Method for optimizing imaging parameters to record neuronal and cellular activity at depth with bioluminescence.

Significance: Optical imaging has accelerated neuroscience in recent years. Genetically encoded fluorescent activity sensors of calcium, neurotransmitters, and voltage are commonly used for optical recording of neuronal activity. However, fluorescence imaging is limited to superficial regions for in vivo activity imaging, due to photon scattering and absorbance. Bioluminescence imaging offers a promising alternative for achieving activity imaging in deeper brain regions without hardware implanted within the brain. Bioluminescent reporters can be genetically encoded and produce photons without external excitation. The use of enzymatic photon production also enables prolonged imaging sessions without the risk of photobleaching or phototoxicity, making bioluminescence suitable for non-invasive imaging of deep neuronal populations. Aim: To facilitate the adoption of bioluminescent activity imaging, we sought to develop a low cost, simple in vitro method that simulates in vivo conditions to optimize imaging parameters for determining optimal exposure times and optical hardware configurations to determine what frame rates can be captured with an individual lab's imaging hardware with sufficient signal-to-noise ratios without the use of animals prior to starting an in vivo experiment. Approach: We developed an assay for modeling in vivo optical conditions with a brain tissue phantom paired with engineered cells that produce bioluminescence. We then used this assay to limit-test the detection depth versus maximum frame rate for bioluminescence imaging at experimentally relevant tissue depths using off-the-shelf imaging hardware. Results: We developed an assay for modeling in vivo optical conditions with a brain tissue phantom paired with engineered cells that produce bioluminescence. With this method, we demonstrate an effective means for increasing the utility of bioluminescent tools and lowering the barrier to adoption of bioluminescence activity imaging. Conclusions: We demonstrated an improved method for optimizing imaging parameters for activity imaging in vivo with bioluminescent sensors.

Resolving inter-crystal scatter in a light-sharing depth-encoding PET detector.

Objective.Inter-crystal scattering (ICS) in light-sharing positron emission tomography (PET) detectors leads to ambiguity in positioning the initial interaction, which significantly degrades the contrast, quantitative accuracy, and spatial resolution of the resulting image. Here, we attempt to resolve the positioning ambiguity of ICS in a light-sharing depth-encoding detector by exploiting the confined, deterministic light-sharing enabled by the segmented light guide unique to Prism-PET.Approach.We first considered a test case of ICS between two adjacent crystals using an analytical and a neural network approach. The analytical approach used a Bayesian estimation framework constructed from a scatter absorption model-the prior-and a detector response model-the likelihood. A simple neural network was generated for the same scenario, to provide mutual validation for the findings. Finally, we generalized the solution to three-dimensional event positioning that handles all events in the photopeak using a convolutional neural network with unique architecture that separately predicts the identity and depth-of-interaction (DOI) of the crystal containing the first interaction.Main results.The analytical Bayesian method generated an estimation error of 20.5 keV in energy and 3.1 mm in DOI. Further analysis showed that the detector response model was sufficiently robust to achieve adequate performance via maximum likelihood estimation (MLE), without prior information. We then found convergent results using a simple neural network. In the generalized solution using a convolutional neural network, we found crystal identification accuracy of 83% and DOI estimation error of 3.0 mm across all events. Applying this positioning algorithm to simulated data, we demonstrated significant improvements in image quality over the baseline, centroid-based positioning approach, attaining 38.9% improvement in intrinsic spatial resolution and enhanced clarity in hot spots of diameters 0.8 to 2.5 mm.Significance.The accuracy of our findings exceeds those of previous reports in the literature. The Prism-PET light guide, mediating confined and deterministic light-sharing, plays a key role in ICS recovery, as its mathematical embodiment-the detector response model-was the essential driver of accuracy in our results.

Bioluminescent Genetically Encoded Glutamate Indicators for Molecular Imaging of Neuronal Activity.

Genetically encoded optical sensors and advancements in microscopy instrumentation and techniques have revolutionized the scientific toolbox available for probing complex biological processes such as release of specific neurotransmitters. Most genetically encoded optical sensors currently used are based on fluorescence and have been highly successful tools for single-cell imaging in superficial brain regions. However, there remains a need to develop new tools for reporting neuronal activity in vivo within deeper structures without the need for hardware such as lenses or fibers to be implanted within the brain. Our approach to this problem is to replace the fluorescent elements of the existing biosensors with bioluminescent elements. This eliminates the need of external light sources to illuminate the sensor, thus allowing deeper brain regions to be imaged noninvasively. Here, we report the development of the first genetically encoded neurotransmitter indicators based on bioluminescent light emission. These probes were optimized by high-throughput screening of linker libraries. The selected probes exhibit robust changes in light output in response to the extracellular presence of the excitatory neurotransmitter glutamate. We expect this new approach to neurotransmitter indicator design to enable the engineering of specific bioluminescent probes for multiple additional neurotransmitters in the future, ultimately allowing neuroscientists to monitor activity associated with a specific neurotransmitter as it relates to behavior in a variety of neuronal and psychiatric disorders, among many other applications.

Interleaved signal multiplexing readout in depth encoding Prism-PET detectors.

BACKGROUND: Given the large number of readout pixels in clinical positron emission tomography (PET) scanners, signal multiplexing is an indispensable feature to reduce scanner complexity, power consumption, heat output, and cost. PURPOSE: In this paper, we introduce interleaved multiplexing (iMux) scheme that utilizes the characteristic light-sharing pattern of depth-encoding Prism-PET detector modules with single-ended readout. METHODS: In the iMux readout, four anodes from every other silicon photomultiplier (SiPM) pixels across rows and columns, which overlap with four distinct light guides, are connected to the same application-specific integrated circuit (ASIC) channel. The 4-to-1 coupled Prism-PET detector module was used which consisted of a 16 ×  16 array of 1.5 × 1.5 × 20 mm3 lutetium yttrium oxyorthosilicate (LYSO) scintillator crystals coupled to an 8 × 8 array with 3 ×  3 mm2 SiPM pixels. A deep learning-based demultiplexing model was investigated to recover the encoded energy signals. Two different experiments were performed with non-multiplexed and multiplexed readouts to evaluate the spatial, depth of interaction (DOI), and timing resolutions of our proposed iMux scheme. RESULTS: The measured flood histograms, using the decoded energy signals from our deep learning-based demultiplexing architecture, achieved perfect crystal identification of events with negligible decoding error. The average energy, DOI, and timing resolutions were 9.6 ± 1.5%, 2.9 ± 0.9 mm, and 266 ± 19 ps for non-multiplexed readout and 10.3 ± 1.6%, 2.8 ± 0.8 mm, and 311 ± 28 ps for multiplexed readout, respectively. CONCLUSIONS: Our proposed iMux scheme improves on the already cost-effective and high-resolution Prism-PET detector module and provides 16-to-1 crystal-to-readout multiplexing without appreciable performance degradation. Also, only four SiPM pixels are shorted together in the 8 ×  8 array to achieve 4-to-1 pixel-to-readout multiplexing, resulting in lower capacitance per multiplexed channel.

A conformal TOF-DOI Prism-PET prototype scanner for high-resolution quantitative neuroimaging.

BACKGROUND: Positron emission tomography (PET) has had a transformative impact on oncological and neurological applications. However, still much of PET's potential remains untapped with limitations primarily driven by low spatial resolution, which severely hampers accurate quantitative PET imaging via the partial volume effect (PVE). PURPOSE: We present experimental results of a practical and cost-effective ultra-high resolution brain-dedicated PET scanner, using our depth-encoding Prism-PET detectors arranged along a compact and conformal gantry, showing substantial reduction in PVE and accurate radiotracer uptake quantification in small regions. METHODS: The decagon-shaped prototype scanner has a long diameter of 38.5 cm, a short diameter of 29.1 cm, and an axial field-of-view (FOV) of 25.5 mm with a single ring of 40 Prism-PET detector modules. Each module comprises a 16 × 16 array of 1.5 × 1.5 × 20-mm3 lutetium yttrium oxyorthosillicate (LYSO) scintillator crystals coupled 4-to-1 to an 8 × 8 array of silicon photomultiplier (SiPM) pixels on one end and to a prismatoid light guide array on the opposite end. The scanner's performance was evaluated by measuring depth-of-interaction (DOI) resolution, energy resolution, timing resolution, spatial resolution, sensitivity, and image quality of ultra-micro Derenzo and three-dimensional (3D) Hoffman brain phantoms. RESULTS: The full width at half maximum (FWHM) DOI, energy, and timing resolutions of the scanner are 2.85 mm, 12.6%, and 271 ps, respectively. Not considering artifacts due to mechanical misalignment of detector blocks, the intrinsic spatial resolution is 0.89-mm FWHM. Point source images reconstructed with 3D filtered back-projection (FBP) show an average spatial resolution of 1.53-mm FWHM across the entire FOV. The peak absolute sensitivity is 1.2% for an energy window of 400-650 keV. The ultra-micro Derenzo phantom study demonstrates the highest reported spatial resolution performance for a human brain PET scanner with perfect reconstruction of 1.00-mm diameter hot-rods. Reconstructed images of customized Hoffman brain phantoms prove that Prism-PET enables accurate radiotracer uptake quantification in small brain regions (2-3 mm). CONCLUSIONS: Prism-PET will substantially strengthen the utility of quantitative PET in neurology for early diagnosis of neurodegenerative diseases, and in neuro-oncology for improved management of both primary and metastatic brain tumors.

Laminar Flame Speed, Ignition Delay Time, and CO Laser Absorption Measurements of a Gasoline-like Blend of Pentene Isomers.

The combustion properties of a gasoline-like blend of pentene isomers were determined using multiple types of experimental measurements. The representative mixture (Mix A) is composed of 5.7% 1-pentene (1-C5H10), 39.4% 2-pentene (2-C5H10), 12.5% 2-methyl-1-butene (2M1B), and 42.4% 2-methyl-2-butene (2M2B) (% mol). Laminar flame speeds were measured at equivalence ratios of 0.7-1.5 in a constant-volume combustion chamber, and ignition delay times (including both OH* and CH* diagnostics) as well as CO time-history profiles were performed in shock tubes, in highly diluted mixtures (0.995 He/Ar), at a stoichiometric condition for temperatures ranging from 1350 to 1750 K, and at near-atmospheric pressure. Two additional unbalanced mixtures removing either 2M2B (Mix B) or 2-C5H10 (Mix C) were studied in a shock tube to collect CO time histories, representing the most stringent validation constraints, as these two pentenes constitute the biggest proportions in Mix A and exhibit opposite behaviors in terms of reactivity due to their chemical structure differences. Numerical predictions using a recent validated chemical kinetics mechanism encompassing all pentene isomers from Grégoire et al. ( Fuel2022, 323, 124223) are presented. The use of a complex blend of four pentene isomers in the present paper provided a capstone test of the current mechanism's ability to model pentene-isomer combustion chemistry, with very good results that reflect positively on the current state of the art in pentene isomer kinetics modeling.

Impact of Methanol and Butanol on Soot Formation in Gasoline Surrogate Pyrolysis: A Shock-Tube Study.

The influence of methanol and butanol on soot formation during the pyrolysis of a toluene primary reference fuel mixture with a research octane number (RON) of 91 (TPRF91) was investigated by conducting shock-tube experiments. The TPRF91 mixture contained 17 mol % n-heptane, 29 mol % iso-octane, and 54 mol % toluene. To assess the contribution of individual fuel compounds on soot formation during TPRF91 pyrolysis, the pyrolysis of argon diluted (1) toluene, (2) iso-octane, and (3) n-heptane mixtures were also studied. To enable the interpretation of the TPRF91 + methanol and TPRF91 + butanol experiments, the influence of both alcohols on soot formation during the thermal decomposition of toluene and iso-octane was also investigated in a separate series of measurements. Pyrolysis was monitored behind reflected shock waves at pressures between 2.1 and 4.2 bar and in the temperature range of 2060-2815 K. Laser extinction at 633 nm was used to determine the soot yield as a function of reaction time. For selected experiments, the temporal variation in temperature was also measured via time-resolved two-color CO absorption using two quantum-cascade lasers at 4.73 and 4.56 µm. It was found that soot formed during TPRF91 pyrolysis is primarily caused by the thermal decomposition of toluene. Adding methanol to TPRF91 results in a slight reduction of soot formation, whereas admixing butanol results in shifting soot formation to higher temperatures, but in that case, no overall soot reduction was observed during TPRF91 pyrolysis. Measured soot yields were compared to simulations based on a previous and an updated version of a detailed reaction mechanism from the CRECK modeling group [Nobili, A.; Cuoci, A.; Pejpichestakul, W.; Pelucchi, M.; Cavallotti, C.; Faravelli, T. Combust. Flame 2022; 10.1016/j.combustflame.2022.112073]. Rate-of-production analyses for reactions involving BINS at different experimental conditions were carried out. Although in the case of TPRF91 and toluene pyrolysis, no quantitative agreement was obtained between the experiment and simulation, the comparison nevertheless shows that the new version of the CRECK mechanism is a significant improvement over the previous one. In the case of n-heptane decomposition and iso-octane pyrolysis with and without alcohols, the updated reaction mechanism shows excellent agreement between simulation and measured soot yields.

Behavioral context improves optogenetic stimulation of transplanted dopaminergic cells in unilateral 6-OHDA rats.

Stem cell therapy has long been a popular method of treatment for Parkinson's disease currently being researched in both preclinical and clinical settings. While early clinical results are based upon fetal tissue transplants rather than stem cell transplants, the lack of successful integration in some patients and gradual loss of effect in others suggests a more robust protocol is needed. We propose a two-front approach, one where transplants are directly stimulated in coordination with host activity elicited by behavioral tasks, which we refer to as behavioral context. After a pilot with unilateral 6-OHDA rats transplanted with dopaminergic cells differentiated from mesenchymal stem cells that were optogenetically stimulated during a swim task, we discovered that early stimulation predicted lasting reduction of motor deficits, even in the absence of later stimulation. This led to a follow-up with n = 21 rats split into three groups: one stimulated while performing a swim task (Stim-Swim; St-Sw), one not stimulated while swimming (NoStim-Swim; NSt-Sw), and one stimulated while stationary in a bowl (Stim-NoSwim; St-NSw). After initial stimulation (or lack thereof), all rats were retested two and seven days later with the swim task in the absence of stimulation. The St-Sw group gradually achieved and maintained symmetrical limb use, whereas the NSt-Sw group showed persistent asymmetry and the St-NSw group showed mixed results. This supports the notion that stem cell therapy should integrate targeted stimulation of the transplant with behavioral stimulation of the host tissue to encourage proper functional integration of the graft.

Improved Locomotor Recovery in a Rat Model of Spinal Cord Injury by BioLuminescent-OptoGenetic (BL-OG) Stimulation with an Enhanced Luminopsin.

Irrespective of the many strategies focused on dealing with spinal cord injury (SCI), there is still no way to restore motor function efficiently or an adequate regenerative therapy. One promising method that could potentially prove highly beneficial for rehabilitation in patients is to re-engage specific neuronal populations of the spinal cord following SCI. Targeted activation may maintain and strengthen existing neuronal connections and/or facilitate the reorganization and development of new connections. BioLuminescent-OptoGenetics (BL-OG) presents an avenue to non-invasively and specifically stimulate neurons; genetically targeted neurons express luminopsins (LMOs), light-emitting luciferases tethered to light-sensitive channelrhodopsins that are activated by adding the luciferase substrate coelenterazine (CTZ). This approach employs ion channels for current conduction while activating the channels through treatment with the small molecule CTZ, thus allowing non-invasive stimulation of all targeted neurons. We previously showed the efficacy of this approach for improving locomotor recovery following severe spinal cord contusion injury in rats expressing the excitatory luminopsin 3 (LMO3) under control of a pan-neuronal and motor-neuron-specific promoter with CTZ applied through a lateral ventricle cannula. The goal of the present study was to test a new generation of LMOs based on opsins with higher light sensitivity which will allow for peripheral delivery of the CTZ. In this construct, the slow-burn Gaussia luciferase variant (sbGLuc) is fused to the opsin CheRiff, creating LMO3.2. Taking advantage of the high light sensitivity of this opsin, we stimulated transduced lumbar neurons after thoracic SCI by intraperitoneal application of CTZ, allowing for a less invasive treatment. The efficacy of this non-invasive BioLuminescent-OptoGenetic approach was confirmed by improved locomotor function. This study demonstrates that peripheral delivery of the luciferin CTZ can be used to activate LMOs expressed in spinal cord neurons that employ an opsin with increased light sensitivity.

Efficient neutralization of daratumumab in pretransfusion samples using a novel recombinant monoclonal anti-idiotype antibody.

BACKGROUND: Anti-CD38 antibodies such as daratumumab (DARA) are critical therapies for multiple myeloma and other diseases. Unfortunately, anti-CD38 antibodies cause panreactivity in indirect antiglobulin tests (IATs), complicating blood compatibility testing. The anti-CD38 interference is most often mitigated by treating reagent red blood cells (RBCs) with dithiothreitol (DTT). However, when using the DTT method, not all RBC antibody specificities can be detected (e.g., anti-K), and the DTT method is impractical for some transfusion services. We evaluated the ability of a new anti-idiotype antibody to neutralize DARA in vitro and eliminate the anti-CD38 interference. STUDY DESIGN AND METHODS: A recombinant monoclonal rabbit anti-DARA idiotype antibody ("anti-DARA") was generated. The ratio of anti-DARA required to neutralize DARA in spiked samples was evaluated in IATs performed in gel. IATs performed in tube were used to demonstrate that anti-DARA allows alloantibody detection in the presence of DARA. Plasma samples from 29 patients receiving DARA were treated with a fixed quantity of anti-DARA (120 µg) before performing antibody detection tests (screens) in tube. RESULTS: Anti-DARA used at or above a 1:1 ratio with DARA eliminated the DARA interference with IATs. Anti-DARA allowed detection of both alloanti-E and alloanti-K in the presence of DARA. In 27/29 (93.1%) clinical samples, 120 µg anti-DARA was sufficient to neutralize the DARA in 100 µl patient plasma. DISCUSSION: An anti-DARA:DARA ratio as low as 1:1 is sufficient to neutralize DARA in solution. A fixed amount of anti-DARA eliminates the anti-CD38 interference in most patient samples.

High-resolution and high-sensitivity PET for quantitative molecular imaging of the monoaminergic nuclei: A GATE simulation study.

PURPOSE: Quantitative in vivo molecular imaging of fine brain structures requires high-spatial resolution and high-sensitivity. Positron emission tomography (PET) is an attractive candidate to introduce molecular imaging into standard clinical care due to its highly targeted and versatile imaging capabilities based on the radiotracer being used. However, PET suffers from relatively poor spatial resolution compared to other clinical imaging modalities, which limits its ability to accurately quantify radiotracer uptake in brain regions and nuclei smaller than 3 mm in diameter. Here we introduce a new practical and cost-effective high-resolution and high-sensitivity brain-dedicated PET scanner, using our depth-encoding Prism-PET detector modules arranged in a conformal decagon geometry, to substantially reduce the partial volume effect and enable accurate radiotracer uptake quantification in small subcortical nuclei. METHODS: Two Prism-PET brain scanner setups were proposed based on our 4-to-1 and 9-to-1 coupling of scintillators to readout pixels using 1.5 × 1.5 × 20 $1.5 \times 1.5 \times 20$  mm3 and 0.987 × 0.987 × 20 $0.987 \times 0.987 \times 20$  mm3 crystal columns, respectively. Monte Carlo simulations of our Prism-PET scanners, Siemens Biograph Vision, and United Imaging EXPLORER were performed using Geant4 application for tomographic emission (GATE). National Electrical Manufacturers Association (NEMA) standard was followed for the evaluation of spatial resolution, sensitivity, and count-rate performance. An ultra-micro hot spot phantom was simulated for assessing image quality. A modified Zubal brain phantom was utilized for radiotracer imaging simulations of 5-HT1A receptors, which are abundant in the raphe nuclei (RN), and norepinephrine transporters, which are highly concentrated in the bilateral locus coeruleus (LC). RESULTS: The Prism-PET brain scanner with 1.5 mm crystals is superior to that with 1 mm crystals as the former offers better depth-of-interaction (DOI) resolution, which is key to realizing compact and conformal PET scanner geometries. We achieved uniform 1.3 mm full-width-at-half-maximum (FWHM) spatial resolutions across the entire transaxial field-of-view (FOV), a NEMA sensitivity of 52.1 kcps/MBq, and a peak noise equivalent count rate (NECR) of 957.8 kcps at 25.2 kBq/mL using 450-650 keV energy window. Hot spot phantom results demonstrate that our scanner can resolve regions as small as 1.35 mm in diameter at both center and 10 cm away from the center of the transaixal FOV. Both 5-HT1A receptor and norepinephrine transporter brain simulations prove that our Prism-PET scanner enables accurate quantification of radiotracer uptake in small brain regions, with a 1.8-fold and 2.6-fold improvement in the dorsal RN as well as a 3.2-fold and 4.4-fold improvement in the bilateral LC compared to the Biograph Vision and EXPLORER, respectively. CONCLUSIONS: Based on our simulation results, the proposed high-resolution and high-sensitivity Prism-PET brain scanner is a promising cost-effective candidate to achieve quantitative molecular neuroimaging of small but important brain regions with PET clinically viable.

Epidemiological and Immunological Features of Obesity and SARS-CoV-2.

Obesity is a key correlate of severe SARS-CoV-2 outcomes while the role of obesity on risk of SARS-CoV-2 infection, symptom phenotype, and immune response remain poorly defined. We examined data from a prospective SARS-CoV-2 cohort study to address these questions. Serostatus, body mass index, demographics, comorbidities, and prior COVID-19 compatible symptoms were assessed at baseline and serostatus and symptoms monthly thereafter. SARS-CoV-2 immunoassays included an IgG ELISA targeting the spike RBD, multiarray Luminex targeting 20 viral antigens, pseudovirus neutralization, and T cell ELISPOT assays. Our results from a large prospective SARS-CoV-2 cohort study indicate symptom phenotype is strongly influenced by obesity among younger but not older age groups; we did not identify evidence to suggest obese individuals are at higher risk of SARS-CoV-2 infection; and remarkably homogenous immune activity across BMI categories suggests immune protection across these groups may be similar.

Adapting Disease Prevention Protocols for Human Spaceflight During COVID-19.

BACKGROUND: The National Aeronautics and Space Administration (NASA) Flight Crew Health Stabilization Program (HSP) was historically implemented to minimize infectious disease transmission to astronauts in the immediate prelaunch period. The first ever commercial application and adaptation of the NASA HSP was implemented during the Crew Demo-2 mission in the time of the Coronavirus disease 2019 (COVID-19) pandemic. This article details and discusses the first commercial implementation and adaptation of the HSP prior to the Crew Demo-2 launch.METHODS: This is a retrospective descriptive analysis of the application of NASA disease prevention protocols for human spaceflight during the COVID-19 pandemic. In the context of the pandemic, extra precautions added to the HSP included daily symptom surveys completed by Primary Contacts of the crew, COVID-19 RT-PCR testing, and improved quarantine protocols.RESULTS: Of the 91 SpaceX Primary Contacts who completed a total of 2720 daily symptom surveys prior to launch, 22 individuals (24.2) and 198 surveys (7.3) returned positive for potential symptoms of COVID-19. Two individuals were removed due to symptoms indistinguishable from COVID-19. Through this survey, systematic quarantine, and PCR testing, the Crew Demo-2 mission was successful with no known infectious diseases transmitted.CONCLUSIONS: Overall, the commercial implementation of the NASA Health Stabilization Program by SpaceX with adjustments required during the COVID-19 pandemic was a success, with protocols allowing identification and removal of potentially infectious persons from the program. The principles of the HSP may provide an adequate infectious disease playbook for commercial spaceflight operations going forward.Petersen E, Pattarini JM, Mulcahy RA, Beger SB, Mitchell MR, Hu YD, Middleton KN, Frazier W, Mormann B, Esparza H, Asadi A, Musk ER, Alter G, Nilles E, Menon AS. Adapting disease prevention protocols for human spaceflight during COVID-19. Aerosp Med Hum Perform. 2021; 92(7):597602.

Discrete SARS-CoV-2 antibody titers track with functional humoral stability.

Antibodies serve as biomarkers of infection, but if sustained can confer long-term immunity. Yet, for most clinically approved vaccines, binding antibody titers only serve as a surrogate of protection. Instead, the ability of vaccine induced antibodies to neutralize or mediate Fc-effector functions is mechanistically linked to protection. While evidence has begun to point to persisting antibody responses among SARS-CoV-2 infected individuals, cases of re-infection have begun to emerge, calling the protective nature of humoral immunity against this highly infectious pathogen into question. Using a community-based surveillance study, we aimed to define the relationship between titers and functional antibody activity to SARS-CoV-2 over time. Here we report significant heterogeneity, but limited decay, across antibody titers amongst 120 identified seroconverters, most of whom had asymptomatic infection. Notably, neutralization, Fc-function, and SARS-CoV-2 specific T cell responses were only observed in subjects that elicited RBD-specific antibody titers above a threshold. The findings point to a switch-like relationship between observed antibody titer and function, where a distinct threshold of activity-defined by the level of antibodies-is required to elicit vigorous humoral and cellular response. This response activity level may be essential for durable protection, potentially explaining why re-infections occur with SARS-CoV-2 and other common coronaviruses.

Restoring Function After Severe Spinal Cord Injury Through BioLuminescent-OptoGenetics.

The ability to manipulate specific neuronal populations of the spinal cord following spinal cord injury (SCI) could prove highly beneficial for rehabilitation in patients through maintaining and strengthening still existing neuronal connections and/or facilitating the formation of new connections. A non-invasive and highly specific approach to neuronal stimulation is bioluminescent-optogenetics (BL-OG), where genetically expressed light emitting luciferases are tethered to light sensitive channelrhodopsins (luminopsins, LMO); neurons are activated by the addition of the luciferase substrate coelenterazine (CTZ). This approach utilizes ion channels for current conduction while activating the channels through the application of a small chemical compound, thus allowing non-invasive stimulation and recruitment of all targeted neurons. Rats were transduced in the lumbar spinal cord with AAV2/9 to express the excitatory LMO3 under control of a pan-neuronal or motor neuron-specific promoter. A day after contusion injury of the thoracic spine, rats received either CTZ or vehicle every other day for 2 weeks. Activation of either neuron population below the level of injury significantly improved locomotor recovery lasting beyond the treatment window. Utilizing histological and gene expression methods we identified neuronal plasticity as a likely mechanism underlying the functional recovery. These findings provide a foundation for a rational approach to spinal cord injury rehabilitation, thereby advancing approaches for functional recovery after SCI. SUMMARY: Bioluminescent optogenetic activation of spinal neurons results in accelerated and enhanced locomotor recovery after spinal cord injury in rats.

A new high-pressure aerosol shock tube for the study of liquid fuels with low vapor pressures.

A new shock-tube facility for studying gas-phase and condensed-phase mixtures has been developed for the investigation of various hydrocarbon species at the Qatar campus of Texas A&M University. At present, the facility is intended for studying combustion behaviors of long-chain hydrocarbon molecules and mixtures thereof under realistic engine conditions. Equipped with an aerosol generation and entrainment apparatus, the facility also possesses an enlarged driver section and double-diaphragm interface between the driver and driven sections. The driver section diameter is 19.37 cm with a configurable length of 1 m-6 m. Additionally, the stainless-steel driven section has an inner surface with a mirror finish and internal diameter of 15.24 cm. The driven section is also configurable in length up to approximately 5.2 m. As with most modern shock tubes, this shock tube is equipped for use with current methods of shock velocity detection, optical diagnostics, and other diagnostic techniques. In addition to the study of aerosolized liquids (fuels and non-fuels) related to combustion chemistry, reaction kinetics, evaporation studies, and particle-fluid interactions, among others, the facility is capable of investigating traditional gas-phase mixtures like those previously undertaken in a similar facility in the Petersen Group Laboratory at Texas A&M University. The operating limits of the title facility include temperatures and pressures up to 4000 K and 100 atm, respectively. The design and characterization of a novel aerosol introduction method is also presented, which yielded measured aerosol loading uniformities of 92%-97%. Finally, ignition delay time measurements of stoichiometric mixtures of decane in air are presented, which show excellent agreement with those recently recorded in heated shock tubes.

Epidemiological and immunological features of obesity and SARS-CoV-2.

Obesity is a key correlate of severe SARS-CoV-2 outcomes while the role of obesity on risk of SARS-CoV-2 infection, symptom phenotype, and immune response are poorly defined. We examined data from a prospective SARS-CoV-2 cohort study to address these questions. Serostatus, body mass index, demographics, comorbidities, and prior COVID-19 compatible symptoms were assessed at baseline and serostatus and symptoms monthly thereafter. SARS-CoV-2 immunoassays included an IgG ELISA targeting the spike RBD, multiarray Luminex targeting 20 viral antigens, pseudovirus neutralization, and T cell ELISPOT assays. Our results from a large prospective SARS-CoV-2 cohort study indicate symptom phenotype is strongly influenced by obesity among younger but not older age groups; we did not identify evidence to suggest obese individuals are at higher risk of SARS-CoV-2 infection; and, remarkably homogenous immune activity across BMI categories suggests natural- and vaccine-induced protection may be similar across these groups.

A Shock-Tube Study of the Rate Constant of PH3 + M ⇄ PH2 + H + M (M = Ar) Using PH3 Laser Absorption.

Phosphine (PH3) is a highly reactive and toxic gas. Prior experimental investigations of PH3 pyrolysis reactions have included only low-temperature measurements. This study reports the first shock-tube measurements of PH3 pyrolysis using a new PH3 laser absorption technique near 4.56 µm. Experiments were conducted in mixtures of 0.5% PH3/Ar behind reflected shock waves at temperatures of 1460-2013 K and pressures of ∼1.3 and ∼0.5 atm. The PH3 time histories displayed two-stage behavior similar to that previously observed for NH3 decomposition, suggesting by analogy that the rate constant for PH3 + M ⇄ PH2 + H + M (R1) could be determined. A simple three-step mechanism was assembled for data analysis. In a detailed kinetic analysis of the first-stage PH3 decomposition, values of k1,0 were obtained and best described by (in cm3·mol-1·s-1) k1,0 = 7.78 × 1017 exp(-80,400/RT), with units of cal, mol, K, s, and cm3. Agreement between the 1.3 and 0.5 atm data confirmed that the measured k1,0 was in the low-pressure limit. Agreement of the experimental k1,0 with ab initio estimates resolved the question of the main pathway of PH3 decomposition: it proceeds as PH3 ⇄ PH2 + H instead of PH3 ⇄ PH + H2.

Expanding Knowledge and Exposure to Aerospace Medicine by Creating a Medical Student Curriculum.

BACKGROUND: Aerospace Medicine is a small medical specialty. With the increasing need for aircraft pilots, continued low Earth orbit NASA operations, and the emergence of commercial spaceflight, there is a necessity for recruiting and educating the next generation of Aerospace Medicine specialists. This study was designed to create and validate a short Aerospace Medicine curriculum.METHODS: Medical students at the University of Texas Medical Branch were recruited to attend a series of six 1-h meetings covering Aerospace Medicine career options and key Aerospace Medicine topics. A survey addressing student demographics, interest in a career in Aerospace Medicine, and knowledge of key Aerospace Medicine topics was administered at the beginning and end of the curriculum. Interest in pursuing a career in Aerospace Medicine pre- and postcurriculum was compared with an independent t-test. The knowledge-based portion of the survey was also evaluated using an independent t-test.RESULTS: There were 23 participants who were recruited and filled out the initial survey and 15 participants who attended the final meeting and filled out the postcurriculum survey. Mean interest in pursuing a career in Aerospace Medicine did not change significantly (75.45% before involvement in the curriculum and 83.08% after participation). Knowledge of foundational Aerospace Medicine topics increased from 64.25% before involvement in the curriculum to 73.33% at the end of the study. There was an average of 12 participants at each meeting.DISCUSSION: This demonstrates the utility of this curriculum as an educational tool for medical students. Future efforts will focus on dissemination of the curriculum nationally and internationally.Kreykes AJ, Petersen EH, Lowry CL. Expanding knowledge and exposure to aerospace medicine by creating a medical student curriculum. Aerosp Med Hum Perform. 2020; 91(5):448-452.

High-Resolution Depth-Encoding PET Detector Module with Prismatoid Light-Guide Array.

Depth-encoding detectors with single-ended readout provide a practical, cost-effective approach for constructing high-resolution and high-sensitivity PET scanners. However, the current iteration of such detectors uses a uniform glass light-guide to achieve depth encoding, resulting in nonuniform performance throughout the detector array due to suboptimal intercrystal light sharing. We introduce Prism-PET, a single-ended-readout PET detector module with a segmented light-guide composed of an array of prismatoids that introduce enhanced, deterministic light sharing. Methods: High-resolution PET detector modules were fabricated with single-ended readout of polished multicrystal lutetium yttrium orthosilicate scintillator arrays directly coupled 4-to-1 and 9-to-1 to arrays of 3 × 3 mm silicon photomultiplier pixels. Each scintillator array was coupled at the nonreadout side to a light-guide (one 4-to-1 module with a uniform glass light-guide, one 4-to-1 Prism-PET module, and one 9-to-1 Prism-PET module) to introduce intercrystal light sharing, which closely mimics the behavior of dual-ended readout, with the additional benefit of improved crystal identification. Flood histogram data were acquired using a 3-MBq 22Na source to characterize crystal identification and energy resolution. Lead collimation was used to acquire data at specific depths to determine depth-of-interaction (DOI) resolution. Results: The flood histogram measurements showed excellent and uniform crystal separation throughout the Prism-PET modules, whereas the uniform glass light-guide module had performance degradation at the edges and corners. A DOI resolution of 5.0 mm full width at half maximum (FWHM) and an energy resolution of 13% FWHM were obtained in the uniform glass light-guide module. By comparison, the 4-to-1 coupled Prism-PET module achieved a DOI resolution of 2.5 mm FWHM and an energy resolution of 9% FWHM. Conclusion: PET scanners based on our Prism-PET modules with segmented prismatoid light-guide arrays can achieve high and uniform spatial resolution (9-to-1 coupling with ∼1-mm crystals), high sensitivity (20-mm-thick detectors and intercrystal Compton scatter recovery), good energy and timing resolutions (using polished crystals and after applying DOI correction), and compact size (depth encoding eliminates parallax error and permits smaller ring-diameter).