Electrophysiological studies of intramural neurones from the mammalian heart and airways

This thesis reports the electrophysiological and neurochemical characteristics of intramural neurones from ganglia of the rat trachea in situ, and from the atria and interatrial septum of the guinea-pig heart in culture. On the basis of their firing characteristics, three different types of intracardiac neurones could be distinguished. Two of these cell types, consisting of 65-75% of the neurones studied, had tetrodotoxin (TTX)-resistant calcium-dependent components to their action potentials and pronounced after-hyperpolarizations following spike discharge. Both cell types were highly refractory, but could be distinguished by whether they fired a single (AHS cells) or a short burst of action potentials (AHm cells) in response to current stimulation. A third type of intracardiac neurone (M cells), consisting of 10-15% of the cells studied, had TTX-sensitive spikes, fired tonically and had no significant after-hyperpolarization. The firing characteristics of paratracheal neurones ranged between two extremes. At one extreme, the cells fired tonically at low frequencies, whilst at the other, cells fired high frequency, repetitive bursts of action potentials. All paratracheal neurones displayed calcium-dependent action potentials and after-hyperpolarizations, however the after-hyperpolarization only became pronounced following a train of action potentials. All paratracheal neurones and many AH type intracardiac neurones displayed marked inward and outward rectification in their current-voltage relationships. This largely resulted from activation of time- and voltage-dependent inward rectifier and M-currents. The neurochemical differentiation of the cells in the two preparations was examined by exogenous application of various neurotransmitters. In AH type intracardiac neurones, M1 and M2 muscarinic receptor activation induced changes in up to four different membrane conductances. These included the inhibition of a voltage-sensitive calcium conductance; inhibition of the M-current; an increase in resting potassium conductance and an increase in a conductance of unknown ionic nature. The effects of exogenous application of purine compounds to intracardiac neurones were also investigated. Adenosine, acting via P1-purinoceptors, inhibited the current underlying the after-hyperpolarization in AH type cells. Adenosine 5'- triphosphate (ATP), acting via P2-purinoceptors, activated a mixed sodium- and calcium-dependent conductance in 41% of M and 43% of AH type cells. In a further 31% of AH type cells, ATP produced a multi-component response consisting of a transient, chloride-dependent inward current, followed by a potassium-dependent outward current and a slow prolonged inward current of unknown ionic nature. The effects of ionophoretic and bath application of γ-aminobutyric acid (GABA) to rat paratracheal neurones were investigated. GABA, acting via GABAA receptors, induced an increase in membrane chloride conductance resulting in membrane depolarization in over 90% of paratracheal neurones studied

Evidence for two attentional components in visual working memory

How does executive attentional control contribute to memory for sequences of visual objects, and what does this reveal about storage and processing in working memory? Three experiments examined the impact of a concurrent executive load (backward counting) on memory for sequences of individually presented visual objects. Experiments 1 and 2 found disruptive concurrent load effects of equivalent magnitude on memory for shapes, colors, and colored shape conjunctions (as measured by single-probe recognition). Crucially, these effects were only present for items 1 and 2 in a 3-item sequence; the final item was always impervious to this disruption. This pattern of findings was precisely replicated in Experiment 3 using a cued verbal recall measure of shape-color binding, with error analysis providing additional insights concerning attention-related loss of early-sequence items. These findings indicate an important role for executive processes in maintaining representations of earlier encountered stimuli in an active form alongside privileged storage of the most recent stimulus

Exploring the sentence advantage in working memory: Insights from serial recall and recognition

Immediate serial recall of sentences has been shown to be superior to that of unrelated words. This study was designed to further explore how this effect might emerge in recall and to establish whether it also extends to serial recognition, a different form of response task that has relatively reduced output requirements. Using auditory or visual presentation of sequences, we found a substantial advantage for sentences over lists in serial recall, an effect shown on measures of recall accuracy, order, intrusion, and omission errors and reflected in transposition gradients. In contrast however, recognition memory based on a standard change detection paradigm gave only weak and inconsistent evidence for a sentence superiority effect. However, when a more sensitive staircase procedure imported from psychophysics was used, a clear sentence advantage was found although the effect sizes were smaller than those observed in serial recall. These findings suggest that sentence recall benefits from automatic processes that utilise long-term knowledge across encoding, storage, and retrieval

Effects of a Whole-School Health Intervention on Clustered Adolescent Health Risks: Latent Transition Analysis of Data from the INCLUSIVE Trial

Whole-school interventions are a promising approach to preventing bullying and aggression while promoting broader health. The main analyses from a trial of the INCLUSIVE whole-school intervention reported reductions in bullying victimisation but not aggression and improved mental well-being. Latent transition analysis can examine how interventions ‘move’ people between classes defined by multiple outcomes over time. We examined at baseline what classes best defined individuals’ bullying, aggression and mental well-being and what effects did the intervention have on movement between classes over time? INCLUSIVE was a two-arm cluster-randomised trial with 20 high schools per arm, with 24-month and 36-month follow-ups. We estimated sequential latent class solutions on baseline data. We then estimated a latent transition model including baseline, 24-month and 36-month follow-up measurements. Our sample comprised 8179 students (4082 control, 4097 intervention arms). At baseline, classes were (1) bullying victims, (2) aggression perpetrators, (3) extreme perpetrators and (4) neither victims nor perpetrators. Control students who were extreme perpetrators were equally likely to stay in this class (27.0% probability) or move to aggression perpetrators (25.0% probability) at 24 months. In the intervention group, fewer extreme perpetrators students remained (5.4%), with more moving to aggression perpetrators (65.1%). More control than intervention extreme perpetrators moved to neither victims nor perpetrators (35.2% vs 17.8%). Between 24 and 36 months, more intervention students moved from aggression perpetrators to neither victims nor perpetrators than controls (30.1% vs 22.3%). Our findings suggest that the intervention had important effects in transitioning students to lower-risk classes

Executive and perceptual attention play different roles in visual working memory: Evidence from suffix and strategy effects

Four experiments studied the interfering effects of a to-be-ignored ‘stimulus suffix’ on cued recall of feature bindings for a series of objects. When each object was given equal weight (Experiment 1) or rewards favored recent items (Experiments 2 and 4), a recency effect emerged that was selectively reduced by a suffix. The reduction was greater for a ‘plausible’ suffix with features drawn from the same set as the memory items, in which case a feature of the suffix was frequently recalled as an intrusion error. Changing pay-offs to reward recall of early items led to a primacy effect alongside recency (Experiments 3 and 4). Primacy, like recency, was reduced by a suffix and the reduction was greater for a suffix with plausible features, such features often being recalled as intrusion errors. Experiment 4 revealed a trade-off such that increased primacy came at the cost of a reduction in recency. These observations show that priority instructions and recency combine to determine a limited number of items that are the most accessible for immediate recall and yet at the same time the most vulnerable to interference. We interpret this outcome in terms of a labile, limited capacity ‘privileged state’ controlled by both central executive processes and perceptual attention. We suggest further that this privileged state can be usefully interpreted as the focus of attention in the episodic buffer

What does visual suffix interference tell us about spatial location in working memory?

A visual object can be conceived of as comprising a number of features bound together by their joint spatial location. We investigate the question of whether the spatial location is automatically bound to the features or whether the two are separable, using a previously developed paradigm whereby memory is disrupted by a visual suffix. Participants were shown a sample array of four colored shapes, followed by a postcue indicating the target for recall. On randomly intermixed trials, a to-be-ignored suffix array consisting of two different colored shapes was presented between the sample and the postcue. In a random half of suffix trials, one of the suffix items overlaid the location of the target. If location was automatically encoded, one might expect the colocation of target and suffix to differentially impair performance. We carried out three experiments, cuing for recall by spatial location (Experiment 1), color or shape (Experiment 2), or both randomly intermixed (Experiment 3). All three studies showed clear suffix effects, but the colocation of target and suffix was differentially disruptive only when a spatial cue was used. The results suggest that purely visual shape-color binding can be retained and accessed without requiring information about spatial location, even when task demands encourage the encoding of location, consistent with the idea of an abstract and flexible visual working memory system

Effects of a Whole-School Health Intervention on Clustered Adolescent Health Risks: Latent Transition Analysis of Data from the INCLUSIVE Trial.

Whole-school interventions are a promising approach to preventing bullying and aggression while promoting broader health. The main analyses from a trial of the INCLUSIVE whole-school intervention reported reductions in bullying victimisation but not aggression and improved mental well-being. Latent transition analysis can examine how interventions 'move' people between classes defined by multiple outcomes over time. We examined at baseline what classes best defined individuals' bullying, aggression and mental well-being and what effects did the intervention have on movement between classes over time? INCLUSIVE was a two-arm cluster-randomised trial with 20 high schools per arm, with 24-month and 36-month follow-ups. We estimated sequential latent class solutions on baseline data. We then estimated a latent transition model including baseline, 24-month and 36-month follow-up measurements. Our sample comprised 8179 students (4082 control, 4097 intervention arms). At baseline, classes were (1) bullying victims, (2) aggression perpetrators, (3) extreme perpetrators and (4) neither victims nor perpetrators. Control students who were extreme perpetrators were equally likely to stay in this class (27.0% probability) or move to aggression perpetrators (25.0% probability) at 24 months. In the intervention group, fewer extreme perpetrators students remained (5.4%), with more moving to aggression perpetrators (65.1%). More control than intervention extreme perpetrators moved to neither victims nor perpetrators (35.2% vs 17.8%). Between 24 and 36 months, more intervention students moved from aggression perpetrators to neither victims nor perpetrators than controls (30.1% vs 22.3%). Our findings suggest that the intervention had important effects in transitioning students to lower-risk classes

Transmission of equine influenza virus during an outbreak is characterized by frequent mixed infections and loose transmission bottlenecks.

The ability of influenza A viruses (IAVs) to cross species barriers and evade host immunity is a major public health concern. Studies on the phylodynamics of IAVs across different scales - from the individual to the population - are essential for devising effective measures to predict, prevent or contain influenza emergence. Understanding how IAVs spread and evolve during outbreaks is critical for the management of epidemics. Reconstructing the transmission network during a single outbreak by sampling viral genetic data in time and space can generate insights about these processes. Here, we obtained intra-host viral sequence data from horses infected with equine influenza virus (EIV) to reconstruct the spread of EIV during a large outbreak. To this end, we analyzed within-host viral populations from sequences covering 90% of the infected yards. By combining gene sequence analyses with epidemiological data, we inferred a plausible transmission network, in turn enabling the comparison of transmission patterns during the course of the outbreak and revealing important epidemiological features that were not apparent using either approach alone. The EIV populations displayed high levels of genetic diversity, and in many cases we observed distinct viral populations containing a dominant variant and a number of related minor variants that were transmitted between infectious horses. In addition, we found evidence of frequent mixed infections and loose transmission bottlenecks in these naturally occurring populations. These frequent mixed infections likely influence the size of epidemics

Study protocol for the optimisation, feasibility testing and pilot cluster randomised trial of Positive Choices: a school-based social marketing intervention to promote sexual health, prevent unintended teenage pregnancies and address health inequalities in England.

BACKGROUND: Since the introduction of the Teenage Pregnancy Strategy (TPS), England's under-18 conception rate has fallen by 55%, but a continued focus on prevention is needed to maintain and accelerate progress. The teenage birth rate remains higher in the UK than comparable Western European countries. Previous trials indicate that school-based social marketing interventions are a promising approach to addressing teenage pregnancy and improving sexual health. Such interventions are yet to be trialled in the UK. This study aims to optimise and establish the feasibility and acceptability of one such intervention: Positive Choices. METHODS: Design: Optimisation, feasibility testing and pilot cluster randomised trial.Interventions: The Positive Choices intervention comprises a student needs survey, a student/staff led School Health Promotion Council (SHPC), a classroom curriculum for year nine students covering social and emotional skills and sex education, student-led social marketing activities, parent information and a review of school sexual health services.Systematic optimisation of Positive Choices will be carried out with the National Children's Bureau Sex Education Forum (NCB SEF), one state secondary school in England and other youth and policy stakeholders.Feasibility testing will involve the same state secondary school and will assess progression criteria to advance to the pilot cluster RCT.Pilot cluster RCT with integral process evaluation will involve six different state secondary schools (four interventions and two controls) and will assess the feasibility and utility of progressing to a full effectiveness trial.The following outcome measures will be trialled as part of the pilot:Self-reported pregnancy and unintended pregnancy (initiation of pregnancy for boys) and sexually transmitted infections,Age of sexual debut, number of sexual partners, use of contraception at first and last sex and non-volitional sexEducational attainmentThe feasibility of linking administrative data on births and termination to self-report survey data to measure our primary outcome (unintended teenage pregnancy) will also be tested. DISCUSSION: This will be the first UK-based pilot trial of a school-wide social marketing intervention to reduce unintended teenage pregnancy and improve sexual health. If this study indicates feasibility and acceptability of the optimised Positive Choices intervention in English secondary schools, plans will be initiated for a phase III trial and economic evaluation of the intervention. TRIAL REGISTRATION: ISRCTN registry (ISCTN12524938. Registered 03/07/2017)

Moderated mediation analyses to assess intervention mechanisms for impacts on victimisation, psycho-social problems and mental wellbeing: Evidence from the INCLUSIVE realist randomized trial.

Realist evaluations aim to evaluate interventions by understanding the mechanisms they trigger, assessing not merely what works but what works for whom, under what conditions, and how. Significant disagreement in the literature exists as to whether randomized trials can be used as a tool for realist evaluation. INCLUSIVE, which was the first realist randomized trial explicitly designed as such, evaluated the impact of Learning Together, a school-based intervention for students aged 12-15 that included restorative practice, on bullying victimisation, mental wellbeing and psychological problems. Drawing on hypotheses generated through qualitative research, this analysis tested if school belonging was a mediator of intervention effects, and in which contexts. We estimated a series of fully longitudinal multilevel moderated mediation models including intervention allocation, student reports of school belonging at 24 months and victimisation and wellbeing outcomes at 36 months, and stratified on the basis of whether, at baseline, schools were: a) rated 'outstanding' for leadership, b) below the median for average levels of victimisation, and c) above the median on school inclusivity. Findings suggested that in unstratified models, belonging was not a mediator for any outcome; but in each of the strata defined above, belonging was a significant mediator at the student level. However, in the strata where belonging was not a mediator, the intervention still had a significant effect on each outcome. Analyses point to a strong but conditional role for belonging as a mediator of intervention pathways; in schools where belonging was not a mediator (e.g. above-median victimisation levels), other mechanisms may have been activated. This is consistent with a realist understanding of context-mechanism linkages generating outcomes. Our analyses suggest that realist evaluations can be pursued within randomized trials and that such analyses can offer more nuanced evidence regarding in which contexts interventions might effectively be implemented