No description available.

No description available.

Stretch is known to result in an electrically less stable ventricular substrate, yet the reported effects of stretch on measured electrophysiological parameters have been inconsistent and even contradictory. The goal of this study was to evaluate the effects of acute mechanical stretch on cardiac electrical features thought to be key in generation of arrhythmia, namely restitution of action potential duration (APD), electrical memory, and onset of alternans. Microelectrodes were used to record intracellular potentials pre, during, and post-stretch from isolated right ventricular tissues from swine. In separate experiments, the effects of two levels of stretch were quantified. Pacing protocols employing explicit diastolic interval (DI) control and cycle length (CL) control were used to obtain measures of restitution of APD, memory, and alternans of APD. Stretching the tissue had varying effects on APD, restitution and memory. Stretch increased APD, restitution slopes and memory by as much as 24, 30 and 53 % in some cases, while it decreased these by up to 18, 37 and 81 % in others. During stretch, alternans of APD were observed in some cases, which occurred at slower rates of activation than before stretch. Histology of tissue samples showed localized changes in orientation of cells relative to the direction of stretch. Our results show that among individual trials, stretch altered the measured electrophysiological properties, sometimes markedly. However, when pooled together, these changes cancelled each other and the averages showed no statistically significant difference after stretch. A potential mechanism that explains this divergent and inconsistent response to stretch is the presence of local, micron level, variation in orientation of myocytes. Upon stretch, these divergent effects likely increase dispersion of repolarization diffusely and might thus be the reason behind the consistently observed increase in arrhythmic substrate after stretch.

In recent years, there has been significant research and development in the area of advanced circuits and systems for the recording of the electroneurogram (ENG) from peripheral nerve signals. This thesis presents an emulator of peripheral nerve for the testing of bio-potential recording systems under development reducing the need for early in vitro experiments and providing reproducible results. The emulator can be configured as an artificial nerve for ENG recording, which emulates the natural behavior of a nerve and provides an interface to the circuit under test. It is representative of a real nerve in terms of impedances, electrode voltages and action potential propagation characteristics as seen when recording from a nerve cuff electrode. Its dynamic behavior is controlled by a series of linked microcontrollers. The emulator provides different user selectable scenarios including single fiber action potential (SFAP), compound action potential propagation following stimulation (CAP), naturally occurring nerve traffic, and additional interference. This emulator circuit is designed using MATLAB and Cadence Spectre to perform circuit simulation. Measured results of the emulator based on a PCB including microcontrollers (PIC series, Microchip) are reported.

Processing information in the nervous system is energetically expensive, constraining the ability of the system to survive disturbances caused by stress. While some organisms compensate for extreme changes in the abiotic features of their environment, the mechanisms underlying this are poorly understood. We used the locust Descending Contralateral Movement Detector (DCMD) neuron to study how the propagation characteristics of action potentials (APs) change following an acute energy stress in control and heat shock (HS) pre-treated animals. We also attempted to determine if Ca2+ is involved in the DCMD AP and the possible changes indicated above. Conduction velocity decreased over an hour of recording in all groups, except those with minimal dissections, and we observed an increase in AP half-width and a decrease in the slope of the rising phase of the AP over time. After HS pre-treatment the response to a standard looming stimulus was delayed, showed significantly fewer APs and a lower peak frequency compared to controls. Brief application of sodium azide (NaN3) as an acute metabolic inhibitor did not subsequently affect DCMD’s conduction velocity or ability to fire at high frequencies during the recording period. There were no significant differences from control animals with extracellular Ca2+ manipulations; however we cannot conclude that Ca2+ does not contribute to DCMD’s AP because Na+ could have flowed through Ca2+ channels in the absence of extracellular Ca2+. Furthermore, examination of possible performance impairments with decreased Ca2+ currents, to indicate if Ca2+ current manipulation may account for the performance impairment, could not be conducted because no differences in AP characteristics were observed with Ca2+ manipulations. We suggest that the slowing of propagation in all groups represents a response to energetic stress and that HS modifies neuronal properties in ways that can be interpreted as saving energy in case of future stressors. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2009-08-11 08:36:26.571

The presented studies investigate dynamics of action potential duration (APD) tobetter understand the underlying mechanism for repolarization alternans.We recorded trans-membrane potentials (TMP) in canine endocardial muscle tissueusing standard glass microelectrode under the control of an explicit diastolic interval (DI)control pacing protocol, i.e. feedback protocol. During sequential sinusoidal DI activation,the trajectory of APD dynamics has multiple values of APD correspondent to the sameDI, i.e. restitution is a bi-modal relationship. Our results indicate that: 1) there is a delay,similar to hysteresis, of change in APD responding to change in DI, 2) and the timecourse of the delay is asymmetric for fast or slow pacing history. The alternans wasobserved during constant DI pacing, i.e. the DI preceding each APD was invariant orchanged within a limited range. This finding suggests that alternans of APD do not needthe oscillation of preceding DI, i.e. DI dependent restitution is not a necessary conditionfor the alternans. This result implies that DI independent component exists in themechanism of the alternans. Nonetheless, the amplitude of alternans was statisticallylarger during constant pacing cycle length (PCL) pacing than that during constant DIpacing, even though both PCL and DI pacing trials used similar average activation rate.These results also demonstrate the ability of the feedback protocol to analyze the memoryeffects and dissect different components in the mechanism of alternans.Two computational models, Luo-Rudy dynamics (LRD) and cardiac ventricle model(CVM) were used to study the hysteresis in restitution. By perturbing membrane current:L-type calcium current, rapid and slow potassium rectifier, and intracellular calciumtransfer rate in sarcoplasmic reticulum (SR) and using sinusoidal DI pacing sequence, weshowed that the asymmetric calcium current across the membrane and its interaction withcalcium buffer in SR during increasing and decreasing DI phase plays an important rolein the hysteresis. CVM was used to study the alternans during constant DI pacing.However CVM failed to replicate the alternans that occurred in the experiments. Thisresult implies that CVM lacks the electrophysiological kinetics related to alternans thatwas shown in our experiment.

Because games set in persistent virtual game worlds (VGWs) have massive numbers of players, these games need methods of characterisation for playable characters (PCs) that differ from the methods used in traditional narrative media. VGWs have a number of particularly interesting qualities. Firstly, VGWs are places where players interact with and create elements carrying narrative potential. Secondly, players add goals, motives and driving forces to the narrative potential of a VGW, which sometimes originates from the ordinary world. Thirdly, the protagonists of the world are real people, and when acting in the world their characterisation is not carried out by an author, but expressed by players characterising their PCs. How they can express themselves in ways that characterise them depend on what they can do, and how they can do it, and this characterising action potential (CAP) is defined by the game design of particular VGWs. In this thesis, two main questions are explored. Firstly, how can CAP be designed to support players in expressing consistent characters in VGWs? Secondly, how can VGWs support role-play in their rule-systems? By using iterative design, I explore the design space of CAP by building a semiautonomous agent structure, the Mind Module (MM) and apply it in five experimental prototypes where the design of CAP and other game features is derived from the MM. The term semiautonomy is used because the agent structure is designed to be used by a PC, and is thus partly controlled by the system and partly by the player. The MM models a PC's personality as a collection of traits, maintains dynamic emotional state as a function of interactions with objects in the environment, and summarises a PC's current emotional state in terms of 'mood'. The MM consists of a spreading-activation network of affect nodes that are interconnected by weighted relationships. There are four types of affect node: personality trait nodes, emotion nodes, mood nodes, and sentiment nodes. The values of the nodes defining the personality traits of characters govern an individual PC's state of mind through these weighted relationships, resulting in values characterising for a PC's personality. The sentiment nodes constitute emotionally valenced connections between entities. For example, a PC can 'feel' anger toward another PC. This thesis also describes a guided paper-prototype play-test of the VGW prototype World of Minds, in which the game mechanics build upon the MM's model of personality and emotion. In a case study of AI-based game design, lessons learned from the test are presented. The participants in the test were able to form and communicate mental models of the MM and game mechanics, validating the design and giving valuable feedback for further development. Despite the constrained scenarios presented to test players, they discovered interesting, alternative strategies, indicating that for game design the 'mental physics' of the MM may open up new possibilities.The results of the play-test influenced the further development of the MM as it was used in the digital VGW prototype the Pataphysic Institute. In the Pataphysic Institute the CAP of PCs is largely governed by their mood. Depending on which mood PCs are in they can cast different 'spells', which affect values such as mental energy, resistance and emotion in their targets. The mood also governs which 'affective actions' they can perform toward other PCs and what affective actions they are receptive to. By performing affective actions on each other PCs can affect each others' emotions, which - if they are strong - may result in sentiments toward each other. PCs' personalities govern the individual fluctuations of mood and emotions, and define which types of spell PCs can cast. Formalised social relationships such as friendships affect CAP, giving players more energy, resistance, and other benefits. PCs' states of mind are reflected in the VGW in the form of physical manifestations that emerge if an emotion is very strong. These manifestations are entities which cast different spells on PCs in close proximity, depending on the emotions that the manifestations represent. PCs can also partake in authoring manifestations that become part of the world and the game-play in it. In the Pataphysic Institute potential story structures are governed by the relations the sentiment nodes constitute between entities.Because games set in persistent virtual game worlds (VGWs) have massive numbers of players, these games need methods of characterisation for playable characters (PCs) that differ from the methods used in traditional narrative media. VGWs have a number of particularly interesting qualities. Firstly, VGWs are places where players interact with and create elements carrying narrative potential. Secondly, players add goals, motives and driving forces to the narrative potential of a VGW, which sometimes originates from the ordinary world. Thirdly, the protagonists of the world are real people, and when acting in the world their characterisation is not carried out by an author, but expressed by players characterising their PCs. How they can express themselves in ways that characterise them depend on what they can do, and how they can do it, and this characterising action potential (CAP) is defined by the game design of particular VGWs. In this thesis, two main questions are explored. Firstly, how can CAP be designed to support players in expressing consistent characters in VGWs? Secondly, how can VGWs support role-play in their rule-systems? By using iterative design, I explore the design space of CAP by building a semiautonomous agent structure, the Mind Module (MM) and apply it in five experimental prototypes where the design of CAP and other game features is derived from the MM. The term \textit{semiautonomy} is used because the agent structure is designed to be used by a PC, and is thus partly controlled by the system and partly by the player. The MM models a PC's personality as a collection of traits, maintains dynamic emotional state as a function of interactions with objects in the environment, and summarises a PC's current emotional state in terms of 'mood'. The MM consists of a spreading-activation network of affect nodes that are interconnected by weighted relationships. There are four types of affect node: personality trait nodes, emotion nodes, mood nodes, and sentiment nodes. The values of the nodes defining the personality traits of characters govern an individual PC's state of mind through these weighted relationships, resulting in values characterising for a PC's personality. The sentiment nodes constitute emotionally valenced connections between entities. For example, a PC can 'feel' anger toward another PC. This thesis also describes a guided paper-prototype play-test of the VGW prototype World of Minds, in which the game mechanics build upon the MM's model of personality and emotion. In a case study of AI-based game design, lessons learned from the test are presented. The participants in the test were able to form and communicate mental models of the MM and game mechanics, validating the design and giving valuable feedback for further development. Despite the constrained scenarios presented to test players, they discovered interesting, alternative strategies, indicating that for game design the 'mental physics' of the MM may open up new possibilities.The results of the play-test influenced the further development of the MM as it was used in the digital VGW prototype the Pataphysic Institute. In the Pataphysic Institute the CAP of PCs is largely governed by their mood. Depending on which mood PCs are in they can cast different 'spells', which affect values such as mental energy, resistance and emotion in their targets. The mood also governs which 'affective actions' they can perform toward other PCs and what affective actions they are receptive to. By performing affective actions on each other PCs can affect each others' emotions, which - if they are strong - may result in sentiments toward each other. PCs' personalities govern the individual fluctuations of mood and emotions, and define which types of spell PCs can cast. Formalised social relationships such as friendships affect CAP, giving players more energy, resistance, and other benefits. PCs' states of mind are reflected in the VGW in the form of physical manifestations that emerge if an emotion is very strong. These manifestations are entities which cast different spells on PCs in close proximity, depending on the emotions that the manifestations represent. PCs can also partake in authoring manifestations that become part of the world and the game-play in it. In the Pataphysic Institute potential story structures are governed by the relations the sentiment nodes constitute between entities. / A thesis submitted in 2009 in partial fulfilment of the requirements of the University ofTeesside for the degree of Doctor of Philosophy. The research programme was carriedout at and with the support of Gotland University.

Normal cardiac function is dependent on a healthy conduction system to maintain coordinated and synchronised activity. In the presence of heart failure, dyssynchronous ventricular activation due to left bundle branch block or right ventricular pacing can result in worsening symptoms and increased mortality; cardiac resynchronisation therapy in the form of biventricular pacing has therefore become an established and effective treatment. However, it also appears that right ventricular pacing can be a cause of heart failure in some individuals, even when there is no evidence of associated pre-existing cardiac disease. A better understanding of the processes leading to dyssynchrony-induced cardiomyopathy will allow better identification and treatment of patients who are at risk, and will contribute to our knowledge about heart failure in general. This PhD adopted a translational approach to cardiac dyssynchrony, by developing a novel model of atrial-synchronous ventricular pacing in adult Welsh Mountain sheep. The right ventricle was paced from the apex continuously for 3 months at a rate that was determined by the intrinsic atrial rate; this allowed the ventricular activation pattern to be altered without changing the heart rate. In parallel, a previously-developed model of rapid ventricular pacing was studied. In this model, the heart was paced continuously at a fixed rate of 210 bpm, which led to the development of symptomatic heart failure. In vivo parameters were characterised using standard clinical techniques of electrocardiography and echocardiography. Autonomic nervous system activity was investigated by examining the heart rate responses to pharmacological blockade using atropine and propranolol, and to beta-adrenergic stimulation using dobutamine. Heart rate variability was analysed in the time and frequency domains. In vitro, patch clamping studies were performed on ventricular myocytes isolated through enzymatic digestion from the interventricular septum and left ventricular free wall. Using the perforated patch current clamp technique at 37 C, action potential duration was measured and the associated triggered calcium transient was analysed using the calcium-sensitive fluorescent indicator Fura-2AM.Heart failure was associated with in vivo evidence of autonomic dysfunction, including a 38 % increase in the resting heart rate, blunting of the heart rate response to dobutamine, and almost complete loss of vagal tonic heart rate control. This pattern was not present in dyssynchrony. At a cellular level, normal sheep had heterogeneity of action potential duration, which was longer in the septum than the free wall. Heart failure disrupted this pattern, and was also associated with approximately a 40 % reduction in the magnitude of the calcium transient in both the septum and the free wall. Dyssynchrony was associated with a similar reduction in the calcium transient, but this was isolated to the free wall. RV apical pacing therefore induced a phenotype that resembled a localised cardiomyopathy, but without the associated autonomic dysfunction of the heart failure model. However, it was possible to identify a subgroup within these subjects that displayed a pattern of autonomic changes similar to those seen in heart failure, and this appeared to be associated with the most profound cellular changes. This raises the possibility that early dyssynchrony-induced cardiomyopathy may manifest as changes in the autonomic profile, which may be detectable in clinical practice.

The single largest cause of compound attrition during drug development is due to inadequate tools capable of predicting and identifying protein interactions. Several tools have been developed to explore how a compound interferes with specific pathways. However, these tools lack the potential to chronically monitor the time dependent temporal changes in complex biochemical networks, thus limiting our ability to identify possible secondary signaling pathways that could lead to potential toxicity. To overcome this, we have developed an in silico neuronal-metabolic model by coupling the membrane electrical activity to intracellular biochemical pathways that would enable us to perform non-invasive temporal proteomics. This model is capable of predicting and correlating the changes in cellular signaling, metabolic networks and action potential responses to metabolic perturbation. The neuronal-metabolic model was experimentally validated by performing biochemical and electrophysiological measurements on NG108-15 cells followed by testing its prediction capabilities for pathway analysis. The model accurately predicted the changes in neuronal action potentials and the changes in intracellular biochemical pathways when exposed to metabolic perturbations. NG108-15 cells showed a large effect upon exposure to 2DG compared to cyanide and malonate as these cells have elevated glycolysis. A combinational treatment of 2DG, cyanide and malonate had a much higher and faster effect on the cells. A time-dependent change in neuronal action potentials occurred based on the inhibited pathway. We conclude that the experimentally validated in silico model accurately predicts the changes in neuronal action potential shapes and proteins activities to perturbations, and would be a powerful tool for performing proteomics facilitating drug discovery by using action potential peak shape analysis to determine pathway perturbation from an administered compound.

No description available.