GFAP immunoreactivity and transcription in trigeminal and dental tissues of rats and transgenic GFP/GFAP mice

Neuroimmune cell interactions and chronic infections in oral cancers

Inflammation is a process that is associated with the activation of distal immunosuppressive pathways that have evolved to restore homeostasis and prevent excessive tissue destruction. However, long-term immunosuppression resulting from systemic and local inflammation that may stem from dysbiosis, infections, or aging poses a higher risk for cancers. Cancer incidence and progression dramatically increase with chronic infections including HIV infection. Thus, studies on pro-tumorigenic effects of microbial stimulants from resident microbiota and infections in the context of inflammation are needed and underway. Here, we discuss chronic infections and potential neuro-immune interactions that could establish immunomodulatory programs permissive for tumor growth and progression.

Formation and Developmental Specification of the Odontogenic and Osteogenic Mesenchymes

Within the mandible, the odontogenic and osteogenic mesenchymes develop in a close proximity and form at about the same time. They both originate from the cranial neural crest. These two condensing ecto-mesenchymes are soon separated from each other by a very loose interstitial mesenchyme, whose cells do not express markers suggesting a neural crest origin. The two condensations give rise to mineralized tissues while the loose interstitial mesenchyme, remains as a soft tissue. This is crucial for proper anchorage of mammalian teeth. The situation in all three regions of the mesenchyme was compared with regard to cell heterogeneity. As the development progresses, the early phenotypic differences and the complexity in cell heterogeneity increases. The differences reported here and their evolution during development progressively specifies each of the three compartments. The aim of this review was to discuss the mechanisms underlying condensation in both the odontogenic and osteogenic compartments as well as the progressive differentiation of all three mesenchymes during development. Very early, they show physical and structural differences including cell density, shape and organization as well as the secretion of three distinct matrices, two of which will mineralize. Based on these data, this review highlights the consecutive differences in cell-cell and cell-matrix interactions, which support the cohesion as well as mechanosensing and mechanotransduction. These are involved in the conversion of mechanical energy into biochemical signals, cytoskeletal rearrangements cell differentiation, or collective cell behavior.

Modulation of astroglial glutamine synthetase activity affects nociceptive behaviour and central sensitization of medullary dorsal horn nociceptive neurons in a rat model of chronic pulpitis

Previous studies indicate that the astroglial glutamate-glutamine shuttle may be involved in acute pulpal inflammatory pain by influencing central sensitization induced in nociceptive neurons in the trigeminal subnucleus caudalis [the medullary dorsal horn (MDH)] by application of an inflammatory irritant to the rat tooth pulp. The aim of this study was to test if intrathecal application to the rat medulla of the astroglial glutamine synthetase inhibitor methionine sulfoximine (MSO) can influence the central sensitization of MDH nociceptive neurons and the animal's associated behaviour that are manifested in a model of chronic pulpitis pain induced by exposure of a mandibular molar pulp. This model was found to be associated with nocifensive behaviour and enhanced reflex activity evoked by mechanical stimulation of the rat's facial skin and with immunocytochemical evidence of astroglial activation in the MDH. These features were apparent for up to 28 days post-operatively. During this post-operative period, the nocifensive behaviour and enhanced reflex activity were significantly attenuated by intrathecal application of MSO (5 μL, 10 mM) but not by vehicle application. In electrophysiological recordings of nociceptive neuronal activity in the MDH, central sensitization was also evident in pulp-exposed rats but not in intact rats and could be significantly attenuated by MSO application but not by vehicle application. These behavioural and neuronal findings suggest that the astroglial glutamate-glutamine shuttle is responsible for the maintenance of inflammation-induced nocifensive behavioural changes and the accompanying central sensitization in MDH nociceptive neurons in this chronic pulpitis pain model.

Phenotypes of articular disc cells in the rat temporomandibular joint as demonstrated by immunohistochemistry for nestin and GFAP

The articular disc is a dense collagenous tissue containing disc cells that are phenotypically described as chondrocyte-like cells or fibrochondrocytes. Despite the possible existence of these phenotypes in systemic joints, little is known about the detailed classification of the articular disc cells in the temporomandibular joint. In this immunocytochemical study we examined the localization and distribution patterns of nestin and glial fibrillary acidic protein (GFAP) in the articular disc of the rat temporomandibular joint at postnatal day 1, and weeks 1, 2, 4 and 8, based on the status of tooth eruption and occlusion. Nestin and GFAP are intermediate filament proteins whose expression patterns are closely related to cell differentiation and cell migration. Both types of immunopositive cell greatly increased postnatally to a stable level after postnatal week 4, but they showed different distribution patterns and cell morphologies. Nestin-reactive disc cells, which were characterized by a meagre cytoplasm and thin cytoplasmic processes, were scattered in the articular disc, whereas GFAP-positive cells, characterized by broader processes, existed exclusively in the deeper area. In mature discs, the major proportion of articular disc cells exhibited GFAP immunoreactivity. Furthermore, a double-immunostaining demonstrated that the nestin-negative cells, consisting of GFAP-positive and -negative cells, exhibited immunoreactions for heat shock protein 25. These findings indicate that the articular disc cells comprise at least three types in the rat temporomandibular joint and suggest that their expressions closely relate to mechanical loading forces within the joint, including occlusal force, as observed through postnatal development.

Adaptive calcified matrix response of dental pulp to bacterial invasion is associated with establishment of a network of glial fibrillary acidic protein+/glutamine synthetase+ cells

We report evidence for anatomical and functional changes of dental pulp in response to bacterial invasion through dentin that parallel responses to noxious stimuli reported in neural crest-derived sensory tissues. Sections of resin-embedded carious adult molar teeth were prepared for immunohistochemistry, in situ hybridization, ultrastructural analysis, and microdissection to extract mRNA for quantitative analyses. In odontoblasts adjacent to the leading edge of bacterial invasion in carious teeth, expression levels of the gene encoding dentin sialo-protein were 16-fold greater than in odontoblasts of healthy teeth, reducing progressively with distance from this site of the carious lesion. In contrast, gene expression for dentin matrix protein-1 by odontoblasts was completely suppressed in carious teeth relative to healthy teeth. These changes in gene expression were related to a gradient of deposited reactionary dentin that displayed a highly modified structure. In carious teeth, interodontoblastic dentin sialo-protein(-) cells expressing glutamine synthetase (GS) showed up-regulation of glial fibrillary acidic protein (GFAP). These cells extended processes that associated with odontoblasts. Furthermore, connexin 43 established a linkage between adjacent GFAP(+)/GS(+) cells in carious teeth only. These findings indicate an adaptive pulpal response to encroaching caries that includes the deposition of modified, calcified, dentin matrix associated with networks of GFAP(+)/GS(+) interodontoblastic cells. A regulatory role for the networks of GFAP(+)/GS(+) cells is proposed, mediated by the secretion of glutamate to modulate odontoblastic response.

Survival and migration of human and rat olfactory ensheathing cells in intact and injured spinal cord

Increasing evidence indicates the potential of olfactory ensheathing cells (OECs) for treating spinal cord injuries. The present study compared proliferation and migration of adult rat and human OECs transplanted into the spinal cord of athymic (immunodeficient) rats. OECs were purified from the nasal lamina propria and prelabeled with a cytoplasmic dye. After OEC injection into the thoracic spinal cord, animals were perfused 4 hr, 24 hr, and 7 days later. Both rat and human OECs showed similar migration. Cells were seen leaving the injection site after 4 hr, and by 7 days both rat and human OECs had migrated approximately 1 mm rostrally and caudally within the cord (rat: 1,400 +/- 241 microm rostral, 1,134 +/- 262 microm caudal, n = 5; human: 1,337 +/- 192 microm rostral, 1,205 +/- 148 microm caudal, n = 6). Proliferation of transplanted OECs was evident at 4 hr, but most had ceased dividing by 24 hr. In 10 animals, the spinal cord was injured by a contralateral hemisection made 5 mm rostral to the transplantation site at the time of OEC transplantation. After 7 days, macrophages were numerous both around the injury and at the transplantation site. In the injured cord, rat and human OECs migrated for shorter distances, in both rostral and caudal directions (rat: 762 +/- 118 microm rostral, 554 +/- 142 microm caudal, n = 4; human: 430 +/- 55 microm rostral, 399 +/- 161 microm caudal, n = 3). The results show that rat and human OECs rapidly stop dividing after transplantation and have a similar ability to survive and migrate within the spinal cord of immunocompromised hosts. OECs migrated less in animals with a concomitant contralateral hemisection.

Autologous olfactory ensheathing cell transplantation in human spinal cord injury

Olfactory ensheathing cells transplanted into the injured spinal cord in animals promote regeneration and remyelination of descending motor pathways through the site of injury and the return of motor functions. In a single-blind, Phase I clinical trial, we aimed to test the feasibility and safety of transplantation of autologous olfactory ensheathing cells into the injured spinal cord in human paraplegia. Participants were three male paraplegics, 18-55 years of age, with stable, complete thoracic injuries 6-32 months previously, with stable spinal column, no implanted prostheses, and no syrinx. Olfactory ensheathing cells were grown and purified in vitro from nasal biopsies and injected into the region of damaged spinal cord. The trial design includes a matched injury group as a control for the assessors, who are blind to treatment status. Assessments, made before transplantation and at regular intervals subsequently, include MRI, medical, neurological and psychosocial assessments, and standard American Spinal Injury Association and Functional Independence Measure assessments. One year after cell implantation, there were no medical, surgical or other complications to indicate that the procedure is unsafe. There is no evidence of spinal cord damage nor of cyst, syrinx or tumour formation. There was no neuropathic pain reported by the participants, no change in psychosocial status and no evidence of deterioration in neurological status. Participants will be followed for 3 years to confirm long-term safety and to compare neurological, functional and psychosocial outcomes with the control group. We conclude transplantation of autologous olfactory ensheathing cells into the injured spinal cord is feasible and is safe up to one year post-implantation.