No description available.

The aim of this project was to determine the neurotrophic factor survival requirements of PNS neurons during development and to clarify the role of certain receptors in mediating responsiveness. Members of the neurotrophin family of neurotrophic factors (NGF, BDNF, NT3 and NT4/5) and neurotrophic cytokines (CNTF, LIF, OSM, IL-6 and CT-1) were studied. The activity of a recently identified neurotrophin, NT4/5, was investigated in vitro. In cultures of mouse neurons, mammalian NT4/5 promoted the survival of the same kinds of neurons as BDNF and was as potent as BDNF, which is consistent with the action of both neurotrophins on the same receptor, TrkB. However, both mammalian NT-4/5 and the Xenopus homologue were less potent than mammalian BDNF on chicken embryo neurons, which is consistent with the lower evolutionary conservation of NT4/5. Interestingly, mammalian NT4/5 exhibited differences in potency on certain populations of chicken neurons that responded equally well to BDNF, and this may reflect differences in TrkB receptors in these different populations of neurons. To clarify the role of the common neurotrophin receptor in modulating the response of neurons to NGF, I then compared the actions of NGF with a mutated NGF protein that binds to TrkA, but does not bind to p75. At subsaturating concentrations, the NGF mutant was less effective than NGF in promoting the survival of embryonic sensory neurons and postnatal sympathetic neurons but was equally effective as NGF in promoting the survival of embryonic sympathetic neurons, indicating that binding of NGF to p75 enhances the sensitivity of NGF-dependent neurons to NGF at certain stages of development. To investigate if neurotrophic cytokines act on developing sensory neurons, I studied their effects in vitro. Whereas trigeminal neurons were responded to cytokines in the late fetal period, nodose neurons were supported by these factors throughout embryonic development. These findings indicate that different populations of PNS neurons display different patterns of responsiveness to neurotrophic cytokines during development.

BDNF binds to two transmembrane receptors: trkB, which is a tyrosine kinase essential for signalling, and p75, which is a common neurotrophin receptor whose role is contoversial. To determine the relationship between BDNF synthesis, BDNF receptor expression, and neuronal responsiveness, the expression of BDNF, trkB, and p75 mRNAs were studied for different populations of sensory neurons whose axons reach their targets and become dependent on BDNF for survival at different times. BDNF mRNA was expressed in the peripheral and central targets of these neurons prior to the arrival of sensory axons. The onset of BDNF responsiveness was preceded by the expression of first p75 mRNA then trkB mRNA, and neurons that start responding to BDNF early were the first to express trkB mRNA. BDNF upregulated trkB mRNA expression just shortly before the onset of BDNF dependence. BDNF is expressed not only in sensory neuron targets but in some of these neurons themselves. To determine whether BDNF is synthesized in NGF-dependent or BDNF-dependent neurons, BDNF mRNA expression was studied in purified populations of cranial sensory neurons that depend on either NGF or BDNF for survival. During the period of neuronal death, BDNF mRNA expression was highest in NGF-dependent cutaneous sensory neurons, lower in BDNF-dependent cutaneous sensory neurons, and undetectable in BDNF-dependent proprioceptive neurons. In coculture, NGF-dependent neurons promoted the survival of BDNF-dependent neurons by the production and release of BDNF, implying a paracrine role for BDNF during the period of naturally occurring neuronal death. To determine if the level of p75 expression in sensory neurons is related to the particular neurotrophin they require for survival, p75 mRNA levels were measured in purified populations of cranial sensory neurons. No clear relationship between the level of p75 mRNA expression and neuron type was observed. Studies of the regulation of p75 mRNA expression in sympathetic neuroblasts revealed that retinoic acid increased and membrane depolarization using KCl decreased the levels of p75 mRNA.

No description available.

Heart rate is modulated by the opposing activities of sympathetic and parasympathetic inputs to pacemaker cardiomyocytes in the sinoatrial (SA) node. Parasympathetic activity on nodal myocytes is mediated by acetylcholine-dependent stimulation of M2 muscarinic receptors and activation of Gαi/o signalling. Although, regulators of G-protein signalling (RGS) proteins are potent inhibitors of Gαi/o signalling in many tissues, the RGS protein(s) that regulate parasympathetic tone in the SA node are unknown. Our results demonstrate that RGS4 mRNA levels are higher in the SA node compared to right atrium. Conscious freely moving RGS4-null mice showed a greater extent of bradycardia in response to parasympathetic agonists compared to wild-type animals. Moreover, anaesthetized rgs4-null mice had lower baseline heart rates and greater heart rate increases following atropine administration. Retrograde-perfused hearts from rgs4-null mice also showed enhanced negative chronotropic responses to carbachol, while isolated SA node myocytes showed greater sensitivity to carbachol-mediated reduction in the action potential firing rate. Finally, rgs4-null SA node cells showed decreased levels of G-protein-coupled inward rectifying potassium (GIRK) channel desensitization, and altered modulation of acetylcholine-sensitive potassium current (IKACh) kinetics following carbachol stimulation. Taken together, our studies establish that RGS4 plays an important role in regulating sinus rhythm by inhibiting parasympathetic signalling and IKACh activity. Following these results, we predicted that loss of RGS4 expression and function will result in increased levels of parasympathetic effector activity leading to increased susceptibility to atrial fibrillation. Susceptibility to atrial fibrillation (AF) depends strongly on parasympathetic activity. Since RGS4 inhibits parasympathetic / M2-dependent Gαi/o signalling in the SA node, we explored whether changes in RGS4 levels altered the susceptibility of atrial fibrillation. We found that, RGS4 levels were decreased in atria of tachypaced dogs prior to their development of chronic AF. Moreover, in vivo ECG recordings of anaesthetized mice showed greater susceptibility to AF while optical mapping of isolated atrial preparations using a voltage-sensitive dye revealed greatly increased susceptibility to rotor formation when RGS4 was ablated. Consistent with altered parasympathetic signalling in the myocardium of rgs4-null mice, IKACh evoked by carbachol application were greater in isolated atrial myocytes from rgs4-null mice. These IKACh changes were, as expected, associated with marked action potential duration shortening in response to parasympathetic activation, but not to slower conduction velocities. Together, our findings establish that RGS4 protects atrial tissues from excess parasympathetic signalling that predispose to atrial fibrillation.

In the thesis, we study the data collected from VICU of Kaohsiung Veterans General Hospital.The data consists of the following two kinds. The data of the first kind is ten minute ECG data with sampling frequency 500Hz. The data of the second kind is long term one minute average heart rate. There are two main topics studies in this thesis. In the first part, we consider the standard deviations which be taked log and medians of RR intervals, PR intervals and RT intervals, respectively derived from first kind data. By considering the odds ratio¡Bsensitivity and specificity, and we select the heart classification vectors. The object is to classify among normal and ventricular heart disease (VSD), normal and ventricular heart disease with congestive heart failure (VSD+CHF). We proposed a method of both variables and two-step classification procedure. Furthermore, we built the logistic regression models. In the second part, we derive the distribution of the spectrum power ratio of low frequency to high frequency. Shewhart control chart and Tabular cusum chart are constructed to monitor RG. Also, we discover the periodicity of RG. Finally, there exists positive correlation between RA¡]or RG¡^ and autocorrelation of lag one of RR interval.

Spectral analysis of heart rate variability (HRV) has been applied in many medical research to study autonomic nervous system activity. In these studies, the researchers found that (i) ratio of low frequency (LF) to high frequency (HF) spectrum power is a useful measure of sympathetic/parasympathetic balance, and (ii) low heart rate variability is an important risk factors for patients. Therefore, continuous monitoring of the ratio and heart rate variability have the potential to early detect physiological deterioration of patients. This thesis consists of the following two parts. In the first part, we establish control charts monitoring heart rates and low HRV. Numerical method is applied to compute exact control limits of the EWRMS and EWMV charts. The distribution of the conventional LF/HF ratio statistic is difficult to derive, significant of alterations in HRV parameters can not be assessed efficiently. We resolve this problem in the second part, a new equivalently useful ratio statistic is proposed whose distribution can be derived more easily. Based on the derived distribution, the probability control limits of the proposed statistic are calculated. In application, we construct Shewhart charts of the newly proposed ratio statistic and EWRMS, EWMV charts of the heart rate variability to monitor the risk factors of patients in vascular intensive care unit. Furthermore, we define a risk score which combining the two risk factors together, heart rate variability and LF/HF spectrum power ratio. The results show that the higher risk scores corresponding to patients after operation in severer condition.

Heart rate is modulated by the opposing activities of sympathetic and parasympathetic inputs to pacemaker cardiomyocytes in the sinoatrial (SA) node. Parasympathetic activity on nodal myocytes is mediated by acetylcholine-dependent stimulation of M2 muscarinic receptors and activation of Gαi/o signalling. Although, regulators of G-protein signalling (RGS) proteins are potent inhibitors of Gαi/o signalling in many tissues, the RGS protein(s) that regulate parasympathetic tone in the SA node are unknown. Our results demonstrate that RGS4 mRNA levels are higher in the SA node compared to right atrium. Conscious freely moving RGS4-null mice showed a greater extent of bradycardia in response to parasympathetic agonists compared to wild-type animals. Moreover, anaesthetized rgs4-null mice had lower baseline heart rates and greater heart rate increases following atropine administration. Retrograde-perfused hearts from rgs4-null mice also showed enhanced negative chronotropic responses to carbachol, while isolated SA node myocytes showed greater sensitivity to carbachol-mediated reduction in the action potential firing rate. Finally, rgs4-null SA node cells showed decreased levels of G-protein-coupled inward rectifying potassium (GIRK) channel desensitization, and altered modulation of acetylcholine-sensitive potassium current (IKACh) kinetics following carbachol stimulation. Taken together, our studies establish that RGS4 plays an important role in regulating sinus rhythm by inhibiting parasympathetic signalling and IKACh activity. Following these results, we predicted that loss of RGS4 expression and function will result in increased levels of parasympathetic effector activity leading to increased susceptibility to atrial fibrillation. Susceptibility to atrial fibrillation (AF) depends strongly on parasympathetic activity. Since RGS4 inhibits parasympathetic / M2-dependent Gαi/o signalling in the SA node, we explored whether changes in RGS4 levels altered the susceptibility of atrial fibrillation. We found that, RGS4 levels were decreased in atria of tachypaced dogs prior to their development of chronic AF. Moreover, in vivo ECG recordings of anaesthetized mice showed greater susceptibility to AF while optical mapping of isolated atrial preparations using a voltage-sensitive dye revealed greatly increased susceptibility to rotor formation when RGS4 was ablated. Consistent with altered parasympathetic signalling in the myocardium of rgs4-null mice, IKACh evoked by carbachol application were greater in isolated atrial myocytes from rgs4-null mice. These IKACh changes were, as expected, associated with marked action potential duration shortening in response to parasympathetic activation, but not to slower conduction velocities. Together, our findings establish that RGS4 protects atrial tissues from excess parasympathetic signalling that predispose to atrial fibrillation.

Although parasympathetic activity (PNS) is the primary driver and sympathetic activity (SNS) is a significant inhibitor of colonic propulsive activity, they are rarely measured, and hence, they almost play no role in diagnosing dysfunction or standard treatments for chronic conditions such as refractory constipation. We aimed to develop methodologies for the assessment of autonomic nervous system (ANS) activity, establish criteria for autonomic dysfunction, and study if stimulation of lumbar and sacral autonomic nerves using low-level laser therapy (LLLT) could affect the ANS and explore it as a potential treatment of autonomic dysfunction to restore colonic motility. By studying the active standing test and the table tilt test as a method to evoke activity in the ANS, we rejected LF power, SD1 and SD2 of Poincare plot, Pre-ejection-period (PEP), complex-correlation-measure (CCM) and detrended fluctuation analysis (DFA). Respiratory-Sinus-Arrhythmia (RSA), Root-Mean-Square-of-Successive-Differences (RMSSD) were selected for PNS activity, the Baevsky’s-Stress-Index (SI) was chosen for SNS activity, and SI/RSA and SI/RMSSD were introduced as a measure of autonomic balance. We explored high-resolution-colonic-manometry with concurrent electrocardiography to observe whether these parameters could be associated with ANS changes during colonic motor patterns. High-amplitude-propagating-pressure-waves were associated with a strong parasympathetic activity and decreased sympathetic activity. Comparing ANS reactivity of patients with severe motility disorders to controls in response to postural changes, we observed that most patients have low PNS and elevated SNS baseline activity and reactivity. This established a way to evaluate autonomic dysfunction in patients with colon motor disorders. A single session of LLLT using LED and laser light on the lumbar and sacral spine in 41 patients with chronic gastrointestinal motor dysfunction indicated that treatments with LED light followed by laser light significantly increased parasympathetic activity and decreased sympathetic nervous system activities. These results initiated a study into the effects of LLLT on restoring autonomic dysfunction in chronic refractory colonic motility disorders. / Thesis / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.