Investigating the formation and remodelling of myelinated axons in vivo

Myelin is a crucial component of the vertebrate nervous system, both in facilitating rapid conduction of action potentials and in metabolically supporting axons. Recent research has theorised that myelin sheaths play a more intricate role in nervous system function by regulating circuits in response to experience. The number, length, thickness, and distribution of myelin sheaths along an axon all influence its underlying conduction properties. Thus, establishing or changing particular myelin patterns along axons could refine the precise timing of signals to change circuit outputs. Yet, how the myelin patterns along single axons are established, how myelin is remodelled over time, and how neuronal activity affects these processes, is not yet fully understood. I sought to investigate how myelin is formed, remodelled and maintained over time along individual axons in the larval zebrafish central nervous system. I first characterised the formation of myelin patterns along two different subtypes of axon in the larval zebrafish spinal cord. Using transgenic tools and confocal microscopy, I performed live imaging of single axons over a period of time during developmental myelination. Reticulospinal (RS) axons are involved in locomotor circuits, and are myelinated in a synaptic vesicle release-dependent manner; whereas, Commissural Primary Ascending (CoPA) axons are involved in sensory processing circuits, and are myelinated in a synaptic vesicle release-independent manner. I hypothesised that myelin patterns along axons are formed in a circuit-dependent fashion, and, therefore, that axons from different circuits would exhibit different myelin patterns. However, I found that both RS and CoPA axons have very similar myelin patterns, in terms of their myelin sheath number, length, myelin coverage, and nodal gap length, and that these patterns are established within a defined time window after the onset of myelination. I, then, assessed how myelin sheaths are remodelled along RS and CoPA axons over time, and found that myelin sheaths could either grow or shrink in length, or could be fully retracted from the axon itself. I hypothesised that myelin remodelling would occur along axons which use activity-related signals to regulate their myelination, and therefore, that RS axons would exhibit more myelin remodelling than CoPA axons. However, I found that RS and CoPA axons exhibited very similar degrees of myelin remodelling. Finally, I used a chemogenetic tool and live imaging by confocal microscopy to investigate how increasing activity in individual RS axons affects the dynamics of myelin sheath growth and the formation of myelin patterns. I found that increasing neuronal activity promotes the early growth of myelin sheaths within a critical period; after this period, neuronal activity no longer affects myelin sheath dynamics along RS axons. By promoting this early sheath growth, activity can change the myelin pattern established along individual RS axons. Collectively, this research begins to elucidate how individual myelinated axons are formed and maintained during nervous system development, and the cellular mechanisms by which neuronal activity may regulate this process

Myelin Dynamics Throughout Life:An Ever-Changing Landscape?

Myelin sheaths speed up impulse propagation along the axons of neurons without the need for increasing axon diameter. Subsequently, myelin (which is made by oligodendrocytes in the central nervous system) allows for highly complex yet compact circuitry. Cognitive processes such as learning require central nervous system plasticity throughout life, and much research has focused on the role of neuronal, in particular synaptic, plasticity as a means of altering circuit function. An increasing body of evidence suggests that myelin may also play a role in circuit plasticity and that myelin may be an adaptable structure which could be altered to regulate experience and learning. However, the precise dynamics of myelination throughout life remain unclear – does the production of new myelin require the differentiation of new oligodendrocytes, and/or can existing myelin be remodelled dynamically over time? Here we review recent evidence for both de novo myelination and myelin remodelling from pioneering longitudinal studies of myelin dynamics in vivo, and discuss what remains to be done in order to fully understand how dynamic regulation of myelin affects lifelong circuit function

Critical perspectives on ‘consumer involvement’ in health research: epistemological dissonance and the know-do gap

Researchers in the area of health and social care (both in Australia and internationally) are encouraged to involve consumers throughout the research process, often on ethical, political and methodological grounds, or simply as ‘good practice’. This paper presents findings from a qualitative study in the UK of researchers’ experiences and views of consumer involvement in health research. Two main themes are presented in the paper. Firstly, we explore the ‘know-do gap’ which relates to the tensions between researchers’ perceptions of the potential benefits of, and their actual practices in relation to, consumer involvement. Secondly, we focus on one of the reasons for this ‘know-do gap’, namely epistemological dissonance. Findings are linked to issues around consumerism in research, lay/professional knowledges, the (re)production of professional and consumer identities and the maintenance of boundaries between consumers and researchers

Systematic Review of the Empirical Evidence of Study Publication Bias and Outcome Reporting Bias

BACKGROUND: The increased use of meta-analysis in systematic reviews of healthcare interventions has highlighted several types of bias that can arise during the completion of a randomised controlled trial. Study publication bias has been recognised as a potential threat to the validity of meta-analysis and can make the readily available evidence unreliable for decision making. Until recently, outcome reporting bias has received less attention. METHODOLOGY/PRINCIPAL FINDINGS: We review and summarise the evidence from a series of cohort studies that have assessed study publication bias and outcome reporting bias in randomised controlled trials. Sixteen studies were eligible of which only two followed the cohort all the way through from protocol approval to information regarding publication of outcomes. Eleven of the studies investigated study publication bias and five investigated outcome reporting bias. Three studies have found that statistically significant outcomes had a higher odds of being fully reported compared to non-significant outcomes (range of odds ratios: 2.2 to 4.7). In comparing trial publications to protocols, we found that 40-62% of studies had at least one primary outcome that was changed, introduced, or omitted. We decided not to undertake meta-analysis due to the differences between studies. CONCLUSIONS: Recent work provides direct empirical evidence for the existence of study publication bias and outcome reporting bias. There is strong evidence of an association between significant results and publication; studies that report positive or significant results are more likely to be published and outcomes that are statistically significant have higher odds of being fully reported. Publications have been found to be inconsistent with their protocols. Researchers need to be aware of the problems of both types of bias and efforts should be concentrated on improving the reporting of trials

Intra- and Inter-clade Cross-reactivity by HIV-1 Gag Specific T-Cells Reveals Exclusive and Commonly Targeted Regions: Implications for Current Vaccine Trials

The genetic diversity of HIV-1 across the globe is a major challenge for developing an HIV vaccine. To facilitate immunogen design, it is important to characterize clusters of commonly targeted T-cell epitopes across different HIV clades. To address this, we examined 39 HIV-1 clade C infected individuals for IFN-γ Gag-specific T-cell responses using five sets of overlapping peptides, two sets matching clade C vaccine candidates derived from strains from South Africa and China, and three peptide sets corresponding to consensus clades A, B, and D sequences. The magnitude and breadth of T-cell responses against the two clade C peptide sets did not differ, however clade C peptides were preferentially recognized compared to the other peptide sets. A total of 84 peptides were recognized, of which 19 were exclusively from clade C, 8 exclusively from clade B, one peptide each from A and D and 17 were commonly recognized by clade A, B, C and D. The entropy of the exclusively recognized peptides was significantly higher than that of commonly recognized peptides (p = 0.0128) and the median peptide processing scores were significantly higher for the peptide variants recognized versus those not recognized (p = 0.0001). Consistent with these results, the predicted Major Histocompatibility Complex Class I IC50 values were significantly lower for the recognized peptide variants compared to those not recognized in the ELISPOT assay (p<0.0001), suggesting that peptide variation between clades, resulting in lack of cross-clade recognition, has been shaped by host immune selection pressure. Overall, our study shows that clade C infected individuals recognize clade C peptides with greater frequency and higher magnitude than other clades, and that a selection of highly conserved epitope regions within Gag are commonly recognized and give rise to cross-clade reactivities

Clinical trials in amyotrophic lateral sclerosis:a systematic review and perspective

Amyotrophic lateral sclerosis is a progressive and devastating neurodegenerative disease. Despite decades of clinical trials, effective disease modifying drugs remain scarce. To understand the challenges of trial design and delivery, we performed a systematic review of phase II, phase II/III and phase III amyotrophic lateral sclerosis clinical drug trials on trial registries and PubMed between 2008 and 2019. We identified 125 trials, investigating 76 drugs and recruiting more than 15000 people with amyotrophic lateral sclerosis. 90% of trials used traditional fixed designs. The limitations in understanding of disease biology, outcome measures, resources and barriers to trial participation in a rapidly progressive, disabling and heterogenous disease hindered timely and definitive evaluation of drugs in two-arm trials. Innovative trial designs, especially adaptive platform trials may offer significant efficiency gains to this end. We propose a flexible and scalable multi-arm, multi-stage trial platform where opportunities to participate in a clinical trial can become the default for people with amyotrophic lateral sclerosis

Observation of viscosity transition in alpha-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of alpha-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35aEuro-% at -10aEuro-A degrees C and 80aEuro-% at -38aEuro-A degrees C, confirming previous calculations of the viscosity-transition conditions. Consequently, alpha-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere.Peer reviewe

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at The European Organisation for Nuclear Research (CERN), we deployed a new in situ optical method to detect the viscous state of α-pinene SOA particles and measured their transition from the amorphous highly viscous state to states of lower viscosity. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical particles at relative humidities near the deliquescence point. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to a spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity-transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical, and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

Association of cardiovascular risk factors with MRI indices of cerebrovascular structure and function and white matter hyperintensities in young adults

Importance: Risk of stroke and brain atrophy in later life relate to levels of cardiovascular risk in early adulthood. However, it is unknown whether cerebrovascular changes are already present in young adults. Objective: To examine relationships between modifiable cardiovascular risk factors and cerebrovascular structure, function and white matter integrity in young adults. Design, Setting, and Participants: A cross-sectional observational study completed between August 2014 and May 2016 at the University of Oxford, United Kingdom. Participants recruited through active and passive recruitment from the local community, including invitation from the Oxford University Hospitals Hypertension Service. Exposures: Clinic and ambulatory blood pressure (mmHg), body mass index (kg/m2), objective physical activity (hours/week), alcohol intake (drinks/week), smoking (pack years), peak oxygen uptake (ml/kg/min), peak exercise blood 65 pressure (mmHg), lipid profile (mg/dL), insulin resistance and use of anti-66 hypertension medication. 67 Main Outcomes and Measures: Cerebral vessel density (vessels/cm3), caliber (μm) and tortuosity, brain white matter hyperintensity lesion count (number), and in a subgroup (n=52) brain blood arrival time (seconds) and cerebral blood flow (ml/100g/min) assessed by brain magnetic resonance. Results: 125 participants (mean age 25±5 years, 49% female) were recruited. Cerebrovascular morphology and white matter hyperintensity count correlated with cardiovascular risk factors in univariable and multivariable models. In a risk score, for each healthier modifiable risk factor, characterised as: ambulatory blood pressure ; BMI < 25kg/m2; top tertile of cardiovascular fitness; non-smoker; <8 alcoholic drinks/week; normotensive exercise blood pressure response; cholesterol <200mg/dL; and fasting glucose <100mg/dL, vessel density increased by 0.3 vessels/cm3 (95%CI 0.1 to 0.5, p=0.003), vessel caliber by 8μm (95%CI 3 to 13, p=0.01) and white matter hyperintensity lesions reduced by 1.6 lesions (95%CI 0.6 to 2.8, p=0.006). In subgroup analysis, cerebral blood flow varied with vessel density and increased by 2.5ml/min/100g per risk score (95%CI 0.05 to 4.98, p=0.05). Conclusions and Relevance: In this preliminary study, involving young adults without clinical evidence of cerebrovascular disease, modifiable cardiovascular risk factors were associated with MR indices of cerebral vessel structure and function, and white matter hyperintensities. Further research is needed to determine the clinical importance of these findings for the primordial prevention of cerebrovascular disease