The postganglionic parasympathetic fibers originating in the otic ganglion are distributed in several branches of the trigeminal mandibular nerve: an HRP study in the guinea pig

Clinical anatomy of the inferior labial gland: a narrative review

Objective

In this article we review the literature on the inferior labial gland from a clinical and anatomical perspective.

Background

Regardless of its importance in clinical practice, there are no medical literature that comprehensively reviewed the inferior labial gland.

Methods

A database search using PubMed and Google Scholar was conducted. The following keywords were used in the search: "lower labial salivary gland", "lower labial gland", "inferior labial salivary gland", AND "inferior labial gland".

Conclusions

The human labial glands are types of minor salivary gland that continuously secrete small amounts of mucous and serous substances to maintain oral health. The inferior labial glands are innervated by the inferior labial branch of the mental nerve, and the inferior labial branch of the facial artery is the main arterial supply to the lower lip. Although they only have an auxiliary role in saliva production compared to the major salivary glands, minor salivary glands provide a certain amount of lubrication in the oral cavity by the continuous outflow of saliva. The inferior labial gland not only promotes moisturization in the oral cavity but also secretes substances with antibacterial effects, which is important for the function of the oral cavity. A recent study showed that the rate of salivary secretion from the inferior labial glands does not change with age, and in some cases the inferior labial glands are used for diagnosing intractable diseases such as Sjogren's syndrome and cystic fibrosis. In addition, since the inferior labial glands themselves can be the site of cyst and/or neoplasia development, we should be careful to distinguish them from other diseases. Elucidation of the anatomy, physiology, and pathology of the inferior labial glands, is important for understanding human health and diseases.

Dual innervation of the submandibular gland by nerve to mylohyoid and chorda tympani

The chorda tympani typically utilises the lingual nerve and submandibular ganglion to transmit parasympathetic fibres to the submandibular gland. During a routine anatomy dissection, the submandibular gland was found to be innervated by both the lingual nerve and the nerve to mylohyoid. The clinical implications of this variant dual innervation to the submandibular gland is not clear due to its rarity: however, recognising such a variation should be borne in mind during surgical intervention near the nerve to mylohyoid.

Topography, syntopy and morphology of the human otic ganglion: a cadaver study

The human otic ganglion (OG) is not readily accessible during ordinary anatomical teaching courses because of insufficient time and severe difficulties encountered in dissection. Accordingly, most anatomical descriptions of its location, relation to neighbouring structures, size and shape are supported only by drawings, but not by photographs. The aim of this study has been to present the OG with associated roots and branches in dissected anatomic specimens. Following cumbersome dissection and precise photo-documentation, a detailed analysis of location, syntopy and morphology was performed. We carried out this study in 21 infratemporal fossae of 18 cadavers and were able to identify the OG, the mandibular-, the inferior alveolar- and the lingual nerve in all of them. We found no significant variation regarding the location of the GO in the infratemporal fossa and its syntopy to the adjacent structures. An OG resembling the classic description was found only in 90.50% of the cases. All 3 roots (parasympathetic, sympathetic and sensory) could be identified only in 82.3% of the specimens. The established presence of ganglionic branches varied from 0% (communicating rami to the meningeal branch of the mandibular nerve, to the greater petrosal nerve and to the lingual nerve) to 90% (r. communicans to n. canalis pterygoideus). We conclude that precise knowledge of this enormous variety might be very helpful not only to students of medicine and dentistry during anatomical dissection courses, but also to head and neck surgeons, ear-nose-throat specialists and neurosurgeons when treating pathology of pre- and postganglionic fibres.

Variations in the posterior division branches of the mandibular nerve in human cadavers

INTRODUCTION

The lingual, inferior alveolar and auriculotemporal nerves, being branches of the posterior division of the mandibular nerve, mainly innervate the mandibular teeth and all the major salivary glands. Anomalous communications among these branches are widely reported due to their significance to various treatment procedures undertaken in the region. This study was performed as detailed exploration of the functional perspectives of such communicating branches would further enhance the scope of these procedures.

METHODS

A total of 36 specimens were dissected to examine the infratemporal region. The branches from the posterior division of the mandibular nerve--namely the lingual, inferior alveolar and auriculotemporal nerves--were carefully dissected, and their branches were studied and analysed for abnormal course.

RESULTS

Communication between branches of the posterior division of the mandibular nerve was observed in four specimens. In two of the four specimens, communication between the mylohyoid and lingual nerves was observed. A rare and seldom reported type of communication between the auriculotemporal and inferior alveolar nerves is described in this study. This communicating nerve split into two to form a buttonhole for the passage of the mylohyoid nerve.

CONCLUSION

Such communicating branches between nerves found in this study are developmental in origin and thought to maintain functional integrity through an alternative route.

Quantification of neuropeptides (calcitonin gene-related peptide, substance P, neurokinin A, neuropeptide Y and vasoactive intestinal polypeptide) expressed in healthy and inflamed human dental pulp

AIM

To quantify the expression of calcitonin gene-related peptide (CGRP), substance P (SP), neurokinin A (NKA), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) in healthy and inflamed human dental pulp tissue.

METHODOLOGY

Six pulp samples were obtained from teeth having a clinical diagnosis of acute irreversible pulpitis. Another 12 pulp samples were obtained from premolars where extraction was indicated for orthodontic purposes. In six of these premolar teeth inflammation was induced by mechanical pulp exposure prior to sample collection. All samples were processed and 125I-labelled; neuropeptides were quantified by competition assays. ANOVA and Mann-Whitney's (post hoc) tests were used to establish statistically significant differences between the groups.

RESULTS

Expression of five neuropeptides was found in all human pulp samples. Statistical analysis revealed a significantly higher (P < 0.05) expression of CGRP, SP, NKA and NPY in both inflammatory conditions compared with healthy pulp control values. VIP expression remained stable during the inflammatory conditions.

CONCLUSION

Expression of CGRP, SP and NKA released from C-fibres and NPY released from sympathetic fibres is significantly higher in the inflamed human pulp compared with healthy pulp. Expression of VIP released from parasympathetic fibres is not increased during the inflammatory conditions of human dental pulp.

Expression of immunoreactivity to neurokinin-1 receptor by subsets of cranial parasympathetic neurons: correlation with neuropeptides, nitric oxide synthase, and pathways

We examined the patterns of coexistence of immunoreactivity to the neurokinin-1 (NK(1)) tachykinin receptor, nitric oxide synthase, and neuropeptides in the sphenopalatine and otic ganglia of guinea pigs using a combination of multiple-labeling immunohistochemistry and pathway tracing in vitro. Most neurons had immunoreactivity to vasoactive intestinal peptide (85-96%) and neuropeptide Y (60%). Subpopulations of vasoactive intestinal peptide-immunoreactive neurons also had immunoreactivity to nitric oxide synthase (37-48%) or enkephalin (25-35%), but these formed mutually exclusive populations. Almost all neurons expressing NK(1) receptor immunoreactivity contained immunoreactivity to enkephalin, vasoactive intestinal peptide, and neuropeptide Y, but not nitric oxide synthase. Using a combination of retrograde axonal tracing and axonal crushing, we found that most neurons with immunoreactivity to nitric oxide synthase projected along the nasopalatine and ethmoidal nerves to the nasal mucosa. In contrast, most neurons with immunoreactivity to enkephalin followed the zygomatic nerve to the facial skin and lacrimal gland. Based on their peptide content, we conclude that the neurons with immunoreactivity to enkephalin and NK(1) receptor projected selectively to the skin. In both the sphenopalatine and the otic ganglia, about half of the neurons with NK(1) receptor immunoreactivity were surrounded by varicose nerve fibers with substance P immunoreactivity. Many of these fibers are likely to have originated in the trigeminal ganglion. Taken together, these observations establish a strong anatomical basis for a range of interactions between trigeminal and cranial parasympathetic pathways that may underlie pathophysiological conditions such as trigeminal neuralgia.

Nerve injury-induced pain in the trigeminal system

This article reviews some recent findings on peripheral mechanisms related to the development of oro-facial pain after trigeminal nerve injury. Chronic injury-induced oro-facial pain is not in itself a life-threatening condition, but patients suffering from this disorder undoubtedly have a reduced quality of life. The vast majority of the work on pain mechanisms has been carried out in spinal nerve systems. Those studies have provided great insight into mechanisms of neuropathic spinal pain, and much of the data from them is obviously relevant to studies of trigeminal pain. However, it is now clear that the pathophysiology of the trigeminal nerve (a cranial nerve) is in many ways different to that found in spinal nerves. Whereas some of the changes seen in animal models of trigeminal nerve injury mimic those occurring after spinal nerve injury (e.g., the development of spontaneous activity from the damaged axons), others are different, such as the time-course of the spontaneous activity, some of the neuropeptide changes in the trigeminal ganglion, and the lack of sprouting of sympathetic terminals in the ganglion. Recent findings provide new insights that help our understanding of the etiology of chronic injury-induced oro-facial pain. Future investigations will hopefully explain how data gained from these studies relate to clinical pain experience in man and should enable the rapid development of new therapeutic regimes.

Expression of sodium channel SNS/PN3 and ankyrin(G) mRNAs in the trigeminal ganglion after inferior alveolar nerve injury in the rat

The inferior alveolar nerve is a sensory branch of the trigeminal nerve that is frequently damaged, and such nerve injuries can give rise to persistent paraesthesia and dysaesthesia. The mechanisms behind neuropathic pain following nerve injury is poorly understood. However, remodeling of voltage-gated sodium channels in the neuronal membrane has been proposed as one possible mechanism behind injury-induced ectopic hyperexcitability. The TTX-resistant sodium channel SNS/PN3 has been implicated in the development of neuropathic pain after spinal nerve injury. We here study the effect of chronic axotomy of the inferior alveolar nerve on the expression of SNS/PN3 mRNA in trigeminal sensory neurons. The organization of sodium channels in the neuronal membrane is maintained by binding to ankyrin, which help link the sodium channel to the membrane skeleton. Ankyrin(G), which colocalizes with sodium channels in the initial segments and nodes of Ranvier, and is necessary for normal neuronal sodium channel function, could be essential in the reorganization of the axonal membrane after nerve injury. For this reason, we here study the expression of ankyrin(G) in the trigeminal ganglion and the localization of ankyrin(G) protein in the inferior alveolar nerve after injury. We show that SNS/PN3 mRNA is down-regulated in small-sized trigeminal ganglion neurons following inferior alveolar nerve injury but that, in contrast to the persistent loss of SNS/PN3 mRNA seen in dorsal root ganglion neurons following sciatic nerve injury, the levels of SNS/PN3 mRNA appear to normalize within a few weeks. We further show that the expression of ankyrin(G) mRNA also is downregulated after nerve lesion and that these changes persist for at least 13 weeks. This decrease in the ankyrin(G) mRNA expression could play a role in the reorganization of sodium channels within the damaged nerve. The changes in the levels of SNS/PN3 mRNA in the trigeminal ganglion, which follow the time course for hyperexcitability of trigeminal ganglion neurons after inferior alveolar nerve injury, may contribute to the inappropriate firing associated with sensory dysfunction in the orofacial region.

Autonomic and sensory innervation of cat molar gland and blood vessels in the lower lip, gingiva and cheek

Innervation of the molar gland and blood vessels in the lower lip, gingiva and cheek mucous membrane was investigated in the cat with the aid of whole mount acetylthiocholinesterase (WATChE) histochemistry and retrograde neuronal tracing methods with horseradish peroxidase (HRP) and HRP-conjugated wheat germ agglutinin (WGA-HRP). The molar gland was found to be supplied from the buccal nerve and branches of the mylohyoid nerve on the basis of microdissection of WATChE-stained mandibular preparations under a dissecting microscope. The rostral half of the lower lip-gingiva was innervated by mental branches from the inferior alveolar nerve. The caudal half of the lower lip-gingiva and cheek mucous membrane were observed to be supplied from the buccal nerve. Following injections of HRP/WGA-HRP into the molar gland, lower lip-gingiva and cheek, many retrogradely labeled ganglion neurons were observed in the ipsilateral main and accessory otic ganglia, superior cervical ganglion and mandibular division of the trigeminal ganglion. In the pterygopalatine ganglion, a small number of positive neurons were found, but in a few cases in which the injected tracer was restricted to the lower lip-gingiva and anterior half of the molar gland, labeled neurons were not detected in the main ganglion nor in its accessory microganglia. These findings indicate that the cat molar gland receives a postganglionic parasympathetic supply from the otic ganglia, postganglionic sympathetic input from the superior cervical ganglion and sensory innervation from the trigeminal ganglion by way of the buccal nerve and mylohyoid nerve. Vessels in the rostral half of the lower lip-gingiva receive the same inputs from the inferior alveolar nerve, and vessels in the caudal half receive inputs from the buccal nerve. The vessels in the cheek mucous membrane receive dual parasympathetic supplies from the otic ganglia and the pterygopalatine ganglion by way of the buccal nerve.

Anatomic study of the otic ganglion in humans

The presentation in the literature of the anatomy of the human otic ganglion (OG) has not varied much over the past three quarters of a century. Precise, similar descriptions of its size, color, shape, and relation with neighboring structures are portrayed in numerous textbooks and articles. We have carried out a study of the OG in 30 infratemporal fossae of 15 cadavers. Otic ganglia resembling the classic description were found in less than 60% of the cases. In 13%, some thickening could be seen adjacent to the mandibular nerve and in 27%, no definite structure could be observed. Except for a fleeting mention of this occurrence in a textbook from 1927, substantiated by personal communication with an authority in the field, we could find no record of the possible absence of this structure in the available literature. We describe our findings and stress the apparent anatomic variability of the OG. The pertinent literature is reviewed.

Distribution of postganglionic parasympathetic fibers originating in the pterygopalatine ganglion in the maxillary and ophthalmic nerve branches of the trigeminal nerve; HRP and WGA-HRP study in the guinea pig

The distribution of the postganglionic parasympathetic fibers originating in the pterygopalatine ganglion (PTPG) has been traced in the guinea pig by means of the HRP and WGA-HRP methods. The greatest number of labeled cells were observed when WGA-HRP was injected in the lacrimal gland. After applying HRP to all the ramifications of the maxillary and ophthalmic divisions of the trigeminal nerve, labeled neurons were found in the PTPG. Numerous PTPG fibers were detected in the ethmoidal and sphenopalatine nerves. The presence of PTPG fibers in the supraorbital, infratrochlear, zygomaticotemporal, zygomaticofacial-inferior palpebral, sphenopalatine and infraorbital-superior alveolar nerves has not hitherto been reported in mammals.

Contralateral projections of trigeminal mandibular primary afferents in the guinea pig as seen by transganglionic transport of horseradish peroxidase

Transganglionic transport of horseradish peroxidase (HRP) was used to investigate contralateral projections of trigeminal mandibular fibers in the guinea pig. After application of HRP to the buccal, lingual, auriculotemporal, mylohyoid, mental and inferior alveolar nerves, crossing fibers and contralateral endings were found in the caudal region of the nucleus of the solitary tract (most of these belonging to the buccal and lingual nerves), the dorsomedial region of the subnucleus caudalis of the trigeminal sensory nuclear complex (TSNC), and the dorsal horns of the first 5 cervical spinal cord segments (C1-C5). The greatest numbers of crossing fibers in the medullary and cervical dorsal horn segments belonged to the mental and mylohyoid nerves, though these nerves did not project contralaterally to C4-C5. Contralateral buccal and lingual endings were scattered sparsely from the subnucleus caudalis to C5, and only very few contralateral auriculotemporal terminals were observed. Though laminae I-V of the dorsomedial region of the medullary and cervical dorsal horns all exhibited contralateral endings of the mental and mylohyoid nerves, most such endings were found in laminae IIi-III, followed by lamina IV, which suggests their involvement in the reception of mechanical stimuli and in the sensory motor reflexes of the orofacial region. The contralateral buccal and lingual terminals were distributed somatotopically in the first 5 cervical cord segments, with the lingual endings rostral to the buccal terminals within each segment. In C4 and C5 lingual endings appeared exclusively in laminae I and IIo, suggesting that like the ipsilateral lingual projections at this level, which also terminate in these laminae, they may be involved in pain and temperature sensation.

Target-related patterns of co-existence of neuropeptide Y, vasoactive intestinal peptide, enkephalin and substance P in cranial parasympathetic neurons innervating the facial skin and exocrine glands of guinea-pigs

The patterns of co-existence of neuropeptides in cranial autonomic neurons of guinea-pigs have been examined with quantitative double-labelling immunofluorescence and retrograde axonal tracing using Fast Blue. Within the sphenopalatine, otic, sublingual and submandibular ganglia, and a prominent intracranial ganglion associated with the glossopharyngeal nerve, most neurons contained immunoreactivity of vasoactive intestinal peptide, neuropeptide Y, enkephalin and substance P in combinations that were correlated with their projections. Hair follicles in the facial skin formed a major target of sphenopalatine ganglion cells. The combinations of peptides co-existing in these neurons depended upon the region of the skin where the follicles were located. The parotid gland was innervated by neurons with cell bodies in the otic ganglion or the intracranial ganglion. Most of these neurons contained immunoreactivity to all four peptides. The sublingual gland was innervated by local ganglion cells usually containing immunoreactivity to neuropeptide Y, vasoactive intestinal peptide and substance P. The submandibular gland was innervated by local ganglion cells containing enkephalin immunoreactivity and low levels of immunoreactivity to neuropeptide Y. Presumptive vasodilator neurons, containing immunoreactivity to vasoactive intestinal peptide but no other peptide examined here, comprised less than 10% of cranial autonomic ganglion cells. These results demonstrate that the patterns of co-existence of neuropeptides in cranial autonomic neurons show a high degree of target specificity. The discovery that hair follicles form a major parasympathetic target implies a broader range of actions of cranial autonomic neurons than has been suspected until now.

Otic ganglion parasympathetic neurons innervate the pulp of the mandibular incisor of the guinea pig

Neurons innervating the pulp of the lower incisor of the guinea pig have been traced using the fluorochrome Fast blue. Besides those located in the ipsilateral Gasser's ganglion, a small number of parasympathetic cells in the ipsilateral otic ganglion were also found to innervate the pulp (chiefly the deepest region) via the inferior alveolar nerve. This is the first anatomical evidence of the presence of parasympathetic fibers in the teeth of mammals. It is suggested that these parasympathetic neurons stimulate the vasodilation of the arterioles supplying the tooth pulp.