NGF mice. This effect could be reversed in the pancreas by overexpression of NGF in pancreatic islets. The observations are consistent with a model in which NGF gradients are not required to guide sympathetic axons to their targets, but are required for the establishment of the normal density and pattern of sympathetic innervation within target tissues.