James Leggett

Oleamide is a selective endogenous agonist of rat and human CB1 cannabinoid receptors

The ability of the endogenous fatty acid amide, cis‐oleamide (ODA), to bind to and activate cannabinoid CB1 and CB2 receptors was investigated. ODA competitively inhibited binding of the nonselective cannabinoid agonist [3H]CP55,940 and the selective CB1 antagonist [3H]SR141716A to rat whole‐brain membranes with Ki values of 1.14 μM (0.52–2.53 μM, Hill slope=0.80, n=6) and 2.63 μM (0.62–11.20 μM, Hill slope=0.92, n=4), respectively. AEA inhibited [3H]CP55,940 binding in rat whole‐brain membranes with a Ki of 428 nM (346–510 nM, Hill slope=−1.33, n=3). ODA competitively inhibited [3H]CP55,940 binding in human CB1 (hCB1) cell membranes with a Ki value of 8.13 μM (4.97–13.32 μM, n=2). In human CB2 transfected (hCB2) HEK‐293T cell membranes, 100 μM ODA produced only a partial (42.5±7%) inhibition of [3H]CP55,940 binding. ODA stimulated [35S]GTPγS binding in a concentration‐dependent manner (EC50=1.64 μM (0.29–9.32 μM), R2=0.99, n=4–9), with maximal stimulation of 188±9% of basal at 100 μM. AEA stimulated [35S]GTPγS binding with an EC50 of 10.43 μM (4.45–24.42 μM, R2=1.00, n=3, 195±4% of basal at 300 μM). Trans‐oleamide (trans‐ODA) failed to significantly stimulate [35S]GTPγS binding at concentrations up to 100 μM. ODA (10 μM)‐stimulated [35S]GTPγS binding was reversed by the selective CB1 antagonist SR141716A (IC50=2.11 nM (0.32–13.77 nM), R2=1.00, n=6). The anatomical distribution of ODA‐stimulated [35S]GTPγS binding in rat brain sections was indistinguishable from that of HU210. Increases of similar magnitude were observed due to both agonists in the striatum, cortex, hippocampus and cerebellum. ODA (10 μM) significantly inhibited forskolin‐stimulated cyclic AMP (cAMP) accumulation in mouse neuroblastoma N1E 115 cells (P=0.02, n=11). ODA‐mediated inhibition was completely reversed by 1 μM SR141716A (P<0.001, n=11) and was also reversed by pretreatment with 300 ng ml−1 pertussis toxin (P<0.001, n=6). These data demonstrate that ODA is a full cannabinoid CB1 receptor agonist. Therefore, in addition to allosteric modulation of other receptors and possible entourage effects due to fatty acid amide hydrolase inhibition, the effects of ODA may be mediated directly via the CB1 receptor.

Slice-selective single scan proton COSY with dynamic nuclear polarisation

Short acquisition time and single scan capability of gradient-assisted ultrafast multidimensional spectroscopy makes it possible to record 2D spectra of highly polarised spin systems in the liquid state using dynamic nuclear polarization (DNP) in conjunction with fast dissolution. We present a slice selective experiment, suitable for back-to-back acquisition of two independent single-scan 2D experiments from different sample volumes. This scheme maximizes the amount of information obtainable from a sample that is prepolarised with a non-repeatable DNP technique. It is particularly suitable for samples with the short longitudinal relaxation times common to proton NMR spectroscopy. This technique is demonstrated by applying two filtered proton 2D COSY experiments on a DNP-polarised mixture of glutamine and glutamate to selectively amplify the correlation pattern of the protons connected to the beta and gamma carbons of either one of the two amino acids. Particular emphasis was put on the reproducibility of the experiments, especially the polarisation enhancement. Data for the liquid-state proton enhancement from amino acids and small proteins was assembled in a map that allowed the prediction of signal levels in liquid-state NMR experiments employing dissolution DNP.

Moving magnetoencephalography towards real-world applications with a wearable system

Imaging human brain function with techniques such as magnetoencephalography typically requires a subject to perform tasks while their head remains still within a restrictive scanner. This artificial environment makes the technique inaccessible to many people, and limits the experimental questions that can be addressed. For example, it has been difficult to apply neuroimaging to investigation of the neural substrates of cognitive development in babies and children, or to study processes in adults that require unconstrained head movement (such as spatial navigation). Here we describe a magnetoencephalography system that can be worn like a helmet, allowing free and natural movement during scanning. This is possible owing to the integration of quantum sensors, which do not rely on superconducting technology, with a system for nulling background magnetic fields. We demonstrate human electrophysiological measurement at millisecond resolution while subjects make natural movements, including head nodding, stretching, drinking and playing a ball game. Our results compare well to those of the current state-of-the-art, even when subjects make large head movements. The system opens up new possibilities for scanning any subject or patient group, with myriad applications such as characterization of the neurodevelopmental connectome, imaging subjects moving naturally in a virtual environment and investigating the pathophysiology of movement disorders.

Hemispherical gradient coils for magnetic resonance imaging

Hemispherical gradient coils offer an open geometry that is well suited to imaging of the human brain. The windings of a hemispherical gradient coil are on average closer to the target region than those of a comparable cylindrical coil, and consequently hemispherical coils can produce higher efficiency at fixed inductance. The mathematical formalism needed for the design of hemispherical gradient coils is described here, including expressions relating the current distribution on the hemisphere to the magnetic field generated, as well as the stored energy and power dissipation. In addition, expressions for the torque experienced by the current distribution in the presence of the main magnetic field have been derived and used to develop an approach allowing the design of torque‐balanced, hemispherical transverse gradient coils. Hemispherical coil designs suitable for brain imaging are presented and shown to have improved performance compared with their cylindrical counterparts. Small, prototype, hemispherical z‐ and x‐gradient coils have been constructed and tested in phase‐mapping experiments at 3 T. The experimental results show good agreement with theoretical predictions, validating the mathematical expressions used in the coil design process. The formalism also allows the design of coils wound on a complete spherical surface, and the performance of such coils is additionally described here. Magn Reson Med, 2005.

Quantifying the transfer and settling in NMR experiments with sample shuttling

Nuclear magnetic resonance (NMR) in combination with pulsed magnetic field gradients has proven very successful for measuring molecular diffusion, where the correlation time of the motion is much shorter than the timescale of the experiment. In this article, it is demonstrated that a single-scan NMR technique to measure molecular diffusion can be employed to also study incoherent random motions over macroscopic length scales that show correlation times similar to the timescale of the experiment. Such motions are observed, for example, after the mixing of two components or after transferring a sample from one container into another. To measure the fluid settling, a series of magnetization helices were encoded onto a sample. Stimulated gradient echo trains were then generated after different mixing times, which enabled the determination of an effective dispersion coefficient for the fluid. This technique was used to optimize the timing of NMR experiments combined with dissolution dynamic nuclear polarization, where a sample was shuttled between two magnets. In addition to the decay of fluid turbulences, the presence of microbubbles in the sample tube at the end of the shuttling step was identified as another contribution to the NMR linewidth. Microbubbles could be indirectly observed through the line broadening effect on the NMR signal due to their different susceptibility compared to the solvent, which induced field gradients near the interfaces. Using these data, the signal attenuation caused by sample motion in single-scan two-dimensional correlation spectroscopy NMR experiments could be predicted with reasonable accuracy.

Using optically-pumped magnetometers to measure magnetoencephalographic signals in the human cerebellum

We test the feasibility of an optically pumped magnetometer-magnetoencephalographic (OP-MEG) system for the measurement of human cerebellar activity. This is to our knowledge the first study investigating the human cerebellar electrophysiology using OPMs. As a proof of principle, we use an air-puff stimulus to the eyeball in order to elicit cerebellar activity that is well characterised in non-human models. In three subjects, we observe an evoked component at approx. 50ms post-stimulus, followed by a second component at approx. 85-115 ms post-stimulus. Source inversion localises both components in the cerebellum, while control experiments exclude potential sources elsewhere. We also assess the induced oscillations, with time-frequency decompositions, and identify the source in the occipital lobe, a region expected to be active in our paradigm. We conclude that the OP-MEG technology offers a promising way to advance the understanding of the information processing mechanisms in the human cerebellum.

A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography

ABSTRACT Small, commercially‐available Optically Pumped Magnetometers (OPMs) can be used to construct a wearable Magnetoencephalography (MEG) system that allows large head movements to be made during recording. The small dynamic range of these sensors however means that movement in the residual static magnetic field found inside typical Magnetically Shielded Rooms (MSRs) can saturate the sensor outputs, rendering the data unusable. This problem can be ameliorated by using a set of electromagnetic coils to attenuate the spatially‐varying remnant field. Here, an array of bi‐planar coils, which produce an open and accessible scanning environment, was designed and constructed. The coils were designed using a harmonic minimisation method previously used for gradient coil design in Magnetic Resonance Imaging (MRI). Six coils were constructed to null Symbol, Symbol and Symbol as well as the three dominant field gradients Symbol, Symbol and Symbol. The coils produce homogeneous (within ±5%) fields or field gradients over a volume of 40×40×40cm3. This volume is sufficient to contain an array of OPMs, mounted in a 3D‐printed scanner‐cast, during basic and natural movements. Automated control of the coils using reference sensor measurements allows reduction of the largest component of the static field (Symbol) from 21.8±0.2nT to 0.47±0.08nT. The largest gradient (Symbol) was reduced from 7.4nT/m to 0.55nT/m. High precision optical tracking allowed experiments involving controlled and measured head movements, which revealed that a rotation of the scanner‐cast by ±34° and translation of ±9.7cm of the OPMs in this field generated only a 1nT magnetic field variation across the OPM array, when field nulling was applied. This variation could be further reduced to 0.04nT by linear regression of field variations that were correlated with the measured motion parameters. To demonstrate the effectiveness of the bi‐planar coil field cancellation system in a real MEG experiment, a novel measurement of retinotopy was investigated, where the stimulus remains fixed and head movements made by the subject shift the visual presentation to the lower left or right quadrants of the field of view. Left and right visual field stimulation produced the expected responses in the opposing hemisphere. This simple demonstration shows that the bi‐planar coil system allows accurate OPM‐MEG recordings to be made on an unrestrained subject. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. Symbol. No caption available. HIGHLIGHTSThe design and use of bi‐planar coils for magnetic field nulling is described.Field nulling allows large subject movements during onscalp MEG recordings.Optical tracking shows high quality data can be acquired during these movements.A novel measurement of retinotopy where the subject moves their head is shown.

Cognitive neuroscience using wearable magnetometer arrays: Non-invasive assessment of language function

ABSTRACT Recent work has demonstrated that Optically Pumped Magnetometers (OPMs) can be utilised to create a wearable Magnetoencephalography (MEG) system that is motion robust. In this study, we use this system to map eloquent cortex using a clinically validated language lateralisation paradigm (covert verb generation: 120 trials, ˜10min total duration) in healthy adults (n=3). We show that it is possible to lateralise and localise language function on a case by case basis using this system. Specifically, we show that at a sensor and source level we can reliably detect a lateralising beta band (15–30Hz) desynchronization in all subjects. This is the first study of human cognition using OPMs and not only highlights this technologys utility as tool for (developmental) cognitive neuroscience but also its potential to contribute to surgical planning via mapping of eloquent cortex, especially in young children. HIGHLIGHTSFirst cognitive neuroscience experiment using optically pumped magnetometers.Language lateralisation is feasible with optically pumped magnetometers.Robust within‐subject effects at sensor and source level.