Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2006. / Title from first page of PDF file (viewed December 13, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

Pancreatic alpha- and beta-cells play vital roles in maintaining glucose homeostasis. While much work has investigated beta-cell biology, alpha-cell research has been scarce. This is due to limitations in conventional methods of alpha-cell preparation, which expose alpha-cells on the islet mantle to enzymatic and mechanical injury inherent in the preparation. I have employed the pancreas tissue slice preparation, which surmounts these limitations. Pancreas slices can be prepared efficiently, and islet cells examined in situ without requiring culture conditions. Alpha-cells are preserved in their native cellular environment not only in health, but more remarkably, also in disease (type 1 diabetes; T1D) states, which was not previously feasible. In the first part of my study, I deployed this preparation to assess normal mouse alpha-cell physiology. Alpha-cells exhibited well-described features of INa, IKATP, small cell size, low resting membrane conductance, and inducible low and high voltage-activated ICa, the latter correlating with exocytosis determined by capacitance measurements. In contrast to previous reports, our large sampling of alpha-cells revealed a wide-range data distribution of several ion channel parameters. My findings explain the apparent inconsistency of previous reports wherein alpha-cell ion channel properties appeared skewed within narrow portions of this wide distribution, likely caused by different preparations. In the second part of my thesis, I assessed alpha-cell perturbation in streptozotocin-induced T1D in the GluCre-ROSA26EYFP (GYY) mouse. In this T1D model, alpha-cells exhibited more glucagon content per cell, which can be exocytosed in greater quantity upon serial depolarization. Membrane electrical properties revealed larger Na+ current and reduced KV-transient current, which contributed to the apparent increased amplitude and firing frequency of action potentials in membrane electrical recording. These electrical events likely prime alpha-cells to release more glucagon, culminating in larger in vivo glucagon secretory responses to low glucose stimulation in this T1D model. We are now well-positioned to employ this in situ model of pancreas slice preparation to address many other apparently unanswerable questions in alpha-cells in normal and pathophysiologic states, such as diabetes.

Pancreatic alpha- and beta-cells play vital roles in maintaining glucose homeostasis. While much work has investigated beta-cell biology, alpha-cell research has been scarce. This is due to limitations in conventional methods of alpha-cell preparation, which expose alpha-cells on the islet mantle to enzymatic and mechanical injury inherent in the preparation. I have employed the pancreas tissue slice preparation, which surmounts these limitations. Pancreas slices can be prepared efficiently, and islet cells examined in situ without requiring culture conditions. Alpha-cells are preserved in their native cellular environment not only in health, but more remarkably, also in disease (type 1 diabetes; T1D) states, which was not previously feasible. In the first part of my study, I deployed this preparation to assess normal mouse alpha-cell physiology. Alpha-cells exhibited well-described features of INa, IKATP, small cell size, low resting membrane conductance, and inducible low and high voltage-activated ICa, the latter correlating with exocytosis determined by capacitance measurements. In contrast to previous reports, our large sampling of alpha-cells revealed a wide-range data distribution of several ion channel parameters. My findings explain the apparent inconsistency of previous reports wherein alpha-cell ion channel properties appeared skewed within narrow portions of this wide distribution, likely caused by different preparations. In the second part of my thesis, I assessed alpha-cell perturbation in streptozotocin-induced T1D in the GluCre-ROSA26EYFP (GYY) mouse. In this T1D model, alpha-cells exhibited more glucagon content per cell, which can be exocytosed in greater quantity upon serial depolarization. Membrane electrical properties revealed larger Na+ current and reduced KV-transient current, which contributed to the apparent increased amplitude and firing frequency of action potentials in membrane electrical recording. These electrical events likely prime alpha-cells to release more glucagon, culminating in larger in vivo glucagon secretory responses to low glucose stimulation in this T1D model. We are now well-positioned to employ this in situ model of pancreas slice preparation to address many other apparently unanswerable questions in alpha-cells in normal and pathophysiologic states, such as diabetes.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 45-48).

Thesis (M.A.)--York University, 2002. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 63-66). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71617.

The physiologist enjoys a great advantage over the clinical neurologist in the electrical stimulation of muscle, in that he is generally able to kill or anaesthetise his experimental animal and to excise or expose the tissues to be stimulated. The electrical impedance of the preparation is predominantly resistive, and the question of the comfort and safety of the animal scarcely arises. The stimulation of human muscle, on the other hand, normally has to be carried out on ac cious subject, whose comfort and safety must be considered, by means of electric currents applied through electrodes placed in contact with the skin, which exhibits very complex electrical properties. Conflict arises between the requirements of technical accuracy and ease of interpretation of results on the one hand, and comfort and convenience on the other. This thesis represents an attempt to assemble as much as possible of the information required for intelligent solution of the problems encountered in the percutaneous stimulation of muscle. Part I of the thesis reviews published information on nerve, muscle and denervated muscle, the electrical impedance of tissues, and diagnostic and therapeutic stimulation of muscle. Part II describes the author's personal research into the electrical impedance of the body, the interplay between body impedance, stimulator impedance and the electrical excitability characteristics of nerve and muscle, and the influence of these various factors on stimulator performance. In view of the variety of topics involved, the material has been arranged in separate more or less self-contained sections, including discussion of the implications of the results in each section. Technical details of the main electronic devices used are given in the Appendix, (Part III, together with details of the various mathematical analyses and calculations. Part of the work on which this thesis is based was carried out during the tenure of a temporary lectureship in Biophysics donated by the late Sir David Russell, to whom the author is deeply indebted. The author is also greatly indebted to Professor A. E. Ritchie for creating the circumstances which made this work possible, for permitting the author access to unpublished material, and for his patient encouragement and support of this protracted project; to Dr J. Crossland for assistance in the translation of German texts, and to Mr E. Carstairs for advice and assistance in devising the photographic techniques used in recording and reproducing the experimental results.

published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Background: The event related potential (ERP) is an important electrophysiological response to an internal or external stimulus on human body. In some studies, the ERP-based brain computer interface (BCI) systems were created in visual or auditory modality. However, in these type of BCIs, either the eyes or ears of the users are occupied when they are making a choice. It is not convenient to communicate with others. Thus, a somatosensory ERP based BCI can be developed to overcome this issue. According to this, the analysis of somatosensory ERP features is necessary to evaluate if somatosensory ERP is eligible for BCIs as an input. Objective: 1. To study ERP features and design of P300 experiment. 2. To compare three types of P300 features elicited by three modalities. 3. To produce ERP response by electrical stimuli delivered to different position, and analyze ERP features. Methods: Two experiments were conducted. In experiment 1, three modalities, including visual, auditory and electrical modality, were used to produce P300 response. Experiment 2 only presented electrical stimuli. In experiment 1 two electrical stimuli were presented with different intensities at one location, whereas four electrical stimuli were showed at different location with the same intensity. The amplitude and latency were compared among three modalities, and the ERP topography of experiment 2 was also analyzed. Result and conclusion: Fourteen subjects’ data were analyzed in our study. The amplitude and latency of electrical P300 were similar to auditory ERP. But the ERP of visual modality had the largest amplitude and shortest latency. This result shows that electrical P300 can work as well as auditory P300 in BCIs, but not as good as visual P300. In experiment 2, the latency of electrical ERP occurred around 280 ms, and the amplitude and the topography showed that the largest amplitude was located around Cz electrode. This type of ERP in experiment 2 was considered as P3a, which also can be used in BCI systems. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Medical Sciences

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