Intracranial pressure changes during mouse development

Age-related variations in opening pressure in lumbar puncture: Implications for its interpretation in children

INTRODUCTION

Opening pressure in lumbar puncture (LP) is an important parameter in the diagnosis of various neurological diseases. In children pressures may vary according to age. This study aimed to analyze the variation of opening pressure in LP according to age in children.

METHODS

All LPs performed between February 2017 and March 2023 were analyzed. Patients with modifying factors for opening pressure were excluded. Descriptive analysis was conducted, along with a comparison of means and medians, local regression, and quantile regression. To identify the most relevant cutoff points, graphical analyses were employed.

RESULTS

The median opening pressure was 21.0 cm H2O, with a 10th percentile (P10) of 10 and a 90th percentile (P90) of 32. An increase in opening pressure with age was found. Graphical analysis revealed a significant cutoff point at 96 months. The median opening pressure from 1 to 96 months of age was 19.2 cm H2O, with a P10 of 8 and a P90 of 28.9. For children older than 96 months, the median was 22 cm H2O, with a P10 of 11.8 and a P90 of 35.

CONCLUSION

Opening pressures in children vary with age, with no differences related to sex. Graphical analysis indicates that 96 months of age is an important cutoff point. Above this age, standard values could be used, up to 96 months of age, however, it is necessary to conduct studies for reference values. Opening pressure alone is not sufficient for the diagnosis of intracranial hypertension in children.

Microdifferential Pressure Measurement Device for Cellular Microenvironments

Mechanical forces influence cellular proliferation, differentiation, tissue morphogenesis, and functional expression within the body. To comprehend the impact of these forces on living organisms, their quantification is essential. This study introduces a novel microdifferential pressure measurement device tailored for cellular-scale pressure assessments. The device comprises a glass substrate and a microchannel constructed of polydimethylsiloxane, polytetrafluoroethylene tubes, a glass capillary, and a microsyringe pump. This device obviates the need for electrical measurements, relying solely on the displacement of ultrapure water within the microchannel to assess the micropressure in embryos. First, the device was subjected to arbitrary pressures, and the relationship between the pressure and the displacement of ultrapure water in the microchannel was determined. Calibration results showed that the displacement dx [μm] could be calculated from the pressure P [Pa] using the equation dx = 0.36 P. The coefficient of determination was shown to be 0.87, indicating a linear response. When utilized to measure brain ventricular pressure in mouse embryos, the fabricated device yielded an average pressure reading of 1313 ± 640 Pa. This device can facilitate the measurement of pressure within microcavities in living tissues and other areas requiring precise and localized pressure evaluations.

Lumped parameter simulations of cervical lymphatic vessels: dynamics of murine cerebrospinal fluid efflux from the skull

BACKGROUND

Growing evidence suggests that for rodents, a substantial fraction of cerebrospinal fluid (CSF) drains by crossing the cribriform plate into the nasopharyngeal lymphatics, eventually reaching the cervical lymphatic vessels (CLVs). Disruption of this drainage pathway is associated with various neurological disorders.

METHODS

We employ a lumped parameter method to numerically model CSF drainage across the cribriform plate to CLVs. Our model uses intracranial pressure as an inlet pressure and central venous blood pressure as an outlet pressure. The model incorporates initial lymphatic vessels (modeling those in the nasal region) that absorb the CSF and collecting lymphatic vessels (modeling CLVs) to transport the CSF against an adverse pressure gradient. To determine unknown parameters such as wall stiffness and valve properties, we utilize a Monte Carlo approach and validate our simulation against recent in vivo experimental measurements.

RESULTS

Our parameter analysis reveals the physical characteristics of CLVs. Our results suggest that the stiffness of the vessel wall and the closing state of the valve are crucial for maintaining the vessel size and volume flow rate observed in vivo. We find that a decreased contraction amplitude and frequency leads to a reduction in volume flow rate, and we test the effects of varying the different pressures acting on the CLVs. Finally, we provide evidence that branching of initial lymphatic vessels may deviate from Murray's law to reduce sensitivity to elevated intracranial pressure.

CONCLUSIONS

This is the first numerical study of CSF drainage through CLVs. Our comprehensive parameter analysis offers guidance for future numerical modeling of CLVs. This study also provides a foundation for understanding physiology of CSF drainage, helping guide future experimental studies aimed at identifying causal mechanisms of reduction in CLV transport and potential therapeutic approaches to enhance flow.

Normal Pressure Hydrocephalus in Adult Mice Causes Gait Impairment, Cognitive Deficits, and Urinary Frequency with Incontinence

Normal pressure hydrocephalus (NPH) is marked by enlarged cerebral ventricles with normal intracranial pressure, plus three stereotypical symptoms: gait impairment, cognitive dysfunction, and urinary frequency with urge incontinence. The neural circuit dysfunction responsible for each of these symptoms remains unknown, and an adult mouse model would expand opportunities to explore these mechanisms in preclinical experiments. Here, we describe the first mouse model of chronic, communicating hydrocephalus with normal intracranial pressure. Hydrocephalic male and female mice had unsteady gait and reduced maximum velocity. Despite performing well on a variety of behavioral tests, they exhibited subtle learning impairments. Hydrocephalic mice also developed urinary frequency, and many became incontinent. This mouse model, with symptoms resembling human NPH, can be combined with molecular-genetic tools in any mouse strain to explore the neural circuit mechanisms of these symptoms. Preclinical work using this hydrocephalus model will lead to the development of new treatments for NPH symptoms.

Sociodemographic Factors Associated with Delayed Presentation in Craniosynostosis Surgery at a Tertiary Children's Hospital

Background

Craniosynostosis is a common diagnosis requiring early referral to a pediatric plastic surgeon; however, disparities in healthcare may influence presentation timing and affect treatment options and outcomes. This study aimed to explore sociodemographic factors contributing to delay in craniosynostosis surgical consultation.

Methods

A retrospective cohort study of 694 California-based craniosynostosis patients at a tertiary children's hospital was performed from 2006 to 2023. State-specific Area Deprivation Index (ADI) and distance to the hospital were calculated using ZIP codes. Multivariate linear and logistic regressions considered race, insurance type, syndromic status, suture type, and ZIP code-based socioeconomic factors.

Results

Median age of presentation was 4.5 [interquartile range: 2.6-7.6] months with racial/ethnic breakdown of Hispanic/Latinx (41.2%), White (23.6%), Asian (3.7%), Black/African American (2.0%), or other/unreported (29.5%) with 58.4% having public insurance and an average distance to the hospital of 48.3 km. Median ADI was 5.4 [interquartile range: 4.0-7.1]. By linear regression, public insurance (P < 0.001) and higher ADI decile (P < 0.001) independently contributed to an older age of presentation. Patients with public insurance (odds ratio 1.90; P = 0.002) were more likely to present after 4 months of age.

Conclusions

Patients who had public insurance or resided in more disadvantaged areas presented later for craniosynostosis surgical consultation. Eliminating disparities in these populations ensures more equitable access to surgical options and can improve patient outcomes.

Piezo1 agonist restores meningeal lymphatic vessels, drainage, and brain-CSF perfusion in craniosynostosis and aged mice

Skull development coincides with the onset of cerebrospinal fluid (CSF) circulation, brain-CSF perfusion, and meningeal lymphangiogenesis, processes essential for brain waste clearance. How these processes are affected by craniofacial disorders such as craniosynostosis are poorly understood. We report that raised intracranial pressure and diminished CSF flow in craniosynostosis mouse models associate with pathological changes to meningeal lymphatic vessels that affect their sprouting, expansion, and long-term maintenance. We also show that craniosynostosis affects CSF circulatory pathways and perfusion into the brain. Further, craniosynostosis exacerbates amyloid pathology and plaque buildup in Twist1+/-:5xFAD transgenic Alzheimer's disease models. Treating craniosynostosis mice with Yoda1, a small molecule agonist for Piezo1, reduces intracranial pressure and improves CSF flow, in addition to restoring meningeal lymphangiogenesis, drainage to the deep cervical lymph nodes, and brain-CSF perfusion. Leveraging these findings, we show that Yoda1 treatments in aged mice with reduced CSF flow and turnover improve lymphatic networks, drainage, and brain-CSF perfusion. Our results suggest that CSF provides mechanical force to facilitate meningeal lymphatic growth and maintenance. Additionally, applying Yoda1 agonist in conditions with raised intracranial pressure and/or diminished CSF flow, as seen in craniosynostosis or with ageing, is a possible therapeutic option to help restore meningeal lymphatic networks and brain-CSF perfusion.

Understanding the development, pathogenesis, and injury response of meningeal lymphatic networks through the use of animal models

Meningeal lymphatic vessels (MLVs) help maintain central nervous system (CNS) homeostasis via their ability to facilitate macromolecule waste clearance and neuroimmune trafficking. Although these vessels were overlooked for centuries, they have now been characterized in humans, non-human primates, and rodents. Recent studies in mice have explored the stereotyped growth and expansion of MLVs in dura mater, the various transcriptional, signaling, and environmental factors regulating their development and long-term maintenance, and the pathological changes these vessels undergo in injury, disease, or with aging. Key insights gained from these studies have also been leveraged to develop therapeutic approaches that help augment or restore MLV functions to improve brain health and cognition. Here, we review fundamental processes that control the development of peripheral lymphatic networks and how these might apply to the growth and expansion of MLVs in their unique meningeal environment. We also emphasize key findings in injury and disease models that may reveal additional insights into the plasticity of these vessels throughout the lifespan. Finally, we highlight unanswered questions and future areas of study that can further reveal the exciting therapeutic potential of meningeal lymphatics.

Piezo1 agonist restores meningeal lymphatic vessels, drainage, and brain-CSF perfusion in craniosynostosis and aged mice

Skull development coincides with the onset of cerebrospinal fluid (CSF) circulation, brain-CSF perfusion, and meningeal lymphangiogenesis, processes essential for brain waste clearance. How these processes are affected by craniofacial disorders such as craniosynostosis are poorly understood. We report that raised intracranial pressure and diminished CSF flow in craniosynostosis mouse models associates with pathological changes to meningeal lymphatic vessels that affect their sprouting, expansion, and long-term maintenance. We also show that craniosynostosis affects CSF circulatory pathways and perfusion into the brain. Further, craniosynostosis exacerbates amyloid pathology and plaque buildup in Twist1 +/- :5xFAD transgenic Alzheimer's disease models. Treating craniosynostosis mice with Yoda1, a small molecule agonist for Piezo1, reduces intracranial pressure and improves CSF flow, in addition to restoring meningeal lymphangiogenesis, drainage to the deep cervical lymph nodes, and brain-CSF perfusion. Leveraging these findings, we show Yoda1 treatments in aged mice with reduced CSF flow and turnover improve lymphatic networks, drainage, and brain-CSF perfusion. Our results suggest CSF provides mechanical force to facilitate meningeal lymphatic growth and maintenance. Additionally, applying Yoda1 agonist in conditions with raised intracranial pressure and/or diminished CSF flow, as seen in craniosynostosis or with ageing, is a possible therapeutic option to help restore meningeal lymphatic networks and brain-CSF perfusion.

Acute brain slice elastic modulus decreases over time

A common benchmark in the brain tissue mechanics literature is that the properties of acute brain slices should be measured within 8 h of the experimental animal being sacrificed. The core assumption is that-since there is no substantial protein degradation during this time-there will be no change to elastic modulus. This assumption overlooks the possibility of other effects (such as osmotic swelling) that may influence the mechanical properties of the tissue. To achieve consistent and accurate analysis of brain mechanics, it is important to account for or mitigate these effects. Using atomic force microscopy (AFM), tissue hydration and volume measurements, we find that acute brain slices in oxygenated artificial cerebrospinal fluid (aCSF) with a standard osmolarity of 300 mOsm/l experience rapid swelling, softening, and increases in hydration within the first 2 hours after slicing. Reductions in elastic modulus can be partly mitigated by addition of chondroitinase ABC enzyme (CHABC). Increasing aCSF osmolarity to 400 mOsm/l does not prevent softening but may hasten equilibration of samples to a point where measurements of relative elastic modulus are consistent across experiments.

Hydrocephalus in Nfix−/− Mice Is Underpinned by Changes in Ependymal Cell Physiology

Nuclear factor one X (NFIX) is a transcription factor required for normal ependymal development. Constitutive loss of Nfix in mice (Nfix−/−) is associated with hydrocephalus and sloughing of the dorsal ependyma within the lateral ventricles. Previous studies have implicated NFIX in the transcriptional regulation of genes encoding for factors essential to ependymal development. However, the cellular and molecular mechanisms underpinning hydrocephalus in Nfix−/− mice are unknown. To investigate the role of NFIX in hydrocephalus, we examined ependymal cells in brains from postnatal Nfix−/− and control (Nfix+/+) mice using a combination of confocal and electron microscopy. This revealed that the ependymal cells in Nfix−/− mice exhibited abnormal cilia structure and disrupted localisation of adhesion proteins. Furthermore, we modelled ependymal cell adhesion using epithelial cell culture and revealed changes in extracellular matrix and adherens junction gene expression following knockdown of NFIX. Finally, the ablation of Nfix from ependymal cells in the adult brain using a conditional approach culminated in enlarged ventricles, sloughing of ependymal cells from the lateral ventricles and abnormal localisation of adhesion proteins, which are phenotypes observed during development. Collectively, these data demonstrate a pivotal role for NFIX in the regulation of cell adhesion within ependymal cells of the lateral ventricles.

Perivascular pumping in the mouse brain: Improved boundary conditions reconcile theory, simulation, and experiment

Cerebrospinal fluid (CSF) flows through the perivascular spaces (PVSs) surrounding cerebral arteries. Revealing the mechanisms driving that flow could bring improved understanding of brain waste transport and insights for disorders including Alzheimer's disease and stroke. In vivo velocity measurements of CSF in surface PVSs in mice have been used to argue that flow is driven primarily by the pulsatile motion of artery walls - perivascular pumping. However, fluid dynamics theory and simulation have predicted that perivascular pumping produces flows differing from in vivo observations starkly, particularly in the phase and relative amplitude of flow oscillation. We show that coupling theoretical and simulated flows to more realistic end boundary conditions, using resistance and compliance values measured in mice instead of using periodic boundaries, results in velocities that match observations more closely in phase and relative amplitude of oscillation, while preserving the existing agreement in mean flow speed. This quantitative agreement among theory, simulation, and in vivo measurement further supports the idea that perivascular pumping is an important CSF driver in physiological conditions.

Extracellular Matrix in Human Craniofacial Development

The extracellular matrix (ECM) is a highly dynamic amalgamation of structural and signaling molecules whose quantitative and qualitative modifications drive the distinct programmed morphologic changes required for tissues to mature into their functional forms. The craniofacial complex houses a diverse array of tissues, including sensory organs, glands, and components of the musculoskeletal, neural, and vascular systems, alongside several other highly specialized tissues to form the most complex part of the vertebrate body. Through cell-ECM interactions, the ECM coordinates the cell movements, shape changes, differentiation, gene expression changes, and other behaviors that sculpt developing organs. In this review, we focus on several common key roles of the ECM to shape developing craniofacial organs and tissues. We summarize recent advances in our understanding of the ability of the ECM to biochemically and biomechanically orchestrate major events of craniofacial development, and we discuss how dysregulated ECM dynamics contributes to disease and disorders. As we expand our understanding of organ-specific matrix functionality and composition, we will improve our ability to rationally modify matrices to promote regeneration and/or prevent degenerative outcomes in vitro and in vivo.

Characterization of a mouse model of chronic hydrocephalus induced by partial occlusion of the aqueduct of Sylvius in the adult brain

BACKGROUND

Hydrocephalus is a neurologic disturbance produced by the abnormal production, circulation, and absorption of cerebrospinal fluid (CSF). Late-onset idiopathic aqueductal stenosis induces normal pressure hydrocephalus (NPH) in adults. To date, no animal model replicating chronic NPH is available to study the pathophysiological changes observed in these subjects.

NEW METHOD

We performed and characterized a model that induces chronic hydrocephalus in the adult mouse brain by producing a pre-aqueductal semiobstruction using an acetate lamina inserted into the atrium of the aqueduct of Sylvius. After surgical procedure, we analyzed the hydrocephalus development on days 60 and 120 and sham-operated animals were used as controls. We included an additional group of hydrocephalus resolution in which we removed the obstruction and analyzed the morphological changes in the brain.

RESULTS

The hydrocephalus was fully established on day 60 after the obstruction and remained stable for 120 days. In all animals, the intracranial pressure remained ~4.08 mmHg and we did not find statistically significant differences between the hydrocephalus groups and controls. We did not find motor impairments and anxiety-like behaviors among groups and the analysis of microglia and astrogliosis revealed mild glial reactivity.

COMPARISON WITH EXISTING METHODS

This model generates a long-term ventricular enlargement with normal intracranial pressure and moderate glial reactivity. Importantly, this model allows the reversibility of ventricular enlargement after the removal of the obstructive film from the brain.

CONCLUSIONS

This mouse model may be useful to study the long-term cerebral alterations that occur during NPH or after its surgical resolution.

Using Sensitivity Analysis to Develop a Validated Computational Model of Post-operative Calvarial Growth in Sagittal Craniosynostosis

Craniosynostosis is the premature fusion of one or more sutures across the calvaria, resulting in morphological and health complications that require invasive corrective surgery. Finite element (FE) method is a powerful tool that can aid with preoperative planning and post-operative predictions of craniosynostosis outcomes. However, input factors can influence the prediction of skull growth and the pressure on the growing brain using this approach. Therefore, the aim of this study was to carry out a series of sensitivity studies to understand the effect of various input parameters on predicting the skull morphology of a sagittal synostosis patient post-operatively. Preoperative CT images of a 4-month old patient were used to develop a 3D model of the skull, in which calvarial bones, sutures, cerebrospinal fluid (CSF), and brain were segmented. Calvarial reconstructive surgery was virtually modeled and two intracranial content scenarios labeled “CSF present” and “CSF absent,” were then developed. FE method was used to predict the calvarial morphology up to 76 months of age with intracranial volume-bone contact parameters being established across the models. Sensitivity tests with regards to the choice of material properties, methods of simulating bone formation and the rate of bone formation across the sutures were undertaken. Results were compared to the in vivo data from the same patient. Sensitivity tests to the choice of various material properties highlighted that the defined elastic modulus for the craniotomies appears to have the greatest influence on the predicted overall skull morphology. The bone formation modeling approach across the sutures/craniotomies had a considerable impact on the level of contact pressure across the brain with minimum impact on the overall predicated morphology of the skull. Including the effect of CSF (based on the approach adopted here) displayed only a slight reduction in brain pressure outcomes. The sensitivity tests performed in this study set the foundation for future comparative studies using FE method to compare outcomes of different reconstruction techniques for the management of craniosynostosis.

FACEts of mechanical regulation in the morphogenesis of craniofacial structures

During embryonic development, organs undergo distinct and programmed morphological changes as they develop into their functional forms. While genetics and biochemical signals are well recognized regulators of morphogenesis, mechanical forces and the physical properties of tissues are now emerging as integral parts of this process as well. These physical factors drive coordinated cell movements and reorganizations, shape and size changes, proliferation and differentiation, as well as gene expression changes, and ultimately sculpt any developing structure by guiding correct cellular architectures and compositions. In this review we focus on several craniofacial structures, including the tooth, the mandible, the palate, and the cranium. We discuss the spatiotemporal regulation of different mechanical cues at both the cellular and tissue scales during craniofacial development and examine how tissue mechanics control various aspects of cell biology and signaling to shape a developing craniofacial organ.

Quantification of Capillary Perfusion in an Animal Model of Acute Intracranial Hypertension

Intracranial hypertension (IH) is a common feature of many pathologies, including brain edema. In the brain, the extended network of capillaries ensures blood flow to meet local metabolic demands. Capillary circulation may be severely affected by IH, but no studies have quantified the effect of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) on capillary perfusion during the development of brain edema. We used optical coherence tomography angiography to quantify relative changes of fractional perfused volume (FPV) in cortical capillaries and simultaneously monitored ICP and blood pressure (BP) in anesthetized male C57Bl/6NTac mice during development of brain edema induced by water intoxication (WI) within 30 min. WI induced severe IH and brain herniation. ICP and CPP reached 90.2 mm Hg and 38.4 mm Hg, respectively. FPV was significantly affected already at normal ICP (ICP <15 mm Hg, slope ≈ -1.46, p < 0.001) and, at the onset of IH (ICP = 20-22 mm Hg), FPV was 17.9 ± 13.3% lower than baseline. A decreasing trend was observed until the ICP peak (Δ%FPV = -43.6 ± 19.2%). In the ICP range of 7-42 mm Hg, relative changes in FPV were significantly correlated with ICP, BP, and CPP (p < 0.001), with ICP and CPP being the best predictors. In conclusion, elevated ICP induces a gradual collapse of the cerebral microvasculature, which is initiated before the clinical threshold of IH. In summary, the estimate of capillary perfusion might be essential in patients with IH to assess the state of the brain microcirculation and to improve the availability of oxygen and nutrients to the brain.

The Brain's Glymphatic System: Current Controversies

The glymphatic concept along with the discovery of meningeal lymphatic vessels have, in recent years, highlighted that fluid is directionally transported within the central nervous system (CNS). Imaging studies, as well as manipulations of fluid transport, point to a key role of the glymphatic-lymphatic system in clearance of amyloid-β and other proteins. As such, the glymphatic-lymphatic system represents a new target in combating neurodegenerative diseases. Not unexpectedly, introduction of a new plumbing system in the brain has stirred controversies. This opinion article will highlight what we know about the brain's fluid transport systems, where experimental data are lacking, and what is still debated.

Trans-pairing between osteoclasts and osteoblasts shapes the cranial base during development

Bone growth is linked to expansion of nearby organs, as is the case for the cranial base and the brain. Here, we focused on development of the mouse clivus, a sloping surface of the basioccipital bone, to define mechanisms underlying morphological changes in bone in response to brain enlargement. Histological analysis indicated that both endocranial and ectocranial cortical bone layers in the basioccipital carry the osteoclast surface dorsally and the osteoblast surface ventrally. Finite element analysis of mechanical stress on the clivus revealed that compressive and tensile stresses appeared mainly on respective dorsal and ventral surfaces of the basioccipital bone. Osteoclastic bone resorption occurred primarily in the compression area, whereas areas of bone formation largely coincided with the tension area. These data collectively suggest that compressive and tensile stresses govern respective localization of osteoclasts and osteoblasts. Developmental analysis of the basioccipital bone revealed the clivus to be angled in early postnatal wild-type mice, whereas its slope was less prominent in Tnfsf11^−/− mice, which lack osteoclasts. We propose that osteoclast-osteoblast “trans-pairing” across cortical bone is primarily induced by mechanical stress from growing organs and regulates shape and size of bones that encase the brain.

Characterizing and Modeling Bone Formation during Mouse Calvarial Development

The newborn mammalian cranial vault consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Early fusion of these sutures leads to a medical condition known as craniosynostosis. The mechanobiology of normal and craniosynostotic skull growth is not well understood. In a series of previous studies, we characterized and modeled radial expansion of normal and craniosynostotic (Crouzon) mice. Here, we describe a new modeling algorithm to simulate bone formation at the sutures in normal and craniosynostotic mice. Our results demonstrate that our modeling approach is capable of predicting the observed ex vivo pattern of bone formation at the sutures in the aforementioned mice. The same approach can be used to model different calvarial reconstruction in children with craniosynostosis to assist in the management of this complex condition.

Modelling human skull growth: a validated computational model

During the first year of life, the brain grows rapidly and the neurocranium increases to about 65% of its adult size. Our understanding of the relationship between the biomechanical forces, especially from the growing brain, the craniofacial soft tissue structures and the individual bone plates of the skull vault is still limited. This basic knowledge could help in the future planning of craniofacial surgical operations. The aim of this study was to develop a validated computational model of skull growth, based on the finite-element (FE) method, to help understand the biomechanics of skull growth. To do this, a two-step validation study was carried out. First, an in vitro physical three-dimensional printed model and an in silico FE model were created from the same micro-CT scan of an infant skull and loaded with forces from the growing brain from zero to two months of age. The results from the in vitro model validated the FE model before it was further developed to expand from 0 to 12 months of age. This second FE model was compared directly with in vivo clinical CT scans of infants without craniofacial conditions (n = 56). The various models were compared in terms of predicted skull width, length and circumference, while the overall shape was quantified using three-dimensional distance plots. Statistical analysis yielded no significant differences between the male skull models. All size measurements from the FE model versus the in vitro physical model were within 5%, with one exception showing a 7.6% difference. The FE model and in vivo data also correlated well, with the largest percentage difference in size being 8.3%. Overall, the FE model results matched well with both the in vitro and in vivo data. With further development and model refinement, this modelling method could be used to assist in preoperative planning of craniofacial surgery procedures and could help to reduce reoperation rates.

Predicting calvarial growth in normal and craniosynostotic mice using a computational approach

During postnatal calvarial growth the brain grows gradually and the overlying bones and sutures accommodate that growth until the later juvenile stages. The whole process is coordinated through a complex series of biological, chemical and perhaps mechanical signals between various elements of the craniofacial system. The aim of this study was to investigate to what extent a computational model can accurately predict the calvarial growth in wild-type (WT) and mutant type (MT) Fgfr2C342Y/+ mice displaying bicoronal suture fusion. A series of morphological studies were carried out to quantify the calvarial growth at P3, P10 and P20 in both mouse types. MicroCT images of a P3 specimen were used to develop a finite element model of skull growth to predict the calvarial shape of WT and MT mice at P10. Sensitivity tests were performed and the results compared with ex vivo P10 data. Although the models were sensitive to the choice of input parameters, they predicted the overall skull growth in the WT and MT mice. The models also captured the difference between the ex vivoWT and MT mice. This modelling approach has the potential to be translated to human skull growth and to enhance our understanding of the different reconstruction methods used to manage clinically the different forms of craniosynostosis, and in the long term possibly reduce the number of re-operations in children displaying this condition and thereby enhance their quality of life.

A COMPUTATIONAL ANALYSIS OF BONE FORMATION IN THE CRANIAL VAULT USING A COUPLED REACTION-DIFFUSION-STRAIN MODEL

Bones of the murine cranial vault are formed by differentiation of mesenchymal cells into osteoblasts, a process that is primarily understood to be controlled by a cascade of reactions between extracellular molecules and cells. We assume that the process can be modeled using Turing's reaction-diffusion equations, a mathematical model describing the pattern formation controlled by two interacting molecules (activator and inhibitor). In addition to the processes modeled by reaction-diffusion equations, we hypothesize that mechanical stimuli of the cells due to growth of the underlying brain contribute significantly to the process of cell differentiation in cranial vault development. Structural analysis of the surface of the brain was conducted to explore the effects of the mechanical strain on bone formation. We propose a mechanobiological model for the formation of cranial vault bones by coupling the reaction-diffusion model with structural mechanics. The mathematical formulation was solved using the finite volume method. The computational domain and model parameters are determined using a large collection of experimental data that provide precise three dimensional (3D) measures of murine cranial geometry and cranial vault bone formation for specific embryonic time points. The results of this study suggest that mechanical strain contributes information to specific aspects of bone formation. Our mechanobiological model predicts some key features of cranial vault bone formation that were verified by experimental observations including the relative location of ossification centers of individual vault bones, the pattern of cranial vault bone growth over time, and the position of cranial vault sutures.

Changes in the composition of brain interstitial ions control the sleep-wake cycle

Wakefulness is driven by the widespread release of neuromodulators by the ascending arousal system. Yet, it is unclear how these substances orchestrate state-dependent, global changes in neuronal activity. Here, we show that neuromodulators induce increases in the extracellular K(+) concentration ([K(+)]e) in cortical slices electrically silenced by tetrodotoxin. In vivo, arousal was linked to AMPA receptor-independent elevations of [K(+)]e concomitant with decreases in [Ca(2+)]e, [Mg(2+)]e, [H(+)]e, and the extracellular volume. Opposite, natural sleep and anesthesia reduced [K(+)]e while increasing [Ca(2+)]e, [Mg(2+)]e, and [H(+)]e as well as the extracellular volume. Local cortical activity of sleeping mice could be readily converted to the stereotypical electroencephalography pattern of wakefulness by simply imposing a change in the extracellular ion composition. Thus, extracellular ions control the state-dependent patterns of neural activity.