Biology subjects

Johnstone, A.

Publications and source records attributed to Johnstone, A..

8 recordsLinked to original sources

bioRxiv2026

Ryanodine receptor 1 ( RYR1 ) patient-derived muscle cells recapitulate disease phenotypes in 2D and 3D culture models

The Ryanodine Receptor 1 (RyR1) is the major Ca2+ release channel in skeletal muscle and plays a crucial role in excitation-contraction coupling. Pathogenic variants in RYR1 are the most common cause of congenital myopathy, for which there are no approved treatments. Patient-centric disease models may help to facilitate the design and screening of novel therapeutics in a human genomic context. In this report, we describe the differentiation of five dominant RYR1-related myopathy patient-derived induced pluripotent stem cell (iPSC) lines into muscle progenitor cells (MPCs), and subsequently into multinucleated myotubes in 2- and 3- Dimensional (D) culture models. In 2D, we show significantly reduced Ca2+ release in a patient line compared to a healthy control following stimulation with caffeine. In 3D engineered muscle tissues (EMTs), patient-relevant phenotypes including reduced twitch amplitude, delayed relaxation and altered force-frequency relationships were observed in a patient line compared to two healthy controls. We also show that the 2D cultures are a suitable platform for screening the efficacy and cellular toxicity of antisense oligonucleotide therapeutics. Together, these results suggest that iPSC-derived skeletal muscle cultures are useful models for understanding the pathobiology of RYR1-related myopathies and as a testbed for emerging treatments.

Cell Biology↗

bioRxiv2025

Baclofen, a GABAB receptor agonist, impairs motor learning in healthy people and changes inhibitory dynamics in motor areas

Inhibition mediated by {gamma}-aminobutyric acid (GABA) is implicated in motor plasticity and learning, with [GABA] in the motor cortex decreasing during motor learning. However, the causal relationship between [GABA] and learning has yet to be determined. Here, we conducted a within-subject, double-blind, placebo-controlled, crossover study to investigate the effect of increased GABAergic inhibition via GABAB-receptor agonist baclofen on motor learning and Magnetic Resonance Spectroscopic Imaging (MRSI) metrics. Increasing GABA-mediated inhibition with baclofen did not change response times, but significantly impaired motor sequence learning. In parallel, we demonstrated a blunting of the expected decrease in [GABA] during motor learning. These results highlight a causal role for GABAergic inhibition in motor learning and may have clinical implications: baclofen is commonly used to treat post brain-injury spasticity, but may impair motor learning during rehabilitation.

neuroscience↗

bioRxiv2023

Vigilance & Cognitive Flexibility: The Effect of Martial Arts Experience on Task Switching

Martial Arts can be considered both a sport and a therapy, combining physical exercise with intense periods of concentration (similar to meditation). Previous research suggests that both exercise and meditation can lead to improvements in executive functions (i.e., cognitive flexibility) in adult participants. Results from our lab have previously suggested that martial artists show improvements in the alerting attentional network - a measure of vigilance. The current research aims to investigate the impact of Martial Arts training on a task-switching protocol to measure both vigilance and cognitive flexibility in typical adults. Here we recruited adult martial artists with at least two years of experience, and control participants with no experience. Participants had to respond to either the shape or the colour of a figure in pure and mixed blocks to provide measures of mixing costs (sustained vigilance) and switching costs (cognitive flexibility). Results demonstrated martial artists did not differ from controls in the pure block, but displayed improved performance in the mixed block, revealing an improvement in mixing costs (vigilance). These benefits in vigilance mirror those previously found in attentional tasks, providing convergent evidence on the impact of Martial Arts training on vigilance.

animal behavior and cognition↗

bioRxiv2023

Ramped V1 transcranial ultrasonic stimulation modulates but does not evoke visual evoked potentials

Transcranial ultrasonic stimulation (TUS), has been shown to evoke visual evoked potential (VEP)-like potentials on EEG recordings, and also to modulate sensory evoked potentials. However, pulsed TUS is accompanied by an auditory confound, and it is possible that any observed effects were, in-part, evoked by this confound. Therefore, we used ramped TUS pulses, which are not as easily audible, to examine whether primary visual cortex (V1) TUS evokes VEP-like potentials, and modulates VEPs elicited using a checkerboard stimulus. MethodsWe tested 14 healthy participants (31 {+/-} 4.3 yrs, 4 F and 10 M). TUS was applied to the left V1 using a 270 kHz transducer (H115-2AA, Sonic Concepts). Ramped pulses (1 ms ramp, 3.25 ms total pulse duration) were repeated at 250 Hz, with a pulse train duration of 300 ms, an effective duty cycle of 50%, and Isppa without ramping of 16 W/cm2 in water. EEG was recorded from 16 channels using the g.USBamp amplifier (g.tec medical engineering GmbH). In two blocks (TUS-only), real and sham (100 each) TUS trials were repeated every 2 s. In another two blocks (TUS+checkerboard), a checkerboard stimulus was flipped every 0.5 s, and every fourth stimulus was associated with either a real or sham (100 each) TUS trial. The TUS trial started approx. 130 ms (0-5 ms jitter) before the checkerboard flip. All EEG data were analysed using Fieldtrip, and cluster-based permutation tests were used to test for differences between conditions. Results and discussionIn the TUS-only condition, in contrast to a previous study, we found no evoked potentials using ramped pulses which minimised the auditory artifact. In the TUS+checkerboard condition, we observed a modulation of the early-component of the VEP in real TUS, relative to no TUS trials. This suggests that, in line with in-vitro and animal data, there is a direct neuromodulatory effect of ultrasound, in addition to any confounding effects. Moving forward, ramping offers a relatively easy approach to minimise the auditory confound.

neuroscience↗

bioRxiv2022

BDNF and TRiC-inspired Reagents Rescue Cortical Synaptic Deficits in a Mouse Model of Huntington's Disease

Huntingtons disease (HD) results from a CAG repeat expansion in the gene for Huntington (HTT) resulting in expansion of the polyglutamine (Q) tract in the mutant protein (mHTT). Synaptic changes are early manifestations of neuronal dysfunction in HD. However, the mechanism(s) by which mHTT impacts synapse formation and function is not well defined. Herein we explored HD pathogenesis in the BACHD and the {Delta}N17-BACHD mouse models of HD by examining cortical synapse formation and function in primary cultures maintained for up to 35 days (DIV35). We identified synapses by immunostaining with antibodies against pre-synaptic (Synapsin 1) and a post-synaptic (PSD95) marker. Consistent with earlier studies, cortical neurons from both WT and the HD models began to form synapses at DIV14; at this age there were no genotypic differences in synapse numbers. However, from DIV21 through DIV35 BACHD neurons showed progressively smaller numbers of synapses relative to WT neurons. Remarkably, BACHD synaptic deficits were completely rescued by treating cultures with BDNF. Building on earlier studies using reagents inspired by the chaperonin TRiC, we found that addition of the recombinant apical domain of CCT1 partially rescued synapse number. Unexpectedly, unlike BACHD cultures, synapses in {Delta}N17-BACHD cultures showed a progressive increase in number as compared to WT neurons, thus distinguishing synaptic changes in these HD models. Using multielectrode arrays, we discovered age-related functional deficits in BACHD cortical cultures with significant differences present by DIV28. As for synapse number, BDNF treatment prevented most synaptic deficits, including mean firing rate, spikes per burst, inter-burst interval, and synchrony. The apical domain of CCT1 showed similar, albeit less potent effects. These data are evidence that deficits in HD synapse number and function can be replicated in vitro and that treatment with either BDNF or a TRiC-inspired reagent can prevent them. Our findings support the use of cellular models to further explicate HD pathogenesis and its treatments.

neuroscience↗

bioRxiv2022

tDCS induced GABA change is associated with the simulated electric field in M1, an effect mediated by grey matter volume in the MRS voxel

Background and ObjectiveTranscranial direct current stimulation (tDCS) has wide ranging applications in neuro-behavioural and physiological research, and in neurological rehabilitation. However, it is currently limited by substantial inter-subject variability in responses, which may be explained, at least in part, by anatomical differences that lead to variability in the electric field (E-field) induced in the cortex. Here, we tested whether the variability in the E-field in the stimulated cortex during tDCS, estimated using computational simulations, explains the variability in tDCS induced changes in GABA, a neurophysiological marker of stimulation effect. MethodsData from five previously conducted MRS studies were combined. The anode was placed over the left primary motor cortex (M1, 3 studies, N = 24) or right temporal cortex (2 studies, N = 32), with the cathode over the contralateral supraorbital ridge. Single voxel spectroscopy was performed in a 2x2x2cm voxel under the anode in all cases. MRS data were acquired before and either during or after 1mA tDCS using either a sLASER sequence (7T) or a MEGA-PRESS sequence (3T). sLASER MRS data were analysed using LCModel, and MEGA-PRESS using FID-A and Gannet. E-fields were simulated in a finite element model of the head, based on individual MPRAGE images, using SimNIBS. Separate linear mixed effects models were run for each E-field variable (mean and 95th percentile; magnitude, and components normal and tangential to grey matter surface, within the MRS voxel). The model included effects of time (pre or post tDCS), E-field, grey matter volume in the MRS voxel, and a 3-way interaction between time, E-field and grey matter volume. Additionally, we ran a permutation analysis using PALM to determine whether E-field anywhere in the brain, not just in the MRS voxel, correlated with GABA change. ResultsIn M1, higher mean E-field magnitude was associated with greater tDCS-induced decreases in GABA (t(24) = 3.24, p = 0.003). Further, the association between mean E-field magnitude and GABA change was moderated by the grey matter volume in the MRS voxel (t(24) = -3.55, p =0.002). These relationships were consistent across all E-field variables except the mean of the normal component. No significant relationship was found between tDCS-induced GABA decrease and E-field in the temporal voxel. No significant clusters were found in the whole brain analysis. ConclusionsOur data suggest that the electric field induced by tDCS within the brain is variable, and is significantly related to tDCS-induced decrease in GABA, a key neurophysiological marker of stimulation. These findings strongly support individualised dosing of tDCS, at least in M1. Further studies examining E-fields in relation to other outcome measures, including behaviour, will help determine the optimal E-fields required for any desired effects. HighlightsO_LIWe study the link between individually simulated electric field dose and tDCS-induced change in GABA in the cortex. C_LIO_LIThe electric field strength in the brain correlates with a decrease in GABA in the motor cortex. C_LIO_LIThe correlation between the electric field and GABA change is modulated by the amount of grey matter in the MRS voxel. C_LIO_LIWe find no association between the electric field and GABA in the temporal cortex. C_LI

neuroscience↗

bioRxiv2021

The impact of brain lesions on tDCS-induced electric field magnitude

BackgroundTranscranial direct current stimulation (tDCS) has been used to enhance motor and language rehabilitation following a stroke. However, improving the effectiveness of clinical tDCS protocols depends on understanding how lesions may influence tDCS-induced current flow through the brain. ObjectiveWe systematically investigated the effect of brain lesions on the magnitude of electric fields (e-mag) induced by tDCS, and how to overcome lesion-induced inter-individual variability in e-mag. MethodsWe simulated the effect of 630 different lesions - by varying lesion location, distance from the target region of interest (ROI), size and conductivity - on tDCS-induced e-mag in the brains of two participants. Current flow modelling was conducted for two tDCS montages commonly used in clinical applications, which target either primary motor cortex (M1) or Brocas area (BA44), respectively. We further explored how the inherent variability in e-mag that is introduced by inter-lesion differences can be overcome by individualising tDCS protocols. ResultsThe effect on absolute e-mag was highly dependent on lesion size, conductance and the distance from the target ROI. Larger lesions, with high conductivity, closer to the ROI caused e-mag changes of more than 30%. The sign of this change was determined by the location of the lesion. Specifically, lesions located in-line with the predominant direction of current flow increased e-mag in the ROI, whereas lesions located in the opposite direction caused a decrease. Lesions had a large impact on the optimal electrode configuration if attempting to maximise for the total e-mag in the ROI, but little impact if only the component of e-mag flowing radially inward to the cortex was maximised. Knowing the effect of a given lesion on e-mag also allows for individualising tDCS intensity to reduce variability. ConclusionsThese results demonstrate that tDCS-induced electric fields are profoundly influenced by lesion characteristics, and further exacerbate the known variability in e-mag across individuals. Additionally, the dependence of these results on the assigned conductance of the lesion underlines the need for improved estimates of lesion conductivity for current flow models. Our results highlight the need for individualised dose control of tDCS in the lesioned brain to overcome the substantial inter-individual variability in electric fields delivered to a cortical target region. Highlights- Lesions can alter tDCS-induced electric field magnitude (e-mag) in a target by 30% - Lesions can cause increases or decreases to e-mag - Direction of change depends on the position of the lesion relative to current flow - Lesion conductivity - the true value for which is unknown - also impacts change - E-mag variability can be reduced by individualising montage and stimulation intensity

neuroscience↗

bioRxiv2020

Heterogeneous relationships between white matter and behaviour

Several studies have established specific relationships between White Matter (WM) and behaviour. However, these studies have typically focussed on fractional anisotropy (FA), a neuroimaging metric that is sensitive to multiple tissue properties, making it difficult to identify what biological aspects of WM may drive such relationships. Here, we carry out a pre-registered assessment of WM-behaviour relationships in 50 healthy individuals across multiple behavioural and anatomical domains, and complementing FA with myelin-sensitive quantitative MR modalities (MT, R1, R2*). Surprisingly, we only find support for predicted relationships between FA and behaviour in one of three pre-registered tests. For one behavioural domain, where we failed to detect an FA-behaviour correlation, we instead find evidence for a correlation between behaviour and R1. This hints that multimodal approaches are able to identify a wider range of WM-behaviour relationships than focusing on FA alone. To test whether a common biological substrate such as myelin underlies WM-behaviour relationships, we then ran joint multimodal analyses, combining across all MRI parameters considered. No significant multimodal signatures were found and power analyses suggested that sample sizes of 40 to 200 may be required to detect such joint multimodal effects, depending on the task being considered. These results demonstrate that FA-behaviour relationships from the literature can be replicated, but may not be easily generalisable across domains. Instead, multimodal microstructural imaging may be best placed to detect a wider range of WM-behaviour relationships, as different MRI modalities provide distinct biological sensitivities. Our findings highlight a broad heterogeneity in WMs relationship with behaviour, suggesting that variable biological effects may be shaping their interaction. HighlightsO_LIPre-registered testing of microstructural imaging across modalities (FA, MT, R1, R2*) to test WM-behaviour relationships. C_LIO_LIPartial support for FA-behaviour relationships hypothesised based on previous literature. C_LIO_LIMultimodal approaches can help detect WM-behaviour relationships that are not detected with FA alone. C_LIO_LISample sizes of 40 to 200 may be needed to detect myelin-behaviour relationships in joint multimodal analyses. C_LIO_LIVariable biological effects may be shaping WM-behaviour relationships. C_LI

neuroscience↗