Trigeminal Neuralgia Induced by Sour and Spicy Foods: What Is the Underlying Mechanism? A Case Report

This article is a case report of a female patient in whom sour and spicy foods evoked trigeminal neuralgia (TN). An attempt to reveal the underlying pain mechanism is described and discussed. The 81-year-old woman had been suffering from classical TN since the age of 50. Attacks occurred spontaneously or in response to mechanical stimuli. In addition, sour and spicy foods also evoked TN attacks and were therefore avoided for years. Medical treatment was initially effective, but two radiofrequency ablations of the gasserian ganglion were required later on and yielded good, albeit incomplete, pain relief. Sensory examination consisted of application of a mechanical stimulus and sweet, salty, sour, and spicy solutions to the anterior part of the tongue and the mandibular mucosa on both sides. Mechanical stimuli were felt but produced no pain. When applied to the tongue, the tastes of all solutions were identified but produced no pain. When applied to the mucogingival line, none of the solutions was identified but the sour and the spicy solutions provoked TN immediately following their application. These findings suggest that in this patient, sour and spicy solutions may have evoked TN attacks by direct activation of trigeminal C-nociceptors, possibly via interactions with transient receptor potential vanilloid 1 receptors.

Substance P expression in the gingival tissue after upper third molar extraction: effect of ketoprofen, a preliminary study

The aim of this study was to evaluate substance P (SP) levels and the effect of a non-steroidal anti-inflammatory drug (NSAID), ketoprofen, on SP in the pericoronal gingival tissue after extraction of upper third molars. A sample of 20 young non-smoking systemically healthy adults of both sexes, with a healthy upper third molar to extract for orthodontic purposes, was selected. After extraction, a sample of the gingival tissue of the pericoronal region was collected with a sterile scalpel, placed into test tubes and kept frozen at -20°C until the SP determination. SP levels were determined by using a commercially available enzyme immunoassay (ELISA) kit. The subjects were randomly divided into two groups: group 1 received a single dose of ketoprofen 30 minutes prior to the experimental procedure. The subjects of group 2 did not receive any kind of drug administration before extraction. The patients were asked to complete a diary on the postoperative pain. A relevant amount of SP was measured in all the gingival samples. No statistically significant difference could be detected in SP expression between the two groups. In group 1 pain appearance was significantly delayed (6.2±0.13 hours) in comparison with group 2 (3.95±0.2 hours). In this small selected group of subjects and limited study design, preventive administration of ketoprofen did not significantly affect the gingival levels of SP, the clinical recommendation emerging is that of NSAID administration postoperatively but before pain appearance in order to optimize the management of pain of the patient.

The occurrence of paraesthesia of the maxillary division of the trigeminal nerve after dental local anaesthetic use: a case report

Paraesthesia can be a complication of surgical intervention. Its occurrence after dental local anaesthetic use is a rare event in general dental practice. Reported cases have mainly described its presentation for the mandibular division of the trigeminal nerve with very few reports for the maxillary division of this nerve. This report describes a case of paraesthesia in the maxillary region following local anaesthetic use prior to removal of an upper molar tooth.

Orofacial thermal thresholds: time-dependent variability and influence of spatial summation and test site

AIM

To investigate time-dependent variability and influence of test site and stimulation area size on intraoral cold detection, warmth detection, and heat pain thresholds.

METHODS

Thirty healthy volunteers (15 women and 15 men) participated. Six extra- and intraoral sites were examined, and cold detection, warmth detection, and heat pain thresholds were measured. Time variability and influence of spatial summation were also studied at one site-the tip of the tongue-three times over a 6-week period. One-way ANOVA for repeated measures and paired sample t test compared mean values and SD within and between sites for all thresholds.

RESULTS

Several between-site differences were significant (P < .05). Lowest intraoral thresholds for all stimuli were measured at the tongue site, and at the tongue, thresholds for warmth detection and heat pain, but not cold detection, decreased with increasing size of stimulation area (P < .05). Overall, thresholds at the tongue site varied nonsignificantly over time (P > .05).

CONCLUSION

Test site affects orofacial thermal thresholds substantially, whereas time variability and spatial summation on the tongue appear to be modest.

Periodontal anaesthetisation decreases rhythmic synchrony between masseteric motor units at the frequency of jaw tremor

This study links the reduction in jaw physiological tremor around 8 Hz following periodontal mechanoreceptor (PMR) anaesthetisation to changes in coherence between masseteric motor unit discharges. We have recorded single motor unit activity from two separate sites in the right masseter muscle during a low level tonic contraction, both prior to and during anaesthetisation of the peri-incisal PMRs. Anaesthetisation of PMRs decreased coherent activity between motor units circa 8 Hz, and decreased synchrony between the same motor unit pairs. It is proposed that tremor-generating inputs that cause rhythmic synchronisation of masseteric motor units arise from, or are amplified by the PMRs.

Mechanical allodynia and thermal hyperalgesia induced by experimental squamous cell carcinoma of the lower gingiva in rats

We developed a rat model of oral cancer pain by inoculating cancer cells into the lower gingiva. A squamous cell carcinoma (SCC) derived from Fisher rats, SCC-158, was inoculated into the subperiosteal tissue on the lateral side of the lower gingiva in male Fisher rats. Inoculation of cancer cells induced marked mechanical allodynia and thermal hyperalgesia in the ipsilateral maxillary and mandibular nerve area. Infiltration of the tumor cells into the mandible and the completely encompassed inferior alveolar nerve was observed. Calcitonin gene-related peptide (CGRP)-, substance P (SP)-, ATP receptor (P2X(3))-, and capsaicin receptor (TRPV1)-immunoreactive cells strikingly increased in the small-cell group of trigeminal ganglia (TGs) after tumor cell inoculation. The TRPV1-immunoreactive cells also increased in the medium- and large-cell groups. Retrograde tracing combined with immunofluorescence techniques revealed the increased expression of peptides and the receptors in maxillary nerve afferent neurons. These results suggest that inoculation of SCC cells into the lower gingiva produces mechanical allodynia and thermal hyperalgesia, indicating the establishment of a novel rat model of oral cancer pain. Increased expression of CGRP, SP, P2X(3), and TRPV1 in the TG may be involved in the behavioral changes in this model.

PERSPECTIVE

To clarify the mechanisms of oral cancer pain, we examined the expression of calcitonin gene-related peptide, substance P, ATP receptor P2X(3), and capsaicin receptor TRPV1 in trigeminal ganglia. Characterizations of these molecular systems which mediate pain perception are important to develop novel clinical tools for promoting relief of oral cancer pain.

Identification and neuropeptide content of trigeminal neurons innervating the rat gingivomucosal tissue

OBJECTIVES

The purpose of this study was to identify and characterise the neuropeptide content and the size of trigeminal ganglion (TG) neurons innervating the rat gingivomucosal tissue.

DESIGN

Retrograde nerve tracer Fluorogold (FG) was injected into the gingiva (group 1, n=5) or applied into the gingival sulcus (group 2, n=5) of the first right maxillary molar. After 10 days, the ganglia were dissected and FG fluorescence was observed under UV light microscope. Expression of calcitonin gene-related peptide (CGRP) and substance P (SP) in FG-labelled neurons was investigated by immunohistochemistry. Cross-sectional areas of neuron cell bodies containing FG were determined. As a control group, approximately 1000 neuron cell bodies representing the entire TG neuron population was evaluated in five trigeminal ganglia.

RESULTS

In group 1, the percentages of neurons containing CGRP (median 63%, range 48-72%) and SP (median 64%, range 54-64%) were significantly greater than in the control group (CGRP: median 43%, range 42-47% and SP: median 23%, range 21-27%). In group 2, only the percentage of neurons containing SP (median 50%, range 40-56%) was significantly greater than in the control group. FG-labelled neurons were predominantly small or medium sized (less than 1200 microm2). The neurons in the group 1 were significantly smaller than in group 2. In both experimental groups, immunopositive neurons were significantly smaller than immunonegative neurons.

CONCLUSIONS

The majority of neurons in TG that innervate the rat gingivomucosa are small or medium sized and contain CGRP and SP.

Failure to obtain adequate anaesthesia associated with a bifid mandibular canal: a case report

The inferior alveolar nerve (IAN) block is the most common method for obtaining mandibular anaesthesia in dental practice but it is estimated to have a success rate of only 80 to 85 per cent. Causes of failure include problems with operator technique and anatomical variation between individuals. This case report involves a patient who received IAN blocks on two separate occasions that resulted in only partial anaesthesia of the ipsilateral side of the mandible. Radiographic assessment disclosed the presence of bifid mandibular canals that were present bilaterally and that may have affected the outcomes of the local anaesthetic procedures. Previous studies of bifid mandibular canals are reviewed and suggestions provided that should enable clinicians to differentially diagnose, and then manage, cases where IAN blocks result in inadequate mandibular anaesthesia.

Predictive factors in infraorbital sensitivity disturbances following zygomaticomaxillary fractures

The aim of this study was to define if the alterations in sensory modalities could be a predictive factor in the prognostic recovery of the ION. Ten patients that had suffered facial trauma, associated with sensitivity alterations of the ION were evaluated prospectively. Touch detection thresholds (TD) were measured using Von Frey's filaments aesthesiometer. A warm/cold discrimination (W/C) was also done to the patients, on the same areas. The patients were examined in both sides of the face, using the non-traumatized side as control. The tests were done before surgery and several times postoperatively. For statistical analysis of the results, the two-sample t test was used. A significant difference (P < 0.0001) in the mean tactile recovery time between the areas without thermal sensitivity before surgery and those with normal thermal sensitivity before surgery was observed. Therefore, we propose that during the preoperative examination, the surgeon examines the thermal discrimination in order to establish prognosis and approximate recovery times.

Neuromagnetic Evidence that Gingiva Area is Adjacent to Tongue Area in Human Primary Somatosensory Cortex

The somatotopic organization of the human primary somatosensory (SI) area in the cerebral cortex has been intensively studied for the hand, lip, and tongue, but little is known about the gingiva. Penfield concluded that the gingival SI area was above the tongue area, as shown in his famous homunculus map. However, our recent study suggested that the lingual gingiva area was not so different to the tongue area. To delineate the fine SI somatotopy of the gingiva area, evoked magnetic fields were measured in 6 healthy subjects for the stimulus of the anterior or posterior and upper or lower parts of the lip, buccal and lingual gingiva, and tongue. Source position was estimated by a current dipole model at the first peak of the posterior-oriented current in a total of 12 cerebral hemispheres contralateral to the stimulation side. No significant difference was found between the positions of anterior and posterior or upper and lower parts of each structure. Both buccal and lingual gingiva areas were localized adjacent to the tongue area, but significantly lower than the lip area. We believe that the fine SI somatotopy of the human oral structures should be reconsidered.

Somatosensory-evoked fields for gingiva, lip, and tongue

To localize the oral primary somatosensory cortex, we measured somatosensory-evoked fields for the lip, gingiva, and tongue in six healthy subjects. The latency of the first peak of the posterior-oriented current in the contralateral hemisphere was 50.9 +/- 8.3 ms for the gingiva, significantly shorter than those for the lip and tongue peaks. The equivalent current dipole was localized on the central sulcus. The gingival dipole was localized significantly inferior to the lip dipole but not different from the tongue dipole. The moment of the gingival dipole was significantly smaller than that of the lip dipole but not different from that of the tongue dipole. Differences in the above parameters were negligible between the left and right, anterior and posterior, and upper and lower locations within the same organ, except that the dipole location for the anterior upper tongue was significantly inferior to that for the lower tongue.

Converging patterns of inputs from oral structures in the postcentral somatosensory cortex of conscious macaque monkeys

Single neuronal activities were recorded in the oral region of the postcentral gyrus in conscious Japanese monkeys. Among 5,756 neurons isolated, receptive fields (RFs) and submodalities were identified in 1,502 neurons in area 3b, 970 in area 1, and 1,461 in area 2. The relative incidence of neurons that had bilateral RFs increased gradually upon moving caudally from area 3b to area 2 (bilateral integration). A total of 276 neurons had bimaxillary RFs covering both the maxillary and mandibular divisions of the trigeminal nerve, such as the upper and lower lips, upper and lower teeth, palate and tongue, or combinations thereof. There was also a tendency for the relative incidence of neurons with bimaxillary RFs to increase across the postcentral gyrus but with an abrupt change in area 2 (bimaxillary integration). A total of 382 neurons had composite RFs covering more than one of five oral structures: lip, cheek mucosa, teeth/gingiva, tongue, and palate. The relative incidence of neurons with composite RFs was significantly higher in area 2 than in areas 3b and 1 (interstructural integration). These results indicate that the convergence of inputs from oral structures proceeds in a hierarchical manner across the postcentral gyrus, but chiefly in area 2 for the bimaxillary and interstructural integrations. The relative incidence of neurons with composite RFs was higher among neurons associated with the teeth/gingiva or palate than among neurons associated with the tongue or lip in all three areas. We interpret this to mean that anatomical or functional differences between oral structures might be reflected in the converging patterns in the oral representation.

Localization of the neuropeptide galanin in nerve fibers and epithelial keratinocytes of the rat molar gingiva

Knowledge of the histochemical substrates of cellular and neurovascular connections in the gingiva is essential in order to understand the initial mechanisms of inflammation in the periodontium. Since the localization of the neuroendocrine peptide galanin in the gingiva is still unclear, we used immunohistochemical, in situ hybridization and immunoblot techniques to assess the localization of galanin in the gingiva of rat molars. Galanin-immunoreactive nerve fibers were located around blood vessels in the lamina propria, beneath the epithelium, in the epithelial-proprial junction and in the basal layer of the epithelium. Galanin was highly expressed in the suprabasal keratinocytes of the gingival epithelium. The localization of galanin in gingival nerve fibers and the expression of galanin in keratinocytes of the gingival epithelium indicate that galanin may be a possible regulator of different cellular functions in the gingiva.

Regeneration of nerve fibres in the peri-implant epithelium incident to implantation in the rat maxilla as demonstrated by immunocytochemistry for protein gene product 9.5 (PGP9.5) and calcitonin gene-related peptide (CGRP)

The response of nerve fibres in the peri-implant epithelium to titanium implantation was investigated with an experimental model using rat maxilla and immunohistochemical techniques. The latter employed antibodies to protein gene product 9.5 (PGP9.5), and to calcitonin gene-related peptide (CGRP). In control rats without an implantation, a dense innervation of PGP9.5- and CGRP-positive nerve fibres was recognized throughout the junctional epithelium, as has been previously reported. A titanium-implantation induced a remarkable inflammatory reaction, as well as the destruction of covering epithelial cells. By 3-5 days post-implantation, inflammatory reaction showed a tendency to disappear, and the peri-implant epithelium showed proliferation and down-growth along the implant. At this stage, no nerve fibres were found around the peri-implant epithelium. At 10 days, a few nerve fibres reached the basal cell layers of the peri-implant epithelium, and entered it 15 days after implantation when the peri-implant epithelial cells showed morphological features roughly resembling those of normal junctional epithelial cells. At the complete osseointegration stage (days 20-30), the PGP9.5- and CGRP-positive nerve fibres, thin and beaded in appearance, were found distributed in the peri-implant epithelium. After 20 days, the numerical density of the intraepithelial nerves in the peri-implant epithelium appeared the same as, or less than, that in the normal junctional epithelium. These findings indicate that the peri-implant epithelium shows the same innervation as that in normal junctional epithelium, and that the intraepithelial nerve fibres in the peri-implant epithelium might have diverse functions, which have been suggested in the literature.

NK1, NK2, NK3 and CGRP1 receptors identified in rat oral soft tissues, and in bone and dental hard tissue cells

The distribution of the tachykinin receptors neurokinin-1 (NK1), neurokinin-2 (NK2) and neurokinin-3 (NK3), and the calcitonin gene-related peptide-1 (CGRP1) receptor were examined in rat teeth and tooth-supporting tissues by immunohistochemical methods and light and confocal microscopy. Western blot analysis was performed to identify the NK1- and the CGRP1-receptor proteins in the dental pulp. The results showed that odontoblasts and ameloblasts, cementoblasts and cementocytes, osteoblasts and osteocytes are all supported with the tachykinin receptors NK1 and NK2, but a distinct, graded cellular labeling pattern was demonstrated. The ameloblasts were also positive for CGRP1 receptor. Blood vessels in oral tissues expressed the tachykinin receptors NK1, NK2 and NK3, and the CGRP1 receptor. Both gingival and Malassez epithelium were abundantly supplied by NK2 receptor. Pulpal and periodontal fibroblasts demonstrated NK1 and NK2 receptors. Western blot analysis identified both the NK1- and the CGRP1-receptor proteins in the dental pulp. These results clearly indicate that the neuropeptides substance P, neurokinin A, neurokinin B and CGRP, released from sensory axons upon stimulation, directly modulate the function of the different types of bone and dental hard tissue cells, and regulate functions of blood vessels, fibroblasts and epithelial cells in oral tissues.

Neurons of the trigeminal main sensory nucleus participate in the generation of rhythmic motor patterns

The trigeminal principal sensory nucleus (NVsnpr) contains both trigemino-thalamic neurons and interneurons projecting to the reticular formation and brainstem motor nuclei. Here we describe the inputs and patterns of firing of NVsnpr neurons during fictive mastication in anaesthetized and paralysed rabbits to determine the role that NVsnpr may play in patterning mastication. Of the 272 neurons recorded in NVsnpr, 107 changed their firing patterns during repetitive stimulation of the left or right sensorimotor cortex to induce fictive mastication. Thirty increased their firing tonically. Seventy-seven became rhythmically active, but only 31 fired in phase with mastication. The others discharged in bursts at more than twice the frequency of trigeminal motoneurons. Most rhythmic masticatory neurons were concentrated in the dorsal part, and those which fired during the jaw closing phase of the cycle were confined to the anterior pole of the nucleus. Most of these cells had inputs from muscle spindle afferents, whereas most of those firing during jaw opening had inputs from periodontal receptors. Non-masticatory rhythmical neurons had receptive fields on the lips and face. The majority of rhythmical masticatory units were modulated during fictive mastication evoked by both the left and right cortices and only four changed their phase of firing when switching from one cortex to the other. When coupled with the finding that NVsnpr neurons exhibit spontaneous bursting in vitro[Sandler et al. (1998) Neuroscience, 83, 891], the results described here suggest that neurons of dorsal NVsnpr may form the core of the central pattern generator for mastication.

Anatomy of the lingual nerve in relation to possible damage during clinical procedures

Damage to the lingual nerve, resulting in transient or permanent paraesthesia or anaesthesia, is a common undesirable complication of surgical interventions to the lower third molar region. The anatomy of the nerve, as it travels from its origin high in the infra-temporal fossa, to the floor of the mouth is quite variable. The most critical part of its course is where it enters the sublingual region just alongside the lingual alveolar plate of the lower third molar. A significant number of lingual nerves are located above the alveolar bone in the gingival tissues, or very close to the bone. Retraction of the lingual mucosa can lead to lingual nerve trauma. There is no doubt that the lingual nerve is extremely vulnerable in this region and clinicians must assume that it is closely adjacent to the lingual region of the lower third molar, in all cases, in order to minimize possible damage.

Orofacial mechanoreceptors in humans: encoding characteristics and responses during natural orofacial behaviors

We used microneurography to characterize stimulus-encoding properties of low-threshold mechanoreceptive afferents in human orofacial tissues. Signals were recorded from single afferents in the infraorbital, lingual and inferior alveolar nerves while localized, controlled, mechanical stimuli were delivered to the facial skin, lips, oral mucosa and teeth. We likewise analyzed activity in these afferents during orofacial behaviors such as speech, chewing and biting. The afferents in the soft tissues functionally resemble four types described in the human hand: hair follicle afferents, slowly adapting (SA) type I and type II afferents and fast adapting (FA) type I afferents. Afferents in the facial skin, lips and buccal mucosa respond not only to contact with environmental objects, but also to contact between the lips, changes in air pressure generated for speech sounds, and to facial skin and mucosa deformations that accompany lip and jaw movements associated with chewing and swallowing. Hence, in addition to exteroceptive information, these afferents provide proprioceptive information. In contrast, afferents terminating superficially in the tongue do not signal proprioceptive information about tongue movements in this manner. They only respond when the receptive field is brought into contact with other intraoral structures or objects, e.g. the teeth or food. All human periodontal afferents adapt slowly to maintained tooth loads. Populations of periodontal afferents encode information about both which teeth are loaded and the direction of forces applied to individual teeth. Most afferents exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at low forces (below 1 N). Accordingly, periodontal afferents efficiently encode tooth load when subjects first contact, hold, and gently manipulate food by the teeth. In contrast, only a minority of the afferents encodes the rapid and strong force increase generated when biting through food. We conclude, that humans use periodontal afferent signals to control jaw actions associated with intraoral manipulation of food rather than exertion of jaw power actions.

Integration of the upper and lower lips in the postcentral area 2 of conscious macaque monkeys (Macaca fuscata)

The representation of the lip in area 2 of the postcentral somatosensory cortex was studied in conscious macaque monkeys by recording single-neurone activities. Seventy penetrations were made in the oral region of six hemispheres of four animals and 1157 neurones were isolated. The receptive field characteristics of 839 neurones were identified. Among them, 363 neurones along 47 penetrations responded to mechanical lip stimulation (lip neurones). A substantial number of lip neurones (17%, 62/363) had composite receptive fields that included not only the lip but also other oral structures. Although, the majority of lip neurones had receptive fields on either the upper or the lower lip (unilabial neurones), about 20% had receptive fields including both the upper and lower lips (bilabial neurones). Receptive field features of bilabial neurones were summarized as follows: (1) the receptive fields always included the corresponding sites of the upper and lower lips that would come into contact when the jaw closed; (2) the submodality preferences of the upper and lower portions of the receptive fields were identical in all cases; (3) if a light stroking stimulus in a specific direction was adequate, portions of the receptive field on the upper and lower lips responded with a common directional preference. Furthermore, bilabial receptive fields were unlikely to be the simple 'dimer' of unilabial receptive fields: the relative incidence of neurones with bilateral or composite receptive fields was much higher in bilabial than in unilabial neurones. That is, bilabial integration was accompanied by the integration of both sides of the lips, and of the lip and other adjacent oral structures. These features of bilabial neurones appear to be suitable for the form discrimination of objects held in the anterior part of the mouth. These neurones may be the prerequisite neural basis for the oral stereognosis that would take place in the neighbouring association cortices.

Nociceptive behaviour induced by dental application of irritants to rat incisors: a new model for tooth inflammatory pain

Animal models simulating acute human pulpitis are still lacking. The rat incisors present a particular situation where most of their innervation is considered to be unmyelinated and concentrated mainly in the tooth pulp. This study reports on a new model for dental pain induced by inflammatory agents applied to the tooth pulps of incisors. In different groups of rats, artificial crowns were fixed on the lower incisors, after cutting 1-2mm of their distal extremities. A volume of 7-10 microl of solutions of saline, capsaicin (1-10mg/ml) or formalin (2.5% or 5%) was injected in the crown cavity, and the nociceptive behaviour was quantitated following a devised scoring method of four scales. Intradental application of capsaicin produced nociceptive scores in the form of one plateau for 1-2h depending on the concentration used. Similar results were obtained with intradental application of formalin 2.5%. The one plateau of nociceptive scores obtained with formalin contrasts with the biphasic aspect of nociceptive behaviour described with the intradermal formalin test. This discrepancy could be attributed to a difference in the types of afferent fibres involved in each situation. Pretreatment with morphine (2 mg/kg) attenuated, in a naloxone-reversible manner, the nociceptive behaviour observed following intradental application of capsaicin. Pretreatment with meloxicam (a cyclo-oxygenase-2 inhibitor) exerted a less pronounced attenuation of the nociceptive scores when compared with morphine. These results provide evidence for the validity of the described model for the simulation of tooth pulp inflammatory pain in awake animals.

Differential neural activation of vascular alpha-adrenoceptors in oral tissues of cats

The aim of this study was to determine the relative contribution of alpha(1)- and alpha(2)-adrenoceptors involved in sympathetic-evoked vasoconstrictor responses in tissues perfused by the lingual arterial circulation in pentobarbital anesthetized cats. Blood flow in the lingual artery was measured by ultrasonic flowmetry. Laser-Doppler flowmetry was utilized to measure oral tissue vasoconstrictor responses in the maxillary gingiva and from the surface of the tongue. Electrical stimulation of the preganglionic superior cervical sympathetic nerve resulted in frequency-dependent blood flow decreases at all three sites. These responses were stable over time and were uniformly antagonized by administration of phentolamine (0.3 - 3.0 mg kg(-1)). The selective alpha(1)-adrenoceptor antagonist, prazosin (10 - 300 microg kg(-1)), attenuated vasoconstriction in the lingual artery and gingiva, but was ineffective in blocking vasoconstriction in the tongue. Subsequent administration of rauwolscine (300 microg kg(-1)) antagonized remaining vasoconstrictor responses. In contrast, rauwolscine (10 - 300 microg kg(-1)), given alone, blocked evoked vasoconstriction in the tongue, and was without effect on gingival or lingual artery vasoconstrictor responses. Subsequent administration of prazosin (300 microg kg(-1)) largely antagonized remaining neurally elicited responses. These results suggest that neural vasoconstrictor responses in some regional vascular beds in the cat oral cavity are mediated by both alpha(1)- and alpha(2)-adrenoceptors. In contrast, tongue surface vasoconstrictor responses to sympathetic nerve activation appear to be mediated primarily by alpha(2)-adrenoceptors.

VRl- and VRL-l-like immunoreactivity in normal and injured trigeminal dental primary sensory neurons of the rat

The vanilloid receptor VR1 and the vanilloid receptor-like protein VRL-1 are associated with polymodal nociceptors, and may be important for pain processing in normal and injured teeth. Using immunohistochemistry, we have studied the distribution of these receptors in rat pulpal or gingival trigeminal ganglion neurons that were identified through retrograde labeling with fluoro-gold. Twenty-one percent to 34% of tooth pulp-innervating neurons were VRl-positive, while 32%-51% were VRL-1-immunoreactive. However, double-labeling experiments revealed that VR1 and VRL-1 rarely co-existed in the same cells, but rather seemed to be confined to separate subpopulations. Among the gingival neurons, about 25% were VR1-positive and about 41% were VRL-1-immunoreactive. A lesion of the inferior alveolar nerve, which supplies mandibular teeth and gingiva, resulted in a marked down-regulation of VR1 in the affected trigeminal ganglion cells. A down-regulation of VRL-l was also indicated. The results suggest that both VR1 and VRL-1 could have significant roles in pulpal and gingival nociceptive transduction.

Blood flow changes in human dental pulps when capsaicin is applied to the adjacent gingival mucosa

OBJECTIVE

The purpose of this study was to determine whether changes occur in pulpal blood flow when capsaicin is applied to the adjacent gingival or alveolar mucosa in human beings.

STUDY DESIGN

Laser Doppler flowmetry was used to measure changes in pulpal blood flow (PBF) after applying capsaicin to adjacent gingival mucosa in 20 human volunteers. The procedure was repeated on 10 subjects after administration of an ipsilateral inferior alveolar nerve block and on the other 10 subjects after application of topical anesthetic to their adjacent gingival and alveolar mucosa.

RESULTS

PBF increased in 16 subjects and did not change in 4 subjects after capsaicin application. Ipsilateral inferior alveolar nerve block did not alter this effect. Pretreatment with topical lidocaine resulted in no change or decreased PBF in 8 subjects and increased PBF in 2 subjects.

CONCLUSION

Changes occur in the PBF of the mandibular canine teeth of some humans when capsaicin is applied to the adjacent gingival or alveolar mucosa.

The complexity of receptive fields of periodontal mechanoreceptive neurons in the postcentral area 2 of conscious macaque monkey brains

The representation of the oral structures in area 2 of the postcentral somatosensory cortex was studied in conscious macaque monkeys by recording single-neuron activities. A total of 58 penetrations were made in the oral region of five hemispheres in three animals and 707 neurons were isolated. The receptive field characteristics were identified for 480 neurons. Among them, 62 neurons along 21 penetrations responded to mechanical tooth stimulation (periodontal mechanoreceptive neurons). The overwhelming majority (81%, 50/62) of periodontal mechanoreceptive neurons had receptive fields on several teeth in either jaw. Moreover, six had receptive fields on corresponding maxillary and mandibular teeth. Thirty-seven percent (23/62) of periodontal mechanoreceptive neurons also had receptive fields on other oral structures surrounding the teeth, such as gingiva (16/23), lip (10/23), and tongue mucosa (1/23). Among them, four neurons had receptive fields on both the gingiva and lip. These receptive field features were readily interpreted as a combination of the regions stimulated simultaneously during food intake. We therefore speculated that these periodontal mechanoreceptive neurons in area 2 may be the prerequisite neural substrate for the eventual oral stereognosis that will take place in the neighboring association cortices. The coexistence of periodontal mechanoreceptive neurons with simple and complex receptive fields, or small and large receptive fields in the oral region of the postcentral area 2 suggests that this region could be the stage for the integration of sensory information from the periodontal ligament and from other oral structures.

Modulation of the periodontally evoked masseter reflexes by mechanical stimulation of the face

The current study was designed to determine if facial skin stimulation has a modulatory effect on the jaw reflexes that are elicited by tooth stimulation. This was investigated in eight human volunteers. The testing involved six sessions (three control and three test runs) of 50 identical tooth stimuli of 2 N, at 400 N/s, with 0.5 N preload, to the upper left central incisor. The stimulus typically induced an inhibitory reflex that was immediately followed by an excitatory reflex. All reflexes were recorded by surface electromyogram (SEMG) from the ipsilateral masseter. During the control runs, the tooth stimulus was delivered alone while the test runs involved mechanical stimulation of the skin as the tooth stimulus was repeated. The mechanical skin stimulation was achieved by rubbing a toothbrush with approximately 5 N of force, over the area of the face innervated by the maxillary division of the trigeminal nerve. The effect of skin stimulation on the periodontally induced reflex was measured by comparing the control and test reflex activity. When the SEMG of the test reflex was subtracted from the control reflex, the difference was a net increase in the SEMG in all eight subjects. There was also a significant reduction in the decline of the bite force. It is concluded that the skin stimulation can modulate the reflexes that are induced by tooth stimulus. It is postulated that this modulation may be partly responsible for matching the size and consistency of the food bolus with the appropriate bite force during mastication.

Neurogenic inflammation of gingivomucosal tissue in streptozotocin-diabetic rat

Previously it was assumed that nerve fibres are involved in the neurogenic inflammation induced by mechanical or chemical irriations. It has been also suggested that in diabetes mellitus the unmyelinated small diameter fibers are impaired as a result of diabetic neuropathy. Therefore, our aim was to study the alterations of the nerve processes in the gingivomucosal tissue in streptozotocin (STZ)-diabetic rats. Light- and electronmicroscopical examinations were made to analyze the changes in nerve fibres. After one week of steptozotocin treatment, the gingivomucosal tissue had inflammatory cell infiltration and some degenerated nerve fibres were also observed. Dense mitochondria, disorganization of cell organelles, and appearance of myelin-like dense bodies were found in the axons of degenerared nerve fibres. Semiquantitative analysis showed that 14 +/- 4% of the unmyelinated nerve fibres degenerated after one week of STZ treatment. However, degeneration of the myelinated nerve fibers was not observed. Two weeks after STZ treatment, most of the unmyelinated and myelinated nerve fibers showed degeneration (86 +/- 5%) and the placement of the ligature revealed a non-inflammatory connective tissue adjacent to a normal epithelium. The myelin sheath was disrupted and dark axoplasm with cytolysosomes became manifest. These findings demonstrated that both unmyelinated and myelinated nerve fibers are altered and inflammatory reaction exists in the gingivomucosal tissue only in the early stage of diabetes mellitus.

Substance P and substance P receptors in bone and gingival tissues

Substance P (SP) is an important member of the tachykinin family of neuropeptides, which work as neurotransmitters or neuromodulators. Recent advances in the analysis of SP receptors, particularly the neurokinin-1 receptors (NK1-Rs) that have high affinity for SP, have demonstrated that they are distributed not only in the cells of the neuronal or immune systems but also in peripheral cells. Therefore, the effect of SP and its cellular receptors is not limited to the nervous or immune systems, but is more extensive than previously appreciated. SP-like immunoreactive (SP-LI) axons have been localized in both bone and gingival tissue, and SP receptors are widely distributed in osteoclasts, osteoblasts, and junctional epithelial cells, as well as in neutrophils and endothelial cells. The distribution of SP-LI axons and SP receptors suggests that SP may directly modulate bone metabolism and gingival tissue functions through SP receptors.

The trigeminal nerve. Part III: The maxillary division

The maxillary nerve gives sensory innervation to all structures in and around the maxillary bone and the midfacial region including the skin of the midfacial regions, the lower eyelid, side of nose, and upper lip; the mucous membrane of the nasopharynx, maxillary sinus, soft palate, palatine tonsil, roof of the mouth, the maxillary gingivae, and maxillary teeth. This vast and complex division of the trigeminal nerve is intimately associated with many sources of orofacial pain, often mimicking maxillary sinus and/or temporomandibular joint involvement. For those who choose to treat patients suffering with orofacial pain and temporomandibular disorders, knowledge of this nerve must be second nature. Just providing the difficult services of a general dental practice should be stimulus enough to understand this trigeminal division, but if one hopes to correctly diagnose and treat orofacial pain disorders, dedication to understanding this nerve cannot be overstated. In this, the third of a four part series of articles concerning the trigeminal nerve, the second or maxillary division will be described and discussed in detail.

The contribution of mechanoreceptive neurones in the gingival tissues to the masticatory-parotid salivary reflex in man

The masticatory-parotid salivary reflex has been studied in fully dentate subjects. Salivary flow was recorded by siting a modified Lashley cup over the orifice of the parotid duct on one side of the mouth. Subjects chewed on small pieces of silicone rubber for 1-min periods which resulted in a reflex secretion of parotid saliva. The secretion was greatest when the subject chewed on the same side of the mouth (ipsilateral) as the salivary flow was recorded. Less salivary flow resulted when the subjects chewed on the opposite side of the mouth (contralateral). Selected areas of the buccal or lingual gingival tissues were then anaesthetized on the side ipsilateral to the Lashley cup. Anaesthesia of the lingual and buccal gingival tissues together resulted in a reduction of salivary flow in response to similar chewing cycles. Anaesthesia of the lingual gingival tissues alone also resulted in a reduction of salivary flow, but anaesthesia of the buccal gingival tissues alone did not. During mastication it is likely that mechanoreceptors in the gingival tissues will be stimulated which may result in salivary flow. This requires further study as other mechanoreceptive neurones are also known to be involved in the masticatory-parotid salivary reflex.

[Somatosensory trigeminal evoked potentials after gingival stimulation of the mental nerve. Normal values]

OBJECTIVE

Somatosensory evoked potentials were recorded following unilateral stimulation of the mental nerve in the gum of 100 healthy volunteers aged between 17 and 22 years.

METHODS AND RESULTS

Responses were recorded until 100 ms with electrodes placed over the scalp (C5/C6) referenced to central frontal (Fz). In 10 subjects, simultaneous recordings were made in masticatory and facial muscles to detect possible muscle artefacts. Stimulation was effected using a specially-designed stimulator adaptable to each individual. Contralateral responses consisted of four very constant deflexions (N12, P19, N26 and P35) forming a W-shaped complex of mean duration 31.27 ms. Tables of normality were compiled for latencies and amplitudes with confidence intervals of 99.8% reliability. Constancy of deflexions, stability of response (by serial studies), and possible sexual differences were also studied. Muscle artefacts were ruled out, and the participation of the mental nerve in the genesis of the responses was confirmed.

CONCLUSION

We consider the proposed method a reliable alternative to other procedures used to obtain TEPs.

Nerve fibers immunoreactive to calcitonin gene-related peptide, substance P, neuropeptide Y, and dopamine beta-hydroxylase in innervated and denervated oral tissues in ferrets

The effect of sensory and sympathetic denervation on the localization and distribution of nerve fibers immunoreactive (IR) to calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide Y (NPY), and dopamine beta-hydroxylase (DBH) was studied in the dental pulp, periodontal ligament (PDL), and gingiva in ferrets. Unilateral axotomy was performed by resection of the inferior alveolar nerve (IAN) 10 days before the experiment (Group 1); sympathectomy, by unilateral removal of the cervical ganglion 5 days before the experiments (Group 2). Immunohistochemistry was performed on free-floating sections by the avidin-biotin-peroxidase technique. A considerably higher density of sensory fibers IR to CGRP and SP was found in the dental pulp than in PDL and gingiva. The majority of pulpal fibers were located in the walls of blood vessels. A subodontoblastic network of fibers IR to CGRP and SP was lacking in incisors and canines and was found only in the coronal pulp in premolars and molars. Sympathetic fibers were sparsely distributed in the pulp, and they were mainly confined to large vessels running centrally in the root pulp as well as the larger vessels in apical PDL and alveolar bone. Gingiva was well supplied with CGRP- and SP-IR nerves, and some NPY and DBH fibers were located in association with larger vessels. Round cell-like structures within the basal part of the epithelium were CGRP-IR. Axotomy induced a complete loss of CGRP- and SP-IR fibers in the anterior part of the jaws, whereas sympathectomy caused a reduction, but not a total loss, of NPY- and DBH-IR nerves. It is concluded that, except for some distributional differences, the oral tissues in the ferret have an abundant sensory innervation similar to that found in other species.

Effects of a bite-raising splint on the duration of the chewing cycle and the EMG activities of masticatory muscles during chewing in freely moving rabbits

Metal bite-raising splints of 0.5 mm thickness were attached to the upper molar teeth on both sides of the jaw in rabbits. The effects of these splints on masticatory behaviour during the chewing of soft food (bread) by freely moving rabbits were investigated. We recorded electromyograms (EMGs) of the masseter and digastric muscles. The animals exhibited prolongation of the chewing cycle, decreased EMG activity of the masseter muscle and increased EMG activity of the digastric muscle during chewing after introduction of the bite-raising splints. The effects of the splints on the activities of masticatory muscles were abolished by bilateral sectioning of the maxillary and inferior alveolar nerves. It seems likely that afferents from oral sensory receptors were responsible for the changes in masticatory behaviour after the introduction of the occlusal splint.

The role of gingival mechanoreceptors in the reflex control of human jaw-closing muscles

Electromyographic (EMG) experiments were undertaken to investigate the jaw reflexes evoked by activation of gingival receptors in 12 humans. EMG recordings were made from an active masseter muscle whilst ramp-plateau mechanical stimuli were applied to the gingiva. Stimuli with a constant rate of rise (0.2 N/msec) and a variable plateau force (up to 2 N), evoked a complex set of short- and long-latency inhibitory and excitatory responses. These occurred as a sequence of inhibition-excitation-inhibition-excitation, although not all of these elements were seen on every occasion. The median thresholds of these four responses ranged from 0.5 to 1 N but overall there were no significant differences between them (p > 0.05, Friedman's ANOVA). In other experiments, the same reflexes were recorded in response to application to the gingiva of 1 N ramp-plateau stimuli (5 msec rise time) and 1 N tap stimuli applied to the adjacent tooth. The application of a local anaesthetic agent to the stimulated gingiva produced reductions in the mean magnitude of almost all the responses but these were significant (p < 0.05; ANOVA) only for the long-latency inhibitions evoked by ramping the gingiva and the long-latency excitations evoked by either stimulus. It is concluded that mechanoreceptors in the gingiva can mediate long-latency inhibitory and excitatory jaw reflexes, and that these receptors may also contribute to long-latency reflexes evoked by tapping teeth. The scarcity of effects of gingival anaesthesia on the short-latency reflexes may be due to such responses being mediated by receptors deeper in the periodontium.

Synergetic interpretation of patterned vasomotor activity in microvascular perfusion: discrete effects of myogenic and neurogenic vasoconstriction as well as arterial and venous pressure fluctuations

Synergetic concepts allow to identify emergent coordination phenomena between interacting physiological systems, for example between the cutaneous microcirculation, the sympathetic nervous system and the cardiac and pulmonary systems. The temporal patterns (oscillations of various frequencies) that are found in the data obtained with laser-Doppler anemometers (LDA; e.g. Periflux 2 used in the study) can be investigated by simultaneous recording of photoplethysmographic data obtained in the identical region of interest, as well as in cutaneous regions treated with vasoparalytic procedures which permit to record the dynamics of the arterial system. These strategies were applied to studies in the cutaneous microcirculation (volar side of the index fingers) as well as to mucosal microcirculation (maxillar gingiva) in healthy subjects and in patients suffering from autonomic dysfunction (cutaneous microcirculation) or gingivitis. By this procedure, it could be corroborated that - contrary to popular notions - the temporal fluctuations in the LDA records do not necessarily reflect myogenic vasomotion, but can have multiple causes. In a confirming recent study [Schmid-Schönbein et al., J Auton Nerv Syst, 57, 136-140, 1996], we have demonstrated that the LDA fluctuations under conditions of normal ambient temperature and hand position most likely reflect neurogenic vasoconstriction. Under exceptional conditions, different patterns emerge. Prolonged exposure to ambient temperature (18 degrees C) leads to marked vasoconstriction, with occasional vasodilator escape ('miniature hunting reaction'). Normal subjects under gravitational load and in warm environment (28 degrees C ambient) silence their neurogenetic vasoconstriction reactions, which allows sinusoidal vasomotion to dominate. A similar phenomenon is seen in neuropathic patients at 21-24 degrees C (presumably due to structural defects). Fluctuations in LDA signal taken from the healthy gingiva are entrained to arterial, those taken from inflamed gingiva to respiratory activity. The theory and practice of nonlinear analysis is discussed, and data compression procedures allowing to portray characteristic temporal patterns for future diagnostic procedures are presented.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Effect of intermittent long-lasting electrical tooth stimulation on pulpal blood flow and immunocompetent cells: a hemodynamic and immunohistochemical study in young rat molars

Release of sensory neuropeptides after stimulation of afferent nerve fibers has previously been shown to induce vasodilation and increased vascular permeability in the dental pulp, a condition recognized as neurogenic inflammation. In the present study a possible role for the sensory neuropeptides in transendothelial migration of immunocompetent cells was investigated. The dental pulp is an isolated tissue densely innervated with sensory fibers containing neuropeptides, and following electrical stimulation of the crown, the effect on pulpal blood flow and immunocompetent cells can be studied in a noninvasive model. A laser Doppler flowmeter was used to measure relative changes in pulpal blood flow during long-lasting intermittent stimulation of innervated and denervated rat first molars. In the innervated teeth, stimulation promptly increased pulpal blood flow by on average 45% at the start of the experiment, whereas almost no blood flow increase was recorded after 4 to 5 h stimulation. Surgical sectioning of the inferior alveolar nerve abolished blood flow increase upon stimulation. After stimulation, a quantitative analysis of CD43+, CD4+, CD11+, and I-A antigen-expressing cells was performed, and the effect of stimulation on calcitonin gene-related peptide (CGRP)-immunoreactive and substance P (SP)-immunoreactive (IR) nerve fibers was studied. Immunohistochemistry was performed by the avidin-biotin peroxidase method. Stimulation resulted in an almost complete depletion of CGRP- and SP-IR nerve fibers in the first molar pulp, whereas nerve fibers in the gingiva and neighboring teeth were unaffected. A significant increase in the number of CD43+ cells was found in the innervated tooth after stimulation compared to the stimulated denervated (P < 0.01) and unstimulated control (P < 0.05) first molars. For I-A antigen-expressing cells a significant increase (P < 0.05) was found between the innervated stimulated and unstimulated control, but not between the innervated and denervated stimulated first molars. Hence, from the present experiment it is concluded that the pulpal nerves participate in and facilitate transendothelial migration of CD43+ cells during acute neurogenic inflammation.

Immunohistochemical localization of calbindin D28k in the periodontal Ruffini endings of rat incisors

It was examined whether calbindin D28k (CB) might be located in the rat incisor periodontal Ruffini ending, an essential mechanoreceptor in periodontal ligament, by light- and electron-microscopic immunohistochemistry. Some thick nerve fibers showing CB-like immunoreactivity (LI) entered the lingual half of the periodontal ligament of the incisor and showed the dendritic terminal arborization. Electron-dense immunoreaction products indicating CB-LI were distributed diffusely in axoplasm of the axon terminals, no mitochondria, however, were not labeled. Neither cell bodies nor cytoplasmic extensions of the terminal Schwann cells exhibited CB-LI. CB was presumed to be involved in the maintenance of Ca2+ homeostasis in the mechano-electric transduction in mechanoreceptors in the periodontal ligament.

Combined retrograde tracing and immunohistochemistry of trigeminal ganglion neurons projecting to gingiva or tooth pulps in the lower jaw of the cichlid Tilapia mariae

Rat trigeminal ganglion neurons projecting to the oral mucosa or to tooth pulps have different cell diameters and contain different chemical markers. In the present paper we examine whether trigeminal ganglion neurons sending axons to gingiva or tooth pulps in the lower jaw of the cichlid Tilapia mariae differ in a similar way. Retrograde tracing with fluorescent latex microspheres revealed labelled gingival and pulpal neurons in the caudal part of the trigeminal ganglion. The gingival neurons had a unimodal size distribution (peak 11 microns; range 8-14 microns) and the pulpal neurons exhibited a bimodal size distribution (peaks 12 and 25 microns; range 10-40 microns). Immunohistochemistry revealed a calcitonin gene-related peptide-like immunoreactivity in some 40% of the gingival neurons and a substance P-like immunoreactivity in 30%. Of the small pulpal neurons about 60% exhibited a calcitonin gene-related peptide-like immunoreactivity and 15% showed a substance P-like immunoreactivity. Of the large pulpal neurons some 70% exhibited a calcitonin gene-related peptide-like immunoreactivity. These neurons did not show a substance P-like immunoreactivity. In some animals a few trigeminal ganglion neurons showed a neuropeptide Y- or a vasoactive intestinal polypeptide-like immunoreactivity. Perikarya with a tyrosine hydroxylase- or a choline acetyl transferase-like immunoreactivity were not observed. We conclude that gingiva and tooth pulps in the lower jaw of T. mariae are innervated by trigeminal ganglion neurons, the cell diameters and neuropeptide contents of which differ in a pattern similar to that in the rat. Hence, this seems to represent a conserved evolutionary pattern.

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.

Effect of capsaicin treatment or inferior alveolar nerve resection on dentine formation and calcitonin gene-related peptide- and substance P-immunoreactive nerve fibres in rat molar pulp

The aim of this study was to investigate whether decreased sensory innervation induced by capsaicin treatment or axotomy of the inferior alveolar nerve has an effect upon dentine formation in the rat first molar. Dentine formation was visualized by intravital injection of Procion brilliant Red H8BS and denervation was verified immunohistochemically for the neuropeptides calcitonin gene-related peptide (CGRP) and substance P. The observation times were 6 weeks for the capsaicin-treated group and 11 days for the axotomized group. Capsaicin injections caused a consistent reduction in numbers of CGRP- and substance P-immunoreactive fibres in the pulps and a somewhat smaller reduction in the periodontal tissues. Unilateral axotomy of the inferior alveolar nerve induced an almost complete loss of immunoreactive fibres in the pulp and in the mesial gingiva of the first molar. Dentine formation at the mesial pulp horn and at the central pulp floor was significantly reduced in both groups compared to controls. The results suggest that sensory neuropeptides such as CGRP and substance P may play a part in dentine formation.

Occurrence of axons with certain immunohistochemical markers in teleost gingiva and teeth

The occurrence of axons with certain neurochemical markers in gingiva and teeth in the lower jaw of the cichlid Tilapia mariae was examined by immunohistochemistry. It was found that gingival and pulpal axons can be labelled with antibodies against calcitonin gene-related peptide, substance P, tyrosine hydoxylase, neuropeptide Y, choline acetyl transferase and vasoactive intestinal polypeptide. It is concluded that both gingival and dental domains in T. mariae contain axons with sensory and autonomic chemical phenotypes, the occurrence and distribution of which are generally similar to the mammalian counterpart.

Effects of streptozotocin-induced diabetes on neurogenic inflammation of gingivomucosal tissue in rat

It has been suggested that the unmyelinated small diameter afferent nociceptive C-fibres are impaired in diabetes mellitus. We have recently demonstrated that these fibres are the prerequisite for neurogenic inflammation induced by mechanical or chemical irritations. These experiments were designed to characterize the neurogenic inflammatory responses of gingivomucosal tissue in the early phase of experimental induced diabetes mellitus in rat. Effect of dental ligature on the gingivomucosal (GM) vascular permeability was studied in control rats and in rats pretreated with streptozotocin at d 7 and 14 following streptozotocin administration. In separate groups of control and streptozotocin diabetic rats studies were also performed to investigate the effect of local capsaicin application on GM vascular permeability on d 14. Vascular permeability was assessed by means of Evans blue extravasation. The ligature placed around the mandibular left first molar caused a significant increase vascular permeability of GM tissue on the ipsilateral side on both d 7 and 14 after the ligation in control rats. In streptozotocin diabetic rats on d 7, there was also a significant elevation of Evans blue extravasation in the tissue tested on the ligature side. However, on d 14 the ligation failed to produce any changes in Evans blue extravasation on the ipsilateral side, i.e. no difference in GM vascular permeability could be recorded between the two sides in streptozotocin diabetic rats. Topical capsaicin administration produced significant Evans blue extravasation in GM tissue of control rats compared to that observed in diabetic rats on d 14 after streptozotocin treatment. Electron microscopic and light microscopic studies demonstrated fibre degeneration of the C neurones and less inflammatory cells in streptozotocin-induced diabetes in the gingivomucosal tissue. These findings appear to indicate that the inflammatory responses induced by mechanical (dental ligature) and/or chemical irritants (topical application of capsaicin) in the gingivomucosal tissue are altered in streptozotocin diabetic rats and this alteration is due to the diabetes-induced damage to the unmyelinated C fibres.

Immunocytochemical study of nerve fibers containing substance P in the junctional epithelium of rats

Nerve fibers with substance P-like immunoreactivity (SP-IR) in the junctional epithelium (JE) of 32-42-d-old rats were examined by both light and electron microscopy using the avidin-biotin-peroxidase complex method. The density of nerve fibers with SP-IR was highest in the middle portion of the JE; however, a few fibers were localized in the coronal portion of the JE and close to the enamel surface. Also, rich innervation was found especially in the basal cell layer of the JE. Unmyelinated axons with SP-IR in the connective tissue underlying the JE were enveloped by Schwann cells but lost their Schwann cell sheath almost completely in the JE. The axons often formed varicosities with SP-IR as terminals in various areas of the JE. The terminals contained numerous large granular vesicles, small clear vesicles and a few mitochondria, and were surrounded by the cytoplasmic processes of the junctional epithelial cells. These terminals were sometimes located close to neutrophils in the JE; the minimum gap distance between the terminals and the processes of junctional epithelial cells or neutrophils was about 20 nm. A few terminals with SP-IR came close to the enamel surface, and the minimal distance between the terminals and the enamel surface was about 5 microns. SP-IR in the nerve terminals in the JE fixed with 0.1% or 0.25% glutaraldehyde was distributed diffusely in the axoplasm or was confined to the granular vesicles. These findings show that substance P is contained in the large granular vesicles in the nerve terminals, and suggest that these terminals may function as modulators of junctional epithelial cells and neutrophils.

Alteration in facial sensibility in adolescents following sagittal split and chin osteotomies of the mandible

Static two-point discrimination, pressure, and vibratory threshold values were measured bilaterally at standard coordinates in the area of the face innervated by the mental nerve in 115 adolescents (230 nerves). The patients were divided into four groups: normal adolescents who had not undergone any orthognathic surgery (group I controls, n = 134 nerves, mean age 18 years, SD = 3), those 1 year after undergoing bilateral sagittal split osteotomies of the mandible (group II, n = 14 nerves, mean age 19 years, SD = 2), those 1 year after undergoing an osteoplastic genioplasty (group III, n = 40, mean age 19 years, SD = 3), and those 1 year after undergoing a combination of bilateral sagittal split osteotomies and an osteoplastic genioplasty (group IV, n = 42 nerves, mean age 19 years, SD = 3). Subjective residual numbness at the 1 year postoperative interval was reported by 2 of 7 patients in group II, 2 of 20 patients in group III, and 14 of 21 patients (67 percent) in group IV. Long-term subjective numbness involved only the chin skin in 16 of 18 patients experiencing residual numbness and was perceived as problematic in the remaining 2 (group IV) patients whose subjective numbness also was measured objectively in the chin, lower lip (mucosa and skin), and gingiva. Objectively, the mean threshold values of the three sensory modalities tested were higher in group IV patients than in the remaining groups at all coordinates tested, but significant differences (p < 0.05) were found only between the mean two-point discrimination of group IV patients and the control group in the region of the chin skin. The high percentage of patients documented to have subjective and objective sensory disturbance after undergoing a combination of sagittal split osteotomies of the mandible and an osteoplastic genioplasty (group IV) may be explained by the "double crush syndrome."

Sensory nerve disturbance following Le Fort I osteotomy

This study assessed sensory nerve disturbance after Le Fort I osteotomy using the electric pulp test, pin-prick sensation, fine touch, and cold sensation. After 6 months, 78% of teeth positive preoperatively to an electric pulp tester regained sensitivity. Return of palatal sensation was affected by whether or not the greater palatine nerve (GPN) was divided during surgery. After 6 months, where the GPN was intact, all patients had fine touch sensation (88% at the preoperative level), and all had pin-prick sensation (97% at preoperative level). When the GPN was divided, all patients had fine touch sensation (13% at preoperative level), and all had pin-prick sensation (63% at preoperative level). The differences in the return to preoperative sensation were significant for fine touch (P=0.0001++) and for pin-prick (P-0.03) by chi-square analysis. Sensation returned more quickly and more completely in the two cases where the contralateral GPN was intact. In the buccal mucosa, 95% of patients regained some fine touch sensation after 6 months, but none returned to the preoperative level. Similarly, 85% regained some pin-prick sensation, but none achieved preoperative levels. Cold sensation, pin-prick sensation, and fine touch on the face returned to the preoperative level in all patients by 6 weeks postoperatively.

Periodontal and gastric convergences within the hypothalamic ventromedial nucleus area--single unit study on anesthetized rats

Unitary activities were recorded in the ventromedial nucleus of the hypothalamus (VHM) of anesthetized rats. Cells responding to periodontal stimulation (100-200 g disto-mesial traction applied to an upper incisive) were selected. The effects of gastric stimulation (2-5 ml distension) were then investigated. Out of the 40 cells activated (22 cells) or inhibited (18 cells) by periodontal stimulation, only seventeen were influenced by gastric stimulation. Eight of them responded in the same way and nine in the opposite way. Unlike the periodontal stimulation, which elicited specific spatio-temporal patterns, the gastric stimulation had only weak effects. These data nevertheless demonstrate that periodontal-gastric convergences exist in the VHM nucleus, which is consistent with the role previously ascribed to this area in alimentary behaviour.

Axonal transport of fluorescent carbocyanine dyes allows mapping of peripheral nerve territories in gingiva

Sensory innervation of gingival tissue can cause neurogenic inflammation that depends on the extent of the branching area of the peripheral nerve fibers. We designed the present study to determine whether single trigeminal axons branch to both the buccal and palatal gingiva of maxillary molars of adult rats. Accumulation via retrograde transport of DiI (red) or DiA (green) fluorescent carbocyanine dyes in neurons of trigeminal ganglia was evaluated 7 days after applying one dye to the buccal sulcus and the other to the palatal sulcus. Both dyes were absorbed through the junctional epithelium, and the two sites each labeled similar numbers and sizes of neurons in the lateral zone of the maxillary division (44% from buccal and 46% from palatal gingiva). Double-labeled neurons had the same size (32.5 +/- 6.70 microns, mean circumference +/- S.D.) and location as single-labeled neurons, and they were 9% of the total. This study shows that exogenous dyes can diffuse into mucosa and thereby allow in vivo mapping of sensory nerve branching patterns to several intact tissues per animal. We found that 9% of the labeled cells extended to both the buccal and palatal gingiva. Thus, inflammation that spreads from one gingival region to the other could have a neurogenic mechanism involving trigeminal sensory neurons that extend their peripheral branches to innervate both buccal and palatal gingiva of adult rat molars.

Expression of neuropeptides (CGRP, substance P) during and after orthodontic tooth movement in the rat

The present study was designed to investigate the changes in patterns of calcitonin gene-related peptide (CGRP) and substance P (SP) innervation during buccally-directed orthodontic tooth movement (OTM) of the first maxillary molar in the rat. In addition, the CGRP- and SP-innervation was examined 14 and 28 days after the orthodontic force was discontinued. Comparisons were made with the innervation found in control animals. Orthodontic appliances produced a buccally directed force in the range of 20-50 g on the upper right first molar for either 24 hours or 3 days. When the orthodontic appliances were removed one group of animals were killed immediately, whereas the other groups were killed after a healing period of 14 days or 28 days. After fixation the upper jaws were decalcified, frozen, and sectioned in the frontal plane at the level of the first and second molars. The sections were processed for CGRP, SP, and routine morphology. An increase was found in the number of nerve fibres showing CGRP-like immunoreactivity (LI) in the pulp, periodontal ligament (PDL) and marginal gingivae with the fibres showing a higher intensity of immunolabelling after 24 hours or 3 days of OTM. The contralateral first upper molar showed an increase in the expression of CGRP. Fourteen days after removal of the appliances, there was still a marked CGRP-innervation of the PDL in test teeth as well as in contralateral teeth. After 28 days, a decrease in CGRP-innervation was observed, but this innervation was still more pronounced than that found in the controls. The pattern of SP-innervation changed similarly to that of the CGRP-innervation, however, the nerve fibres showing SP-LI were considerably fewer than those showing CGRP-LI at all stages and in all areas. This study suggests that CGRP- and SP-changes not only occur in the tooth exposed to buccally directed OTM, but also in the contralateral tooth and that the changes are evident for a considerable time after terminating OTM.