Length of the spinal dural sac, sex differences and correlation with the length of the spinal cord and vertebral column in adults

In 94 corpses (59 male and 35 female) of mature persons the length of the spinal dura mater sac has been studied. The average length of the sac is 621 +/- 3 mm. In men its average length is 636 +/- 4 mm, it makes 40 mm more in length than that in women (596 +/- 4 mm). The length of various parts in the dura mater sac is not the same: the cervical part makes 23% of the whole length, the thoracic--47%, the lumbar--23%, the sacral--7%. In men the cervical part of the sac in average is 6 mm longer than the lumbar part, and in women--quite the reverse, it is 7 mm shorter than the lumbar part. The sacral part of the sac in women is 3 mm longer that that in men. The sex differences noted are statistically significant. It is stated that the length of the spinal cord, its dura mater and the vertebral column are related as 1:1.5:1.7, the length of their cervical parts--as 1:1.5:1.4. the thoracic--as 1:1.3:1.3, the lumbar--as 1:2.4:3, the sacrococcygeal--as 1:1.4:4.9, respectively. During ontogenesis the greatest increase in the dura mater sac takes place in the cervical part as compared to the spinal cord and the vertebral column; in the thoracic part the intensity of their growth is equal: in the lumbar and in the sacrococcygeal part the increase of the vertebral column is the greatest.     

Morphofunctional characteristics of the microcirculatory bed of the human spinal dura mater]

Some morphofunctional peculiarities in microcirculatory pathways of the dura mater of the human spinal cord are described. They are concerned with the structure of arteriolo-venular anastomoses through which a rather large amount of arterial blood is transported into the venous bed. Around the vessels of arterial type running at an angle to the longitudinal axis of the vessel connective tissue fibres of the dura mater, there is a tissue layer intensively impregnated with silver salts and stained PAS-positively. The venous part of the dura mater microcirculatory pathways has a large number of accessory reservoirs in the form of venous "lakes". Functional importance of the peculiarities mentioned above for the dura mater and the perimedullar apparatus is clarified.     

Ependyma and meninges of the spinal cord of the mouse

Summary In addition to ependymal epithelial cells, numerous tanycytes are found along the entire central canal of the mouse. These tanycytes are arranged in clusters in the cervical, thoracic and lumbar segments of the spinal cord. In the conus medullaris, tanycytes separate and ensheath bundles of myelinated and unmyelinated axons; their processes take part in the formation of the stratum marginale gliae. In the caudal part of the spinal cord, the ventral wall of the central canal is thin and some areas are reduced to a single-cell thickness. In this region, ependymal cells participate directly in the formation of the stratum marginale gliae.The meninges consist of the intima piae, the pia mater, the arachnoid, a subdural neurothelium and the dura mater. The subarachnoid space appears occluded and opens only around the spinal roots. In the vicinity of the spinal ganglia, the dura mater, the subdural neurothelium and the arachnoid form a cellular reticulum.     

A one-dimensional model of the spinal cerebrospinal-fluid compartment

Modeling of the cerebrospinal fluid (CSF) system in the spine is strongly motivated by the need to understand the origins of pathological conditions such as the emergence and growth of fluid-filled cysts in the spinal cord. In this study, a one-dimensional (1D) approximation for the flow in elastic conduits was used to formulate a model of the spinal CSF compartment. The modeling was based around a coaxial geometry in which the inner elastic cylinder represented the spinal cord, middle elastic tube represented the dura, and the outermost tube represented the vertebral column. The fluid-filled annuli between the cord and dura, and the dura and vertebral column, represented the subarachnoid and epidural spaces, respectively. The system of governing equations was constructed by applying a 1D form of mass and momentum conservation to all segments of the model. The developed 1D model was used to simulate CSF pulse excited by pressure disturbances in the subarachnoid and epidural spaces. The results were compared to those obtained from an equivalent two-dimensional finite element (FE) model which was implemented using a commercial software package. The analysis of linearized governing equations revealed the existence of three types of waves, of which the two slower waves can be clearly related to the wave modes identified in previous similar studies. The third, much faster, wave emanates directly from the vertebral column and has little effect on the deformation of the spinal cord. The results obtained from the 1D model and its FE counterpart were found to be in good general agreement even when sharp spatial gradients of the spinal cord stiffness were included; both models predicted large radial displacements of the cord at the location of an initial cyst. This study suggests that 1D modeling, which is computationally inexpensive and amenable to coupling with the models of the cranial CSF system, should be a useful approach for the analysis of some aspects of the CSF dynamics in the spine. The simulation of the CSF pulse excited by a pressure disturbance in the epidural space, points to the possibility that regions of the spinal cord with abnormally low stiffness may be prone to experiencing large strains due to coughing and sneezing.     

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.     

Structure and dynamics of the size of the epidural space in human fetuses and newborn infants

Basing on our definition of the ES as a complex of peridural anatomical formations and taking into account certain peculiarities of their topographic distribution, 4 areas (anterior, posterior and two lateral) are defined. The posterior area of the ES by its sizes predominates over all the others. The ES value is determined by differences in rates of size increment of the vertebral canal and in rates of size increment of the spinal cord dura mater (SCDM). Position of the SCDM sac concerning the central axis of the canal predetermines++ the size of the ES four areas. The dimensions of the ES areas are not similar at various levels of the spinal column. For example, the dimensions of the ES posterior area in newborns are the greatest in the cervical part at CVII, in the thoracic--at ThIV-VII, in the lumbar--at LI-III, and the dimensions of the ES anterior area--at CVII, ThI-IV, LIV-V and Sr. The lateral ES areas are the widest at CI, ThIII, LV and SI. The greatest increase in the rate of increment of linear sizes and area is observed for the spinal canal and spinal cord in 5-, 8- and 9-month-old fetuses and for SCDM--in 5- and 8-month-old fetuses and for ES--in 6-, 8- and 9-month-old fetuses. The topographic peculiarities in the ES structure revealed and rearrangement of its dimensions in the fetuses and newborns can be useful in interpretation of problems on functional formation of the vertebral column, spinal cord and its tunics, and be of applied aspect at various manipulations performed in these formations in premature infants and in newborns.     

Mechanism of formation of intramedullary cavities and their role in the regeneration of the spinal cord

The spinal cord preparations of 38 dogs and 20 rabbits have been studied with the aim to investigate the influence of the cerebrospinal fluid on the spinal cord nervous tissue. The spinal cord preparations of 8 patients having trauma of the vertebral column with interruption of the spinal cord have also been studied. As demonstrate histological investigations, the cerebral tissue of the pieces, put into the flask with liquor, in the subarachnoidal space of the canine spinal cord, in diastasis between the ends of the cut spinal cord during 6 h up to 7 days, swells, becomes edematous. Cavities occupying about 30% of the area in the slices studied appear in it. At hemisection of the rabbit spinal cord without closure of the defect in the meninx vasculosa with the glue MK-6, the area of the cavity formation varies from 24 up to 35%, comparing the whole area of the preparation, while in rabbits with hemisection and successive gluing of the defect in the meninx vasculosa the area of the nervous tissue destruction makes 13-18%. It has been proved that the scar forming in the traumatized segment of the spinal cord does not present a continuous formation, but contains a large amount of cavities that prevent regeneration of nerve fibers. The experimental data concerning lysing effect of the cerebrospinal fluid on the traumatized nervous tissue are confirmed by the results obtained at investigating the preparations of the spinal cord of the patients died as the cause of the spinal cord trauma.     

Adrenergic innervation of the extramedullary arteries of the spinal cord of cats]

The adrenergic nerves of the radical and longitudinal arteries and the dura mater at the level of cervical, thoracic and lumbar segments of the ventral and dorsal sides of the spinal cord were studied in 70 mature cats by methods of Falck and Glenner. The adrenergic fibres form developed plexuses different in the density of disposition of nerve conductors on the arteries of different segments of the spinal cord. The adrenergic fibres are also found in the pia mater tissue. Nerve fibres containing active monoaminoxidase are less in number than adrenergic ones found by Falck's method. It is probably due to activation of catecholamines being realized by other ways in addition to oxydative desamination.     

Anatomical basis for cerebrospinal fluid resorption by the structures of the microcirculatory bed in the human spinal dura mater

By means of noninjective methods of investigation a specific capillary network of a sinusoidal type, peculiar arteriolovenular anastomoses, additional reservoirs in the area of postcapillaries and venules described in the microcirculatory bed of the spinal dura mater. The peculiarity of this vascular bed is thought by the authors to be connected with liquor resorption from the subdural space of the spinal cord.     

Basic fibroblast growth factor and transforming growth factor beta-1 expression in the developing dura mater correlates with calvarial bone formation

Numerous studies have found dura mater-calvarial mesenchyme interactions during calvarial bone induction; however, the exact molecular mechanisms governing these inductive events remain unknown. Recent studies have implicated basic fibroblast growth factor (FGF-2) and transforming growth factor-beta1 (TGF-beta1) in regulating bone formation. The purpose of this study was, therefore, to investigate the expression of FGF-2 and TGF-beta1 during calvarial bone formation in rats. Eight rats were killed on embryonic days 14, 18, and 20 and neonatal day 1 (n = 32). Four animals at each time point were analyzed by in situ hybridization, and the remainder were analyzed by immunohistochemistry. The results indicated that the dura mater underlying the developing calvarial bone strongly expressed FGF-2 and TGF-beta1 mRNA at all time points examined. In contrast, minimal growth factor expression was noted in the overlying calvarial mesenchyme until embryonic day 18, but it increased significantly with increasing age. Importantly, FGF-2 and TGF-beta1 mRNA expression in the dura mater underlying the developing calvarium preceded and was significantly greater than expression in the calvarium mesenchyme (p < 0.05). Interestingly, minimal expression of FGF-2 and TGF-beta1 mRNA was noted for all time points in the dura mater underlying the posterior frontal suture and within the posterior frontal suture connective tissue (p < 0.01 when compared with the dura mater underlying the developing calvarium). Immunohistochemical findings closely paralleled mRNA expression, with intense staining for FGF-2 and TGF-beta1 in the dura mater underlying the developing calvarial mesenchyme. Increasing FGF-2 and TGF-beta1 staining was noted within calvarial osteoblasts with increasing age, particularly in cells located near the endocranial surface (i.e., in contact with the developing dura mater). These findings, together with the known biologic functions of FGF-2 and TGF-beta1, implicate these growth factors in the regulation of calvarial bone growth by the developing dura mater. The possible mechanisms of this interaction are discussed.     

The origins of syringomyelia: numerical models of fluid/structure interactions in the spinal cord

A two-dimensional axi-symmetric numerical model is constructed of the spinal cord, consisting of elastic cord tissue surrounded by aqueous cerebrospinal fluid, in turn surrounded by elastic dura. The geometric and elastic parameters are simplified but of realistic order, compared with existing measurements. A distal reflecting site models scar tissue formed by earlier trauma to the cord, which is commonly associated with syrinx formation. Transients equivalent to both arterial pulsation and percussive coughing are used to excite wave propagation. Propagation is investigated in this model and one with a central canal down the middle of the cord tissue, and in further idealized versions of it, including a model with no cord, one with a rigid cord, one with a rigid dura, and a double-length untapered variant of the rigid-dura model. Analytical predictions for axial and radial wave-speeds in these different situations are compared with, and used to explain, the numerical outcomes. We find that the anatomic circumstances of the spinal cerebrospinal fluid cavity probably do not allow for significant wave steepening phenomena. The results indicate that wave propagation in the real cord is set by the elastic properties of both the cord tissue and the confining dura mater, fat, and bone. The central canal does not influence the wave propagation significantly.     

Angeli's salt and spinal motor neuron injury

Nitroxyl anion or its conjugate acid (NO_-/HNO) and nitric oxide (NO) may both have pro-oxidative and cytotoxic properties. Superoxide dismutase (SOD) enzyme has been shown to convert reversibly HNO to NO. Mutations found in the SOD enzyme in some familial amyotrophic lateral sclerosis (ALS) patients affect redox properties of the SOD enzyme in a manner, which may affect the equilibrium between NO and HNO. Therefore, we studied the effects of HNO releasing compound, Angeli's salt (AS), on both motor and sensory functions after intrathecal administration in the lumbar spinal cord of a male rat. These functions were measured by rotarod, spontaneous activity, paw- and tail-flick tests. In addition, we compared the effect of AS to NO releasing papanonoate, old AS solution and sulphononoate in the motor performance test. The effect of intrathecal delivery of AS on the markers of the spinal cord injury and oxidative/nitrosative stress were further studied.

Results: Freshly prepared AS (5 or 10 μmol), but not papanonoate, caused a marked decrease in the rotarod performance 3-7 days after the intrathecal administration. The peak motor deficiency was noted 3 days after AS (5 μmol) delivery. Old, degraded, AS solution and nitrous oxide releasing sulphononoate did not decrease motor performance in the rotarod test. AS did not affect the sensory stimulus evoked responses as measured by the paw-flick and tail-flick tests. Immunohistological examination revealed that AS caused injury related changes in the expression of glial fibrillary acidic protein (GFAP), fibroblast growth factor (FGF-2) and laminins in the spinal cord. Moreover, AS increased nitrotyrosine immunoreactivity in the spinal motor neurons.

Therefore, we conclude that AS, but not NO releasing papanonoate, causes motor neuron injury but does not affect the function of sensory nerves in behavioural tests.     

Enkephalin-degrading enzymes and angiotensin-converting enzyme in human and rat meninges

The neutral endopeptidase NEP 24.11 (enkephalinase) has been visualized in human spinal cord by in vitro autoradiography using [3H]HACBO-Gly as a radiolabelled probe. The specific binding was present in the substantia gelatinosa and particularly dense in meninges surrounding the spinal cord. Enzymatic studies using [3H][D-Ala2, Leu]enkephalin as substrate confirmed the presence of NEP in dura and pia mater of human tissue. In addition, the human meninges were shown to contain high concentrations of angiotensin-converting enzyme (ACE) and aminopeptidases. The three enzymes have also been detected in rat tissues but their distribution pattern differs from that of human tissue. In dura mater, 45% of the [Leu]enkephalin hydrolysis was due to enkephalinase and 38% to bestatin-sensitive aminopeptidases. In contrast in pia mater aminopeptidases were more efficient in hydrolyzing enkephalin. The possible role of these enzymes in the meninges could be to maintain the homeostatic concentration of neuropeptides in the central nervous system.     

Electrophysiological and Anatomical Correlates of Spinal Cord Optical Coherence Tomography

Despite the continuous improvement in medical imaging technology, visualizing the spinal cord poses severe problems due to structural or incidental causes, such as small access space and motion artifacts. In addition, positional guidance on the spinal cord is not commonly available during surgery, with the exception of neuronavigation techniques based on static pre-surgical data and of radiation-based methods, such as fluoroscopy. A fast, bedside, intraoperative real-time imaging, particularly necessary during the positioning of endoscopic probes or tools, is an unsolved issue. The objective of our work, performed on experimental rats, is to demonstrate potential intraoperative spinal cord imaging and probe guidance by optical coherence tomography (OCT). Concurrently, we aimed to demonstrate that the electromagnetic OCT irradiation exerted no particular effect at the neuronal and synaptic levels. OCT is a user-friendly, low-cost and endoscopy-compatible photonics-based imaging technique. In particular, by using a Fourier-domain OCT imager, operating at 850 nm wavelength and scanning transversally with respect to the spinal cord, we have been able to: 1) accurately image tissue structures in an animal model (muscle, spine bone, cerebro-spinal fluid, dura mater and spinal cord), and 2) identify the position of a recording microelectrode approaching and inserting into the cord tissue 3) check that the infrared radiation has no actual effect on the electrophysiological activity of spinal neurons. The technique, potentially extendable to full three-dimensional image reconstruction, shows prospective further application not only in endoscopic intraoperative analyses and for probe insertion guidance, but also in emergency and adverse situations (e.g. after trauma) for damage recognition, diagnosis and fast image-guided intervention.     

Effects of dorsal root section and occlusion of dorsal spinal artery on the neurotransmitter candidates in rat spinal cord

In order to obtain further evidence of putative neurotransmitters in primary sensory neurons and interneurons in the dorsal spinal cord, we have studied the effects of unilateral section of dorsal roots and unilateral occlusion of the dorsal spinal artery on cholinergic enzyme activity and on selected amino acid levels in the spinal cord. One week after sectioning dorsal roots from caudal cervical (C₇) to cranial thoracic (T₂) levels, the specific activity of choline acetyltransferase (ChAT) was significantly decreased and acetylcholinesterase (AChE) showed a tendency to decrease in the dorsal quadrant on the operated side of the spinal cord. Dorsal root sectioning had little effect on the levels of free glutamic acid or other amino acids in the dorsal spinal cord. These results suggest that primary sensory neurons may include some cholinergic axons, and that levels of putative amino acid transmitters are not regulated by materials supplied by axonal transport from the dorsal root ganglia. By contrast, one week following unilateral occlusion of the dorsal spinal artery, the activities of ChAT and AChE were unchanged in the operated quadrant of the spinal cord, while decreases of Asp, Glu, and GABA, and an increase in Tau were detected. These findings are consistent with the proposals that such amino acids, but not ACh, may function as neurotransmitter candidates in interneurons of the dorsal spinal cord.Abbreviation used ACh acetylcholine - AChE acetylcholinesterase - Asp aspartic acid - ChAT choline acetyltransferase - GABA -aminobutyric acid - Glu glutamic acid - Gly glycine - SP substance P - Tau taurine     

骨髓间充质干细胞经BDNF基因修饰后移植治疗大鼠半横断脊髓损伤的电生理研究

目的采用电生理的研究方法,观察脑源性神经营养因子(BDNF)基因修饰的骨髓间充质干细胞对脊髓损伤的修复作用。方法随机将大鼠分成3组:空白组10只(只切除椎板,暴露脊髓硬脊膜);SCI组10只;SCI术后细胞移植组10只;从以上三组大鼠随机抽取8只于细胞移植后1 d、7 d、14 d、21 d、30 d、60 d进行SEP(皮层体感诱发电位)、MEP(运动诱发电位)等电生理检测技术,并观察大鼠的运动评分恢复程度。结果细胞移植4d后,大鼠饮食和活动开始增加;后肢变化过程如下:损伤后1~4 d损伤侧后肢迟缓性瘫痪,拖地行走,损伤对侧后肢由损伤初期的运动减弱逐渐恢复,损伤后5~9 d损伤侧后肢痉挛性瘫痪;10~14 d损伤侧下肢恢复少量活动,损伤对侧后肢恢复至较损伤前稍弱的状态;15~21 d损伤侧后肢活动能力较之前有明显改善,至30 d损伤侧后肢活动能力及肌张力恢复程度最明显,30 d以后无更明显改善。免疫组化发现损伤处诱导标记的骨髓间充质干细胞存活,行为学观察发现细胞移植改善了损伤大鼠运动能力。结论骨髓间充质干细胞经BDNF基因修饰后可以促进脊髓损伤大鼠的神经再生及部分传导功能恢复。     

Radiation-induced apoptosis in the neonatal and adult rat spinal cord

This study was designed to characterize radiation-induced apoptosis in the spinal cord of the neonatal and young adult rat. Spinal cords (C2-T2) of 1-, 2- and 10-week-old rats were irradiated with a single dose of 8, 18 or 22 Gy. Apoptosis was assessed histologically according to its specific morphological features or by using the TUNEL assay. Cell proliferation was assessed immunohistochemically using BrdU. Identities of cell types undergoing apoptosis were assessed using immunohistochemistry or in situ hybridization using markers for neurons, glial progenitor cells, microglia, oligodendrocytes and astrocytes. The time course of radiation-induced apoptosis in 1- or 2-week-old rat spinal cord was similar to that in the young adult rat spinal cord. A peak response was observed at about 8 h after irradiation, and the apoptosis index returned to the levels in nonirradiated spinal cords at 24 h. The neonatal rat spinal cord demonstrated increased apoptosis compared to the adult. Values for total yield of apoptosis over 24 h induced by 8 Gy in the neonatal rat spinal cord were significantly greater than that in the adult. Immunohistochemistry studies using Leu7, galactocerebroside, Rip and adenomatous polyposis coli tumor suppressor protein indicated that most apoptotic cells were cells of the oligodendroglial lineage regardless of the age of the animal. No evidence of Gfap or factor VIII-related antigen-positive apoptotic cells was observed, and there was a small number of apoptotic microglial cells (lectin-Rca1 positive) in the neonatal and adult rat spinal cord. In the neonatal but not adult rat spinal cord, about 10% of the apoptotic cells appeared to be neurons and were immunoreactive for synaptophysin. Labeling indices (LI) for BrdU in nonirradiated 1- and 2-week-old rat spinal cord were 20.0 and 16.3%, respectively, significantly greater than the LI of 1.0% in the 10-week-old rat spinal cord. At 8 h after a single dose of 8 Gy, 13.4% of the apoptotic cells were BrdU-positive in 10-week-old rat spinal cord, whereas 62.4 and 44.1% of the apoptotic cells showed BrdU incorporation in 1- and 2-week-old rat spinal cord, respectively. Regardless of the age of the animal, the apoptosis indices in BrdU-positive cells were greater than those in BrdU-negative cells. We conclude that the neonatal spinal cord demonstrates a greater level of apoptosis after exposure to ionizing radiation than the young adult spinal cord. This increase in apoptosis may be associated in part with the greater percentage of proliferating cells in the neonatal spinal cord, which demonstrate a greater level of radiation-induced apoptosis than nonproliferating cells.     

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.     

Effect of bone fragment impact velocity on biomechanical parameters related to spinal cord injury: A finite element study

Several experimental and computational studies have investigated the effect of bone fragment impact on the spinal cord during trauma. However, the effect of the impact velocity of a fragment generated by a burst fracture on the stress and strain inside the spinal cord has not been computationally investigated, even though spinal canal occlusion and peak pressure at various impact velocities were provided in experimental studies. These stresses and strains are known factors related to clinical symptoms or injuries. In this study, a fluid-structure interaction model of the spinal cord, dura mater, and cerebrospinal fluid was developed and validated. The von-Mises stress distribution in the cord, the longitudinal strain, the cord compression and cross-sectional area at the impact center, and the obliteration of the cerebrospinal fluid layer were analyzed for three pellet sizes at impact velocities ranging from 1.5 m/s to 7.5 m/s. The results indicate that stress in the cord was substantially elevated when the initial impact velocity of the pellet exceeded a threshold of 4.5 m/s. Cord compression, reduction in cross-sectional area, and obliteration of the cerebrospinal fluid increased gradually as the velocity of the pellet increased, regardless of the size of the pellet. The present study provides insight into the mechanisms underlying spinal cord injury.     

Cell death of asynaptic neurons in regenerating spinal cord

The weakly electric fish Sternarchus albifrons possesses a unique class of asynaptic neurons, the electromotor neurons, whose axons constitute the electric organ. The cell bodies of origin of the electrocyte axons are located in the spinal cord. Both spinal cord and electromotor neurons ( electrocytes ) regenerate after amputation of the tail. Sternarchus spinal cords which have regenerated for 1 or more years show a progression in number of perikarya of electromotor neurons along the rostro-caudal axis. The most recently regenerated region of the cord is at the caudal end, which consists of a tube of ependyma. Progressing rostrally along regenerated spinal cord from the caudal end, numerous cells are generated and large numbers of electromotor neurons differentiate. The maximum number of electromotor neurons per transverse section of regenerated cord is five times higher than in normal mature cord. Rostral to this, the number of electromotor neurons decreases gradually to the normal number near the transition zone (the border with unregenerated cord). As the more rostral regenerated cord has presumably had a longer period of regeneration, we conclude that excess numbers of electromotor neurons are generated initially, and that subsequently the number of these neurons is decreased by cell death. This conclusion is supported by the fact that younger regenerates (2-4 months) have larger-than-normal numbers of perikarya of electromotor neurons extending up to the transition zone (Anderson and Waxman , 1981). No evidence of migration or depletion of electromotor neurons from unregenerated cord rostral to the amputation has been observed. Since the axons of the electromotor neurons in Sternarchus do not normally form any synapses, this study provides evidence that factors other than synaptic competition must be responsible for determining cell death during regeneration of these spinal neurons.