Acute Neuropixels Recordings in the Marmoset Monkey

High-density linear probes, such as Neuropixels, provide an unprecedented opportunity to understand how neural populations within specific laminar compartments contribute to behavior. Marmoset monkeys, unlike macaque monkeys, have a lissencephalic (smooth) cortex that enables recording perpendicular to the cortical surface, thus making them an ideal animal model for studying laminar computations. Here we present a method for acute Neuropixels recordings in the common marmoset (Callithrix jacchus). The approach replaces the native dura with an artificial silicon-based dura that grants visual access to the cortical surface, which is helpful in avoiding blood vessels, ensures perpendicular penetrations, and could be used in conjunction with optical imaging or optogenetic techniques. The chamber housing the artificial dura is simple to maintain with minimal risk of infection and could be combined with semichronic microdrives and wireless recording hardware. This technique enables repeated acute penetrations over a period of several months. With occasional removal of tissue growth on the pial surface, recordings can be performed for a year or more. The approach is fully compatible with Neuropixels probes, enabling the recording of hundreds of single neurons distributed throughout the cortical column.

Effects of surface profile on porcine dural mechanical properties

BACKGROUND

Cerebrospinal fluid leakage through the spinal meninges is difficult to diagnose and treat. Moreover, its underlying mechanism remains unknown. Considering that the dura mater is structurally the strongest and outermost membrane among the three-layered meninges, we hypothesized that a dural mechanical tear would trigger spontaneous cerebrospinal fluid leakage, especially when a traumatic loading event is involved. Thus, accurate biomechanical properties of the dura mater are indispensable for improving computational models, which aid in predicting blunt impact injuries and creating artificial substitutes for transplantation and surgical training.

METHOD

We characterized the surface profile of the spinal dura and its mechanical properties (Young's moduli) with a distinction of its inherent anatomical sites (i.e., the cervical and lumbar regions as well as the dorsal and ventral sides of the spinal cord).

FINDINGS

Although the obtained Young's moduli exhibited no considerable difference between the aforementioned anatomical sites, our results suggested that the wrinkles structurally formed along the longitudinal direction would relieve stress concentration on the dural surface under in vivo and supraphysiological conditions, enabling mechanical protection of the dural tissue from a blunt impact force that was externally applied to the spine.

INTERPRETATION

This study provides fundamental data that can be used for accurately predicting cerebrospinal fluid leakage due to blunt impact trauma.

The relationship between myodural bridge, atrophy and hyperplasia of the suboccipital musculature, and cerebrospinal fluid dynamics

The Myodural Bridge (MDB) is a physiological structure that is highly conserved in mammals and many of other tetrapods. It connects the suboccipital muscles to the cervical spinal dura mater (SDM) and transmits the tensile forces generated by the suboccipital muscles to the SDM. Consequently, the MDB has broader physiological potentials than just fixing the SDM. It has been proposed that MDB significantly contributes to the dynamics of cerebrospinal fluid (CSF) movements. Animal models of suboccipital muscle atrophy and hyperplasia were established utilizing local injection of BTX-A and ACE-031. In contrast, animal models with surgical severance of suboccipital muscles, and without any surgical operation were set as two types of negative control groups. CSF secretion and reabsorption rates were then measured for subsequent analysis. Our findings demonstrated a significant increase in CSF secretion rate in rats with the hyperplasia model, while there was a significant decrease in rats with the atrophy and severance groups. We observed an increase in CSF reabsorption rate in both the atrophy and hyperplasia groups, but no significant change was observed in the severance group. Additionally, our immunohistochemistry results revealed no significant change in the protein level of six selected choroid plexus-CSF-related proteins among all these groups. Therefore, it was indicated that alteration of MDB-transmitted tensile force resulted in changes of CSF secretion and reabsorption rates, suggesting the potential role that MDB may play during CSF circulation. This provides a unique research insight into CSF dynamics.

The relationship between myodural bridges, hyperplasia of the suboccipital musculature, and intracranial pressure

During mammalian evolution, the Myodural Bridges (MDB) have been shown to be highly conserved anatomical structures. However, the putative physiological function of these structures remains unclear. The MDB functionally connects the suboccipital musculature to the cervical spinal dura mater, while passing through the posterior atlanto-occipital and atlanto-axial interspaces. MDB transmits the tensile forces generated by the suboccipital muscles to the cervical dura mater. Moreover, head movements have been shown to be an important contributor to human CSF circulation. In the present study, a 16-week administration of a Myostatin-specific inhibitor, ACE-031, was injected into the suboccipital musculature of rats to establish an experimental animal model of hyperplasia of the suboccipital musculature. Using an optic fiber pressure measurement instrument, the present authors observed a significant increase in intracranial pressure (ICP) while utilizing the hyperplasia model. In contrast, surgically severing the MDB connections resulted in a significant decrease in intracranial pressure. Thus, these results indicated that muscular activation of the MDB may affect CSF circulation, suggesting a potential functional role of the MDB, and providing a new research perspective on CSF dynamics.

Recognition and differentiation of dural puncture click sensation: A subjective and objective prospective study of dural puncture forces using fine-gauge spinal needles

BACKGROUND

We hypothesized that the click perceived when puncturing the dura-arachnoid with fine-gauge spinal needles can be subjectively identified, and investigated whether it may be distinguishable among different needle types.

METHODS

Subjective and objective evaluations were performed. First, physicians punctured the polyamide film or porcine dura mater (n = 70 and n = 20, respectively) with seven types of spinal needles and numerically evaluated the perceived click sensations. Using an 11-point numerical rating scale (from "0" for "no click sensation" to "10" for "the strongest click perceived") data, subjective differentiation among needle types was assessed. Second, in the objective part of the study, total forces elicited by polyamide film or porcine dura mater punctures with each needle were measured using a biomechanical testing device, and load-displacement curves evaluated. Third, the results of subjective and objective evaluations were compared.

RESULTS

All participants recognized the click and could discriminate among needles of different tip shape. The load-displacement curves for polyamide film and porcine dura mater were similar and needle-specific. The subjective numerical rating scale values corresponded well with the objectively measured changes in total forces (R2 = 0.862 and R2 = 0.881 for polyamide film and porcine dura mater, respectively), indicating that an increase in the largest drop in total force value of 0.30 N or 0.21 N would produce an increase of numerical rating scale value of 1 for polyamide film and porcine dura mater, respectively.

CONCLUSIONS

We provide an objective proof of the click sensation felt upon dural puncture using different fine-gauge spinal needles. Click recognition could be used as an additional indicator of successful spinal puncture.

Functional characterization of the dural sinuses as a neuroimmune interface

Despite the established dogma of central nervous system (CNS) immune privilege, neuroimmune interactions play an active role in diverse neurological disorders. However, the precise mechanisms underlying CNS immune surveillance remain elusive; particularly, the anatomical sites where peripheral adaptive immunity can sample CNS-derived antigens and the cellular and molecular mediators orchestrating this surveillance. Here, we demonstrate that CNS-derived antigens in the cerebrospinal fluid (CSF) accumulate around the dural sinuses, are captured by local antigen-presenting cells, and are presented to patrolling T cells. This surveillance is enabled by endothelial and mural cells forming the sinus stromal niche. T cell recognition of CSF-derived antigens at this site promoted tissue resident phenotypes and effector functions within the dural meninges. These findings highlight the critical role of dural sinuses as a neuroimmune interface, where brain antigens are surveyed under steady-state conditions, and shed light on age-related dysfunction and neuroinflammatory attack in animal models of multiple sclerosis.

Fabrication and Properties of a Biomimetic Dura Matter Substitute Based on Stereocomplex Poly(Lactic Acid) Nanofibers

Background

Duraplasty is one of the most critical issues in neurosurgical procedures because the defect of dura matter will cause many complications. Electrospinning can mimic the 3D structure of the natural extracellular matrix whose structure is similar to that of dura matter. Poly(L-lactic acid) (PLLA) has been used to fabricate dura matter substitutes and showed compatibility to dural tissue. However, the mechanical properties of the PLLA substitute cannot match the mechanical properties of the human dura mater.

Methods and Results

We prepared stereocomplex nanofiber membranes based on enantiomeric poly(lactic acid) and poly(D-lactic acid)-grafted tetracalcium phosphate via electrospinning. X-ray diffraction results showed the formation of stereocomplex crystallites (SC) in the composite nanofiber membranes. Scanning electron microscope observation images showed that composites nanofibers with higher SC formation can keep its original morphologies after heat treatment, suggesting the heat resistance of composite nanofiber membranes. Differential scanning calorimeter tests confirmed that the melting temperature of composite nanofiber membranes was approximately 222°C, higher than that of PLLA. Tensile testing indicated that the ultimate tensile strength and the elongation break of the stereocomplex nanofiber membranes were close to human dura matter. In vitro cytotoxicity studies proved that the stereocomplex nanofiber membranes were non-toxic. The neuron-like differentiation of marrow stem cells on the stereocomplex nanofiber membranes indicated its neuron compatibility.

Conclusion

The stereocomplex nanofiber membranes have the potential to serve as a dura mater substitute.

Investigation of wave propagation through head layers with focus on understanding blast wave transmission

Blast-induced traumatic brain injury (bTBI) is a critical health concern. This issue is being addressed in terms of identifying a cause-effect relationship between the mechanical insult in the form of a blast and resulting injury to the brain. Understanding wave propagation through the head is an important aspect in this regard. The objective of this work was to study the blast wave propagation through the layered architecture of the head with an emphasis on understanding the wave transmission mechanism. Toward this end, one-dimensional (1D) finite element head model is built for a simplified surrogate, human, and rat. Motivated from experimental investigations, four different head layer configurations have been considered. These configurations are: (A) Skull-Brain, (B) Skin-Skull-Brain, (C) Skin-Skull-Dura-Arachnoid-CSF-Pia-Brain, (D) Skin-Skull-Dura-Arachnoid-AT-Pia-Brain. The validated head model is subjected to flattop and Friedlander loading implied in the blast, and the resulting response is evaluated in terms of brain pressures. Our results suggest that wave propagation through head parenchyma plays an important role in blast wave transmission. The thickness, material properties of head layers, and rise time of an input pulse govern the temporal evolution of pressure in the brain. The key findings of this work are: (a) Skin and meninges amplify the applied input pressure, whereas air sinus has an attenuation effect. (b) Model is able to describe experimentally recorded peak pressures and rise times in the brain, including variations within the aforementioned experimental head models of TBI. This reinforces that the wave transmission is an important loading pathway to the brain. (c) Equivalent layer theory for modeling meningeal layers as a single layer has been proposed, and it gives reasonable agreement with each meningeal layer modeled explicitly. This modeling approach has a great utility in 3D head models. The potential applications of 1D head model in evaluation of new helmet materials, brain sensor calibration, and brain pressure estimation for a given explosive strength have also been demonstrated. Overall, these results provide important insights into the understanding of mechanics of blast wave transmission in the head.

A microfabricated, 3D-sharpened silicon shuttle for insertion of flexible electrode arrays through dura mater into brain

OBJECTIVE

Electrode arrays for chronic implantation in the brain are a critical technology in both neuroscience and medicine. Recently, flexible, thin-film polymer electrode arrays have shown promise in facilitating stable, single-unit recordings spanning months in rats. While array flexibility enhances integration with neural tissue, it also requires removal of the dura mater, the tough membrane surrounding the brain, and temporary bracing to penetrate the brain parenchyma. Durotomy increases brain swelling, vascular damage, and surgical time. Insertion using a bracing shuttle results in additional vascular damage and brain compression, which increase with device diameter; while a higher-diameter shuttle will have a higher critical load and more likely penetrate dura, it will damage more brain parenchyma and vasculature. One way to penetrate the intact dura and limit tissue compression without increasing shuttle diameter is to reduce the force required for insertion by sharpening the shuttle tip.

APPROACH

We describe a novel design and fabrication process to create silicon insertion shuttles that are sharp in three dimensions and can penetrate rat dura, for faster, easier, and less damaging implantation of polymer arrays. Sharpened profiles are obtained by reflowing patterned photoresist, then transferring its sloped profile to silicon with dry etches.

MAIN RESULTS

We demonstrate that sharpened shuttles can reliably implant polymer probes through dura to yield high quality single unit and local field potential recordings for at least 95 days. On insertion directly through dura, tissue compression is minimal.

SIGNIFICANCE

This is the first demonstration of a rat dural-penetrating array for chronic recording. This device obviates the need for a durotomy, reducing surgical time and risk of damage to the blood-brain barrier. This is an improvement to state-of-the-art flexible polymer electrode arrays that facilitates their implantation, particularly in multi-site recording experiments. This sharpening process can also be integrated into silicon electrode array fabrication.

Flexible Micropillar Electrode Arrays for In Vivo Neural Activity Recordings

Flexible electronics that can form tight interfaces with neural tissues hold great promise for improving the diagnosis and treatment of neurological disorders and advancing brain/machine interfaces. Here, the facile fabrication of a novel flexible micropillar electrode array (µPEA) is described based on a biotemplate method. The flexible and compliant µPEA can readily integrate with the soft surface of a rat cerebral cortex. Moreover, the recording sites of the µPEA consist of protruding micropillars with nanoscale surface roughness that ensure tight interfacing and efficient electrical coupling with the nervous system. As a result, the flexible µPEA allows for in vivo multichannel recordings of epileptiform activity with a high signal-to-noise ratio of 252 ± 35. The ease of preparation, high flexibility, and biocompatibility make the µPEA an attractive tool for in vivo spatiotemporal mapping of neural activity.

Cortical Spreading Depolarization (CSD) Recorded from Intact Skin, from Surface of Dura Mater or Cortex: Comparison with Intracortical Recordings in the Neocortex of Adult Rats

In cerebral cortex of anesthetized rats single waves of spreading depolarization (CSD) were elicited by needle prick. CSD-related changes of DC (direct current) potentials were either recorded from the intact skin or together with concomitant changes of potassium concentration with K⁺-selective microelectrodes simultaneously at the surface of the dura mater or of the cortex ([K⁺]_s) and in the extracellular space at a cortical depth of 1200 µm. At the intact skin CSD-related DC-shifts had amplitudes of less than 1 mV and had only in a minority of cases the typical CSD-like shape. In the majority these DC-shifts rose and recovered very slowly and were difficult to identify without further indicators. At dura surface CSD-related DC shifts were significantly smaller and rose and recovered slower than intracortically recorded CSD. Concomitant increases in [K⁺]_s were delayed and reached maximal values of about 5 mM from a baseline of 3 mM. They rose and recovered slower than simultaneously recorded intracortical changes in extracellular potassium concentration ([K⁺]_e) that were up to 65 mM. The results suggest that extracellular potassium during CSD is diffusing through the subarachnoid space and across the dura mater. In a few cases CSD was either absent at the dura or at a depth of 1200 µm. Even full blown CSDs in this cortical depth could remain without concomitant deflections at the dura. Our data confirmed in principle the possibility of non-invasive recordings of CSD-related DC-shifts. For a use in clinical routine sensitivity and specificity will have to be improved.

Electrical fields induced inside the rat brain with skin, skull, and dural placements of the current injection electrode

Transcranial electrical stimulation (tES) is rapidly becoming an indispensable clinical tool with its different forms. Animal data are crucially needed for better understanding of the underlying mechanisms of tES. For reproducibility of results in animal experiments, the electric fields (E-Fields) inside the brain parenchyma induced by the injected currents need to be predicted accurately. In this study, we measured the electrical fields in the rat brain perpendicular to the brain surface, i.e. vertical electric field (VE-field), when the stimulation electrode was placed over the skin, skull, or dura mater through a craniotomy hole. The E-field attenuation through the skin was a few times larger than that of the skull and the presence of skin substantially reduced the VE-field peak at the cortical surface near the electrode. The VE-field declined much quicker in the gray matter underneath the pial surface than it did in the white matter, and thus the large VE-fields were contained mostly in the gray matter. The transition at the gray/white matter border caused a significant peak in the VE-field, as well as at other local inhomogeneties. A conductivity value of 0.57 S/m is predicted as a global value for the whole brain by matching our VE-field measurements to the field profile given by analytical equations for volume conductors. Finally, insertion of the current return electrode into the shoulder, submandibular, and hind leg muscles had virtually no effects on the measured E-field amplitudes in the cortex underneath the epidural electrodes.

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.

Spinal dura mater: biophysical characteristics relevant to medical device development

Understanding the relevant biophysical properties of the spinal dura mater is essential to the design of medical devices that will directly interact with this membrane or influence the contents of the intradural space. We searched the literature and reviewed the pertinent characteristics for the design, construction, testing, and imaging of novel devices intended to perforate, integrate, adhere or reside within or outside of the spinal dura mater. The spinal dura mater is a thin tubular membrane composed of collagen and elastin fibres that varies in circumference along its length. Its mechanical properties have been well-described, with the longitudinal tensile strength exceeding the transverse strength. Data on the bioelectric, biomagnetic, optical and thermal characteristics of the spinal dura are limited and sometimes taken to be similar to those of water. While various modalities are available to visualise the spinal dura, magnetic resonance remains the best modality to segment its structure. The reaction of the spinal dura to imposition of a foreign body or other manipulations of it may compromise its biomechanical and immune-protective benefits. Therefore, dural sealants and replacements are of particular clinical, research and commercial interest. In conclusion, existing devices that are in clinical use for spinal cord stimulation, intrathecal access or intradural implantation largely adhere to traditional designs and their attendant limitations. However, if future devices are built with an understanding of the dura's properties incorporated more fully into the designs, there is potential for improved performance.

Early Composite Cranioplasty in Infants with Severe Aplasia Cutis Congenita: A Report of Two Cases

Objective

Severe cutis aplasia congenita has traditionally been treated with initial soft tissue coverage and delayed cranioplasty. We advocate the technique of early composite reconstruction of both bone and soft tissues.

Methods

Two cases of cutis aplasia congenita with large skull defects (6 × 10 cm, 8 × 8 cm) of superficial layers, skull, and dura are presented. In each case, composite reconstruction was undertaken before 2 weeks of age with restoration of bony and soft tissue coverage through autologous, full-thickness cranial bone grafts and scalp flaps. Both children have been followed up over 2 years with clinical examination and computed tomography (CT) scans.

Results

In both cases, defects were completely repaired postoperatively and remained closed 2 years later. Complete regeneration of calvarial bone graft donor sites were documented by CT scan. Head shape and circumference were normal at 2-year follow up.

The myodural bridge existing in the Nephocaena phocaenoides

Recent studies have identified that the myodural bridge (MDB) between the rectus capitis posterior minor (RCPmi) and the cervical spinal dura mater in the posterior atlanto-occipital interspace in humans. And it was supposed that the MDB may play essential physiological roles. As a result, the MDB is possibly a highly conserved structure in the evolution of mammals. However, there is little confirmative description about the existence of the MDB in marine mammals. The objective of this study was to explore the existence and the fiber property of the MDB in the Neophocaena phocaenoides. Six cadavers of the Neophocaena phocaenoides with formalin fixation were used in this study. One was used for head and neck CT scanning and three-dimensional (3D) reconstruction and suboccipital region dissection, two were for sectional observation by P45 plastinated sheets of head and neck, and three were for histological analysis of suboccipial structures. This is the first study to demonstrate the existence of the MDB in the aquatic mammals. The rectus capitis dorsal minor (RCDmi) originated from the inferior border of the occiput and inserted into the cervical spinal dura mater. At the ventral aspect of the RCDmi, the MDB directly extended through the posterior atlanto-occipital interspace and connected with the cervical spinal dura mater which was consisted of type Ⅰ collagen. In addition, the dorsal atlanto-occipital membrane was not found in the Neophocaena phocaenoides. The tendinous myodural bridge extended from the RCDmi to the spinal dura mater through the posterior atlanto-occipital interspace in the Neophocaena phocaenoides.

Effect of Hypotension and Carbon Dioxide Changes in an Improved Genuine Closed Cranial Window Rat Model

The genuine closed cranial window model, in which the thinned parietal bone constitutes the covering of the preparation, has contributed to a better understanding of the pathophysiological mechanisms in migraine. In its present form, only measurements of the middle meningeal artery (MMA) are performed. The aim of this study was, in addition, to measure pial artery/arteriole (PA) diameter and cortical cerebral blood flux in the same cranial window. The model was evaluated by studying the effects of hypotension and changes in arterial carbon dioxide pressure (PaCO2), because these parameters might influence the interpretation of pharmacological experiments. Out of 23 successful experiments it was possible to measure all three parameters in 19 animals. In four, PA diameter could not be measured, while MMA diameter and local cortical cerebral blood flux (LCBFFlux) always could. Haemorrhage-induced hypotension (-64 + 0.8 mmHg) caused an increase of MMA diameter of 11.8 + 8.4%, PA diameter of 61.2 + 7.7% and a decrease in LCBFFlux of - 36.4 + 2.5%. The decrease in blood pressure did not significantly change the MMA ( P = 0.38); however, the PA diameter and the LCBF-Flux were affected ( P < 0.001). All three parameters were sensitive to hypo- and hypercapnia. In conclusion, we have shown that not only MMA but also PA diameter and LCBFFlux can be measured in the same cranial window. Tight control of PaCO2 is essential in pharmacological experiments. If test substances possess hypotensive actions, it may be difficult to interpret whether the PA dilation is caused by the induced hypotension per se or is a direct pharmacological action or a combination. In contrast, the MMA does not autoregulate and MMA diameter changes in pharmacological studies may exclusively be due to direct pharmacological effects.

Effects of N-, P/Q- and L-type Calcium Channel Blockers on Nociceptive Neurones of the Trigeminal Nucleus with Input from the Dura

In anaesthetized rats, extracellular recordings were made from neurones of the spinal trigeminal nucleus, involved in the processing of nociceptive input from the dura. Blockers of voltage-gated calcium channels (VGCCs) were administered topically to the exposed brainstem. Blockade of N-type (CaV2.2) channels reduced spontaneous activity and responses of the neurones to cold and chemical stimuli applied to the dura, suggesting that N-type channels regulate excitatory synaptic activation. Blockade of L-type (CaV1) channels enhanced spontaneous discharges of the neurones. Blockade of P/Q-type (CaV2.1) channels slightly decreased responses to chemical and cold stimuli but markedly increased spontaneous activity, an effect which was absent during concomitant application of GABA to the brainstem. The data suggest that P/Q-type VGCCs regulate a tonic synaptic inhibitory control of the brainstem neurones. The risk of migraine by genetic modifications of P/Q-type channels may thus be sought in disturbed inhibition in the network that processes nociceptive dura input.

Experimental study on the mechanical interaction between silicon neural microprobes and rat dura mater during insertion

In vivo insertion experiments are essential to optimize novel neural implants. Our work focuses on the interaction between intact dura mater of rats and as-fabricated single-shaft silicon microprobes realized by deep reactive ion etching. Implantation parameters like penetration force and dimpling through intact dura mater were studied as a function of insertion speed, microprobe cross-section, tip angle and animal age. To reduce tissue resistance, we proposed a unique tip sharpening technique, which was also evaluated in in vivo insertion tests. By doubling the insertion speed (between 1.2 and 10.5 mm/min), an increase of 10-35% in penetration forces was measured. When decreasing the cross-section of the microprobes, penetration forces and dimpling was reduced by as much as 30-50% at constant insertion speeds. Force was noticed to gradually decrease by decreasing tip angles. Measured penetration forces through dura mater were reduced even down to 11±3 mN compared to unsharpened (49±13 mN) probes by utilizing our unique tip sharpening technique, which is very close to exerted penetration force in the case of retracted dura (5±1.5 mN). Our findings imply that age remarkably alters the elasticity of intact dura mater. The decreasing stiffness of dura mater results in a significant rise in penetration force and decrease in dimpling. Our work is the first in vivo comparative study on microelectrode penetration through intact and retracted dura mater.

Microarray analysis of gene expression after electrical stimulation of the dura mater surrounding the superior sagittal sinus in conscious adult rats

BACKGROUND

The molecular and cellular origins of migraine headache are among the most complex problems in contemporary neurology. Up to now the pathogenesis of migraine still remains unclearly defined. The objective of this study was to explore new factors that may be related to the mechanism of migraine.

METHODS

The present study performed a comprehensive analysis of gene expression in the trigeminal nucleus caudalis induced by electrical stimulation of dura mater surrounding the superior sagittal sinus in conscious rats using microarray analysis followed by quantitative real-time reverse-transcribed polymerase chain reaction (qRT-PCR) verification. Student's two sample t-test was employed when two groups were compared. A P value <0.05 was considered to be statistically significant.

RESULTS

Comparing the placebo and the electrical stimulation groups, 40 genes were determined to be significantly differentially expressed. These significantly differentially expressed genes were involved in many pathways, including transporter activity, tryptophan metabolism, G protein signaling, kinase activity, actin binding, signal transducer activity, anion transport, protein folding, enzyme inhibitor activity, coenzyme metabolism, binding, ion transport, cell adhesion, metal ion transport, oxidoreductase activity, mitochondrion function, and others. Most of the genes were involved in more than 2 pathways. Of particular interest is the up-regulation of Phactr3 and Akap5 and the down-regulation of Kdr.

CONCLUSION

These findings may provide important clues for a better understanding of the molecular mechanism of migraine.

Mechanical properties of cervical dura mater

The aim of the study was to determine experimentally the stress as strain function as well as the orthotropy and heterogeneity of porcine dura mater of the cervical spinal cord. Material was divided into groups based on the place of collection, considering the dorsal side and ventral side, specifying the number of cervical vertebra, and the direction of tension of the sample - longitudinal or circumferential. Experimental studies were conducted with the MTS Synergie 100 testing machine. The tensile test was performed for each sample at a speed of 2 mm/min until the sample's break. There were determined the characteristics of stress as a function of strain in particular samples. Distribution maps of the stress and strain values at the characteristic points were then drawn (the beginning and the end of the linear range of the stress-strain characteristic and the point corresponding to the complete sample damage) for each set of samples, taking account of their collection place and direction of tension. The results confirmed the orthotropy of mechanical properties of dura mater. Stress and strain differed also in the value at the height of each vertebra and exhibited diversification on the ventral side compared to dorsal one.

[Effect of migrepin on activity of trigeminal nucleus caudalis neurons]

Neurophysiological experiments on anesthetized rats were used to study the effects of various doses (12.5, 25, 37.5 mg/kg, i.v.) of drug composition migrepin (representing a combination of potassium-2,4-dichlorobenzoate, carbamazepine, and caffeine) on background firing of the trigeminal nucleus caudalis neurons and their responses to electrical stimulation of the dura mater. It was found that migrepin produces direct, dose-dependent inhibitory action on functional activity of TNC neurons. The results confirmed anti-migraine properties of the drug but did not exclude the necessity to study its action in clinical trials.

Nonviral transfection of mouse calvarial organ in vitro using Accell-modified siRNA

BACKGROUND

Understanding the biology of cranial suture fusion and the precise role of involved molecules implicated in the process will help to identify key factors involved in regulation of suture fusion. Modulation of these key factors may serve as a tissue-engineering technique to replace the traditional surgical procedures for the correction of premature suture fusion. Modulation of gene expression by RNA interference is a widely used technique with high potential. Because there is no available report of calvarial organ transfection in vitro, the authors studied the development of a successful nonviral delivery technique of small inhibitory RNA (siRNA) to an in vitro calvarial organ culture system.

METHODS

In this study, 19-day-old male CD1 mice were euthanized and parallel craniotomies made through the parietal and frontal calvaria, 2 mm to either side of the sagittal suture, with care taken to preserve the underlying dura mater. Organs grown in vitro in a defined medium were transfected with transforming growth factor-beta1-specific Accell-modified siRNA followed by RNA isolation and quantitative polymerase chain reaction analysis.

RESULTS

Transfection of a calvarial organ with transforming growth factor-beta1-specific Accell-modified siRNA effectively knocks down the mRNA level.

CONCLUSIONS

Observations from this study indicate that in an in vitro calvarial organ culture system, a specific, efficient, and durable RNA interference activity can be achieved when Accell-modified siRNA is used. In addition to bypassing the need for toxic lipid carriers, the modifications introduced in Accell-modified siRNAs make it more stable and less off-target. This technique can potentially be used for in vivo studies once the initial effect of gene-specific siRNA on in vitro suture fusion has been determined.

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.

Cranial Suture Response to Stress: Expression Patterns of Noggin and Runx2

BACKGROUND

Current theory on normal cranial suture fusion entrusts the dura with the regulatory role. Studies suggest that the dura responds to stress with changes in gene expression. Noggin (bone morphogenetic protein inhibitor) expression is decreased in normal (rat and mouse) cranial suture fusion, but its role in craniosynostosis and the response to stress has not been studied.

METHODS

Posterior frontal (fusing) and sagittal (patent) rat cranial sutures were held static, oscillated, or distracted for 10 days in an organ culture microdistraction device beginning at 5 days of age (n = 30 sutures, or 10 sutures per group). The percentage of fusion equaled the score received for bony closure. Noggin, Runx2, and alkaline phosphatase expression was localized by immunohistochemistry for all groups.

RESULTS

Both the posterior frontal and sagittal sutures demonstrated a significant (p < 0.05) increase in fusion percentage with oscillation relative to the static control. Noggin was not expressed in the fusing posterior frontal suture but was expressed in the normally patent sagittal suture. Conversely, Runx2 was expressed in the posterior frontal suture but not in the sagittal suture. However, when a mechanical stress was applied, both the posterior frontal and sagittal sutures expressed Runx2 but not Noggin, as in the static fusing suture.

CONCLUSIONS

The application of mechanical stress to cranial sutures results in fusion of both the posterior frontal suture and the normally patent sagittal suture. Runx2 is expressed but Noggin is not expressed. Thus, mechanical stress influences sutural fusion and may play a role in craniosynostosis.

Intracranial physiological calcifications in adults on computed tomography in Tabriz, Iran

Intracranial physiological calcifications are unaccompanied by any evidence of disease and have no demonstrable pathological cause. They are often due to calcium and sometimes iron deposition in the blood vessels of different structures of the brain. Computed tomography (CT) is the most sensitive means of detection of these calcifications. The aim of this study was the assessment of intracranial physiological calcifications in adults. We studied 1569 cases ranging in age from 15 to 85 in Tabriz Imam Khomeini Hospital, Iran. These patients had a history of head trauma and their CT scan did not show any evidence of pathological findings. The structures evaluated consisted of (A) the pineal gland, (B) the choroid plexus, (C) the habenula, (D) the basal ganglia, (E) the tentorium cerebelli, sagittal sinus and falx cerebri, (F) vessels and (G) lens and other structures which could be calcified. Of the 1569 subjects, 71.0% had pineal calcification, 66.2% had choroid plexus calcification, 20.1% had habenular calcification, 7.3% had tentorium cerebelli, sagittal sinus or falx cerebri calcifications, 6.6% had vascular calcification, 0.8% had basal ganglia calcification and 0.9% had lens and other non-defined calcifications. In general, the frequency of intracranial physiological calcifications was greater in men than in women. All types of calcification increased at older ages except for lens and other non-defined calcifications. We evaluated all the cranial structures and determined percentages for all types of intracranial physiological calcification. These statistics can be used for comparing physiological and pathological intracranial calcifications. Moreover, these statistics may be of interest from the clinical perspective and are potentially of clinical use.

Spread of contrast during L4 and L5 nerve root infiltration under fluoroscopic guidance

BACKGROUND

Lumbar selective nerve root blocks have been performed to establish the origin of lumbar radiculopathy in clinically difficult cases. The diagnostic ability of selective nerve root blocks remains controversial because of concern over potential spread of an injectate onto adjacent structures.

OBJECTIVE

To investigate the spread of different volumes of water-soluble contrast during L4 and L5 selective nerve root blocks.

DESIGN

Retrospective, observational case series.

METHODS

Analysis of medical records and X-ray images obtained during L4 and L5 selective nerve root blocks.

RESULTS

During L4 selective nerve root block 1 ml of contrast spread onto L5 nerve roots in 46.1% of subjects and during L5 nerve root block 1 ml of contrast spread onto S1 nerve root in 57.7%. There was statistically significant difference (p<0.0001) between spread of contrast onto the medially located nerve root in the same lumbar segment and nerve roots in the lumbar segment above.

CONCLUSIONS

Injection of 1 ml of contrast under fluoroscopic guidance does not guarantee selective spread of the contrast around L4 or L5 nerve roots only. There is also spread toward the more medial nerve root in the same spinal segment during L4 and L5 nerve root infiltration. These findings suggest that it is possible to differentiate between L4 and L5 nerve root pathology using a sequential nerve root blocks under fluoroscopic guidance.

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.

The calcitonin gene-related peptide (CGRP) receptor antagonist BIBN4096BS reduces neurogenic increases in dural blood flow

In an in vivo preparation of the exposed rat cranial dura mater electrical field stimulation causes increases in blood flow that are mainly due to the vasodilatory effect of calcitonin gene-related peptide (CGRP) released from meningeal afferents. In this preparation the effect of BIBN4096BS, a non-peptide competitive antagonist of CGRP receptors, was examined. Additionally, in an in vitro preparation of the hemisected rat skull the effect of BIBN4096BS on CGRP release stimulated by activation of meningeal afferents was analysed. Injection of BIBN4096BS at cumulative doses of 300 microg/kg and 900 microg/kg caused dose-dependent inhibition of the electrically evoked blood flow increases. The basal blood flow and vital parameters were not significantly changed by any dose. In the hemisected skull BIBN4096BS at 10(-6) M did not alter the CGRP release evoked by depolarizing K(+) concentrations or antidromic electrical stimulation of the trigeminal ganglion. We conclude that neurogenic increases in dural blood flow are reduced by BIBN4096BS without changing basal vascular parameters. This peripheral effect may be important with regard to CGRP receptor inhibition as an antimigraine strategy.

Evaluation of the anatomic effect of physical therapy exercises for mobilization of lumbar spinal nerves and the dura mater in dogs

OBJECTIVE

To adapt and standardize neural tissue mobilization exercises, quantify nerve root movement, and assess the anatomic effects of lumbar spinal nerve and dural mobilization in dogs.

ANIMALS

15 canine cadavers.

PROCEDURES

5 cadavers were used in the preliminary part of the study to adapt 3 neural tissue mobilization physical therapy exercises to canine anatomy. In the other 10 cadavers, the L4 to L7 nerve roots and the dura at the level of T13 and L1 were isolated and marked. Movements during the physical therapy exercises were standardized by means of goniometric control. Movement of the nerve roots in response to each exercise was digitally measured. The effects of body weight and crownrump length on the distance of nerve root movement achieved during each exercise were also assessed. Each exercise was divided into 4 steps, and the overall distance of neural movement achieved was compared with distances achieved between steps.

RESULTS

Neural tissue mobilization exercises elicited visible and measurable movement of nerve roots L4 to L7 and of the dura at T13 and L1 in all cadavers.

CONCLUSIONS AND CLINICAL RELEVANCE

The physical therapy exercises evaluated had measurable effects on nerve roots L4 to L7 and the dura mater in the T13 and L1 segments. These exercises should be evaluated in clinical trials to validate their efficacy as primary treatments or ancillary postsurgical therapy in dogs with disorders of the thoracolumbar and lumbosacral segments of the vertebral column.

Combined direct anastomosis and encephaloduroarteriogaleosynangiosis using inverted superficial temporal artery–galeal flap and superficial temporal artery–galeal pedicle in adult moyamoya disease

BACKGROUND

We evaluated the efficacy of combined STA-MCA anastomosis and EDAGS using inverted STAGF and STAGP for the treatment of adult MMD.

METHODS

This study included 8 patients with nonhemorrhagic MMD. There were 6 women and 2 men who were between 23 and 62 years old (mean = 37.8 years) in the sample. The combined surgery was performed on 12 sides in the 8 patients. The surgical results were assessed for clinical outcome, angiographic revascularization, and hemodynamic change on HMPAO brain SPECT. The follow-up period ranged from 6 to 62 months (mean = 27 months).

RESULTS

Clinical symptoms and signs were improved or stabilized, and the extent of revascularization evident on external carotid angiograms was excellent in all 8 patients. The CBF on HMPAO SPECT also improved in all 12 sides that were operated on with the combined surgery, except for the preexisting infarcted area, on the basal as well as Diamox stimulation studies. One patient had a transient speech disturbance after surgery, and another patient had delayed wound healing.

CONCLUSIONS

The combined STA-MCA anastomosis and EDAGS using inverted STAGF/P seems to be one of the most effective surgical modalities for the treatment of nonhemorrhagic MMD in adults.

N-Methyl-D-Aspartate (NMDA) and non-NMDA receptor antagonists suppress the superior sagittal sinus-evoked activity of C1 spinal neurons responding to tooth pulp electrical stimulation in rats

The aim of the present study was to determine whether there is a convergence of inputs from tooth pulp (TP) and the superior sagittal sinus (SSS) on rat C1 spinal neurons, and to examine the effects of iontophoretically applied N-methyl-D: -aspartate (NMDA) and non-NMDA receptor antagonists on the SSS-evoked activity of C1 neurons. Extracellular single unit-recordings were made from 20 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal, using a multibarrel electrode in pentobarbital-anesthetized rats. Ninety percent of C1 neurons (18/20) responding to TP stimulation also responded to the SSS stimulation. These neurons were considered to be SSS-afferent inputs from Adelta-fibers (5.8 +/- 0.6 m/s; n = 18), based on the calculation of nerve conduction velocity. After the iontophoretic application (30, 50, and 70 nA) of an NMDA receptor blocker (5R-10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cycloheptene-5,10-imine hydrogen maleate (MK801) or a non-NMDA receptor blocker (6-cyano-7-nitroquinoxaline-2,3-dione) (CNQX), the mean number of spikes responding to the SSS stimulation significantly decreased (30, 50, and 70 nA; P < 0.05). These results suggest that there is a convergence of inputs from SSS and TP afferents on C1 neurons; it is possible that both NMDA and non-NMDA receptors located on C1 neurons may be targets for the treatment of the trigeminal referred pain associated with migraine.

Cortical cooling induces conditioned consumption reduction in male rats

Previous studies have shown that male rats acquire a conditioned reduction in consumption of a sucrose solution when consumption of that taste solution is followed by cooling the caudate putamen. Because the shaft of the cold probe was not insulated, this cooling also included the cortex and meninges overlying the caudate putamen. When cooling the meninges was eliminated as a factor, the conditioned consumption reduction was weaker but it was not abolished. This suggests that meninges cooling contribute to the conditioned consumption reduction induced when all three structures are cooled, but it is not sufficient. Five experiments were designed to determine whether cooling the cortex also contributes. In the first experiment, the temperature of the cortex and meninges overlying the caudate putamen was measured during cooling. In the following three experiments the ability of male rats to acquire a conditioned consumption reduction was determined after pairing a sucrose solution with cooling the cortex and meninges overlying the caudate putamen, cooling the cortex with and without cooling the dura meninges membrane, and cooling the cortex with and without cooling the entire meninges. When the cortex was cooled without cooling the caudate putamen, dura, or entire meninges, a conditioned consumption reduction was acquired. The last experiment demonstrated that contingent pairing of sucrose and cortical cooling was required to obtain consumption reduction. These results clearly indicate that cortical cooling contributes to the acquisition of conditioned consumption reduction induced when the caudate putamen and overlying cortex and meninges are cooled. Two hypotheses are suggested to account for the ability of neural cooling to act as an unconditioned stimulus in the conditioned consumption reduction paradigm: (1) neuronal inactivation produces physiological changes that can serve as unconditioned stimuli and (2) cooling itself produces physiological changes that can serve as unconditioned stimuli.

Age-dependent residual tensile strains are present in the dura mater of rats

The objectives of this study were to determine whether residual tensile strains exist in the dura mater of mammals in vivo, and whether the strains are age-dependent. We made incisions in the parietal dura mater of immature and mature rats, and measured the retraction of the dura mater from each incision. We then used a finite-element model to calculate the strain present in the parietal dura mater of each rat. We found that age-dependent residual tensile strains are present in the dura mater of rats. The mean average residual strain of the immature rats was significantly larger than that of the mature rats (4.96+/-1.54% (s.d.) versus 0.39+/-0.13%, p<0.0001), with the mean strain calculated in the mature rats of the order of the minimum measurement that could be made using our experimental approach. In addition, in the immature rats mean residual strain in the longitudinal direction was significantly larger than mean residual strain in the transverse direction (6.11+/-3.62% versus 3.82+/-2.64%, p=0.0218). Our findings show that age-dependent residual tensile strains exist in the dura mater of rats. We speculate that these strains may reflect the rate and direction of cranial growth and may also influence cranial healing.

Simulation of intra-orbital optic nerve electrical stimulation

In blind subjects who still have functional retinal ganglion cells, electrical stimuli applied to the optic nerve can produce localised visual sensations. This has been demonstrated with an intracranially implanted self-sizing spiral cuff electrode, but, to avoid skull opening, intra-orbital cuff implantation is now considered. In its orbital segment, the optic nerve is surrounded by subarachnoidal cerebrospinal fluid (CSF) and dura mater. Dura mater is a tough fibrous tissue that can impede electrical stimulation. In the study, the issue of whether or not to remove the dura mater at the implantation site was addressed using simulation on numerical models. Several volume conductor models were built representing, respectively: the cuff implanted directly around the nerve; the cuff over the nerve after connective tissue encapsulated the implant; and the cuff electrode placed around the dura mater. Stimulation-induced electric potential fields were computed for these configurations using a full 3D finite elements software. Responses of fibres within the nerve were computed. A large range of dural conductivities and several CSF thicknesses were considered. In all simulated conditions, the presence of dura mater around a layer of CSF increased excitation thresholds. Selectivity performance also decreased, but was found to be independent of the CSF thickness. However, simulations showed that, if the diameter of the cuff electrode is adapted to the target nerve, the injected charge associated with activation is limited within a reasonable range. Electrical stimulation of the optic nerve with a cuff electrode implanted around the dura mater should therefore be feasible.

Morphological Study of the Spinal Canal Content for Subarachnoid Endoscopy

STUDY DESIGN AND OBJECTIVE

This study was designed to examine the morphology of the spinal dural sac and contents, using magnetic resonance imaging in order to define the inner geometrical dimensions that confine the manoeuvre of an endoscope inserted in the lumbar region and along the thoracic and cervical spine.

BACKGROUND

The morphology of the spine has been studied since the development of myelography. However, most studies have measured the diameters of the spinal cord only, not the size of the subarachnoid space. In addition, the few studies available on the subarachnoid space have focused on the cervical spine, leaving a near-complete dearth of data on the subarachnoid space dimensions along the thoracic spine.

METHODS

Based on MRI images of the spine from 42 patients, the dimensions of the spinal cord, dural sac, and subarachnoid space were measured at mid-vertebral and inter-vertebral disc levels.

RESULTS

It was found that at each selected transverse level, the subarachnoid space tends to be symmetrical on the right and left sides of the cord, and measures 2.5 mm on average. However, the posterior and anterior segments, measured on the mid-sagittal plane, are generally asymmetrical and vary widely in size, ranging from 1 to 5 mm. These measurements match those found in previous studies, where these are available. The coefficient of variance for the dimensions of the subarachnoid space is as high as 42.4%, while that for the dimensions of the spinal cord is 10-15%.

CONCLUSIONS

The findings presented here expand our knowledge of the spinal canal's morphology, and show that an endoscope designed to travel within the subarachnoid space must be smaller than 2.5 mm in diameter.

The nonpeptide calcitonin gene-related peptide receptor antagonist BIBN4096BS lowers the activity of neurons with meningeal input in the rat spinal trigeminal nucleus

Calcitonin gene-related peptide (CGRP) has been suggested to play a major role in the pathogenesis of migraines and other primary headaches. CGRP may be involved in the control of neuronal activity in the spinal trigeminal nucleus (STN), which integrates nociceptive afferent inputs from trigeminal tissues, including intracranial afferents. The activity of STN neurons is thought to reflect the activity of central trigeminal nociceptive pathways causing facial pain and headaches in humans. In a rat model of meningeal nociception, single neuronal activity in the STN was recorded. All units had receptive fields located in the exposed parietal dura mater. Heat and cold stimuli were repetitively applied to the dura in a fixed pattern of ramps and steps. The nonpeptide CGRP receptor antagonist BIBN4096BS was topically applied onto the exposed dura or infused intravenously. BIBN4096BS (300 microg/kg, i.v.) reduced spontaneous activity by approximately 30%, the additional dose of 900 microg/kg intravenously by approximately 50% of the initial activity, whereas saline had no effect. The activity evoked by heat ramps was also reduced after BIBN4096BS (900 microg/kg, i.v.) by approximately 50%. Topical administration of BIBN4096BS (1 mm) did not significantly change the spontaneous neuronal activity within 15 min. We conclude that the endogenous release of CGRP significantly contributes to the maintenance of spontaneous activity in STN neurons. Blockade of CGRP receptors, possibly at central and peripheral sites, may therefore be an effective way to decrease nociceptive transmission. This may offer a new therapeutic strategy for the treatment of facial pain and primary headaches.

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.

Topiramate inhibits trigeminovascular activation: an intravital microscopy study

Activation, or the altered perception of activation, of trigeminal nerves that innervate the cranial vasculature is considered to be a pivotal component of the pathophysiology of acute migraine. Calcitonin gene-related peptide (CGRP) levels are increased during migraine and after trigeminal nerve stimulation in the cat. Both CGRP and nitric oxide (NO) infusion causes headache and delayed migraine in migraineurs. Neurogenic stimulation of a cranial window, CGRP and NO injection all cause meningeal artery dilation in the rat when viewed using intravital microscopy. Topiramate is an antiepileptic drug with established efficacy as a migraine preventive, and has recently been shown to inhibit neurons of the trigeminocervical complex after superior sagittal sinus stimulation. In this study, we used intravital microscopy with neurogenic dural vasodilation, and CGRP- and NO-induced dilation to examine whether intravenous topiramate has effects on the trigeminovascular system. Topiramate was able to attentuate neurogenic dural vasodilation maximally after 15 min by 52% at 30 mg kg(-1) (t(5) = 6.78, n = 6); there was no significant inhibition at 10 mg kg(-1). There was also significant attenuation of the NO-induced dilation maximally after 15 min, at both 10 and 30 mg kg(-1) by 21% (t(6) = 6.09, n = 7) and 41% (t(6) = 5.3, n = 7), respectively. CGRP-induced dilation was not inhibited at either dose of topiramate. The study demonstrates that topiramate is likely to inhibit neurogenic dural vasodilation by inhibiting the release of CGRP from prejunctional trigeminal neurons, thus attenuating the dural vasodilation. Topiramate is not able to act postsynaptically at the blood vessels themselves as the CGRP-induced dilation was not attenuated. The data are consistent with an effect of topiramate on trigeminovascular activation which may form part of its preventive antimigraine mechanisms of action.

Orexin 1 Receptor Activation Attenuates Neurogenic Dural Vasodilation in an Animal Model of Trigeminovascular Nociception

The pathophysiology underlying the pulsating quality of the pain of a migraine attack is not fully understood, although trigeminal vascular afferents containing the sensory neuropeptide calcitonin gene-related peptide (CGRP) must have a role. Antimigraine drugs, such as triptans, serotonin 5-hydroxytryptamine(1B/1D) receptor agonists, reproducibly block neurogenic vasodilation associated with CGRP release. We examined the effects of the hypothalamic neuropeptides orexin A and orexin B on neurogenic dural vasodilation, dissecting out the receptor pharmacology with the novel orexin 1 (OX1) receptor antagonist N-(2-methyl-6-benzoxazolyl)-N''-1,5-naphthyridin-4-yl urea (SB-334867). Electrical stimulation of dural afferents (50-300 microA) resulted in reproducible dural vasodilation of 136 +/- 9%. Orexin A 30 microg kg(-1), but not 3 and 10 microg kg(-1), inhibited the dilation brought about by electrical stimulation over 60 min and maximally after 15 min by 60% (t7= 7.138; P < 0.001; n = 8). This response was reversed by pretreatment with the OX1 receptor antagonist SB-334867. Addition of CGRP(8-37) at the point of maximal effect of orexin A produced a further significant decrease in neurogenic dural vasodilation compared with orexin A only. CGRP administration (1 microg kg(-1)) produced a reproducible dural blood vessel dilation of 145 +/- 7% that was not inhibited by intravenous administration of orexin A (30 microg kg(-1)). Orexin B had no significant effect even at the highest dose. The current study demonstrates that orexin A is able to inhibit neurogenic dural vasodilation via activation of the OX1 receptor, resulting in inhibition of prejunctional release of CGRP from trigeminal neurons.

Properties of neurons in the trigeminal nucleus caudalis responding to noxious dural and facial stimulation

Extracellular single unit recordings were made in the rat trigeminal nucleus caudalis (Vc) from cells with Adelta and C-fibre latency responding to electrical stimulation of the thinned cranium overlying the middle meningeal artery (MMA). The neurons had an ipsilateral facial receptive field (FRF) that mainly extended over areas innervated by the first and second division of the trigeminal nerve but in some cases also included areas innervated by the third division of the trigeminal nerve. No wind-up of either long latency C-fibre or short latency Adelta responses was seen during trains of electrical stimulation. Sensitisation of mechanical stimulation of the FRF could also not be observed at any time during dural stimulation. In contrast, extracellular single unit recordings in the Vc activated by electrical stimulation of the facial skin resulted in a significant wind-up response of long latency response in six of ten cells studied. The facial-elicited wind-up response was significantly enhanced, 18 min after the electrical stimulation protocol was started, indicating that the process of wind-up had generated central excitability. The findings in this study demonstrate a clear difference between the effects of electrical stimulation of cutaneous and non-cutaneous inputs. In the trigeminal system, this has implications for the study of pathways such as those involved in headache, where it is believed that an enhanced dural input to the Vc may generate central sensitisation and partly explain the hyperalgesia and allodynia reported by patients.

Mechanisms behind postspinal headache and brain stem compression following lumbar dural puncture--a physiological approach

BACKGROUND

The cause of postspinal headache and its specific characteristics are unknown, and whether lumbar dural puncture (LP) triggers brain-stem compression in patients with brain oedema is still controversial.

METHODS

Hydrostatic effects of distal opening of the dural sac towards the atmosphere are described and applied to the normal brain and the brain with disrupted BBB. Analogue analyses from previous results using an isolated skeletal muscle enclosed in a rigid shell were applied to the brain in an attempt to simulate and verify the haemodynamic effects of distal opening of the spinal canal.

RESULTS

The theoretical considerations and the experimental results are compatible with the hypothesis that hydrostatic effects of distal opening of the fluid-filled spinal canal may obliterate the normal subdural venous collapse after a change from the horizontal to vertical position, which may be compatible with postural postspinal headache as occurring close to pain-sensitive meningeal regions. The hydrostatic forces may also initiate transcapillary filtration and aggravate oedema when permeability is increased, which may cause a narrower situation in the brain stem region, perhaps aggravated by venous stasis and a Cushing reflex-induced increase in blood pressure. An magnetic resonance imaging (MRI) picture illustrates how this scenario may separate the subdural space into an upper high- and a lower low-pressure cavity, pressing the brain downwards with sagging of the brain. A life-threatening positive feedback situation for brain-stem compression may develop.

CONCLUSION

The present study strongly suggests that postspinal headache and brain-stem compression and other LP-related effects are predictable following LP, without involving CSF leakage, and can be explained by hydrostatic effects triggered by distal opening of the normally closed dural space to the atmosphere.

Effects on intracranial pressure of dural puncture in supine and head-elevated positions. A study on the cat

BACKGROUND

Lumbar dural puncture may reduce intracranial pressure (ICP) due to a hydrostatic pressure gradient created by distal opening of the spinal fluid column towards the atmosphere. The magnitude of the reduction in hydrostatic force on the brain should depend on the vertical distance between the brain and the dural opening, and thus will increase by head elevation. No studies have analyzed ICP after dural puncture in supine and upright positions.

METHODS

This study on the cat records ICP, mean arterial pressure, and central venous pressure before and after dural puncture in supine and head-elevated positions. The dural puncture was performed at a level corresponding to the lumbar region.

RESULTS

Initially ICP was 10.9 +/- 1.9 mmHg (mean +/- SD), which decreased to 5.1 +/- 2.0 mmHg after 24.5 cm (18 mmHg) of head elevation (n = 7). Intracranial pressure decreased to 5.2 +/-3.5 mmHg following dural puncture in the supine position and to -11.3 +/- 4.2 mmHg after the head elevation (n = 7). Active drainage of CSF fluid in the supine position in a volume similar to that spontaneously drained after head elevation reduced ICP by 2.0 +/- 0.5 mmHg (n = 3).

CONCLUSIONS

The results show that a significant ICP reduction may occur following opening of the spinal canal. The reduction can be explained more by hydrostatic forces than by loss of CSF; also explaining why it is more significant when upright than supine. The decrease in ICP increases transvascular pressure, which may induce the disappearance of the normally present subdural venous collapse with an increase in venous blood volume.

The falcine trigeminocardiac reflex: case report and review of the literature

BACKGROUND

Trigeminocardiac reflex (TCR), the reproducible hypotension and bradycardia upon stimulation of the trigeminal nerve, has been reported during craniofacial surgery and during surgery within the cerebellopontine angle, petrosal sinus, orbit, and trigeminal ganglion. Whereas the falx cerebri is known to be innervated by the nervus tentorii, a recurrent branch of V1, there have been no reports to date of this response upon mechanical stimulation of the falx.

CASE DESCRIPTION

We report a case of immediate, reproducible, and reflexive response of asystole upon stimulation of the falx cerebri during operative resection of a parafalcine meningioma in a 53-year-old woman. Upon recognition of the reproducible relationship between falcine stimulation and increased vagal tone, the patient was given glycopyrrolate in an effort to block cholinergic hyperactivity. After glycopyrrolate was given, no further dysrhythmias occurred.

CONCLUSION

In this patient, mechanical stimulation of the falx likely resulted in the hyperactivity of the trigeminal ganglion, thereby triggering TCR. The dorsal region of the spinal trigeminal tract includes neurons from hypoglossal and vagus nerves, and projections have been seen between the vagus and trigeminal nuclei. The vagus provides parasympathetic innervation to the heart, vascular smooth muscle, and abdominal viscera. Vagal stimulation via these connections after trigeminal nerve activation likely accounts for the reflexive response of asystole seen in this patient. This is confirmed by the observation that the reflex was inhibited by the anticholinergic effects of glycopyrrolate. Awareness of TCR allows for early detection and appropriate treatment.

Repair of pig dura in vivo using temperature controlled CO2 laser soldering

BACKGROUND AND OBJECTIVES

The purpose of this study was to demonstrate that laser soldering might be successfully used for closing holes or cuts in the dura layer, which encapsulates the brain.

STUDY DESIGN/MATERIALS AND METHODS

A temperature controlled fiberoptic CO(2) laser system and albumin solder were used for spot soldering of fascia patches to holes in the dura of farm pigs, in vitro and in vivo.

RESULTS

The mean burst pressure of the soldered patches in the in vitro experiments was 190 +/- 88 mm Hg-significantly higher than typical maximum CSF pressure of 15 mm Hg. In the in vivo experiments the pigs showed no postoperative complications. Histopathological studies exhibited an accepted level of inflammatory reaction and showed no thermal damage to the underlying brain tissue.

CONCLUSIONS

It has been clearly demonstrated that temperature controlled laser soldering is a very useful technique for the repair of the dura. It provides significant advantages over standard closure techniques: it is easy to apply, the bond is strong and watertight and the procedure is likely to be much faster than suturing. This research work will lead to clinical trials.

Multimodal integration of EEG, MEG and fMRI data for the solution of the neuroimage puzzle

In this paper, advanced methods for the modeling of human cortical activity from combined high-resolution electroencephalography (EEG), magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) data are presented. These methods include a subject's multicompartment head model (scalp, skull, dura mater, cortex) constructed from magnetic resonance images, multidipole source model and regularized linear inverse source estimates of cortical current density. Determination of the priors in the resolution of the linear inverse problem was performed with the use of information from the hemodynamic responses of the cortical areas as revealed by block-designed (strength of activated voxels) fMRI. Examples of the application of these methods to the estimation of the time varying cortical current density activity in selected region of interest (ROI) are presented for movement-related high-resolution EEG data.

Vanilloid type 1 receptors (VR1) on trigeminal sensory nerve fibres play a minor role in neurogenic dural vasodilatation, and are involved in capsaicin-induced dural dilation

Capsaicin, the active substance in chilli peppers, activates the vanilloid type 1 receptor (VR1) rather than the vanilloid-like receptor (VRL1) in the trigeminal ganglion and nucleus of small and medium C- and Adelta-fibres. Capsaicin induces calcitonin gene-related peptide (CGRP) release when VR1 receptors are activated, and this can be reversed by both the VR1 receptor antagonist capsazepine and the CGRP blocker alphaCGRP8-37 in vitro. In this study we used intravital microscopy to look at the possible role of the VR1 receptor in the trigeminovascular system in producing dilation of dural blood vessels. Capsazepine (3 mg kg-1) was given to study the effect of the VR1 receptor in dural vessel dilation produced by either electrical stimulation, CGRP (1 microg x kg-1) or capsaicin (7 microg x kg-1) bolus injection. We also looked at the effect of the CGRP blocker alphaCGRP8-37 (300 microg x kg-1) on capsaicin-induced dilation so that we could see if the results found in vitro could also be found in vivo. Electrical stimulation of the dura mater produced a robust vasodilator response between 130 and 137% of baseline diameter that was no different across four repeat stimuli (F3,18=0.6, P=0.61). CGRP similarly produced a dilatation of 99-111% that was no different across four baseline infusions (F3,15=2.4, P=0.113). Capsaicin also produced a consistent dilation of between 112 and 120% of baseline across three injections (F2,10=0.6, P=0.567). Capsazepine did not inhibit the dilation brought about by either electrical stimulation or CGRP injection, while it was able to inhibit the dilation brought about by capsaicin (t5=3.4, P<0.05). AlphaCGRP8-37 also inhibited the capsaicin-induced dilation (t5=7.4, P<0.05) probably inhibiting the action of released CGRP at the CGRP receptor. The study demonstrates that capsaicin can repeatedly induce dural vessel dilation in vivo, presumably through inducing CGRP release from trigeminal sensory nerve fibres, while C-fibres may have been desensitised. The data imply that the VR1 receptor plays only a minor role in trigeminovascular-induced dural vessel dilation.

Hyperosmotic chemical agent's effect on in vivo cerebral blood flow revealed by laser speckle

We investigated the influence of a hyperosmotic agent (glycerol) on the normal physiological function of tissue by applying the glycerol in vitro and in vivo to rabbit dura mater to assess the changes in the tissue's optical properties. We used a laser speckle imaging technique to study the effect of epidurally applied glycerol on resting cerebral blood flow (CBF). Our results showed that resting CBF decreased as the transparency of the dura mater increased. The challenges for the design of an optical clearing technique were not only the clearing effects and the duration of the action of the chemical agents but also the influence of the glycerol on the tissue's normal physiological function.

Modulation of Dural Nociceptor Mechanosensitivity by the Nitric Oxide-Cyclic GMP Signaling Cascade

The role of the nitric oxide (NO)-cGMP signaling cascade in modulation of peripheral nociception is controversial. Although behavioral studies have suggested both pro- and anti-nociceptive effects, little is known about the direct action of this signaling cascade on primary afferent nociceptive neurons that mediate these behaviors. Here, using single-unit recordings, we examined the direct effect of NO-cGMP signaling on spontaneous activity and mechanical responses of nociceptive afferents that innervate the dura mater. We found that the NO donor sodium nitroprusside (SNP), when applied topically to the neuronal receptive field, induced both sensitization and inhibition of the mechanical responses, albeit in different populations of neurons, which could be distinguished based on their baseline mechanical thresholds. SNP, however, did not change the level of spontaneous activity. Administration of the cGMP analogue 8-pCPT-cGMP mimicked only the inhibitory effect. When SNP was co-applied with either an inhibitor of guanylyl cyclase or a cGMP blocker, sensitization never occurred, and the inhibitory effect of SNP could also be blocked. Our findings suggest that NO can either increase or decrease the mechanical responsiveness of nociceptors and that its action might depend, in part, on the baseline level of neuronal excitability. Our results also implicate cGMP in mediating the inhibitory effect of NO.

Dopamine receptors in the human dura mater

Dopamine receptors (Dar) were studied as a component of the nervous dopaminergic system in the human dura mater. Dar were stained in several dural zones (vascular, perivascular, intervascular) in different regions (basal, calvarial, tentorial, occipital, frontal, parietal, temporal) of the cranial meninges. Specimens of human dura mater were harvested from autopsies of 10 elderly male subjects (age range, 60-75 years). Dar were labeled with specific (H3) markers, studied with radiobinding techniques (including liquid scintillation), stained for light microscope autoradiography, and measured by means of quantitative analysis of images. All results were evaluated with statistical analysis to identify significant results. More dural Dar were found in the basal region than in the calvarial one. Moreover, Dar are more abundant in the vascular and perivascular dural zone than in the intervascular one. The vascular distribution of Dar seemed to indicate that Dar play a role in the control of meningeal blood vessels. The location and distribution of D1 and D2 receptors in the human cranial dura mater confirmed the presence of a dopaminergic system, which could play an important role in controlling blood flow and/or other functions of meningeal membranes.