The developing mouse coronal suture at single-cell resolution

Sutures separate the flat bones of the skull and enable coordinated growth of the brain and overlying cranium. The coronal suture is most commonly fused in monogenic craniosynostosis, yet the unique aspects of its development remain incompletely understood. To uncover the cellular diversity within the murine embryonic coronal suture, we generated single-cell transcriptomes and performed extensive expression validation. We find distinct pre-osteoblast signatures between the bone fronts and periosteum, a ligament-like population above the suture that persists into adulthood, and a chondrogenic-like population in the dura mater underlying the suture. Lineage tracing reveals an embryonic Six2+ osteoprogenitor population that contributes to the postnatal suture mesenchyme, with these progenitors being preferentially affected in a Twist1+/-; Tcf12+/- mouse model of Saethre-Chotzen Syndrome. This single-cell atlas provides a resource for understanding the development of the coronal suture and the mechanisms for its loss in craniosynostosis.

The Flavor Enhancer Maltol Increases Pigment Aggregation in Dermal and Neural Melanophores in Xenopus laevis Tadpoles

Melanophores are pigmented cells that change the distribution of melanosomes, enabling animals to appear lighter or darker for camouflage, thermoregulation, and protection from ultraviolet radiation. A complex series of hormonal and neural mechanisms regulates melanophore pigment distribution, making these dynamic cells a valuable tool to screen toxicants as they rapidly respond to changes in the environment. We found that maltol, a naturally occurring flavor enhancer and fragrance agent, induces melanophore pigment aggregation in a dose-dependent manner in Xenopus laevis tadpoles. To determine if maltol affects camouflage adaptation, we placed tadpoles into maltol baths situated over either a white or a black background. Maltol induced pigment aggregation in a similar dose-dependent pattern regardless of background color. We also tested how maltol treatment compares to melatonin treatment and found that the degree of pigment aggregation induced by maltol is similar to treatment with melatonin but that maltol induces over a much longer time course. Last, maltol had no effect on mRNA expression in the brain of genes that regulate camouflage-related pigment aggregation. The present results suggest that maltol does not exert its effects via the camouflage adaptation mechanism or via melatonin-related mechanisms. These results are the first to identify a putative toxicological effect of maltol exposure in vivo and rule out several mechanisms by which maltol may exert its effects on pigment aggregation. Environ Toxicol Chem 2020;39:381-395. © 2019 SETAC.

In Vivo Evaluation of Novel PLA/PCL Polymeric Patch in Rats for Potential Spina Bifida Coverage

BACKGROUND

Current therapeutic materials for spina bifida repair showed a limited number of options in the market, and none of them have all the requirements as the ideal patch. In fact, sometimes the surgical procedures pose substantial challenges using different patches to fully cover the spina bifida lesion. For this purpose, a tailored patch made of poly (L-lactic acid) and poly (ε-caprolactone) blend was designed and validated in vitro to accomplish all these requirements but was never tested in vivo.

MATERIAL AND METHODS

In our present study, the designed patch was analyzed in terms of rejection from the animal when implanted subcutaneously and as a dural substitute in the spinal cord. Inflammatory reaction (Iba1), astrogliosis (GFAP), was analyzed and functional interaction with spinal cord tissue assessing the (%motor-evoked potentials /compound motor action potential) by electrophysiology.

RESULTS

No evidence of adverse or inflammatory reactions was observed in both models of subcutaneous implantation, neither in the neural tissue as a dural substitute. No signs of astrogliosis in the neural tissue were observed, and no functional alteration with improvement of the motor-evoked potential's amplitude was detected after 4 wk of implantation as a dural substitute in the rat spinal cord.

CONCLUSIONS

Designed patch used as a dural substitute will apparently not produce inflammation, scar formation, or tethering cord and not induce any adverse effect on regular functions of the spinal cord. Further studies are needed to evaluate potential improvements of this novel polymeric patch in the spinal cord regeneration using spina bifida models.

Activation of pial and dural macrophages and dendritic cells by cortical spreading depression

OBJECTIVE

Cortical spreading depression (CSD) has long been implicated in migraine attacks with aura. The process by which CSD, a cortical event that occurs within the blood-brain barrier (BBB), results in nociceptor activation outside the BBB is likely mediated by multiple molecules and cells. The objective of this study was to determine whether CSD activates immune cells inside the BBB (pia), outside the BBB (dura), or in both, and if so, when.

METHODS

Investigating cellular events in the meninges shortly after CSD, we used in vivo two-photon imaging to identify changes in macrophages and dendritic cells (DCs) that reside in the pia, arachnoid, and dura and their anatomical relationship to TRPV1 axons.

RESULTS

We found that activated meningeal macrophages retract their processes and become circular, and that activated meningeal DCs stop migrating. We found that CSD activates pial macrophages instantaneously, pial, subarachnoid, and dural DCs 6-12 minutes later, and dural macrophages 20 minutes later. Dural macrophages and DCs can appear in close proximity to TRPV1-positive axons.

INTERPRETATION

The findings suggest that activation of pial macrophages may be more relevant to cases where aura and migraine begin simultaneously, that activation of dural macrophages may be more relevant to cases where headache begins 20 to 30 minutes after aura, and that activation of dural macrophages may be mediated by activation of migratory DCs in the subarachnoid space and dura. The anatomical relationship between TRPV1-positive meningeal nociceptors, and dural macrophages and DCs supports a role for these immune cells in the modulation of head pain. Ann Neurol 2018;83:508-521.

Role of KATPChannels in the Regulation of Rat Dura and Pia Artery Diameter

The aim of the present study was to examine the effect of KATPchannel openers pinacidil and levcromakalim on rat dural and pial arteries as well as their inhibition by glibenclamide. We used an in-vivo genuine closed cranial window model and an in-vitro organ bath. Glibenclamide alone reduced the dural but not the pial artery diameter compared with controls. Intravenous pinacidil and levcro-makalim induced dural and pial artery dilation that was significantly attenuated by glibenclamide. In the organ bath pinacidil and levcromakalim induced dural and middle cerebral artery relaxation that was significantly attenuated by glibenclamide. In conclusion, KATPchannel openers induce increasing diameter/relaxation of dural and pial arteries after intravenous infusion in vivo and on isolated arteries in vitro. Furthermore, dural arteries were more sensitive to KATPchannel openers than pial arteries.

Sex-, Stress-, and Sympathetic Post-Ganglionic Neuron-Dependent Changes in the Expression of Pro- and Anti-Inflammatory Mediators in Rat Dural Immune Cells

BACKGROUND

Migraine attacks are associated with sterile inflammation of the dura. Immune cells are a primary source of inflammatory mediators, and we therefore sought to further explore the link between dural immune cells and migraine.

OBJECTIVE

Based on the observations that migraine is more common in women than in men, stress is the most common trigger for a migraine attack, and sympathetic post-ganglionic innervation of the dura enables local control of dural immune cells, we hypothesized that stress shifts the balance of inflammatory mediator expression in dural immune cells toward those that trigger a migraine attack, where these changes are larger in females and dependent, at least in part, on sympathetic post-ganglionic innervation of the dura. Our objective was to test this hypothesis.

METHODS

Dura were obtained from naïve or stressed, intact or surgically sympathectomized, adult male and female rats. Dura were assessed immediately or 24 hours after termination of 4 continuous days of unpredictable, mild stressors. Following enzymatic digestion of each dura, myeloid and lymphoid-derived dural immune cells were isolated by fluorescence-activated cell sorting for semi-quantitative polymerase chain reaction analysis.

RESULTS

In myeloid-derived dural immune cells, there was an increase in pro-inflammatory mediator mRNA following stress, particularly in females, which remained elevated with a 24-hour delay after stress. There was a stress-induced decrease in anti-inflammatory mediator mRNA immediately after stress in females, but not males. The stress-induced changes were attenuated in sympathectomized females. In lymphoid-derived dural immune cells, there was a persistent increase in pro-inflammatory mediator mRNA following stress, particularly in females. A stress-induced increase in anti-inflammatory mediator mRNA was also observed in both males and females, and was further attenuated in sympathectomized females.

CONCLUSIONS

Consistent with our hypothesis, there is a stress-induced shift in the balance of pro- and anti-inflammatory mediator expression in dural immune cells that is more pronounced in females, and is dependent, at least in part, on sympathetic post-ganglionic innervation in females. This shift in the balance of inflammatory mediator expression may not only play an important role in triggering migraine attacks, but also suggests it may be possible, if not necessary, to employ different strategies to most effectively treat migraine in men and women.

Efficient Generation of Induced Pluripotent Stem and Neural Progenitor Cells From Acutely Harvested Dura Mater Obtained During Ventriculoperitoneal Shunt Surgery

BACKGROUND

The dura mater can be easily biopsied during most cranial neurosurgical operations. We describe a protocol that allows for robust generation of induced pluripotent stem cells (iPSCs) and neural progenitors from acutely harvested dura mater.

OBJECTIVE

To generate iPSCs and neural progenitor cells from dura mater obtained during ventriculoperitoneal shunt surgery.

METHODS

Dura was obtained during ventriculoperitoneal shunt surgery for normal pressure hydrocephalus from a 60-year-old patient with severe cognitive impairment. Fibroblasts were isolated from the dural matrix and transduced with nonintegrating Sendai virus for iPSC induction. A subset of successfully generated iPSC clones underwent immunocytochemical analysis, teratoma assay, karyotyping, and targeted neural differentiation.

RESULTS

Eleven iPSC clones were obtained from the transduction of an estimated 600,000 dural fibroblasts after 3 passages. Three clones underwent immunocytochemical analysis and were shown to express the transcription factors OCT-4, SOX2, and the embryonic cell markers SSEA-4, TRA-1-60, and Nanog. Two clones were tested for pluripotency and formed teratomas at the injection site in immunodeficient mice. Three clones underwent chromosomal analysis and were found to have a normal metaphase spread and karyotype. One clone underwent targeted neural differentiation and formed neural rosettes as well as TuJ1/SOX1-positive neural progenitor cells.

CONCLUSIONS

IPSCs and neural progenitor cells can be efficiently derived from the dura of patients who need to undergo cranial neurosurgical operations. IPSCs were obtained with a nonintegrating virus and exhibited a normal karyotype, making them candidates for future autotransplantation after targeted differentiation to treat functional deficits.

Use of postmortem human dura mater and scalp for deriving human fibroblast cultures

Fibroblasts can be collected from deceased individuals, grown in culture, reprogrammed into induced pluripotent stem cells (iPSCs), and then differentiated into a multitude of cell types, including neurons. Past studies have generated iPSCs from somatic cell biopsies from either animal or human subjects. Previously, fibroblasts have only been successfully cultured from postmortem human skin in two studies. Here we present data on fibroblast cell cultures generated from 146 scalp and/or 53 dura mater samples from 146 postmortem human brain donors. In our overall sample, the odds of successful dural culture was almost two-fold compared with scalp (OR = 1.95, 95% CI: [1.01, 3.9], p = 0.047). Using a paired design within subjects for whom both tissues were available for culture (n = 53), the odds of success for culture in dura was 16-fold as compared to scalp (OR = 16.0, 95% CI: [2.1–120.6], p = 0.0007). Unattended death, tissue donation source, longer postmortem interval (PMI), and higher body mass index (BMI) were associated with unsuccessful culture in scalp (all p<0.05), but not in dura. While scalp cells proliferated more and grew more rapidly than dura cells [F (1, 46) = 12.94, p<0.008], both tissues could be generated and maintained as fibroblast cell lines. Using a random sample of four cases, we found that both postmortem scalp and dura could be successfully reprogrammed into iPSC lines. Our study demonstrates that postmortem dura mater, and to a lesser extent, scalp, are viable sources of living fibroblasts for culture that can be used to generate iPSCs. These tissues may be accessible through existing brain tissue collections, which is critical for studying disorders such as neuropsychiatric diseases.

Use of a collagen biomatrix (TissuDura) for dura repair: a long-term neuroradiological and neuropathological evaluation

PURPOSE

The aim of this study was to evaluate the clinical, neuroradiological, and neuropathological outcomes of patients treated with equine collagen foil (TissuDura) as a dura mater substitute during cranial and spinal neurosurgical procedures.

MATERIALS AND METHODS

All patients treated at the Department of Neurosurgery of the Second University of Naples with TissuDura between 2005 and 2009 were included. Dural reconstruction was performed using TissuDura, overlaid 1 cm over the dural defect with additional fixation using fibrin glue. No surgical sutures were used. Patients underwent postoperative contrast-enhanced magnetic resonance scans at 1 week, 1 month, and 1 year after surgery to detect any cerebrospinal fluid (CSF) leaks, infections, inflammations, or CSF circulation in the surgical region.

RESULTS

Dural reconstruction was performed in 74 patients, including 50 patients with tumors, two with C2 neurinoma, two with acoustic neurinoma, six with Chiari I malformation, two with severe head injury, and 12 requiring spinal surgery. Clinical and neuroradiological findings were normal and no signs of graft rejection or CSF leaks at postoperative follow-up were observed. In two cases of atypical meningioma, re-operation of the dural reconstruction was performed after 1 year. No adherences between brain and neodura were detected, and histopathological investigations demonstrated dural regeneration.

CONCLUSIONS

Following dural reconstructions with TissuDura without surgical sutures, no local toxicity or complications were observed for up to 1 year. TissuDura demonstrated elasticity, non-reactivity, and good adaptability. The overlay technique using fibrin glue was simple and fast. Future studies and longer follow-up are needed to confirm the efficacy of TissuDura.

Tumor necrosis factor-α induces sensitization of meningeal nociceptors mediated via local COX and p38 MAP kinase actions

The proinflammatory cytokine TNF-α has been shown to promote activation and sensitization of primary afferent nociceptors. The downstream signaling processes that play a role in promoting this neuronal response remain however controversial. Increased TNF-α plasma levels during migraine attacks suggest that local interaction between this cytokine and intracranial meningeal nociceptors plays a role in promoting the headache. Here, using in vivo single unit recording in the trigeminal ganglia of anesthetized rats, we show that meningeal TNF-α action promotes a delayed mechanical sensitization of meningeal nociceptors. Using immunohistochemistry, we provide evidence for non-neuronal localization of the TNF receptors TNFR1 to dural endothelial vascular cells and TNFR2 to dural resident macrophages as well as to some CGRP-expressing dural nerve fibers. We also demonstrate that meningeal vascular TNFR1 is co-localized with COX-1 while the perivascular TNFR2 is co-expressed with COX-2. We further report here for the first time that TNF-α evoked sensitization of meningeal nociceptors is dependent upon local action of cyclooxygenase (COX). Finally, we show that local application of TNF-α to the meninges evokes activation of the p38 MAP kinase in dural blood vessels that also express TNFR1 and that pharmacological blockade of p38 activation inhibits TNF-α evoked sensitization of meningeal nociceptors. Our study suggests that meningeal action of TNF-α could play an important role in the genesis of intracranial throbbing headaches such as migraine through a mechanism that involves at least part activation of non-neuronal TNFR1 and TNFR2 and downstream activation of meningeal non-neuronal COX and the p38 MAP kinase.

Radially aligned, electrospun nanofibers as dural substitutes for wound closure and tissue regeneration applications

This paper reports the fabrication of scaffolds consisting of radially aligned poly(ε-caprolactone) nanofibers by utilizing a collector composed of a central point electrode and a peripheral ring electrode. This novel class of scaffolds was able to present nanoscale topographic cues to cultured cells, directing and enhancing their migration from the periphery to the center. We also established that such scaffolds could induce faster cellular migration and population than nonwoven mats consisting of random nanofibers. Dural fibroblast cells cultured on these two types of scaffolds were found to express type I collagen, the main extracellular matrix component in dural mater. The type I collagen exhibited a high degree of organization on the scaffolds of radially aligned fibers and a haphazard distribution on the scaffolds of random fibers. Taken together, the scaffolds based on radially aligned, electrospun nanofibers show great potential as artificial dural substitutes and may be particularly useful as biomedical patches or grafts to induce wound closure and/or tissue regeneration.

Expression of extracellular matrix-proteins in perisellar connective tissue and dura mater

PURPOSE

To describe the pattern of expression of extracellular matrix (ECM) proteins in perisellar connective tissue.

METHODS

Dural and perisellar specimens from ten individuals were investigated immunohistochemically for collagens I to IV, tenascin, fibronectin, elastin, laminin, and vitronectin.

FINDINGS

Collagen I and III and fibronectin were strongly expressed and collagen IV, tenascin, and vitronectin were moderately expressed in the boundaries of the sella and around the CS. In six of nine specimens from the anterior boundary of the sella, and in 11 of 19 samples from the lateral boundary of the sella (medial wall of CS), two different layers could be detected by the expression of different ECM proteins. None of the antigens generally allowed differentiation between two layers of the pituitary envelope.

CONCLUSIONS

The pituitary boundary may consist of a single or a double layer, infrequently differentiated from each other by the expression of different ECM proteins.

Localization of COX-1 and COX-2 in the intracranial dura mater of the rat

Primary headaches such as migraine can be aborted by systemic administration of non-steroidal anti-inflammatory drugs (NSAIDs), potentially through the non-selective inhibition of cyclooxygenase (COX) activity in the intracranial meninges. In this study we have used single and double labeling immunohistochemistry to examine the distribution of the COX-1 and COX-2 isoforms in the intracranial dura mater of the rat and identify cell types that express them. COX-1 immunoreactivity was found in medium and small dural blood vessels and was co-expressed with the endothelial cell markers vimentin and the endothelial isoform of nitric oxide synthase (ecNOS). COX-1 was also found to be present in most dural mast cells. COX-2 was mainly expressed in ED2-positive resident dural macrophages. Constitutive COX-2 expression was also found in some axonal profiles, many of which were co-labeled with the nociceptor peptide marker CGRP. The findings suggest that NSAIDs may abort headache, at least in part, by inhibiting either neuronal or non-neuronal COX activity in the dura mater.

Osteogenic differentiation of dura mater stem cells cultured in vitro on three-dimensional porous scaffolds of poly(epsilon-caprolactone) fabricated via co-extrusion and gas foaming

A novel scaffold fabrication method utilizing both polymer blend extrusion and gas foaming techniques to control pore size distribution is presented. Seventy-five per cent of all pores produced using polymer blend extrusion alone were less than 50microm. Introducing a gas technique provided better control of pore size distribution, expanding the range from 0-50 to 0-350microm. Varying sintering time, annealing temperature and foaming pressure also helped to reduce the percentage of pore sizes below 50microm. Scaffolds chosen for in vitro cellular studies had a pore size distribution of 0-300microm, average pore size 66+/-17microm, 0.54+/-0.02% porosity and 98% interconnectivity, measured by micro-computed tomography (microCT) analysis. The ability of the scaffolds to support osteogenic differentiation for subsequent cranial defect repair was evaluated by static and dynamic (0.035+/-0.006ms(-1) terminal velocity) cultivation with dura mater stem cells (DSCs). In vitro studies showed minimal increases in proliferation over 28 days in culture in osteogenic media. Alkaline phosphatase expression remained constant throughout the study. Moderate increases in matrix deposition, as assessed by histochemical staining and microCT analysis, occurred at later time points, days 21 and 28. Although constructs cultured dynamically showed greater mineralization than static conditions, these trends were not significant. It remains unclear whether bioreactor culture of DSCs is advantageous for bone tissue engineering applications. However, these studies show that polycaprolactone (PCL) scaffolds alone, without the addition of other co-polymers or ceramics, support long-term attachment and mineralization of DSCs throughout the entire porous scaffold.

Mast cells populations fluctuate along the spinal dura mater of the developing rat

The present study reveals developmental changes in the number, the phenotype and the distribution pattern of mast cells (MCs) along the cervical, the thoracic and the lumbar parts of the spinal dura mater. Postnatal infiltration of spinal dura by MCs does not appear to follow a sequential developmental pattern and meningeal MCs are unevenly distributed along the various parts of the examined dura. At each spinal level, areas most densely populated by MCs are the dorsal dura and the dural sleeves of the dorsal (sensory) spinal roots The developmental time course of the total MCs number is characterized by significant fluctuations in all three parts examined, with notable increases at P1, P4, P21 and P60 (peak value) for the cervical part, at P1 (peak value), P7 and P21 for the thoracic part and at P1, P7 (peak value) and P30 for the lumbar part. At P180, MCs number declines to 56%, 33% and 13% of the peak values for the cervical, the thoracic and the lumbar part, respectively. However, a different developmental pattern is followed by each subpopulation of MCs identified on the basis of their staining characteristics, namely connective tissue type mast cells (CTMCs), mucosal type or cells with characteristics of immature mast cells (MTMCs) and mixed type MCs, in each part examined. The findings may be of importance in elucidating physiological and pathological processes in the dura mater and the vertebral column.

Proliferative capacity and osteogenic potential of novel dura mater stem cells on poly-lactic-co-glycolic acid

The rational design of biomimetic structures for the regeneration of damaged or missing tissue is a fundamental principle of tissue engineering. Multiple variables must be optimized, ranging from the scaffold type to the selection and properties of implanted cell(s). In this study, the osteogenic potential of a novel stem cell was analyzed on biodegradable poly(lactic-co-glycolic acid) (PLGA) biomaterials as a step toward creating new cell-materials constructs for bony regeneration. Dura mater stem cells (DSCs), isolated from rat dura mater, were evaluated and compared to bone marrow stem cells (BMSCs) for proliferative and differentiative properties in vitro. Experiments were carried out on both tissue culture plastic (TCP) and 2D planar films of PLGA. Proliferation of DSCs on both TCP and PLGA films increased over 21 days. Positive fold inductions in all five bone marker genes were observed at days 7, 14, 21 in all experimental samples compared with day 0 controls. DSCs demonstrated greater cell coverage and enhanced matrix staining on 2D PLGA films when compared with BMSCs. These cells can be isolated and expanded in culture and can subsequently attach, proliferate, and differentiate on both TCP and PLGA films to a greater extent than BMSCs. This suggests that DSCs are promising for cell-based bone tissue engineering therapies, particularly those applications involving regeneration of cranial bones.

[Reconstruction of three different kinds of tympanic membrane in vitro by tissue engineering technique]

OBJECTIVE

To reconstruct three different kinds of tympanic membrane in vitro by tissue engineering technique, and to examine their histological structures and mechanical properties.

METHODS

The skin and dura of pig (weight 30 kg) were processed with high satuated saline and enzymes to make extracellular matrix. Meanwhile, fibroblasts (1 x 10(6)/mL, 0.2 mL) were seeded on the surface of these two scaffolds and collagen. The composite tissues were cultured in vitro for 1 week and examined in histological structure and mechanical properties.

RESULTS

Fibroblasts cultured were spindle-shaped and could grow and attach to these scaffolds with a arrangement of sarciniform and parallel. The reconstructed tissue of ECM and collagen appeared to integrate well and had better bio-compatibility. The mean thickness of the collagen, the skin and the dura (all covered with fibroblasts) were 9.4, 10.0 and 10.4 microm respectively. The tension of the collagen was (1.417+/-0.030) N/mm2, of the acellular dermal matrix was (24.500+/-2.040) N/mm2 (being close to the tension of normal tympanic membrane, 26.700 N/mm2), of the acellular dura was (53.300+/-2.600) N/mm2.

CONCLUSION

The results suggest that the tension and the thinkness of acellular dermal matrix is similar to the normal tympanic membrane of guinea pig, it is an ideal material for tympanoplasty.

Dihydrotestosterone Stimulates Proliferation and Differentiation of Fetal Calvarial Osteoblasts and Dural Cells and Induces Cranial Suture Fusion

BACKGROUND

The higher prevalence of metopic and sagittal suture synostosis in male infants suggests a role for androgens in early craniofacial development. These experiments characterize the influence of androgen stimulation on growth and differentiation of fetal dural and calvarial bone cells and on cranial suture fusion.

METHODS

Primary murine fetal (E18) dural cells and calvarial osteoblasts were isolated and cultured. Cells were treated for 48 hours with 5alpha-dihydrotestosterone (0 to 1000 nM). Cell proliferation was examined by nonradioactive proliferation assay; mRNA expression of alkaline phosphatase, transforming growth factor (TGF)-beta1, and the bone matrix proteins osteopontin, osteocalcin, and type 1 collagen was determined by reverse-transcriptase polymerase chain reaction. In separate experiments, intact fetal calvariae were grown in tissue culture with 10 nM 5alpha-dihydrotestosterone for 7 and 14 days and then examined histologically.

RESULTS

Androgen stimulation at 5 nM increased proliferation of fetal dural cells by 46.0 percent and of fetal calvarial osteoblasts by 20.5 percent. Dural expression of osteopontin, osteocalcin, and type 1 collagen was enhanced by 5alpha-dihydrotestosterone, as was that of TGF-beta1 and alkaline phosphatase. Androgen stimulation increased calvarial osteoblast expression of alkaline phosphatase and TGF-beta1 but induced little change in expression of osteocalcin, osteopontin, and type 1 collagen. In tissue culture, 5alpha-dihydrotestosterone stimulated osteoid formation and fusion of sagittal sutures.

CONCLUSIONS

Androgen stimulation of dural cells and osteoblasts isolated from fetal calvaria promotes cell proliferation and osteoblastic differentiation and can induce cranial suture fusion. These results suggest that sex steroid hormone signaling may stimulate sutural osteogenesis by means of osteodifferentiation of dural cells, thus explaining the male prevalence of nonsyndromic craniosynostosis.

Developmental changes of mast cell populations in the cerebral meninges of the rat

It is known that both the dura and the pia mater attract and support the differentiation of mast cells. The present study shows that unevenly distributed mast cells in the cerebral meninges of the rat can be found in perivascular sites and vessel ramification points, but can also be unrelated to the meningeal vasculature. It also documents changes in the number, localization and staining preferences of the mast cells in the two meninges of the developing and mature rat brain. Quantitative examination of all types of histochemically differentiated meningeal mast cells reveals no major (although some exist) differences between right and left side subpopulations, but strongly suggests a different origin and fate of the dural and the pial mast cells. The number of dural mast cells, already high from postnatal day 0, although declining from postnatal day 21 onwards, remains conspicuous up to postnatal day 180. In contrast, pial mast cells are comparatively very few in the first day of the postnatal life, and despite a transient significant increase in the following two weeks, they reach almost zero levels from postnatal day 21.

Differential effects of TGF-beta isoforms on murine fetal dural cells and calvarial osteoblasts

BACKGROUND

Proteins within the transforming growth factor (TGF)-beta family play a central role in both normal and pathologic calvarial morphogenesis. Previous work has suggested differential functions of the TGF-beta isoforms in these processes. Little is known, however, about effects of TGF-betas on the underlying dura. Furthermore, studies on the effects of TGF-beta isoforms on osteoblasts have been conflicting. The purpose of this study was to determine the effect of TGF-beta isoforms, specifically TGF-beta1 and TGF-beta3, on fetal calvarial osteoblast and dural cell differentiation, proliferation, and apoptosis.

METHODS

Primary cultures of fetal calvarial osteoblasts and dural cells were established from embryonic day-18 CD-1 mice. Cells were treated for 48 hours with TGF-beta1 or TGF-beta3. Northern blot analysis, cell counts, and apoptosis assays were performed.

RESULTS

In dural cells, TGF-beta1 stimulated the expression of early osteodifferentiation genes and resulted in a slight decrease in cell number and no effect on apoptosis. Similar results were observed in osteoblasts. TGF-beta3 had little or no effect on the genes studied in both cell types but resulted in increased apoptosis and concomitant decreases in cell number in both cell types.

CONCLUSIONS

This study demonstrates that dural cells respond to TGF-beta and that this response is isoform-specific. TGF-beta1 stimulates osteodifferentiation of previously uncommitted cells in the dura. It also stimulates early events in bone matrix deposition and has little effect on late markers of bone differentiation in osteoblasts and dural cells. Both isoforms result in decreases in cell number. TGF-beta3 results in greater decreases in cell number and isoform-specific stimulation of apoptosis in both dural cells and calvarial osteoblasts.

Convergence of cutaneous, musculoskeletal, dural and visceral afferents onto nociceptive neurons in the first cervical dorsal horn

The convergence of cutaneous, musculoskeletal, dural and visceral afferents onto nociceptive neurons in the first cervical dorsal horn was investigated in urethane/chloralose-anesthetized rats. Electrical stimulation was applied to facial, neck, shoulder and forepaw skin, cornea (COR), dura, second cervical (C2) nerve, hypoglossal nerve, temporomandibular joint, masseter (MAS) muscle and superior laryngeal nerve. In addition, acetic acid was injected intraperitoneally and microinjection of glutamate was applied to the tongue, MAS muscle, splenius cervicis muscle, dura and intrapericardial area. A total of 52 nociceptive neurons classified as wide dynamic range (n = 28) or nociceptive-specific (n = 24) was studied. All nociceptive neurons received afferent input from the skin and at least one COR, musculoskeletal, dural or visceral afferent source in the trigeminal (V) or cervical area but input from afferent sources caudal to the C2 innervation territory was sparse. The proportion of neurons responding to COR, dural, C2 nerve, hypoglossal nerve, temporomandibular joint, MAS muscle and superior laryngeal nerve stimulations was 87, 54, 85, 52, 73, 64 and 31%, respectively. Electrical stimulation of all tested sites showed a double logarithmic stimulus-response relation, and cluster analysis of the excitability to COR, musculoskeletal, dural and visceral stimulations revealed two groups of neurons, one mainly containing wide dynamic range neurons and one mainly containing nociceptive-specific neurons. These findings indicate that afferent convergence in first cervical dorsal horn nociceptive neurons may be limited to the craniofacial area and that they may play an important role in the integration of craniofacial and upper cervical nociceptive inputs.

Isolation and characterization of posterofrontal/sagittal suture mesenchymal cells in vitro

BACKGROUND

Craniosynostosis, the premature fusion of cranial sutures, affects one in 2500 children. In the mouse, the posterofrontal suture is programed to fuse postnatally, but the adjacent sagittal suture remains patent throughout life. To study the cellular process of suture fusion, the authors isolated and studied suture-derived mesenchymal cells.

METHODS

Skulls were harvested from 80 mice (2 to 5 days old), and posterofrontal and sagittal sutures were dissected meticulously. Suture mesenchymal tissue was separated from the underlying dura mater and overlying pericranium and cultured in growth media. After the cells migrated from the explant tissues, the morphologies of the two cell populations were studied carefully, and quantitative real-time polymerase chain reaction was performed to evaluate gene expression.

RESULTS

Both posterofrontal and sagittal cells exhibited highly heterogeneous morphologies, and the posterofrontal cells migrated faster than the sagittal cells. Accordingly, growth factors such as transforming growth factor-beta1 and fibroblast growth factor (FGF)-2 were expressed significantly more highly in posterofrontal compared with sagittal suture mesenchymal cells. In contrast, FGF receptor 2 and FGF-18 were expressed significantly more in sagittal than in posterofrontal suture cells. Importantly, bone morphogenic protein-3, the only osteogenic inhibitor in the bone morphogenic protein family, and noggin, a bone morphogenic protein antagonist, were expressed significantly more in sagittal than in posterofrontal suture cells, suggesting a possible mechanism of suture patency.

CONCLUSIONS

To the authors' knowledge, this is the first analysis of mouse suture-derived mesenchymal cells. The authors conclude that isolation of suture-derived mesenchymal cells will provide a useful in vitro system with which to study the mechanisms underlying suture biology.

MULTIPLE DIFFERENTIATION POTENTIALS OF NEONATAL DURA MATER-DERIVED CELLS

OBJECTIVE

The involvement of the dura mater in calvarial development and bone healing lead to a hypothesis that progenitor cells with multiple differentiation potentials exist within this tissue. The present study investigated the differentiation potentials of dura mater-derived cells by driving them into several cell-restricted lineages.

METHODS

Dissected dura mater tissue of neonatal rats was washed, finely minced, and enzymatically digested. The harvested cells were exposed to different differentiation (osteogenic, adipogenic, and chondrogenic) and basic media.

RESULTS

At defined time points, dura mater-derived cells were observed to differentiate into osteoblastic, adipoblastic, and chondroblastic cells, evidenced by specific biochemical staining. In addition, gene expressions of osteogenesis (alkaline phosphatase, osteocalcin, and osteopontin), chondrogenesis (collagen Type II and aggrecan core protein) and adipogenesis (peroxisome proliferator activated receptor gamma-2) were up-regulated in the differentiated dura mater-derived cells, confirmed by polymerase chain reaction.

CONCLUSION

Preliminarily, it was concluded that a subpopulation of multiple potential mesenchymal cells exists in neonatal dura mater, which explains the function of the dura mater on neurocranium development and calvarial bone healing.

Repair of the dura mater with processed collagen devices

BACKGROUND

We evaluated in a canine duraplasty model how specific differences in device physicomechanical properties, porosity, and crosslinking influenced the biological performance of three processed collagen dural substitutes.

METHODS

Three collagen dural substitutes were studied: Dura-Guard, DuraGen, and Durepair. The initial strength, stiffness, and suture retention force were measured using standard mechanical test methods. The relative pore sizes of each device were assessed with a scanning electron microscope. Differential scanning calorimetry was used to measure their respective collagen denaturation temperatures. The biologic response and performance of the materials were evaluated via an acute (1 month) and long-term (3 and 6 months) canine bilateral duraplasty study.

RESULTS

The mechanical properties of Dura-Guard and Durepair were similar to native dura. We could not quantify the mechanical properties of DuraGen because of its fragile nature. The denaturation temperature of DuraGen and Dura-Guard differed significantly from that reported for native collagens. The denaturation temperature of Durepair was comparable with the values reported for native collagens. All three materials were tolerated well by the animals. DuraGen did not maintain its structural integrity beyond 1 month. Dura-Guard and Durepair persisted for 6 months. Durepair was populated by fibroblasts and blood vessels, whereas Dura-Guard was not.

CONCLUSIONS

The three dural substitutes tested were found to be safe and effective in healing surgically created defects in the dura mater. Although each of these dura substitutes are composed of collagen, differences in the collagen source and processing influenced device physicomechanical properties, porosity, and the nativity of the collagen polymer. These measured differences influenced device intraoperative handling and installation as well as the post-operative biological response, where differences in device resorption, cell penetration, vascularization, and collagen remodeling were observed.

Localization of P2X2 and P2X3 receptors in rat trigeminal ganglion neurons

Purine receptors have been implicated in central neurotransmission from nociceptive primary afferent neurons, and ATP-mediated currents in sensory neurons have been shown to be mediated by both P2X3 and P2X2/3 receptors. The aim of the present study was to quantitatively examine the distribution of P2X2 and P2X3 receptors in primary afferent cell bodies in the rat trigeminal ganglion, including those innervating the dura. In order to determine the classes of neurons that express these receptor subtypes, purine receptor immunoreactivity was examined for colocalization with markers of myelinated (neurofilament 200; NF200) or mostly unmyelinated, non-peptidergic fibers (Bandeiraea simplicifolia isolectin B4; IB4). Forty percent of P2X2 and 64% of P2X3 receptor-expressing cells were IB4 positive, and 33% of P2X2 and 31% of P2X3 receptor-expressing cells were NF200 positive. Approximately 40% of cells expressing P2X2 receptors also expressed P2X3 receptors and vice versa. Trigeminal ganglion neurons innervating the dura mater were retrogradely labeled and 52% of these neurons expressed either P2X2 or P2X3 or both receptors. These results are consistent with electrophysiological findings that P2X receptors exist on the central terminals of trigeminal afferent neurons, and provide evidence that afferents supplying the dura express both receptors. In addition, the data suggest specific differences exist in P2X receptor expression between the spinal and trigeminal nociceptive systems.

[The construction of an in vitro model of dural cells]

AIM

To study the healing mechanism of duraplasty a model of rabbit dural healing was constructed in vitro and the influences of collagen, laminin, polylysine on the migration and proliferation of dural cells were compared.

METHODS

Rabbit dura pieces 1.5 cm x 1.5 cm in size were created and were perforated in their central part with a 2 mm punch to mimic a dural defect. The dural pieces were cultured in 24-well plates which had been coated with collagen, laminin and polylysine respectively and the influence of different extracellular matrix on the migration and proliferation of dural cells was observed. Cells were subcultured on slides for immunocytochemistry to identify the characteristics of dural cells. The dural healing was observed by scanning electronic microscope.

RESULTS

Only the dura pieces cultured on collagen coated wells showed migration of cells into the central defect after a period of 8-10 days and dural defect healing occurred after 13-15 days. Dural cells stained strongly positive with antibodies against vimentin and negative with VIII factor. New collagen fibers were observed in the dural defects.

CONCLUSION

A kind of cell model for dural healing was constructed successfully in vitro. Cell migration from the dural defect margin is an important mechanism in the process of wound healing after duraplasty.

TGF-β2 stimulates cranial suture closure through activation of the Erk-MAPK pathway

Cranial sutures are important growth sites of the skull. During suture closure, the dura mater is one of the most important sources of various positive and negative regulatory signals. Previous results indicate that TGF-beta2 from dura mater strongly accelerates suture closure, however, its exact regulatory mechanism is still unclear. In this study, we confirmed that removal of dura mater in calvarial organ culture strongly accelerates sagittal suture closure and that this effect is further enhanced by TGF-beta2 treatment. TGF-beta2 stimulated cell proliferation in the MC3T3-E1 cell line. Similarly, it stimulated the proliferation of cells in the sutural space in calvarial organ culture. Furthermore, TGF-beta2-mediated enhanced cell proliferation and suture closure were almost completely inhibited by an Erk-MAPK blocker, PD98059. These results indicate that TGF-beta2-induced activation of Erk-MAPK is an important signaling component that stimulates cell proliferation to enrich osteoprogenitor cells, thereby promoting their differentiation into osteoblasts to achieve a rapid calvarial bone expansion.

An in vitro culturing model for rabbit dural cells

The objectives of this study were (a) to construct an in vitro model of rabbit dural healing, (b) to test the influence of collagen, laminin, and poly-L-lysine on the migration and proliferation of dural cells, and (c) to study the healing mechanism of duraplasty. Rabbit dural pieces (1.5 cm x 1.5 cm) were perforated in their central part with a 2 mm punch to mimic a dural defect. The dural pieces were cultured in 24-well plates that had been coated with collagen, laminin, or poly-L-lysine, and the influence of different extracellular matrices on migration and proliferation of dural cells was observed. Cells were subcultured on slides for immunocytochemistry to study their characteristics; dural healing was observed by scanning electron microscopy. The results demonstrated that only the dural pieces that were cultured on collagen-coated wells showed migration of cells into the central defect after a period of 8 to 10 days and that healing of the dural defect occurred by 13 to 15 days. The cultured dural cells stained strongly positive with an antibody to vimentin, but negative with an antibody to factor VIII. New collagen fibers were observed in the dural defects. This report demonstrates that an in vitro model for dural healing was successfully constructed in collagen-coated wells; the results implicate cellular migration of fibroblasts from the dural defect margin as an important mechanism of wound healing following duraplasty.

Expression and Possible Mechanisms of Regulation of BMP3 in Rat Cranial Sutures

BACKGROUND

Clinical genetics data and investigative studies have contributed greatly to our understanding of the role of numerous genes in craniosynostosis. Recent studies have introduced antagonists of osteogenesis as potential key regulators of suture fusion and patency. The authors investigated the expression pattern of the bone morphogenetic protein antagonist BMP3 in rat cranial sutures and the factors regulating its expression in vitro.

METHODS

Microarray analysis was performed on rat posterior frontal and sagittal cranial sutures at 5, 10, 15, 20, and 30 days of life (n = 30 per group). Gene expression was confirmed using quantitative real-time reverse transcriptase polymerase chain reaction. Regulation of BMP3 expression was determined using primary rat calvarial osteoblasts stimulated with recombinant human fibroblast growth factor 2 or recombinant human transforming growth factor beta1, or cultured with primary rat nonsuture dura mater. Gene expression was quantified with quantitative real-time reverse transcriptase polymerase chain reaction.

RESULTS

BMP3 expression in the posterior frontal suture decreased over the time course analyzed, whereas it increased in the sagittal suture. Notably, BMP3 expression was higher in the patent sagittal suture during the window of posterior frontal suture fusion. Stimulation of osteoblasts with recombinant human fibroblast growth factor 2 led to a rapid and sustained suppression of BMP3 expression (85 percent, p < 0.01) when compared with controls. Co-culture with dural cells decreased BMP3 mRNA by 50 percent compared with controls (p < 0.01).

CONCLUSIONS

BMP3 is expressed in rat cranial sutures in a temporal pattern suggesting involvement in cranial suture patency and fusion. Furthermore, BMP3 is regulated in calvarial osteoblasts by recombinant human fibroblast growth factor 2 and by paracrine signaling from dura mater. These data add to our knowledge of the role of osteogenic antagonists in cranial suture biology.

Intermittent Hydrostatic Compression Promotes Nitric Oxide Production and Osteodifferentiation of Fetal Dural Cells

PURPOSE

The aim of these studies was to evaluate the biologic response of fetal dural cell cultures to compressive mechanical force.

METHODS

Primary cell cultures from the dura mater of E18 CD-1 mice were subjected to 2 PSI of intermittent hydrostatic compression (IHC) at a frequency of 0.5 Hz. Quantitative measures of the expression of Osterix (Osx), osteopontin (OP), endothelial nitric oxide synthase (eNOS) and Noggin were performed by RT-PCR following 3, 6, and 12 hours of exposure to IHC. Nitric oxide production was quantified through the measurement of NO metabolites following 6 hours of exposure to IHC.

RESULTS

IHC resulted in an increase in Osx, OP, and eNOS expression compared with controls at all time points. The expression of Noggin decreased at all time points. Exposure to IHC resulted in a significant increase in the production of NO metabolites at 6 hours when compared with controls.

CONCLUSIONS

These experiments indicate that dural cell biology is significantly altered following exposure to IHC. Specifically, IHC promotes production of NO and osteodifferentiation in fetal dural cell cultures, with increases in the expression of osteoinductive genes and decreases in inhibitors of osteogenesis.

Axon diameters and intradural trajectories of the dural innervation in the rat

Neurophysiological studies have characterized the sensory responses of primary afferent nociceptors that innervate the intracranial dura. The present study used anatomical methods to examine in greater detail the axonal trajectories within the dura, as well as the axonal size distribution of the dural innervation. Immunostaining for CGRP in dural wholemounts revealed a network of fibers extending across the entire dura, with an especially dense plexus running along the borders of the transverse and superior sagittal sinuses. The plexus along the caudal border of the transverse sinus partially overlapped the dural area that shows the greatest density of mast cells. Visualization of axon bundles by DiI application in formalin-fixed tissue revealed two separate systems of fibers in the dura that could be distinguished by the orientation of their trajectories: one that runs parallel to the middle meningeal artery (MMA), and another with a more or less orthogonal orientation that runs rostromedially from the transverse sinus across the MMA. Axons traversed large distances across the dura, but the majority of the branching and arborization was usually concentrated in the distal part of the trajectory. In separate animals, measurement of myelinated axon diameters with electron microscopy showed that approximately one-third of the myelinated axons in the nerves supplying the dura (nervus spinosus and tentorial nerves) could be classified as A-beta, since they were comparable in size to the majority of axons in the trochlear nerve and the upper end of the size range in the trigeminal nerve (i.e., > 5 microm).

Hybrid Constructs for Craniofacial Reconstruction: Sustained Gene Delivery Using Demineralized Bone Matrix Putty

These experiments evaluate the efficacy of a demineralized bone matrix putty engineered as a hybrid construct for sustained, site-directed gene transfer using an adenoviral vector. In vitro experiments were performed to evaluate the optimal dosing for gene transfer to fetal calvarial osteoblasts and dural cells and for the sustainability of gene transfer from the hybrid constructs. In the dosing experiments, hybrid constructs were created by combining 0.5 mL of demineralized bone matrix putty (DBX; SYNTHES Maxillofacial, Monument, CO) with 1 x 10(8), 1 x 10(7), or 1 x 10(6) particle-forming units (PFU) of an adenoviral vector carrying the gene encoding green fluorescent protein (AdGFP). These constructs were then placed in direct contact, or in transwell coculture, with fetal murine calvarial osteoblasts or dural cells at a multiplicity of infection (MOI = viral particle/cell ratio) of 1000, 100, and 10. The sustainability of gene transfer was tested through transfer of the hybrid construct to wells containing untransfected cells every 24 hours for 30 days. In both experiments, gene transfer was determined through the visualization of GFP using fluorescence light microscopy 24 hours after the onset of transfection. Optimal dosing for gene transfer occurred at an MOI of 10 for calvarial osteoblasts and 100 for dural cells. At greater concentrations, toxicity was observed in the majority of samples. Gene transfer to fetal dural cells and calvarial osteoblasts was sustained throughout the 30-day period. These experiments suggest that adenoviral vectors could be successfully incorporated within demineralized bone matrix to provide effective, sustained, site-directed gene transfer.

Mechanisms of murine cranial suture patency mediated by a dominant negative transforming growth factor-beta receptor adenovirus

Using a physiologic model of mouse cranial suture fusion, the authors' laboratory has previously demonstrated that transforming growth factor (TGF)-betas appear to be more abundantly expressed in the suture complex of the fusing posterior frontal compared with the patent sagittal suture. Furthermore, the authors have shown that by blocking TGF-beta signaling with a replication-deficient adenovirus encoding a defective, dominant negative type II TGF-beta receptor (AdDN-TbetaRII), posterior frontal suture fusion was inhibited. In this study, the authors attempt to further elucidate the role of TGF-beta in cranial suture fusion by investigating possible mechanisms of AdDN-TbetaRII-mediated cranial suture patency using both an established organ culture model and a novel in vitro co-culture system that recapitulates the in vivo anatomic dura mater/cranial suture relationship. In this article, the authors demonstrate that blocking TGF-beta signaling with the AdDN-TbetaRII construct led to inhibition of cellular proliferation in the suture mesenchyme and subjacent dura mater during the early period of predicted posterior frontal suture fusion. Interestingly, co-culture experiments revealed that transfecting osteoblasts with AdDN-TbetaRII led to alterations in the gene expression levels of two important bone-related molecules (Msx2 and osteopontin). Inhibiting TGF-beta signaling prevented time-dependent suppression of Msx2 and prevented induction of osteopontin, thereby retarding osteoblast differentiation. Furthermore, the authors demonstrated that the AdDN-TbetaRII construct was capable of blocking TGF-beta -mediated up-regulation of collagen IalphaI, an extracellular matrix molecule important for bone formation. Collectively, these data strongly suggest that AdDN-TbetaRII maintains posterior frontal patency, in part by altering early events in de novo bone formation, including cellular proliferation and early extracellular matrix production.

Conditional inactivation of Tgfbr2 in cranial neural crest causes cleft palate and calvaria defects

Cleft palate and skull malformations represent some of the most frequent congenital birth defects in the human population. Previous studies have shown that TGFbeta signaling regulates the fate of the medial edge epithelium during palatal fusion and postnatal cranial suture closure during skull development. It is not understood, however, what the functional significance of TGFbeta signaling is in regulating the fate of cranial neural crest (CNC) cells during craniofacial development. We show that mice with Tgfbr2 conditional gene ablation in the CNC have complete cleft secondary palate, calvaria agenesis, and other skull defects with complete phenotype penetrance. Significantly, disruption of the TGFbeta signaling does not adversely affect CNC migration. Cleft palate in Tgfbr2 mutant mice results from a cell proliferation defect within the CNC-derived palatal mesenchyme. The midline epithelium of the mutant palatal shelf remains functionally competent to mediate palatal fusion once the palatal shelves are placed in close contact in vitro. Our data suggests that TGFbeta IIR plays a crucial, cell-autonomous role in regulating the fate of CNC cells during palatogenesis. During skull development, disruption of TGFbeta signaling in the CNC severely impairs cell proliferation in the dura mater, consequently resulting in calvaria agenesis. We provide in vivo evidence that TGFbeta signaling within the CNC-derived dura mater provides essential inductive instruction for both the CNC- and mesoderm-derived calvarial bone development. This study demonstrates that TGFbeta IIR plays an essential role in the development of the CNC and provides a model for the study of abnormal CNC development.

Dural cell culture. A new approach to study duraplasty

Fistulas of the cerebrospinal fluid are often repaired by insertion of grafts of various kinds. However, current knowledge of wound healing after graft insertion is limited, and only a few animal studies are available. The objective of this study is to test whether an in vitro model is suited to analyze cellular healing aspects after duraplasty and to assess dura substitutes in such conditions in regard to their surface attractiveness for cellular migration from the dura margins. Harvested dura pieces from minipigs were perforated to mimic central dura lesions, placed on various coated surfaces (collagen, laminin, poly-L-lysine) or grafts, and investigated in a cell culture for cellular closure of the perforation. Cellular migration from the dura into the central perforation was noted on collagen-coated surfaces and when defects were filled with collagen gels, but there was no cell growth on surfaces with poly-L-lysine or laminin coating. Immunocytochemistry identified the migrating cells mainly as fibroblasts with some intermingled epithelial cells. Scanning electron microscopy proved cellular closure of defects after dura placement on allogenic non-crosslinked collagen transplants. Less cellular migration was observed on poly-P-dioxanon sheets, while no cells migrated into the central dura perforation after placement on a cartilage substitute. Cell counting indicated enhanced cellular closure of the dura opening after introduction of insulin or fibroblast growth factor (sign test for both: 0.031). Our study succeeded in establishing a cell culture model for duraplasty and indicated cellular migration from the dura borders at the site of the defect during the wound healing process. The cell culture model presented in this report shows that collagen grafts are best suited for duraplasty. In accordance with the immunocytological finding of fibroblast migration from the dura borders additional application of fibroblast-stimulating growth factors accelerated cellular defect closure.

Mechanical Strain Affects Dura Mater Biological Processes: Implications for Immature Calvarial Healing

The human brain grows rapidly during the first 2 years of life. This growth generates tensile strain in the overlying dura mater and neurocranium. Interestingly, it is largely during this 2-year growth period that infants are able to reossify calvarial defects. This clinical observation is important because it suggests that calvarial healing is most robust during the period of active intracranial volume expansion. With a rat model, it was previously demonstrated that immature dura mater proliferates more rapidly and produces more osteogenic cytokines and markers of osteoblast differentiation than does mature dura mater. It was therefore hypothesized that mechanical strain generated by the growing brain induces immature dura mater proliferation and increases osteogenic cytokine expression necessary for growth and healing of the overlying calvaria. Human and rat (n = 40) intracranial volume expansion was calculated as a function of age. These calculations demonstrated that 83 percent of human intracranial volume expansion is complete by 2 years of age and 90 percent of Sprague-Dawley rat intracranial volume expansion is achieved by 2 months of age. Next, the maximal daily circumferential tensile strains that could be generated in immature rat dura mater were calculated, and the corresponding daily biaxial tensile strains in the dura mater during this 2-month period were determined. With the use of a three-parameter monomolecular growth curve, it was calculated that rat dura mater experiences daily equibiaxial strains of at most 9.7 percent and 0.1 percent at birth (day 0) and 60 days of age, respectively. Because it was noted that immature dural cells may experience tensile strains as high as approximately 10 percent, neonatal rat dural cells were subjected to 10 percent equibiaxial strain in vitro, and dural cell proliferation and gene expression profiles were analyzed. When exposed to mechanical strain, immature dural cells rapidly proliferated (5.8-fold increase in proliferating cell nuclear antigen expression at 24 hours). Moreover, mechanical strain induced marked up-regulation of dural cell osteogenic cytokine production; transforming growth factor-beta1 messenger RNA levels increased 3.4-fold at 3 hours and fibroblast growth factor-2 protein levels increased 4.5-fold at 24 hours and 5.6-fold at 48 hours. Finally, mechanical strain increased dural cell expression of markers of osteoblast differentiation (2.8-fold increase in osteopontin levels at 3 hours). These findings suggest that mechanical strain can induce changes in dura mater biological processes and gene expression that may play important roles in coordinating the growth and healing of the neonatal calvaria.

Macrophages and dendritic cells in the rat meninges and choroid plexus: three-dimensional localisation by environmental scanning electron microscopy and confocal microscopy

The present investigation provides novel information on the topographical distribution of macrophages and dendritic cells (DCs) in normal meninges and choroid plexus of the rat central nervous system (CNS). Whole-mounts of meninges and choroid plexus of Lewis rats were incubated with various anti-leucocyte monoclonal antibodies and either visualised with gold-conjugated secondary antibody followed by silver enhancement and subsequent examination by environmental scanning electron microscopy or by the use of fluorochromes and confocal microscopy. Large numbers of MHC class II(+) putative DCs were identified on the internal or subarachnoid aspect of dural whole-mounts, on the surface of the cortex (pia/arachnoid) and on the surface of the choroid plexus. Occupation of these sites would allow DCs access to cerebrospinal fluid (CSF) and therefore allow antigens into the subarachnoid space and ventricles. By contrast, macrophages were less evident at sites exposed to CSF and were more frequently located within the connective tissue of the dura/arachnoid and choroid plexus stroma and also in a sub-pial location. The present data suggest that DC may be strategically located within the CNS to sample CSF-borne antigens. Furthermore, the data suggest that CNS tissue samples collected without careful removal of the meninges may inadvertently be contaminated by DCs and meningeal macrophages.

Neural-dural transition at the medial anterior cranial base: an anatomical and histological study with clinical applications

OBJECT

Few anatomical studies have been focused on the morphological features and microscopic anatomy of the transition from the intracranial space to the medial anterior cranial base. The authors of the current study performed histological analyses to define the structure of the transition from neural foramina to the cranial base (neural-dural transition) at the cribriform plate, particularly as related to cerebrospinal fluid (CSF) fistula formation and surgical intervention in the region.

METHODS

The medial anterior cranial base was resected in six cadaveric specimens. Histological methods were used to study the anatomy of the region on the microscopic level. Results of these examinations revealed a multilayered neural-dural transition at the cribriform plate, which consisted of an arachnoid membrane and a potential subarachnoid space as well as dura mater, periosteum, ethmoid bone, and associated layers of submucosa and mucosa of the paranasal air spaces. A subarachnoid space was identified around the olfactory nerves as they exited the neural foramina of the cribriform plates. The dura mater eventually thinned out and became continuous with the periosteum in the ethmoid bone. The dura, arachnoid membrane, and associated potential subarachnoid space were obliterated at a place 1 to 2 mm into the olfactory foramen. The authors present a case of recurrent CSF rhinorrhea successfully treated using a technique of multilayered reconstruction with pericranium, fat, and bone.

CONCLUSIONS

The findings provide an anatomical basis for CSF fistula formation in the region of the cribriform plate and help to explain the unusual presentations in patients who have CSF rhinorrhea and meningitis. These results may facilitate the treatment of CSF fistulas, repair of defects in the medial anterior cranial base, and approaches to tumors and other pathological entities in the region.

Clinical application of a physically and chemically processed human substitute for dura mater

OBJECT

Allogenic human fascia lata used in neurosurgery as a dura mater substitute can be associated with the risk of virus and bacterium transmission and with a delay in its incorporation due to immunological and inflammatory reactions. The authors review their preliminary experience with a chemically and physically processed fascia lata graft.

METHODS

Grafts that had been treated with solvent detergents, freeze-dried for conservation, and gamma irradiated (25,000 Gy) for sterilization were placed into 17 patients during neurosurgical procedures performed to treat brain tumors, cerebral malformations, trigeminal neuralgia, and posttraumatic lesions. The handling properties of the material, surgical wound features, and hematological parameters were evaluated. The average follow-up period was 23.8 +/- 2.2 months (mean +/- standard deviation). The handling properties and biocompatibility of these human dural substitutes were highly satisfactory and no major complications were observed. Postoperative computerized tomography or magnetic resonance images obtained in 13 patients revealed no abnormal findings at the site of fascia lata implantation. In one patient who underwent a second surgery performed 12 months after the initial operation, this dural substitute was found to have been recolonized by host fibroblastic cells and replaced by autologous collagenous tissue.

CONCLUSIONS

Human fascia lata that has been rendered safe by applying physical and chemical treatment is a fully biocompatible alternative to the dural graft materials currently available.

Neurogenic dural protein extravasation induced by meta-chlorophenylpiperazine (mCPP) involves nitric oxide and 5-HT2B receptor activation

The compound m-chlorophenylpiperazine (mCPP), which is known to trigger migraine-like head pain in some subjects, was evaluated for its ability to induce dural plasma protein extravasation (PPE) in guinea pigs. Intravenous mCPP dose-dependently increased PPE. This effect was inhibited by non-selective 5-HT2 receptor antagonists (methysergide, LY53857, LY215840), by a peripherally restricted 5-HT2 receptor antagonist (xylamidine) and by a 5-HT2B selective receptor antagonist (LY202146). These data suggests that peripheral 5-HT2B receptors mediate mCPP-induced PPE. The nitric oxide synthase inhibitor L-NAME and 5-HT1 agonist sumatriptan also blocked mCPP-induced PPE, suggesting a role for nitric oxide (NO) and the trigeminal system, respectively. NO release has been linked to activation of the 5-HT2B receptor on the vascular endothelium. However, LY202146 did not block PPE induced by electrical stimulation of the trigeminal ganglion. These data are consistent with activation of peripheral 5-HT2B receptors initiating PPE and the theory that selective 5-HT2B antagonists might be effective prophylactic therapies for migraine.

Triptans reduce the inflammatory response in bacterial meningitis

Severe headache and meningism provide clear evidence for the activation of trigeminal neurotransmission in meningitis. The authors assessed the antiinflammatory potential of 5HT1B/D/F receptor agonists (triptans), which inhibit the release of proinflammatory neuropeptides from perivascular nerve fibers. In a 6-hour rat model of pneumococcal meningitis, zolmitriptan and naratriptan reduced the influx of leukocytes into the cerebrospinal fluid, and attenuated the increase of regional cerebral blood flow. Elevated intracranial pressure as well as the brain water content at 6 hours was reduced by triptans. These effects were partially reversed by a specific 5HT1D as well as by a specific 5HT1B receptor antagonist. Meningitis caused a depletion of calcitonin gene-related peptide (CGRP) and substance P from meningeal nerve fibers, which was prevented by zolmitriptan and naratriptan. In line with these findings, patients with bacterial meningitis had significantly elevated CGRP levels in the cerebrospinal fluid. In a mouse model of pneumococcal meningitis, survival and clinical score at 24 hours were significantly improved by triptan treatment. The findings suggest that, besides mediating meningeal nociception, meningeal nerve fibers contribute to the inflammatory cascade in the early phase of bacterial meningitis. Adjunctive treatment with triptans may open a new therapeutic approach in the acute phase of bacterial meningitis.

Co-culture of osteoblasts with immature dural cells causes an increased rate and degree of osteoblast differentiation

For decades surgeons have exploited the ability of infants to reossify large calvarial defects. To demonstrate the role of dura mater-osteoblast communication during the process of calvarial reossification, the authors used a novel in vitro system that recapitulates the in vivo anatomic relationship of these cell populations. Primary cultures of osteoblast cells from 2-day-old Sprague-Dawley rat pups were grown on six-well plates, and cultures of immature, non-suture-associated dura mater cells from 6-day-old Sprague-Dawley rat pups were grown on Transwell inserts. When the osteoblast and dura mater cell cultures reached confluence, they were combined. This Transwell co-culture system permitted the two cell populations to grow together in the same well, but it prevented direct cell-to-cell contact. Therefore, the authors were able to determine, for the first time, whether paracrine signaling from immature, non-suture-associated dura mater could influence the biologic activity of osteoblasts. Osteoblasts co-cultured with dural cells proliferated significantly faster after 2 days (2.1 x 10(5) +/- 2.4 x 10(4) versus 1.4 x 10(5) +/- 2.2 x 10(4), p < or = 0.05) and 4 days (3.1 x 10(5) +/- 5 x 10(4) versus 2.2 x 10(5) +/- 4.0 x 10(4), p < or = 0.01) than did osteoblasts cultured alone. After 20 days, co-cultured osteoblasts expressed greater amounts of mRNA for several markers of osteoblast differentiation, including collagen I alpha I (4-fold), alkaline phosphatase (2.5-fold), osteopontin (3-fold), and osteocalcin (4-fold), than did osteoblasts cultured alone. After 30 days, co-cultured osteoblasts produced bone nodules that were significantly greater both in number (324 +/- 29 nodules versus 252 +/- 29 nodules per well, p , < or = 0.04) and total area of nodules (65 +/- 11 mm(2) versus 24 +/- 1.6 mm(2), p < or = 0.003) than osteoblasts cultured alone. To begin to understand how dural cells effect changes in osteoblast gene expression, the authors compared the expression of candidate genes, transforming growth factor beta 1 and fibroblast growth factor 2, in dural cells and osteoblasts before and after 5 days of culture. Interestingly, the dura mater produced marked amounts of these osteogenic cytokines compared with osteoblasts.The described co-culture system demonstrated that co-cultured osteoblasts proliferated more rapidly and experienced an increased rate and degree of cellular maturation than did osteoblasts cultured alone. The authors hypothesize that this effect was due to paracrine signaling (e.g., transforming growth factor beta 1 and fibroblast growth factor 2) from the dura mater, and they are investigating those mechanisms in ongoing experiments. Collectively these data verify that immature, non-suture-associated dura mater can influence the biologic activity of osteoblasts. Moreover, the production of cytokines derived from the dura mater (e.g., transforming growth factor beta 1 and fibroblast growth factor 2), and they may begin to explain why immature animals and infants with intact dura mater can reossify large calvarial defects.

Transforming growth factor-beta3 (Tgf-beta3) down-regulates Tgf-beta3 receptor type I (Tbetar-I) during rescue of cranial sutures from osseous obliteration

Appropriate biochemical regulation of intramembranous bone growth from sutures is necessary to achieve correct craniofacial morphology. Failure to form sutures (agenesis) or to maintain sutures in their unossified state (craniosynostosis) can result in severe facial dysmorphology. Several factors such as Twist, Msx2, fibroblast growth factors (Fgfs), bone morphogenetic proteins (Bmps) and transforming growth factors-beta (Tgf-betas) regulate suture patency, likely by interacting with one another. Tgf-beta2 and Tgf-beta3 use the same cell surface receptors, yet have opposite effects on suture patency, cellular proliferation and apoptosis within the suture. One possible mechanism by which Tgf-beta3 rescues sutures from obliteration is by regulating the ability of suture cells to respond to Tgf-beta2. As Tgf-beta3 does not regulate protein levels of Tgf-beta2 in sutures, Tgf-beta3 could regulate tissue responsiveness to Tgf-beta2 by regulating Tgf-beta2 access to receptors. Tgf-beta3 is a more potent competitor than Tgf-beta2 for cell surface receptors, so it is proposed that Tgf-beta3 binds to and down-regulates Tgf-beta receptor type I (Tbetar-I) expression by suture cells. This down-regulation would limit the ability of cells to respond to all Tgf-betas, including Tgf-beta2. To test this hypothesis, an in vitro culture model was used in which fetal rat sutures either remain patent or are induced to fuse when cultured in the presence or absence of dura mater, respectively. Tgf-beta3 was added to cultured calvaria and changes in the number of receptor positive cells within the suture were established. Data were compared with that seen in control sutures and in normal sutures in vivo. It was found that the numbers of cells expressing Tbetar-I within the suture matrix increased over time in sutures remaining patent. Osteoblastic cells lining the bone fronts on either side of sutures were Tbetar-I positive during early morphogenesis, but these numbers declined as sutures fused, both in vivo and in vitro. Addition of Tgf-beta3 to calvaria in culture decreased the number of Tbetar-I expressing cells in both fusing and non-fusing sutures, with dramatic decreases in the numbers of osteoblasts expressing Tbetar-I.

Dura mater biology: autocrine and paracrine effects of fibroblast growth factor 2

The dura mater, the outermost layer of the meninges, is thought to be essential for calvarial morphogenesis, postnatal suture fusion, and osseous repair of calvarial defects. Despite numerous studies illustrating the fundamental role of the dura mater, there is little information about the autocrine and paracrine mechanisms regulating dural cell biology during calvarial ossification. Previous work conducted in the authors' laboratory demonstrated that non-suture-associated dural cells from 6-day-old rat pups expressed high levels of fibroblast growth factor 2 (FGF-2), whereas dural cells from 60-day-old adult rats expressed very little FGF-2. Because young mammals can successfully heal large calvarial defects, the authors sought to investigate the autocrine and/or paracrine effects of FGF-2 on the proliferation, gene expression, and alkaline phosphatase production of dural cells. Cultures of non-suture-associated dural cells were established from 6-day-old Sprague-Dawley rat pups and then stimulated with recombinant human FGF-2 (rhFGF-2; 10 ng/ml). Dural cells stimulated with rhFGF-2 proliferated significantly faster than untreated dural cells at 24 hours (2.1 x 10(5) +/- 3.2 x 10(4) versus 1.1 x 10(5) +/- 1.8 x 10(4), p < or = 0.001) and 48 hours (2.3 x 10(5) +/- 4.2 x 10(4) versus 1.2 x 10(5) +/- 1.3 x 10(4), p < or = 0.001). Moreover, dural cells stimulated with rhFGF-2 expressed 7-fold more proliferating cell nuclear antigen than did control cultures. Treatment with rhFGF-2 increased dural cell expression of genes important for skeletal repair: FGF-2 (7-fold), transforming growth factor beta 1 (3-fold), transforming growth factor beta 3 (4-fold), and type I collagen (4-fold). Furthermore, rhFGF-2 increased dural cell expression of osteopontin (2-fold), a "late" marker of osteoblastic differentiation. Interestingly, dural cell alkaline phosphatase activity, an "earlier" marker of osteoblast differentiation, was significantly decreased by treatment with rhFGF-2 compared with control cultures at 24 hours (0.005 +/- 0.001 versus 0.01 +/- 0.003, p < or = 0.01) and 48 hours (0.004 +/- 0.0009 versus 0.01 +/- 0.0009). Together these data provide insight into the autocrine and paracrine effects of FGF-2 on the biology of the dura mater.

Distinct sensitizing effects of the cAMP-PKA second messenger cascade on rat dural mechanonociceptors

Activation of the cAMP/protein kinase A (PKA) second messenger cascade has been implicated in the induction of mechanical hyperalgesia by inflammatory mediators. We examined the role of this cascade in mechanical sensitization of nociceptive neurons that innervate the meninges, a process thought to be involved in the pathophysiology of headache syndromes such as migraine. Single unit activity was recorded in the trigeminal ganglion from 40 mechanosensitive dural afferents (conduction velocitity: 0.3-6.6 m s(-1)) and nine mechanically insensitive dural afferents (MIAs) (conduction velocitity: 0.3-2.8 m s(-1)) while stimulating the dura with a servo force-controlled stimulator or von Frey monofilaments, respectively. Local application to the dura of dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP, 100 microM), a stable membrane-permeant cAMP analogue, produced mechanical sensitization in the majority of mechanosensitive units (19/29, 66 %). Two distinct patterns of mechanical sensitization were observed. Thirty-eight per cent of the units exhibited only a decrease in threshold (TH group), while 28 % showed only an increase in suprathreshold responses (STH group). dbcAMP also induced mechanosensitivity in the majority of MIA units (6/9, 67 %). dbcAMP-induced sensitization was blocked by the PKA inhibitors, Rp-cAMP (1 mM) and H-89 (100 microM). A mixture of inflammatory mediators induced both components of sensitization in the majority of mechanosensitive units tested. However, in each unit, PKA inhibitors blocked only one of the two effects (either TH or STH). Units that were classified as TH or STH also differed in their baseline stimulus-response slopes, thresholds and conduction velocities. These findings implicate the cAMP-PKA cascade in sensitization of dural mechanonociceptors and suggest that this cascade may produce sensitization through at least two different mechanisms operating in separate neuronal populations.

Effects of sepsis on mast cells in rat dura mater: influence of L-NAME and VIP

1. The influence of lipopolysaccharide (LPS)-induced sepsis on the various mast cell phenotypes of rat dura mater were examined both by immunohistochemical and biochemical methods. 2. Three different populations of mast cells were identified in control rats: connective tissue type mast cells (CTMC) which contain rat mast cell protease1 (RMCP1), histamine, serotonin and heparin, mucosal type mast cells (MMC) which contain RMCP2, histamine and serotonin, and intermediate type which contains both RMCP1 and RMCP2 and probably various proportions of amines and heparin. 3. LPS (25 mg kg(-1) i.p.) caused changes in the proportions of the various types of mast cells. The number of MMC and intermediate type mast cells significantly increased and the number of mast cells immunopositive for both heparin and serotonin significantly decreased. Biochemical analysis showed that the histamine concentration of dura increased while its serotonin concentration decreased. 4. While vasoactive intestinal peptide (VIP) (25 ng kg(-1) i.p.) appears to potentiate LPS effects on dura mater mast cells, non-selective inhibition of nitric oxide (NO) synthase by N(g)-nitro-L-arginine methyl ester (L-NAME) (30 mg kg(-1) i.p.) did not influence sepsis-induced mast cell changes. 5. These findings suggest that mast cells of dura mater may play a role in brain protection during sepsis.

Regional differentiation of cranial suture-associated dura mater in vivo and in vitro: implications for suture fusion and patency

Despite its prevalence, the etiopathogenesis of craniosynostosis is poorly understood. To better understand the biomolecular events that occur when normal craniofacial growth development goes awry, we must first investigate the mechanisms of normal suture fusion. Murine models in which the posterior frontal (PF) suture undergoes programmed sutural fusion shortly after birth provide an ideal model to study these mechanisms. In previous studies, our group and others have shown that sutural fate (i.e., fusion vs. patency) is regulated by the dura mater (DM) directly underlying a cranial suture. These studies have led to the hypothesis that calvarial DM is regionally differentiated and that this differentiation guides the development of the overlying suture. To test this hypothesis, we evaluated the messenger RNA (mRNA) expression of osteogenic cytokines (transforming growth factor beta1 [TGF-beta1] and TGF-beta3) and bone-associated extracellular matrix (ECM) molecules (collagen I, collagen III, osteocalcin, and alkaline phosphatase) in freshly isolated, rat dural tissues associated with the PF (programmed to fuse) or sagittal (SAG; remains patent) sutures before histological evidence of sutural fusion (postnatal day 6 [N6]). In addition, osteocalcin protein expression and cellular proliferation were localized using immunohistochemical staining and 5-bromo-2'deoxyuridine (BrdU) incorporation, respectively. We showed that the expression of osteogenic cytokines and bone-associated ECM molecules is potently up-regulated in the DM associated with the PF suture. In addition, we showed that cellular proliferation in the DM associated with the fusing PF suture is significantly less than that found in the patent SAG suture just before the initiation of sutural fusion N6. Interestingly, no differences in cellular proliferation rates were noted in younger animals (embryonic day 18 [E18] and N2). To further analyze regional differentiation of cranial suture-associated dural cells, we established dural cell cultures from fusing and patent rat cranial sutures in N6 rats and evaluated the expression of osteogenic cytokines (TGF-beta1 and fibroblast growth factor 2 [FGF-2]) and collagen I. In addition, we analyzed cellular production of proliferating cell nuclear antigen (PCNA). These studies confirmed our in vivo findings and showed that dural cell cultures derived from the fusing PF suture expressed significantly greater amounts of TGF-beta1, FGF-2, and collagen I. In addition, similar to our in vivo findings, we showed that PF suture-derived dural cells produced significantly less PCNA than SAG suture-derived dural cells. Finally, coculture of dural cells with fetal rat calvarial osteoblastic cells (FRCs) revealed a statistically significant increase in proliferation (*p < 0.001) in FRCs cocultured with SAG suture-derived dural cells as compared with FRCs cocultured alone or with PF suture-derived dural cells. Taken together, these data strongly support the hypothesis that the calvarial DM is regionally differentiated resulting in the up-regulation of osteogenic cytokines and bone ECM molecules in the dural tissues underlying fusing but not patent cranial sutures. Alterations in cytokine expression may govern osteoblastic differentiation and ECM molecule deposition, thus regulating sutural fate. Elucidation of the biomolecular events that occur before normal cranial suture fusion in the rat may increase our understanding of the events that lead to premature cranial suture fusion.

Transforming growth factor-beta 2 and TGF-beta 3 regulate fetal rat cranial suture morphogenesis by regulating rates of cell proliferation and apoptosis

Cranial vault sutures are the major intramembranous bone growth sites during rapid expansion of the neurocranium. To function as bone growth sites, sutures need to remain patent, while allowing rapid bone formation at the edges of the bone fronts. Premature osseous obliteration of sutures (craniosynostosis) by fusion of bone fronts across the suture site prevents further bone formation at this site, often leading to severe facial dysmorphology. Although several growth factor receptor and transcription factor mutations have been implicated in craniosynostosis, the underlying mechanisms leading to sutural obliteration remain unclear. Previous studies have shown that dura secreted soluble factors responsible for maintaining suture patency and that suture fusion observed in the absence of dura was preceded by elevated levels of DNA synthesis and collagen production in the suture region. The use of neutralizing antibodies in a fetal calvarial culture model further demonstrated that removal of transforming growth factor (TGF) -beta 3 activity induced premature sutural obliteration, whereas removal of TGF-beta 2 activity prevented sutural obliteration. Data presented here demonstrate that suture obliteration induced by removal of TGF-beta 3 activity was preceded by elevated levels of DNA synthesis, similar to that seen upon removal of the dura. Addition of exogenous TGF-beta 3 to calvaria cultured without dura both prevented suture obliteration and reduced DNA synthesis to levels comparable to those seen with intact dura. Addition of exogenous TGF-beta 2 to calvarial cultures induced sutural fusion accompanied by elevated levels of cell proliferation. However, sutures rescued from obliteration by removal of TGF-beta 2 activity did not have decreased levels of cell proliferation, but rather appeared to be due to inhibited differentiation. In all calvaria in which sutures remained patent in culture, numbers of apoptotic cells were high within the suture, whereas in sutures destined to fuse, numbers of apoptotic cells were low. Results indicate that one of the critical regulators of suture patency is cell number. Alterations in cell number can trigger premature differentiation of cells, resulting in sutural obliteration. Furthermore, a complex interplay between closely related molecules is required to maintain cranial vault sutures in an unossified state, while allowing new bone to be formed at the edges of the bone fronts.

[Local features of temporal organization of tissue mast cells in the dura mater of mature rat brain]

Rhythms of functional activity of mast cells were studied in frontal, parietal and occipital areas of dura mater of mature rats. Chronological organization of mast cells dura mater was established. Circadian component dominated in all rhythms studied. Local peculiarities of mast cells rhythms were established; frontal area cells displayed most significant oscillations per day. They also showed maximum values of average day number and acrophase. Maximum functional activity was demonstrated in mast cells of frontal and parietal region one hour later than in parietal area of dura mater.