Evidence for the existence of intraepithelial nerve endings in the junctional epithelium of rat molars: an immunohistochemical study using protein gene product 9.5 (PGP 9.5) antibody

Systemic labeling and visualization of dental sensory nerves by the novel fluorescent marker AM1-43

Systemic labeling of sensory nerves was performed by injecting a small amount of the styryl dye AM1-43 subcutaneously to the back skin of 4-week-old mice in order to determine its ability to stain sensory nerves. One or 3 days later, dental tissues were fixed and cryosectioned. Molars showed bright nerve fibers in the periodontal ligament and pulp. Nerve fibers in dentinal tubules approximately 100 microm from the pulp were also labeled. In the incisor, there were only few labelings in the pulp, although free nerve endings and Ruffini-type mechanosensors in the periodontal ligament on the lingual side were brightly labeled. The AM1-43-positive fibers were also labeled by anti-PGP9.5. AM1-43 is an excellent marker for sensory nerves and it may be useful for further investigations of dental innervation and in exploring new analgesics for tooth pain.

The junctional epithelium: from health to disease

The junctional epithelium is located at a strategically important interface between the gingival sulcus, populated with bacteria, and the periodontal soft and mineralized connective tissues that need protection from becoming exposed to bacteria and their products. Its unique structural and functional adaptation enables the junctional epithelium to control the constant microbiological challenge. The antimicrobial defense mechanisms of the junctional epithelium, however, do not preclude the development of gingival and periodontal lesions. The conversion of the junctional to pocket epithelium, which is regarded as a hallmark in disease initiation, has been the focus of intense research in recent years. Research has shown that the junctional epithelial cells may play a much more active role in the innate defense mechanisms than previously assumed. They synthesize a variety of molecules directly involved in the combat against bacteria and their products. In addition, they express molecules that mediate the migration of polymorphonuclear leukocytes toward the bottom of the gingival sulcus. Periodontopathogens-such as Actinobacillus actinomycetemcomitans or, in particular, Porphyromonas gingivalis-have developed sophisticated methods to perturb the structural and functional integrity of the junctional epithelium. Research has focused on the direct effects of gingipains, cysteine proteinases produced by Porphyromonas gingivalis, on junctional epithelial cells. These virulence factors may specifically degrade components of the cell-to-cell contacts. This review will focus on the unique structural organization of the junctional epithelium, on the nature and functions of the various molecules expressed by its cells, and on how gingipains may attenuate the junctional epithelium's structural and functional integrity.

Nerve terminals extend into the temporomandibular joint of adjuvant arthritic rats

The innervation of the temporomandibular joint (TMJ) has attracted particular interest because of the close association with complex mandibular movement. Although the pathological changes of disk innervation may have a crucial role in the development of TMJ pain, the innervation of the TMJ disk by experimentally induced arthritis has rarely been examined in detail. Arthritic rats were induced by injection with 0.1ml solution of Complete Freund's adjuvant (CFA). We investigated three-dimensional distribution of nerve fibers in the TMJ disk using immunohistochemistry for protein gene product-9.5 (PGP-9.5) and calcitonin gene-related peptide (CGRP) in naive and arthritic rats. To clarify the possible role of nerve growth factor (NGF) and its receptor on changes in peripheral innervation of the TMJ, the expressions of trkA and p75 receptor in trigeminal ganglia were examined. Although PGP-9.5 and CGRP immunoreactive (ir) fibers were seen in the peripheral part of the TMJ disk, they were not seen in its central part. The total length and the length density of PGP-9.5 ir and CGRP ir nerve fibers increased in arthritic rats. The innervation area of fibers proliferating in the rostro-medial part merged with that of fibers in the rostro-lateral part in the arthritic rats. In addition, the ratio of trkA- and p75-positive small- and medium-sized cells increased in trigeminal ganglia. It is assumed that increasing innervation of the TMJ disk may be important for the pathophysiology of TMJ pain. NGF and its receptors are likely involved in pathological changes of the TMJ disk.

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.

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.

Responses of periodontal nerve terminals to experimentally induced occlusal trauma in rat molars: an immunohistochemical study using PGP 9.5 antibody

The response of periodontal nerves to experimentally induced occlusal trauma in rat molars was assessed by immunohistochemistry for protein gene product 9.5 (PGP 9.5) at light and electron microscopic levels, and by computerized image analysis. The occlusal surface on the left upper first molar of 8-wk-old male Wistar rats was raised approximately 1 mm under ether anaesthesia. The rats were perfusion-fixed on d 1, 2, 3, 4, and 7 after bite-raising and then decalcified for 2-3 wk. Frozen sagittal cryostat sections were stained by the avidin-biotin complex method. By the second day after bite-raising many Ruffini endings were swollen and their outline unclear at the light microscopic level. Transmission electron microscopy disclosed PGP 9.5 reaction products within Ruffini endings that had unusually long cytoplasmic projections extending through enlarged slits of the Schwann sheaths and also diffuse extracellular PGP 9.5-immunoreactivity near the Ruffini endings. From d 2 to 4, thin nerve fibres on the pressure side of the periodontal ligament were orientated irregularly and had a prominent beaded appearance. An increase in beaded nerve terminals occurred at d 2-4 post elevation, and decreased later. These results suggest that occlusal trauma indices specific changes in the distribution and shape of nerve terminals in the periodontal ligament.

Postnatal development of periodontal ruffini endings in rat incisors: an immunoelectron microscopic study using protein gene product 9.5 (PGP 9.5) antibody

Postnatal development of Ruffini endings was ultrastructurally investigated in the upper incisors of the rat from 1 day to 60 days after birth by means of protein gene product 9.5 (PGP 9.5) immunocytochemistry. The immunostaining with PGP 9.5 antibody clearly demonstrated chronological alterations of the distribution and ultrastructure of the Ruffini endings during postnatal development. At 1 day after birth, the PGP 9.5-positive nerve terminals contained a few mitochondria and vesicles immunonegative for PGP 9.5. Dendritic terminals appeared at 4 days after birth, with a small number of expanded or bulbous portions. These expanded portions possessed morphological features similar to those of the growth cone: several mitochondria and various kinds of vesicles. Typical Ruffini endings with dendritic ramification and expanded portions appeared 7-11 days after birth. At this stage, parts of the axon terminals extended through the slits of Schwann cell covering and formed finger-like projections called axonal spines. These Ruffini endings increased dramatically in number after 24-26 days and were identical in density and morphology to those seen in adult rats. After the commencement of the occlusion between the incisors, the number of large mitochondria increased, in contrast to the decrease of the vesicles in the axon terminals. Moreover, the axonal spines increased both in number and in length. Thus, the periodontal nerve endings showed stage-specific morphological features intimately related in timing to tooth eruption and occlusion. Functional stimuli possibly contribute to the final differentiation and maturation of the periodontal Ruffini endings.

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.