The influence of fixation and cryopreservation of cerebrospinal fluid on antigen expression and cell percentages by flow cytometric analysis.

The pauci-cellular nature of cerebrospinal (CSF), particularly ventricular CSF, and the rapid cell death following sampling, incumbers the use of flow cytometric analysis of these samples in the investigation of central nervous system (CNS) pathologies. Developing a method that allows long-term storage and batched analysis of CSF samples without compromising cell integrity is highly desirable in clinical research, given that CSF is often sampled after hours creating logistical difficulties for fresh processing. We examined percentages and relative proportion of peripheral and brain-derived immune cells in cryopreserved and transfix-treated CSF, compared to freshly processed CSF. Cell proportions were more comparable between Fresh and Cryopreserved CSF (mean of differences = 3.19), than between fresh and transfix-treated CSF (mean of differences = 14.82). No significant differences in cell percentages were observed in fresh versus cryopreserved CSF; however significantly lower cell percentages were observed in transfix-treated CSF compared to Fresh CSF [(CD11b++ (p = 0.01), CD4+ (p = 0.001), CD8+ (p = 0.007), NK cells (p = 0.04), as well as CD69+ activation marker (p = 0.001)]. Furthermore, loss of marker expression of various lymphocyte sub-populations were observed in transfix-treated CSF. Cryopreservation is a feasible option for long-term storage of ventricular CSF and allows accurate immunophenotyping of peripheral and brain-derived cell populations by flow cytometry.

Cell type-specific gene expression dynamics during human brain maturation.

The human brain undergoes protracted post-natal maturation, guided by dynamic changes in gene expression. To date, studies exploring these processes have used bulk tissue analyses, which mask cell type-specific gene expression dynamics. Here, using single nucleus (sn)RNA-Sseq on temporal lobe tissue, including samples of African ancestry, we build a joint paediatric and adult atlas of 54 cell subtypes, which we verify with spatial transcriptomics. We explore the differences in cell states between paediatric and adult cell types, revealing the genes and pathways that change during brain maturation. Our results highlight excitatory neuron subtypes, including the LTK and FREM subtypes, that show elevated expression of genes associated with cognition and synaptic plasticity in paediatric tissue. The new resources we present here improve our understanding of the brain during a critical period of its development and contribute to global efforts to build an inclusive cell map of the brain.

Cerebrovascular Pressure Reactivity Has a Strong and Independent Association With Outcome in Children With Severe Traumatic Brain Injury.

OBJECTIVES: To examine cerebrovascular pressure reactivity index (PRx) in a large cohort of children with severe traumatic brain injury (sTBI) in association with physiologic variables and outcome. DESIGN: Retrospective observational cohort study. SETTING: Red Cross War Memorial Children's Hospital in Cape Town, South Africa. PATIENTS: Pediatric (≤ 14 yr old) sTBI patients with intracranial pressure (ICP) monitoring (postresuscitation Glasgow Coma Score [Glasgow Coma Scale (GCS)] of ≤ 8). MEASUREMENTS AND MAIN RESULTS: Data were analyzed from ICM+ files sampled at 100Hz. PRx (a mathematical indicator of pressure reactivity) was calculated as a moving correlation coefficient between ICP and mean arterial pressure (MAP) as previously described. Associations between PRx, age, GCS, ICP, MAP, and cerebral perfusion pressure (CPP) were examined with summary measures and correlation analysis using high-frequency data. Associations between PRx and mortality/outcome were examined with multivariable logistic regression analysis and the prognostic ability of PRx with receiver operating characteristic (ROCs) curves. The dataset included over 1.7 million minutes (28,634 hr) of MAP and ICP data in 196 children. The series mortality was 10.7% (21/196), and unfavorable outcome 29.6% (58/196). PRx had a moderate positive correlation with ICP ( r = 0.44; p < 0.001), a moderate negative correlation with CPP ( r = -0.43; p < 0.001), and a weak negative correlation with MAP ( r = -0.21; p = 0.004). PRx was consistently higher in patients with poor outcome and had a strong, independent association with mortality (ROC area under the curve = 0.91). A PRx threshold of 0.25 showed the best predictive ability for mortality. CONCLUSIONS: This is the largest cohort of children with PRx analysis of cerebrovascular reactivity to date. PRx had a strong association with outcome that was independent of ICP, CPP, GCS, and age. The data suggest that impaired autoregulation is an independent factor associated with poor outcome and may be useful in directing clinical care.

Increased Light Extraction of Thin-Film Flip-Chip UVB LEDs by Surface Texturing.

Ultraviolet light-emitting diodes (LEDs) suffer from a low wall-plug efficiency, which is to a large extent limited by the poor light extraction efficiency (LEE). A thin-film flip-chip (TFFC) design with a roughened N-polar AlGaN surface can substantially improve this. We here demonstrate an enabling technology to realize TFFC LEDs emitting in the UVB range (280-320 nm), which includes standard LED processing in combination with electrochemical etching to remove the substrate. The integration of the electrochemical etching is achieved by epitaxial sacrificial and etch block layers in combination with encapsulation of the LED. The LEE was enhanced by around 25% when the N-polar AlGaN side of the TFFC LEDs was chemically roughened, reaching an external quantum efficiency of 2.25%. By further optimizing the surface structure, our ray-tracing simulations predict a higher LEE from the TFFC LEDs than flip-chip LEDs and a resulting higher wall-plug efficiency.

Population Pharmacokinetic Analysis of Rifampicin in Plasma, Cerebrospinal Fluid, and Brain Extracellular Fluid in South African Children with Tuberculous Meningitis.

Limited knowledge is available on the pharmacokinetics of rifampicin in children with tuberculous meningitis (TBM) and its penetration into brain tissue, which is the site of infection. In this analysis, we characterize the distribution of rifampicin in cerebrospinal fluid (CSF), lumbar (LCSF) and ventricular (VCSF), and brain extracellular fluid (ECF). Children with TBM were included in this pharmacokinetic analysis. Sparse plasma, LCSF, and VCSF samples were collected opportunistically, as clinically indicated. Brain ECF was sampled using microdialysis (MD). Rifampicin was quantified with liquid chromatography with tandem mass spectrometry in all samples, and 25-desacetyl rifampicin in the plasma samples. The data were interpreted with nonlinear mixed-effects modeling, with the CSF and brain ECF modeled as "effect compartments." Data were available from 61 children, with median (min-max) age of 2 (0.3 to 10) years and weight of 11.0 (4.8 to 49.0) kg. A one-compartment model for parent and metabolite with first-order absorption and elimination via saturable hepatic clearance described the data well. Allometric scaling, maturation, and auto-induction of clearance were included. The pseudopartition coefficient between plasma and LCSF/VCSF was ~5%, while the value for ECF was only ~0.5%, possibly reflecting low recovery of rifampicin using MD. The equilibration half-life between plasma and LCSF/VCSF was ~4 h and between plasma and ECF ~2 h. Our study confirms previous reports showing that rifampicin concentrations in the LCSF are lower than in plasma and provides novel knowledge about rifampicin in the VCSF and the brain tissue. Despite MD being semiquantitative because the relative recovery cannot be quantified, our study presents a proof-of-concept that rifampicin reaches the brain tissue and that MD is an attractive technique to study site-of-disease pharmacokinetics in TBM.

Balamuthia mandrillaris Granulomatous Amoebic Encephalitis: The First African Experience.

We report the first case of Balamuthia mandrillaris granulomatous amoebic encephalitis definitively acquired in Africa. Our case emphasizes initial nonspecific dermatological features, delays in confirmation of the diagnosis, difficulties accessing recommended medication, and uncertainty about optimal treatment of a disease with a frequently fatal outcome.

Quantification of Trace-Level Silicon Doping in Al x Ga1-xN Films Using Wavelength-Dispersive X-Ray Microanalysis.

Wavelength-dispersive X-ray (WDX) spectroscopy was used to measure silicon atom concentrations in the range 35-100 ppm [corresponding to (3-9) × 1018 cm-3] in doped AlxGa1-xN films using an electron probe microanalyser also equipped with a cathodoluminescence (CL) spectrometer. Doping with Si is the usual way to produce the n-type conducting layers that are critical in GaN- and AlxGa1-xN-based devices such as LEDs and laser diodes. Previously, we have shown excellent agreement for Mg dopant concentrations in p-GaN measured by WDX with values from the more widely used technique of secondary ion mass spectrometry (SIMS). However, a discrepancy between these methods has been reported when quantifying the n-type dopant, silicon. We identify the cause of discrepancy as inherent sample contamination and propose a way to correct this using a calibration relation. This new approach, using a method combining data derived from SIMS measurements on both GaN and AlxGa1-xN samples, provides the means to measure the Si content in these samples with account taken of variations in the ZAF corrections. This method presents a cost-effective and time-saving way to measure the Si doping and can also benefit from simultaneously measuring other signals, such as CL and electron channeling contrast imaging.

A 310 nm Optically Pumped AlGaN Vertical-Cavity Surface-Emitting Laser.

Ultraviolet light is essential for disinfection, fluorescence excitation, curing, and medical treatment. An ultraviolet light source with the small footprint and excellent optical characteristics of vertical-cavity surface-emitting lasers (VCSELs) may enable new applications in all these areas. Until now, there have only been a few demonstrations of ultraviolet-emitting VCSELs, mainly optically pumped, and all with low Al-content AlGaN cavities and emission near the bandgap of GaN (360 nm). Here, we demonstrate an optically pumped VCSEL emitting in the UVB spectrum (280-320 nm) at room temperature, having an Al0.60Ga0.40N cavity between two dielectric distributed Bragg reflectors. The double dielectric distributed Bragg reflector design was realized by substrate removal using electrochemical etching. Our method is further extendable to even shorter wavelengths, which would establish a technology that enables VCSEL emission from UVA (320-400 nm) to UVC (<280 nm).

Hydrocephalus in Low and Middle-Income Countries - Progress and Challenges.

Hydrocephalus remains one of the most commonly treated neurosurgical conditions worldwide. Caring for patients with hydrocephalus requires infrastructure and political support and initiative; these are often difficult to obtain in low- and middle-income countries (LMICs). Some innovations that have arisen in LMICs have traveled up the financial gradient to high-income countries, such as the combination of endoscopic third ventriculostomy with choroid plexus coagulation to manage hydrocephalus. The development of neuro-endoscopy has played a major role in managing hydrocephalus worldwide; however, LMICs still face specific challenges, such as limited access to shunt hardware, a disproportionately high incidence of post-infectious hydrocephalus, unique microbiological spectra, and often poor access to follow-up care and neuroimaging. This has received increased attention since the Lancet Commission on Global Surgery. The goal of improving access to quality neurosurgical care through various initiatives in LMICs will be discussed in this manuscript. The need for neurosurgeons continues to grow in LMICs, where better access to neurosurgical care, adequate neurosurgical training and political support, and patient education are needed to improve the quality of life for patients with common neurosurgical conditions. Despite these challenges, treating hydrocephalus remains a worthwhile endeavor for many patients.

Management of Spasticity After Traumatic Brain Injury in Children.

Traumatic brain injury is a common cause of disability worldwide. In fact, trauma is the second most common cause of death and disability, still today. Traumatic brain injury affects nearly 475 000 children in the United States alone. Globally it is estimated that nearly 2 million people are affected by traumatic brain injuries every year. The mechanism of injury differs between countries in the developing world, where low velocity injuries and interpersonal violence dominates, and high-income countries where high velocity injuries are more common. Traumatic brain injury is not only associated with acute problems, but patients can suffer from longstanding consequences such as seizures, spasticity, cognitive and social issues, often long after the acute injury has resolved. Spasticity is common after traumatic brain injury in children and up to 38% of patients may develop spasticity in the first 12 months after cerebral injury from stroke or trauma. Management of spasticity in children after traumatic brain injury is often overlooked as there are more pressing issues to attend to in the early phase after injury. By the time the spasticity becomes a priority, often it is too late to make meaningful improvements without reverting to major corrective surgical techniques. There is also very little written on the topic of spasticity management after traumatic brain injury, especially in children. Most of the information we have is derived from stroke research. The focus of management strategies are largely medication use, physical therapy, and other physical rehabilitative strategies, with surgical management techniques used for long-term refractory cases only. With this manuscript, the authors aim to review our current understanding of the pathophysiology and management options, as well as prevention, of spasticity after traumatic brain injury in children.

Displacement Talbot lithography for nano-engineering of III-nitride materials.

Nano-engineering III-nitride semiconductors offers a route to further control the optoelectronic properties, enabling novel functionalities and applications. Although a variety of lithography techniques are currently employed to nano-engineer these materials, the scalability and cost of the fabrication process can be an obstacle for large-scale manufacturing. In this paper, we report on the use of a fast, robust and flexible emerging patterning technique called Displacement Talbot lithography (DTL), to successfully nano-engineer III-nitride materials. DTL, along with its novel and unique combination with a lateral planar displacement (D2TL), allow the fabrication of a variety of periodic nanopatterns with a broad range of filling factors such as nanoholes, nanodots, nanorings and nanolines; all these features being achievable from one single mask. To illustrate the enormous possibilities opened by DTL/D2TL, dielectric and metal masks with a number of nanopatterns have been generated, allowing for the selective area growth of InGaN/GaN core-shell nanorods, the top-down plasma etching of III-nitride nanostructures, the top-down sublimation of GaN nanostructures, the hybrid top-down/bottom-up growth of AlN nanorods and GaN nanotubes, and the fabrication of nanopatterned sapphire substrates for AlN growth. Compared with their planar counterparts, these 3D nanostructures enable the reduction or filtering of structural defects and/or the enhancement of the light extraction, therefore improving the efficiency of the final device. These results, achieved on a wafer scale via DTL and upscalable to larger surfaces, have the potential to unlock the manufacturing of nano-engineered III-nitride materials.

The Evolution of Selective Dorsal Rhizotomy for the Management of Spasticity.

Selective dorsal rhizotomy is a key technique in the surgical management of spasticity in patients with cerebral palsy. The technique evolved from the late 1800s when pioneers like Dana and Abbe performed dorsal rhizotomy in their treatment of refractory pain. These surgeons noted a reduction in muscle tone associated with the operation. When Sherrington then published his Nobel prize-winning work on the corticospinal tract and its role in the neuromuscular system in the 1890s, the course was set for modifying spasticity by aiming surgery at the dorsal roots. This procedure underwent multiple modifications through the next century and today it is, arguably, the most commonly performed operation to treat cerebral palsy children with spasticity. Selective dorsal rhizotomy is a technique that still teaches us a great deal about neurophysiology on a daily basis and it is thanks to the pioneers, described in this article, that we have this tool in our armamentarium.