IU Indianapolis ScholarWorks :: Browsing by Author "Schild, John H."

Browsing by Author "Schild, John H."

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An afferent explanation for sexual dimorphism in the aortic baroreflex of rat
(American Physiological Society (APS), 2014-09-15) Santa Cruz Chavez, Grace C.; Li, Bai-Yan; Glazebrook, Patricia A.; Kunze, Diana L.; Schild, John H.; Department of Biomedical Engineering, Purdue School of Engineering and Technology, IUPUI
Sex differences in baroreflex (BRx) function are well documented. Hormones likely contribute to this dimorphism, but many functional aspects remain unresolved. Our lab has been investigating a subset of vagal sensory neurons that constitute nearly 50% of the total population of myelinated aortic baroreceptors (BR) in female rats but less than 2% in male rats. Termed “Ah,” this unique phenotype has many of the nonoverlapping electrophysiological properties and chemical sensitivities of both myelinated A-type and unmyelinated C-type BR afferents. In this study, we utilize three distinct experimental protocols to determine if Ah-type barosensory afferents underlie, at least in part, the sex-related differences in BRx function. Electron microscopy of the aortic depressor nerve (ADN) revealed that female rats have less myelin (P < 0.03) and a smaller fiber cross-sectional area (P < 0.05) per BR fiber than male rats. Electrical stimulation of the ADN evoked compound action potentials and nerve conduction profiles that were markedly different (P < 0.01, n = 7 females and n = 9 males). Selective activation of ADN myelinated fibers evoked a BRx-mediated depressor response that was 3–7 times greater in female (n = 16) than in male (n = 17) rats. Interestingly, the most striking hemodynamic difference was functionally dependent upon the rate of myelinated barosensory fiber activation. Only 5–10 Hz of stimulation evoked a rapid, 20- to 30-mmHg reduction in arterial pressure of female rats, whereas rates of 50 Hz or higher were required to elicit a comparable depressor response from male rats. Collectively, our experimental results are suggestive of an alternative myelinated baroreceptor afferent pathway in females that may account for, at least in part, the noted sex-related differences in autonomic control of cardiovascular function.
Analysis of Heart Rate Variability in Male and Female Rats
(Office of the Vice Chancellor for Research, 2015-04-17) Ajayi, Tolulope O.; Santa Cruz Chavez, Grace; Schild, John H.
Heart disease is the leading cause of death in the United States. Quantitative measures of cardiovascular function are often essential to effective clinical interventions. The QRS complex is one such measure widely used by cardiologists. These analyses can involve subtle changes in the magnitude and time course of the QRS complex, to differences in the timing between successive heart beats. Electrocardiograms (ECG) are continuous recordings of the QRS complex at various locations across the body surface and provide a comprehensive measurement of the electrical activity of the heart. Knowledge obtained from investigating ECG signal characteristics can help the cardiologist diagnose possible health or cardiac abnormalities such as arrhythmias and can provide objective measures of heart health following injury such as myocardial infarction. Heart rate variability (HRV) can also serve as a reliable indicator of heart health and has been shown to be a strong indicator of mortality and morbidity following myocardial infarction. Unfortunately, very little is known concerning the neurophysiological mechanisms underlying HRV beyond the broader impact of the autonomic nervous system and associated neurocirculatory reflexes. In this research project, we first implemented several established methods for quantifying HRV in male and female rats such as calculating the power spectral density of a long time series of HRV measures, and calculating the standard deviation of the averages of all beat-to-beat intervals in the recording. These measures compared well to those in the literature supporting the accuracy and reliability of the Matlab scripts created to process these data. Simultaneous recordings of the QRS complex and femoral arterial pressure (BP) provided the opportunity to determine how well BP recordings could be used to quantify HRV. In addition, HRV measurements were compared across populations of male and normal, cycling (OVI) and ovariectomized (OVX) female rats in order to determine if HRV is sexually dimorphic. Mentors: John H. Schild, Grace Santa Cruz Chavez, Department of Biomedical Engineering, Purdue School of Engineering and Technology, IUPUI, Indianapolis, IN
Application of quantitative analysis in treatment of osteoporosis and osteoarthritis
(2013-11-08) Chen, Andy Bowei; Yokota, Hiroki, 1955-; Na, Sungsoo; Schild, John H.
As our population ages, treating bone and joint ailments is becoming increasingly important. Both osteoporosis, a bone disease characterized by a decreased density of mineral in bone, and osteoarthritis, a joint disease characterized by the degeneration of cartilage on the ends of bones, are major causes of decreased movement ability and increased pain. To combat these diseases, many treatments are offered, including drugs and exercise, and much biomedical research is being conducted. However, how can we get the most out of the research we perform and the treatment we do have? One approach is through computational analysis and mathematical modeling. In this thesis, quantitative methods of analysis are applied in different ways to two systems: osteoporosis and osteoarthritis. A mouse model simulating osteoporosis is treated with salubrinal and knee loading. The bone and cell data is used to formulate a system of differential equations to model the response of bone to each treatment. Using Particle Swarm Optimization, optimal treatment regimens are found, including a consideration of budgetary constraints. Additionally, an in vitro model of osteoarthritis in chondrocytes receives RNA silencing of Lrp5. Microarray analysis of gene expression is used to further elucidate the mode of regulation of ADAMTS5, an aggrecanase associated with cartilage degradation, by Lrp5, including the development of a mathematical model. The math model of osteoporosis reveals a quick response to salubrinal and a delayed but substantial response to knee loading. Consideration of cost effectiveness showed that as budgetary constraints increased, treatment did not start until later. The quantitative analysis of ADAMTS5 regulation suggested the involvement of IL1B and p38 MAPK. This research demonstrates the application of quantitative methods to further the usefulness of biomedical and biomolecular research into treatment and signaling pathways. Further work using these techniques can help uncover a bigger picture of osteoarthritis's mode of action and ideal treatment regimens for osteoporosis.
Electrophysiological and Pharmacological Properties of the Neuronal Voltage-gated Sodium Channel Subtype Nav1.7
(2007-12) Sheets, Patrick L.; Cummins, Theodore R.; Nicol, Grant D.; Oxford, Gerry S.; Vasko, Michael R.; Schild, John H.
Voltage-gated sodium channels (VGSCs) are transmembrane proteins responsible for the initiation of action potentials in excitable tissues by selectively allowing Na+ to flow through the cell membrane. VGSC subtype Nav1.7 is highly expressed in nociceptive (pain-sensing) neurons. It has recently been shown that individuals lacking the Nav1.7 subtype do not experience pain but otherwise function normally. In addition, dysfunction of Nav1.7 caused by point mutations in the channel is involved in two inherited pain disorders, primary erythromelalgia (PE) and paroxysmal extreme pain disorder (PEPD). This indicates Nav1.7 is a very important component in nociception. The aims of this dissertation were to 1) investigate if the antipsychotic drug, trifluoperazine (TFP), could modulate Nav1.7 current; 2) examine changes in Nav1.7 properties produced by the PE mutation N395K including sensitivity to the local anesthetic (LA), lidocaine; and 3) determine how different inactivated conformations of Nav1.7 affect lidocaine inhibition on the channel using PEPD mutations (I1461T and T1464I) that alter transitions between the different inactivated configurations of Nav1.7. Standard whole-cell electrophysiology was used to determine electrophysiological and pharmacological changes in WT and mutant sodium currents. Results from this dissertation demonstrate 1) TFP inhibits Nav1.7 channels through the LA interaction site; 2) the N395K mutation alters electrophysiological properties of Nav1.7 and decreases channel sensitivity to the local anesthetic lidocaine; and 3) lidocaine stabilizes Nav1.7 in a configuration that decreases transition to the slow inactivated state of the channel. Overall, this dissertation answers important questions regarding the pharmacology of Nav1.7 and provides insight into the changes in Nav1.7 channel properties caused by point mutations that may contribute to abnormal pain sensations. The results of this dissertation on the function and pharmacology of the Nav1.7 channel are crucial to the understanding of pain pathophysiology and will provide insight for the advancement of pain management therapies.
Experimental and Computational Analysis of Dynamic Loading for Bone Formation
(2013-11-12) Dodge, Todd Randall; Wallace, Joseph; Na, Sungsoo; Yokota, Hiroki, 1955-; Schild, John H.
Bone is a dynamic tissue that is constantly remodeling to repair damage and strengthen regions exposed to loads during everyday activities. However, certain conditions, including long-term unloading of the skeleton, hormonal imbalances, and aging can disrupt the normal bone remodeling cycle and lead to low bone mass and osteoporosis, increasing risk of fracture. While numerous treatments for low bone mass have been devised, dynamic mechanical loading modalities, such as axial loading of long bones and lateral loading of joints, have recently been examined as potential methods of stimulating bone formation. The effectiveness of mechanical loading in strengthening bone is dependent both on the structural and geometric characteristics of the bone and the properties of the applied load. For instance, curvature in the structure of a bone causes bending and increased strain in response to an axial load, which may contribute to increased bone formation. In addition, frequency of the applied load has been determined to impact the degree of new bone formation; however, the mechanism behind this relationship remains unknown. In this thesis, the application of mechanical loading to treat osteoporotic conditions is examined and two questions are addressed: What role does the structural geometry of bone play in the mechanical damping of forces applied during loading? Does mechanical resonance enhance geometric effects, leading to localized areas of elevated bone formation dependent on loading frequency? Curvature in the structure of bone was hypothesized to enhance its damping ability and lead to increased bone formation through bending. In addition, loading at frequencies near the resonant frequencies of bone was predicted to cause increased bone formation, specifically in areas that experienced high principal strains due to localized displacements during resonant vibration. To test the hypothesis, mechanical loading experiments and simulations using finite element (FE) analysis were conducted to characterize the dynamic properties of bone. Results demonstrate that while surrounding joints contribute to the greatest portion of the damping capacity of the lower limb, bone absorbs a significant amount of energy through curvature-driven bending. In addition, results show that enhanced mechanical responses at loading frequencies near the resonant frequencies of bone may lead to increased bone formation in areas that experience the greatest principal strain during vibration. These findings demonstrate the potential therapeutic effects of mechanical loading in preventing costly osteoporotic fractures, and explore characteristics of bone that may lead to optimization of mechanical loading techniques. Further investigation of biomechanical properties of bone may lead to the prescribing of personalized mechanical loading treatments to treat osteoporotic diseases.
Exploration of Sinusoidal Low Frequency Alternating Current Stimulation to Block Peripheral Nerve Activity
(2024-05) Horn, Michael Ryne; Yoshida, Ken; Ward, Mathew P.; Berbari, Edward J.; Schild, John H.
Sinusoidal low frequency alternating current (LFAC) stimulation is a novel mode of electrical modulation observed in the Bioelectroics Lab in 2017. LFAC is capable of blocking the single fiber action potentials (APs) of the earthworm with only a few 100’s of µA. The goal of this dissertation was to further explore and characterize the LFAC waveform to determine it’s feasibility as a method for block in the mammalian peripheral nervous system (PNS). To better understand the mechanisms of LFAC block (LFACb), a blend of in-silico modeling work was explored and the predictions were validated with ex-vivo and in-vivo experiments. This dissertation is divided into five chapters. The first chapter will explore the history of bioelectricity, the current state of in-silico modeling and methods of nerve block used in the PNS. The second chapter explores a major modeling assumption, the conductivity and permittivity of the nerve laminae of a mammalian nerve bundle. Four point electrochemical impedance spectroscopy (EIS) was performed on excised canine vagus nerve to evaluate the electrical properties of the perineurium and epineurium. This study’s result, found that the corner frequency of the perineurium (2.6kHz) and epineurium (370Hz) were much lower than previously assumed. This explain a major difference between LFACb and the more established kilohertz frequency alternating current (kHFAC) block. The third chapter revisits the initial earthworm experiments during the discovery of LFACb. The effect of conduction slowing was observed in these earthworm experiments and were also seen in a mammalian canine vagus nerve and in the Horn-Yoshida-Schild (HYS) autonomic unmyelinated axon mode. These experiments showed that LFACb occurs as a cathodic block in which the sodium channels are held inactive. Chapter 4 explored the window between LFACb and LFAC activation (LFACa). The window between the two states was describes by LFAC amplitude and LFAC frequency in an in-vivo rat sciatic nerve and an in-silico model of a myelinated motor neuron, the McIntyre-Richardson-Grill (MRG) axon model. Geometrical effects were also observed by varying the bipolar pair of contacts used to deliver the LFACb waveform from an asymmetrical tripolar cuff electrode. Plantar flexor force measurements and electromyography (EMG) of the lateral gastrocnemius (LG) and soleus (Sol) were used to quantify the effects of the LFAC waveform. Convergence between in-silico modeling and in-vivo results showed promise that modeling efforts could be used with confidence to explore the LFAC block-activation more completly. LFACa was found to be highly dependent on frequency with increasing frequency lowering the threshold of activation. LFACb was shown to be mostly invariant to frequency. The final chapter takes the information found in this dissertation and summarizes it. Future work on LFAC is also proposed and the hypothesized results presented with the findings from this dissertation and available literature.
Functional contributions of a sex-specific population of myelinated aortic baroreceptors in rat and their changes following ovariectomy
(2014) Santa Cruz Chavez, Grace C.; Schild, John H.; Nicol, Grant D.; Oxford, Gerry S.; Rusyniak, Daniel E.; Vasko, Michael R.
Gender differences in the basal function of autonomic cardiovascular control are well documented. Consistent baroreflex (BRx) studies suggest that women have higher tonic parasympathetic cardiac activation compared to men. Later in life and concomitant with menopause, a significant reduction in the capacity of the BRx in females increases their risk to develop hypertension, even exceeding that of age-matched males. Loss of sex hormones is but one factor. In female rats, we previously identified a distinct myelinated baroreceptor (BR) neuronal phenotype termed Ah-type, which exhibits functional dynamics and ionic currents that are a mix of those observed in barosensory afferents functionally identified as myelinated A-type or unmyelinated C-type. Interestingly, Ah-type afferents constitute nearly 50% of the total population of myelinated aortic BR in female but less than 2% in male rat. We hypothesized that an afferent basis for sexual dimorphism in BRx function exists. Specifically, we investigated the potential functional impact Ah-type afferents have upon the aortic BRx and what changes, if any, loss of sex hormones through ovariectomy brings upon such functions. We assessed electrophysiological and reflexogenic differences associated with the left aortic depressor nerve (ADN) from adult male, female, and ovariectomized female (OVX) Sprague-Dawley rats. Our results revealed sexually dimorphic conduction velocity (CV) profiles. A distinct, slower myelinated fiber volley was apparent in compound action potential (CAP) recordings from female aortic BR fibers, with an amplitude and CV not observed in males. Subsequent BRx studies demonstrated that females exhibited significantly greater BRx responses compared to males at myelinated-specific intensities. Ovariectomy induced an increased overall temporal dispersion in the CAP of OVX females that may have contributed to their attenuated BRx responses. Interestingly, the most significant changes in depressor dynamics occurred at electrical thresholds and frequencies most closely aligned with Ah-type BR fibers. Collectively, we provide evidence that, in females, two anatomically distinct myelinated afferent pathways contribute to the integrated BRx function, whereas in males only one exists. These functional differences may partly account for the enhanced control of blood pressure in females. Furthermore, Ah-type afferents may provide a neuromodulatory pathway uniquely associated with the hormonal regulation of BRx function.
GATING OF THE SENSORY NEURONAL VOLTAGE-GATED SODIUM CHANNEL NAv1.7: ANALYSIS OF THE ROLE OF D3 AND D4 / S4-S5 LINKERS IN TRANSITION TO AN INACTIVATED STATE
(2010-04-01T15:56:49Z) Jarecki, Brian W.; Cummins, Theodore R.; Nicol, Grant D.; Oxford, G. S.; Hudmon, Andrew; Schild, John H.
Voltage-gated sodium channels (VGSCs) are dynamic membrane-spanning proteins crucial for determining the electrical excitability in nerve and muscle. VGSCs transition, or gate, between opened, closed, and inactivated states, in response to changes in transmembrane potential. Altered VGSC gating can affect electrical communication and is implicated in numerous channelopathies. Nav1.7, a VGSC isoform highly expressed in the peripheral nervous system, plays a unique role in pain perception as evidenced by single point missense mutations causing a spectrum of pain syndromes (inherited erythromelalgia; IEM and paroxysmal extreme pain disorder; PEPD) and nonsense mutations resulting in human insensitivity to pain (CIP). These studies indicate Nav1.7 is critical in pain transduction and, as such, structural perturbations to Nav1.7 affecting conformational stability and response to changes in transmembrane potential have the potential to cause pain. Therefore, the aims of this dissertation were to (1) examine the effects of PEPD mutations on the voltage-dependent properties Nav1.7; (2) investigate the effects Nav1.7 alternative splicing has on the impact of IEM and PEPD mutations; (3) evaluate the effects channelopathies, resulting from slowed inactivation, have on modulating an unusual type of sodium current that flows during membrane repolarization; and (4) determine the structural components involved in stabilizing Nav1.7 inactivation. Standard patch-clamp electrophysiology was used to study changes in channel properties. Results from this dissertation demonstrate that (1) PEPD mutations significantly shift the voltage-dependent properties of Nav1.7 channels, destabilize an inactivated state in a residue specific manner, and render nociceptive neurons hyperexcitable; (2) alternative splicing can functionally impact PEPD; (3) channelopathies, resulting from slowed inactivation in neuronal and muscle VGSC isoforms, increase an unusual sodium conductance that flows during repolarization; and (4) specific residues located in distinct regions of Nav1.7 serve as docking sites to stabilize inactivation at different membrane potentials. Overall, this dissertation answers key questions regarding the molecular mechanics required during inactivation and the biophysical consequences of Nav1.7 mutations implicated in painful disorders. The results of this dissertation are important for a more detailed understanding of pain perception and validate the applicability of studying Nav1.7 for discovery of therapeutic targets for treatment of pain. – Theodore R. Cummins, Chair
KCa1.1 β4-subunits is not responsible for iberiotoxin-resistance in baroreceptor neurons in adult male rats
(Elsevier, 2015) Xu, Wen-Xiao; Ban, Tao; Wang, Lu-Qi; Zhao, Miao; Yin, Lei; Li, Guo; Chen, Hanying; Schild, John H.; Qiao, Guo-Fen; Yan, Jing-Long; Li, Bai-Yan; Biomedical Engineering, School of Engineering and Technology
Multi-scale analysis of morphology, mechanics, and composition of collagen in murine osteogenesis imperfecta
(2013-11-06) Bart, Zachary Ryan; Wallace, Joseph; Na, Sungsoo; Yokota, Hiroki, 1955-; Schild, John H.
Osteogenesis imperfecta is a rare congenital disease commonly characterized by brittle bones caused by mutations in the genes encoding Type I collagen, the single most abundant protein produced by the body. The murine model (oim) exists as a natural mutation of this protein, converting its heterotrimeric structure of two Col1a1 molecules and a single Col1a2 molecule into homotrimers composed of only the former. This defect impacts bone mechanical integrity, greatly weakening their structure. Femurs from male wild type (WT), heterozygous (oim/+), and homozygous (oim/oim) mice, all at 12 weeks of age, were assessed using assays at multiple length scales with minimal sample processing to ensure a near-physiological state. Atomic force microscopy (AFM) demonstrated detectable differences in the organization of collagen at the nanometer scale that may partially attribute to alterations in material and structural behavior obtained through mechanical testing and reference point indentation (RPI). Changes in geometric and chemical structure through the use of µ-Computed Tomography and Raman spectroscopy respectively indicate a smaller, brittle phenotype caused by oim. Changes within the periodic D-spacing of collagen point towards a reduced mineral nucleation site, supported by reduced mineral crystallinity, resulting in altered material and structural behavior in oim/oim mice. Multi-scale analyses of this nature offer much in assessing how molecular changes can compound to create a degraded, brittle phenotype.

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