bluuebunny/crossref_metadata_2025 huggingface dataset:
Central Angiotensin Type 2 Receptor (AT2R) Stimulation Promotes Enhanced Extinction of Fear Learning Independent of Cardiovascular Measures
Authors: Swiercz Adam P. , Wiaderkiewicz Jan P. , Moshfegh Cassandra , Hopkins Lauren , Marvar Paul J.
Published: November 2023

Angiotensin II receptor subtypes (AT1R and AT2R) are found in regions of the brain critical to the expression and extinction of conditioned fear, however the neurobiological role(s) remain unknown. We propose that brain angiotensin receptors contribute to modulating inhibitory and excitatory conditioned fear circuits, that maybe important in the pathology of posttraumatic stress disorder (PTSD). The objective of this study was to investigate the role of brain AT2R activation in fear memory. To study learned fear, C57BL/6 J mice (n= 6–10/group) underwent classical Pavlovian fear conditioning, pairing auditory cues with foot shocks. The neural circuitry underlying the fear response is highly conserved across mammalian species, making rodent models a valuable tool in the study of fear learning disorders, such as PTSD. The percentage of time spent freezing in response to a conditioned stimulus is used to quantify the ability to learn and remember fearful associations. Using this model, the expression of learned fear is tested 24 hours after conditioning, and memory retention one day later. Following the acquisition of fear, AT2R mRNA expression was elevated in the central amygdala (CeA) (t(22) = 2.5; p<0.05), a critical region involved in the consolidation of fear memory. To further evaluate the functional role of brain AT2R, we administered (intra‐cerebral ventricle ‐ ICV) the highly selective AT2R agonist Compound 21 (C21). A single ICV injection of C21 at either 0.06ug/ul or 0.1ug/ul was administered prior to fear expression testing. Acute C21 (0.1ug/ul) treated mice showed a significant reduction in both fear expression (% freezing) (saline – 62.5% vs C21 ‐ 41.2%) (t(27) = 2.8; p<0.05) and fear memory retention (saline – 52.9% vs C21 – 22.6%) (t(28) = 3.8; p<0.05) following the acquisition of fear. Similarly, mice receiving C21 ICV for 2 weeks showed a trend for a reduction in fear memory retention (saline – 57.2% vs C21 – 39.6%) (t(14) = 1.0; p=0.06 and this was independent of behavioral measures of anxiety as determined by open field testing. Moreover, C21 did not affect blood pressure or heart rate in telemetry‐implanted mice (Saline‐144 ± 3 SBP mmHg, HR 507 ± 13 bpm, n=5; C21 ‐ 136 ± 3 SBP mmHg; HR 518 bpm ± 26, n=4). These data suggest that activation of central AT2 receptors promote the extinction of learned fear. Further studies are required to determine the neurobiological mechanism(s), which may involve changes in cerebral vascular blood flow and/or modulation of neuronal excitability and plasticity.

Support or Funding Information

NIH R00 HL107675‐03 AHA 15CSA24340001
Stress and Insufficient Nutrition Program Abnormal Growth of the Embryo
Authors: Nishimura Hiroko , Yaoita Eishin , Sequeira Lopez Maria Luisa S.
Published: November 2023

Stress and insufficient nutrition in fetal life impose a risk of low birth weight (LBW) and increased vulnerability for chronic childhood and adult diseases. Using a unique avian embryo model, we reported previously that impaired nutrition caused LBW and, after maturation, a low number of nephrons and glomerular mesangium lesions partly resembling nephrosclerosis. In the present study, we determined in Japanese quail, Coturnix japonica, whether the stress imposed on the embryo during the early period of development induces structural defect, whereas insufficient nutrition causes impaired growth and maturation. We also examined whether α‐smooth muscle actin (α‐SMA) may serve as an injury/inflammation marker in glomerular mesangium. We found: 1) At embryonic day 8–9 (E8–9), 45.1% (n = 31) of embryos derived from eggs in which 10% of the egg‐white was withdrawn (EwW) before the start of incubation showed abnormal growth, malformation, and/or early death. At E15–16 (hatch, E17) the rate of abnormal growth/structure was lower (26.4%, n = 34). 2) The weight of the EwW embryos that showed good growth (0.74 ± 0.03 g, n = 8) was not significantly different from that of controls (CT, 0.79 ± 0.02 g, n = 14) at E8–E9, but it was lower (P < 0.01) at E16 (CT, 5.9 ± 0.2 g, n = 13; EwW, 5.2 ± 0.1 g, n = 14). 3) α‐SMA signals were present in renal arteries and arterioles, glomerular mesangium, and peritubular capillaries of embryonic kidneys. α‐SMA signals were stronger in EwW groups both in E16 embryos and in hatched quail. These results suggest that partial withdrawal of egg‐white (92% is protein) before incubation induces structural defect, possibly due to mechanical stress of egg‐white withdrawal (gentle suction via G18 blunt needle), whereas the effect of low nutrition was more obvious in the later embryonic period. α‐SMA in glomerular mesangium may serve as an injury‐inflammation marker in quail kidneys.
Psychosocial stress exacerbates disease outcome in mice with muscular dystrophy
Authors: Sabharwal Rasna , Poglitsch Marko , Yang Liping , Weiss Robert M
Published: November 2023

Muscular dystrophy is a progressive disease of muscle weakness, muscle atrophy and dilated cardiomyopathy (DCM). We have demonstrated that sarcoglycan delta deficient (Sgcd−/−) mice, an established model of muscular dystrophy, exhibit angiotensin II (Ang II)‐dependent autonomic dysfunction at a young age which worsens with aging, and predicts development of DCM [Exp Physiol 2015]. Patients afflicted with muscular dystrophy often exhibit symptoms of psychosocial stress such as cognitive impairment, depression, sadness, and anxiety. Several studies indicate that there is a bidirectional association between psychosocial stress and cardiac risk. Therefore, our goals were to determine whether (i) psychological stress and autonomic dysfunction synergistically confer susceptibility to cardiac arrhythmias and sudden death in Sgcd−/− mice; and (ii) activation of the cardiac renin angiotensin system (RAS) contributes to these catastrophic events in the Sgcd−/− mice. Blood pressure (BP), heart rate (HR), electrocardiogram and HR variability (HRV) were measured by telemetry in control C57BL/6J (n=6) and Sgcd−/− (n=8) middle‐aged mice (50–60 weeks of age). Cardiac RAS peptides were measured by mass spectrometry while Ang II type 1 receptor (AT1R) expression was quantified by immunofluorescence. Exposure to acute mild psychosocial stress (~15 min exposure to intruder mouse) transiently increased HR and decreased HRV, which was followed by progressive bradyarrhythmias, hypotension, and death in 40% of Sgcd−/− mice (all P<0.05 vs. C57BL/6J). Interestingly, Sgcd−/− mice exhibited profound increases in plasma corticosterone (+86%) and cardiac Ang II (+67%), and AT1Rs (+72%), Masson); while level of the cardioprotective peptide Ang‐[1–7] was markedly decreased (−75%) (all P<0.05 vs. C57BL/6J). We conclude that middle‐aged Sgcd−/− mice exhibit activation of the cardiac RAS and are susceptible to stress‐induced cardiac arrhythmias and sudden death.
Utilization of mechano‐biological models to predict cell adhesion interactions between bone marrow endothelial cells and breast cancer cells.
Authors: Irons Linda , Xie Leike , Owen Markus , Hill Michael A. , Martinez‐Lemus Luis A. , Glinski Olga , Glinsky Vladislav V. , O'Dea Reuben , Brook Bindi , Meininger Gerald A.
Published: November 2023

The purpose of our study was to produce a mechano‐biological model that could characterize and predict adhesive interactions between human breast cancer cells (MB435) and human bone marrow endothelial cells (HBME). Bone is a common site of metastasis for breast cancer and the mechanisms of metastasis are not fully characterized. In this study we have combined experimental and modelling approaches to probe interactions of human bone marrow endothelial cells (HBMEC‐60) with breast cancer cells (MB435). Specifically, atomic force microscopy (AFM) was used to measure adhesion forces between a single MB435 cell (attached to the AFM tip) and a monolayer of HBMEC‐60 cells for differing times of contact. In addition, we developed a stochastic model of the individual adhesive interactions that occur between the two cell‐types to mimic the AFM experimental protocol. This was accomplished by formulating a 2D discrete stochastic‐elastic computational model to study the adhesion binding dynamics that underpin cell‐cell attachment. The model allows detailed quantification in binding dynamics and the location, lifetime, and strength of cell‐cell adhesions. To describe cell‐cell interactions, we considered the following components within a discrete stochastic computational framework: intracellular actin in each cell and adhesion proteins in the cell membranes in 4 possible states: freely diffusing, actin‐bound to the first cell, actin‐bound to the second cell and fully‐bound to cytoskeleton within both cells. Adhesions between the cytoskeleton networks of the two cells were connected to form a network of springs according to the transitions, which obey stochastic binding/unbinding events. Free adhesion molecules diffused via a random walk. The dynamically changing network structure was coupled to the local mechanical environment through force‐dependent binding/unbinding propensities. Experimentally, we found that peak adhesion forces increased with increasing contact time between the MB435 and HBMEC‐60 cells and that total adhesion force increased dramatically within the first 30 sec of contact which then gradually plateaued. These experimental data demonstrate a strong dependence of MB435‐HBME adhesion strength on cell‐cell contact time. Additionally, we found that our stochastic computational model recapitulated these experimental findings, suggesting that important mechanisms have been captured in the model. This validates our experiment vs. model approach and is therefore allowing us to interrogate the model further to derive further insights into the cell‐cell interactions observed here.
Numerical Determination of Wall Shear Stress in Red Blood Cell Membranes
Authors: Cabrales Pedro , Jani Vivek
Published: November 2023

Red cells in microvessels deform extensively in order to flow, thus resulting in high observed apparent viscosities and high stress concentrations localized to the red cell membrane. Flow through microvessels is consequently aided by the high compliance in the red cell membrane. However, changes in the mechanical properties of Red Blood Cells (RBC) as a result of storage lesions, can increase stress concentrations in the membrane, impairing oxygen transport and resulting in increased vesiculation and likely cell lysis. The objective of this study is to determine the mechanical properties and thus wall shear stress experienced by a RBC membrane during capillary flow. The RBC membrane is modeled as a two dimensional Hookean Isotropic Solid. Videos of capillary flow of both fresh RBCs and RBCs stored for 2 weeks were taken in the rat cremaster muscle. The mechanical properties, including the elastic modulus, shear stress, and shear strain, of both conditions were compared for both groups. In order to determine strain, each RBC membrane will be parameterized by N (X,Y) points determined by the Moore Neighbor Tracing algorithm of videos of capillary flow obtained by intravital microscopy of the rat cremaster muscle, from which N deformation gradient tensors, [F], can be obtained numerically for each frame of the video. From these deformation gradient tensors, the updated Cauchy Strain Tensor will be determined as a function of position on the Cartesian plane relative to the centroid of the RBC. The strains determined from the updated Langrangian Green Strain are numerically fit to the Navier‐Lame Equations along the boundary of the RBC to experimentally fit the two Lame's Constants during capillary flow. These constants will then be used to determine the Cauchy Stress Tensor, using Hooke's Law, along the boundary of the RBC, allowing for the calculation of the Wall Shear Stress. The average Elastic Modulus of fresh cells was found to be 5.4 ± 0.4 × 106 N/m2, while of that of RBCs stored for two weeks was found to be statistically larger and was calculated to be 6.0 ± 1.0 × 106 N/m2. Additionally, stored RBCs experienced higher shear strains and wall shear strains over larger areas of the membrane as compared with stored cells. Additionally, stress concentrators in the membrane were observed at the points of contact with the capillary wall. However, for stored cells, the high stress acted on a larger segment of the membrane. This algorithm for determining wall shear stress experienced by RBC membranes in vivo during capillary flow was thus able to detect statistically significant differences in the both the mechanical properties and stress concentrations between fresh cells and stored cells.

Support or Funding Information

This work was supported by NIH grants from the Heart Lung and Blood Institute, P01‐HL110900, R56‐HL123015, and R01‐HL126945.
Mechanical Properties of Lymphangions that Optimize Stroke Work in a Lymphatic Network
Authors: Rohen Scott A. , Hamid Yussra , Ly Kevin M. , Quick Christopher M.
Published: November 2023

Lymphangions, the functional units of a lymphatic vessel bound by two valves, actively contract and relax to pump lymph. Like cardiac ventricles, stroke work (SW) of a lymphangion depends on filling pressure, outlet pressure, systolic contractility and diastolic stiffness. Although radii, contractilities and stiffnesses vary by several order of magnitude, inlet and outlet pressures are surprisingly similar in rat and bovine mesenteric lymphangions when stroke work is maximized. Therefore, the purpose of the present work was to derive a general algebraic formula that relates optimal inlet and outlet pressures to critical mechanical properties of lymphangions. The pressure‐volume relationships of lymphangions, like ventricles, are characterized by time‐varying elastance. An algebraic solution for stroke work was formulated assuming linear relationships in terms of three functional parameters: 1) end‐systolic elastance (Ees), 2) end‐diastolic elastance (Eed) and 3) the difference between end‐diastolic and end‐systolic unstressed volumes (ΔVo). The resulting formula for SW reproduces maximal stroke work for particular inlet and outlet pressures. The formulas for optimal inlet and outlet pressures are functions of two critical quantities: EesΔVo and Ees/Eed. Furthermore, the values of these two quantities are conserved when using parameters characterizing rat and bovine mesenteric lymphatic vessels. The surprising implication is that the mechanical properties of each lymphangion in a lymphatic network can be predicted with a simple assumption: lymphangions in a network have a maximum stroke work at similar transmural pressures. Furthermore, the algebraic solutions provide a novel tool to predict how mechanical properties might adapt to maintain optimal stroke work with acute and chronic perturbations.
Algebraic Formula Predicting the Fraction of Absorbed Fluid Transported By Mesenteric Lymphatic Vessels
Authors: Joglar Alejandro A. , Johnson Chesley M. , Harris Lindsay M. , Dongaonkar Ranjeet M. , Quick Christopher M.
Published: November 2023

When nutrients are absorbed into the interstitial space from the intestinal lumen, they can be transported either by the intestinal capillaries to the portal circulation or by mesenteric lymphatics to the cysterna chyli. Several perturbations can alter the fraction of fluid that is transported by the mesenteric lymphatics, including nutrients present in the intestinal lumen, and microvascular and cysterna chyli hydrostatic pressures. Experimental approaches employed to elucidate the mechanisms governing the relative flow through these two parallel pathways are limited, because critical parameters are difficult to measure and cannot be controlled independently. Conventional mathematical modeling approaches are also limited, because the numerical solution of of the systems of equations are sensitive to assumed parameter values and must employ advanced computational techniques. Therefore, the purpose of the present work was to develop a general algebraic formula that predicts the fraction of fluid that is transported by the mesenteric lymphatic vessels. The basic framework was developed by equating the fluid flow into the intestinal interstitial compartment from the lumen and fluid removed by mesenteric lymph flow and microvascular absorption. Transport of fluid between the interstitium and the capillaries was characterized by the Starling‐Landis equation. Lymph flow from the intestinal interstitium to the cysterna chyli was assumed to be a linear function of interstitial and cysterna chyli hydrostatic pressures. Nutrients were assumed to be actively transported from the intestinal lumen, and water was assumed to be transported iso‐osmotically as characterized by the Starling‐Landis equation. The system of equations were solved algebraically to yield a formula for the fraction of fluid transported by the mesenteric lymphatic vessels. This simple model reproduces measured values of fluid flows, as well as the preferential transport of fluid by mesenteric lymphatic vessels when lipids are absorbed. Not only does it predict how fluid transport is affected by changes in parameters characterizing microvascular and lymphatic function, it provides a novel means to estimate critical parameter values from measured fluid flow.
Novel Mammalian Similarity Principle Predicted from the Standard Minimal Closed‐loop Cardiovascular Model
Authors: Duhon Emily M. , Morea Danielle N. , Rimes Emily L. , Lee MaKenzie D. , Nealy Teylor B. , Quick Christopher M.
Published: November 2023

Allometric scaling laws are empirical relationships relating particular parameters to body weight. Investigators have identified only a small number of allometric invariants for the mammalian cardiovascular system‐‐combinations of parameters that have constant values independent of species weight. Although many allometric invariants have arisen from applying optimality principles, the physics governing blood pressures and flows impose constraints that strictly limit parameter values. Therefore, the purpose of the present work is to derive a novel mammalian similarity principle, assuming a closed‐loop cardiovascular model. First, we assumed the standard minimal closed‐loop model consisting of two ventricles, four vascular compartments, and two resistances. Because ventricles were characterized by the time‐varying elastance model, cardiac contractility was characterized by end‐systolic elastance (Ees). Second, we linearized model equations. Third, we assumed systemic arterial pressure (Psa) is regulated by renal control of blood volume. We then solved the model equations algebraically for stroke volume (SV). The equation was then rearranged to form a novel non‐dimensional relationship (EesSV/Psa) as a function of sets of cardiovascular parameters, most of which are recognized as allometric invariants. We then verified that EesSV/Psa is itself invariant across mammals by substituting measured values from mammalian species of greatly varying weights. Although values of Ees can vary at least four orders of magnitude, EesSV/Psa varies less than a factor of 2. We thus provide a novel allometric invariant derived from the fundamental principles governing blood flow rather than teleological arguments. Furthermore, this algebraic formulation provides a novel tool to scale results from diverse animal models involving cardiac contractility.
Effect of Smoking on Hearing: Evidence from Auditory Evoked Potentials
Authors: Dixit Abhinav , Singh Yogendra Raj , Sharma Praveen
Published: November 2023

Introduction

Auditory Brainstem Responses (ABR) are an important clinical tool for assessment of hearing. Acetylcholine is a neurotransmitter present in the auditory pathway and nicotine acts through acetylcholine receptors. Since smoking is widely prevalent, it is essential to know its effect on auditory pathways especially for interpreting the reports of ABR in smokers.

Methodology

The study was done on 15 normal, healthy non‐smoker males and 15 healthy, smoker males in the age group of 18–40 years. The study was approved by Institutional Ethics Committee and written informed consent was taken from all volunteers. The recordings of ABR were done using Biopac MP 150. A total of 1000 responses were averaged. The recordings of ABR were done in a state of abstinence of 12 hours (overnight abstinence) and 10 minutes after smoking in the smoker group. The smokers were allowed to smoke their own brand of cigarette. Only one set of recordings were done for non‐smoker group. The peak latencies and amplitudes of the ABR waves were analyzed.

Results

The latencies of wave I and II along with Inter‐peak latency I–III and III–V were significantly longer in the smoker group (after abstinence) in comparison to the controls. The amplitudes of waves I, II and V were also significantly reduced. A comparison between the controls and smokers (10 minutes after smoking) revealed significantly prolonged latency of waves I and II in the smoker group accompanied by a significant decrease in the amplitudes of all waves of ABR. There were no significant differences in latencies and amplitudes of the smokers after abstinence and 10 minutes after smoking.

Conclusion

Smoking brings about a decrease in the amplitudes along with prolongation of latencies which is not affected by abstinence or acute consumption.

Support or Funding Information

Intramural Grant of All India Institute of Medical Sciences, Jodhpur
Effects of chronic exposure to THIP on brainstem neuronal excitability in a female mouse model of Rett syndrome
Authors: Zhong Weiwei , Johnson Christopher M , Cui Ningren , Xing Hao , Wu Yang , Mo Huanbiao M , Jiang Chun
Published: November 2023

Rett Syndrome (RTT) is a neurodevelopmental disease with ~ 0.01% morbidity rate in live‐born girls worldwide. Mutations of MECP2 gene encoding methyl CpG binding protein 2 (MeCP2) underlies over 90% of RTT cases clinically. One of the characteristic features of the disease is defective autonomic function, showing breathing instability, gastrointestinal disorders and cardiac arrhythmia. Imbalanced neuron excitation/inhibition ratio may underlie the development of the symptoms. In Mecp2−/Y mice, several groups of brainstem neurons show excessive excitability, which may contribute to the instability of neuronal networks for the autonomic function. One way to control the neuronal hyperexcitability is to enhance the GABAergic inhibition. We have previously reported that THIP (Gaboxadol), an extrasynaptic GABAA receptor agonist, relieved many RTT‐like symptoms in a male mouse model of RTT. However, several questions are still open as to what the THIP effects are at the cellular level, whether increased excitability of brainstem neurons also occurs in female Mecp2+/− mice, how the mosaic expression of MeCP2 affects the neuronal excitability, and how the MeCP2 expression affects neuronal responses to THIP. Thus, we performed studies to address these questions. After symptomatic Mecp2+/− (sMecp2+/−) female mice were identified with a two‐step screening method, the mice were divided into THIP and vehicle groups. Whole‐cell recording was performed in brain slices from the mice with a prior 5‐week exposure to low‐dose THIP or vehicle. Neurons in the locus coeruleus (LC) and the mesencephalic trigeminal nucleus (Me5) showed excessive firing activity in the vehicle‐treated sMecp2+/− mice. When the effect of mosaic expression of MeCP2 on neuronal hyperexcitability was studied in identified LC cells, we found that the level of hyperexcitability was similar in LC neurons with and without MeCP2 expression. THIP pretreatment stabilized the hyperexcitability of both LC and Me5 neurons of sMecp2+/− mice to a level similar to their WT counterparts. The THIP exposure also suppressed the excessive firing activity of MeCP2‐positive and MeCP2‐negative LC neurons, suggesting that the THIP effects appeared to be determined by not only the MeCP2 expression, but also cellular environmental cues. The alleviation of LC neuronal hyperexcitability seems to benefit brainstem autonomic function as THIP also improved breathing abnormalities of these sMecp2+/− mice.

Support or Funding Information

This work was supported by National Institutes of Health [grant number R01‐NS‐073875] and Brain and Behavior fellowship at Georgia State University.
Pseudomonas aeruginosa‐induced pulmonary endothelial amyloid proteins impair long‐term plasticity
Authors: Lin Mike T , Balczon Ron , Morrow K. Adam , Wagener Brant M , Pittet Jean‐Francois , Stevens Troy
Published: November 2023

We have recently reported that following bacterial infection with Pseudomonas aeruginosa, injury to the pulmonary endothelium induces tau hyperphosphorylation and release as a cytotoxic amyloid protein. Further, cytotoxic amyloid production requires an intact type 3 secretion system (PA103 strain), because a non‐functional type 3 secretion system (e.g. ΔPcrV strain) does not result in the production of cytotoxic amyloid oligomers. Aberrant formation of protein aggregation is a common mechanism linked to several neurodegenerative diseases. Therefore, in this study we tested whether endothelial amyloid protein(s) affect synaptic plasticity. We employed the well‐characterized hippocampal Schaffer Collateral‐CA1 synaptic pathway to study the effect of supernatants from PA103‐, ΔPcrV‐, or non‐treated endothelial cells on long‐term potentiation (LTP) as a cellular model for animal learning. In field recordings, high frequency stimulation induced LTP. In mouse hippocampal slices exposed to supernatants from ΔPcrV‐ or non‐infected endothelial cells, the induced LTP were 192 ± 12% (n = 6) and 180 ± 16% (n = 6), respectively. In comparison, in slices exposed to supernatant from PA103‐infected endothelial cells, the LTP was reduced (128 ± 9.0%, n = 9; P < 0.05, ANOVA). Importantly, LTP suppression seemed to be ameliorated when endothelial amyloid(s) were immunodepleted with a pan antibody that recognizes neural amyloids, A11 (LTP: 176 ± 18%, n = 4). These results suggest that A11 neutralizes PA103‐induced amyloid cytotoxicity. Whole cell patch clamp recordings in CA1 pyramidal neurons further showed that hyperexcitability and changes in presynaptic neurotransmitter release might be attributable to the LTP suppression induced by endothelial amyloid cytotoxicity. Taken together, our results suggest that acute pneumonia may directly or indirectly impair brain cognitive function.

Support or Funding Information

Supported by HL66299 and HL60224 (TS) and AHA16POST27250139 (KAM).
Sex and age differences in cardiac autonomic nervous regulation in response to recumbent positions
Authors: Sasaki Konosuke , Bao Sarina , Sato Haruka , Saiki Yoshikatsu , Maruyama Ryoko
Published: November 2023

Not much research has been conducted to determine sex and age differences in autonomic nervous activity during different positions, namely the supine, left recumbent, and right recumbent positions. Our aim was to evaluate whether the left and right recumbent positions affect heart rate variability (HRV) differently than the supine position dose in young and old adults of both sexes. Twenty‐nine young male (22.5 ± 0.5 years), 29 young female (23.1 ± 0.7 years), 18 elderly male (76.1 ± 1.1 years), and 27 elderly female (72.6 ± 1.0 years) volunteers participated in this study. After lying in the supine position, the participants maintained each recumbent position in random order for 10 min. We recorded electrocardiographic data throughout this experiment to evaluate HRV. Heart rate during the left recumbent position was the lowest among the three positions regardless of age or sex. No significant differences were observed for low‐frequency (LF) HRV, high‐frequency (HF) HRV, or their ratio (LF/HF) in young adults of both sexes and elderly women when the position was changed from supine to recumbent. However, in elderly men, the LF/HF ratio during the right recumbent position was significantly lower than that during the supine position. While in supine position, elderly men showed high LF/HF ratios when compared to the other groups. These results suggest that the right recumbent position attenuates cardiac sympathetic nerve activity, which is expressed as the LF/HF ratio, in elderly male adults. Therefore, reduction in heart rate during the left recumbent position may not be associated with autonomic nervous activity.

Support or Funding Information

This work was supported in part by a Grant‐in‐Aid for Challenging Exploratory Research from the Japan Society for the Promotion of Science.
ACE gene titration modulates acute myocardial infarction‐induced autonomic and functional changes in mice
Authors: Moraes Oscar Albuquerque
Published: November 2023

Acute myocardial infarction is one of the leading causes of mortality worldwide. The Angiotensin Converting Enzyme (ACE) act in the production of ANG II and in the degradation of bradykinin. It is believed that higher levels of ACE could modulate susceptibility to coronary occlusion. To investigate this possibility we used adult males mice genetically modified to express different concentrations of ACE similar to that found in humans. Animals (1, 2 or three copies; n = 6 each group) were subjected to acute myocardial infarction (AMI) and evaluated after 7 days. Systolic, diastolic and mean blood pressure as well as heart rate, heart rate (HRV) and blood pressure (BPV) variability and cardiac function by echocardiography were evaluated. Regarding hemodynamic data, AMI induced no difference in systolic, diastolic and mean blood pressure (ECA1: 74.02 ± 3.0; ACE2: 108.65 ± 2.8; ECA3: 102.07 ± 4.1mmHg). Regarding heart rate it was observed a reduction in 3 copies group (ECA1: 654.51 ± 26.34; ACE2: 668.22 ± 10; ECA3: 534.11 ± 33.4 BPM). HRV evaluated in the time domain by SDNN (ACE1: 5.16 ± 0.93; ACE2: 5.84 ± 1:32; ACE 3: 7.69 ± 1.4 ms) and RMSSD indexes (ECA1: 5.91 ± 0.69; ACE2: 5.7 ± 1:14; ECA3: 6.78 ± 1.2ms) was higher in the infarcted ACE3 group, as well as the total variance (ACE1: 30 ± 12.4; ACE2: 37 ± 13.8; ACE3: 69.9 ± 25.6 ms). Regarding the spectral analysis a higher sympathetic modulation (ACE1: 5.14 ± 3; ACE2: 7.2 ± 2.8; ACE3: 12.9 ± 4.1ms2) and lower parasympathetic modulation (ACE1: 7 ± 2; ACE2: 8.6 ± 3.2; ACE3: 9.5 ± 2.8 ms2) was observed in ACE 3 infarcted group. BPV (ACE1: 18.7 ± 6.2; ACE2: 14.85 ± 1.6; ACE3: 13.76 ± 4.2 mmHg2) and the Low Frequency (sympathetic) peripheral component of BPV were reduced in the ACE 3 AMI group (ACE1: 60.5 ± 6.2; ACE2: 54.6 ± 1.7; ACE3: 53 ± 3.3 mmHg2). Echocardiographic data showed a reduction in IRT isovolumetric relaxation time (ITR)(ACE1: 26.1 ± 3.1; ACE2: 32.3 ± 3.4; ACE3: 26.5 ± 3.1 ms), increased E/A ratio (ACE1: 3.40 ± 0.67; ACE2: 3:02 ± 1:36; ACE3: 2.0 ± 0.75) and an increase in FAC – Fractional Area Change (ACE1: 27.9 ± 4.5; ACE2: 26.4 ± 5.7; ACE3: 33.5 ± 1.3) in the ACE 3 group after AMI. Our data suggest that increasing the number of ACE gene copies may promote autonomic imbalance evidenced by increased sympathetic modulation of the cardiovascular system, reduction of parasympathetic modulation of HRV and impaired diastolic function.
Neuromuscular Signaling in Myasthenia Gravis [MG] Patients
Authors: Sainvil Frantz L , Einstein George P , Tulp Orien L
Published: November 2023

Myasthenia gravis (MG) is one of the most common disorders of neuromuscular signaling, with a prevalence of 13 to 21 per 100,000 in the United States. The symptoms experienced by people with MG include muscle weakness and generalized fatigue. In healthy patients, the presynaptic terminals release acetylcholine (ACH) from the motor nerve terminal in quanta, which then diffuse across the synaptic cleft and connect to receptors on the post synaptic membrane of the muscle, resulting in membrane depolarization and muscle contraction. In MG patients, however, the post synaptic ACH membrane receptors are destroyed or damaged mostly due to immunological or genetic abnormalities. Thymic tumors are also commonly seen in patients with MG. In MG, immune system B‐cells interact with helper T‐cells to produce antibodies to the ACH receptors. The destruction of the thymic tolerance can cause or contribute to an immune attack on the ACH receptors. MG can often be treated with cholinesterase inhibitors such as neostigmine bromide or thymectomy to enhance the diminished hormone‐ligand interaction needed to effect depolarization and muscle contraction. The current study utilized a Meta‐analysis approach for data interpretation in order to compare neuromuscular signaling in MG patients who were treated with cholinesterase inhibitors versus those who were treated surgically. Furthermore, this study intends to show that neuromuscular signaling in MG patients who have had surgical interventions tend to have more favorable outcomes than those treated with cholinesterase inhibitors alone. In our studies we also included noninvasive biophotonic diagnostic and electroceutical neuromuscular stimulation as alternative diagnostic and therapeutic measures with good success.

Support or Funding Information

Supported by Institutional resources of USAT College of Medicine and the Einstein Medical Institute
Optogenetic stimulation of PVN‐RVLM neurons increases sympathetic nerve activity in anesthetized rats
Authors: Koba Satoshi , Hanai Eri , Kumada Nao , Kataoka Naoya , Nakamura Kazuhiro , Watanabe Tatsuo
Published: November 2023

The hypothalamic paraventricular nucleus (PVN) sends direct projections to the rostral ventrolateral medulla (RVLM). The present study was conducted to examine the effect of optogenetic stimulation of PVN‐RVLM neurons on sympathetic nerve activity in anesthetized rats. Male rats anesthetized with pentobarbital received unilateral microinjection into the PVN with an adeno‐associated virus (AAV) vector that encodes the reporter protein palGFP (control rats, N=4) or the channel rhodopsin variant, ChIEF‐tdTomato (ChIEF rats, N=8). Two‐to‐five weeks later, in the rats anesthetized with a mixture of urethane and α‐chloralose, photostimulation (473 nm wavelength, 8–10 mW) was provided to the RVLM ipsilateral to the PVN into which AAV had been injected. In ChIEF rats, photostimulation of the RVLM at 40 Hz (5‐ms pulse duration) for 2 min significantly (P < 0.05) evoked renal sympathoexcitatory (+126 ± 20% from baseline, means ± SE) and pressor (+13 ± 1 mmHg) responses while this stimulation had no effect in control rats. Moreover, immunofluorescence staining revealed abundant distribution of PVN‐derived, tdTomato‐labeled axons in the ipsilateral RVLM as compared with that in the contralateral RVLM. Confocal imaging further showed close association of tdTomato‐labeled axons with tyrosine hydroxylase‐positive neurons in the RVLM. These observations suggest that excitation of the PVN‐RVLM monosynaptic pathway elicits sympathoexcitation via, at least in part, stimulation of RVLM catecholaminergic neurons, potentially playing a role in sympathetic adjustments to stress such as exercise.

Support or Funding Information

JSPS KAKENHI 15H05367 & 16K15190 (SK); 16H05128 & 15H05932 (KN).
Spinal Cord Stimulation Reduces Ventricular Arrhythmogenicity During Ischemia
Authors: Dale Erica A , Howard‐Quijano Kimberly , Takamiya Tatsuo , Kubo Yukiko , Kipke Jasmine P , Mahajan Aman
Published: November 2023

Introduction

Sudden cardiac death is a leading cause of mortality in the United States and is often caused by ventricular tachyarrhythmias (VT) and/or ventricular fibrillation (VF; Mozaffarian et al., 2015). Myocardial ischemia triggers imbalances in sympathetic and parasympathetic balance and leads to the pathophysiology of cardiac arrhythmias. Spinal cord stimulation (SCS) is a useful modality for selective spinal neuromodulation of ventricular excitability (Wang et al., 2015), however the mechanisms remain poorly understood. Cardiac stressors elicit distinct neural signatures within the dorsal horn (DH; the spinal relay for cardiac afferents) and the intermediolateral (IML) nucleus of the thoracic spinal cord (the primary nexus point for modulation of sympathetic efferent outflow). We hypothesize that SCS decreases ventricular excitability during acute ischemia via modulation of afferent neural signaling and attenuation of sympathetic efferent output.

Methods

Anesthetized Yorkshire pigs were randomized as follows: 1) epidural SCS via 4 pole lead for 30 min (n=10) or 2) Sham (n=10) before 5 min of myocardial ischemia via ligation of the left anterior descending (LAD) coronary artery. A 56‐lead heart sock was placed for electrophysiological recordings of: activation recovery intervals (ARI), activation time (AT), repolarization time (RT), and dispersion of repolarization (DOR).

Results

SCS reduced myocardial sympathoexcitation after 5 min of LAD ligation since: a) ARI reduction was attenuated (Sham: −79.9 ± 7.1ms vs. SCS: −58.5 ± 7.1; p=0.035); b) RT reduction was attenuated (Sham: −75.5 ± 6.9ms vs. SCS: −49.3 ± 6.9ms; p=0.008); c) there was a greater increase in AT (Sham: 4.2 ± 0.5ms vs. SCS: 6.7 ± 0.5ms; p=0.001) and; d) the increase in DOR was reduced (Sham: 2197.3 ± 262ms2 vs. SCS: 1307.2 ± 262ms2; p=0.006). In addition, there were fewer non‐sustained VTs (1/1 vs. 24/3) and PVCs (6(0–17) vs. 19(0–105); p<0.001) during ischemia and reperfusion.

Conclusion

These results suggest SCS attenuates myocardial sympathoexcitation during acute ischemia by neuromodulation within the spinal cord itself. As evidenced by reduction in measures of myocardial excitation and fewer VTs and PVCs, SCS functionally reduces ventricular arrhythmogenicity. Preliminary results from extracellular recording in the thoracic DH and IML indicate that the spinal cord is capable of complex processing of primary afferent inputs. Further experiments are warranted to elucidate the precise mechanisms of SCS neuromodulation in order to develop novel therapeutics for the patient population.

Support or Funding Information

NHLBI‐NIH (R01) HL084261 (AM), FAER and SCA‐IARS Starter Grant (KH‐Q).
Effects of L‐arginine Supplementation on the Tissue Production of Nitric Oxide and Cardiovascular Modulation by the Paraventricular Nucleus of Hypothalamus
Authors: de Ataides Raquel Hiviny , Ferreira Nathalia Zerbinatti , Lucchetti Bruno Fernando Cruz , Pinge‐Filho Phileno , Martins‐Pinge Marli Cardoso
Published: November 2023

L‐Arginine is the substrate for nitric oxide (NO) synthesis and in the paraventricular nucleus of the hypothalamus (PVN) NO plays an important role in cardiovascular function. The objective of this study was to evaluate the effects of L‐arginine supplementation on cardiovascular responses by PVN and NO production. Wistar rats were used (220–250g) randomly divided into two groups: control (C) or L‐arginine (LA). The supplementation with L‐arginine was conducted in the LA group (62.5 mg/mL/rat/day), by oral gavage, and Group C received water (1 mL) for 4 weeks, 5times/week. Then the animals underwent to guide cannulas implantation to the PVN and artery and femoral vein catheterization. The baseline parameters of mean arterial pressure (MAP) and heart rate (HR) were recorded 24 hours after catheterization and held bilateral administration of 0.9% saline or an nNOS inhibitor (n‐Propyl‐L‐Arginine, 4nmol/100NL) in the PVN. We collected heart, kidneys, thoracic aorta, and punchs of the PVN for nitrite dosages by Cadmium‐Griess method. Spectral analysis was performed by the software Cardio Series (version 2.4). The supplementation with L‐arginine caused resting bradycardia (C: 359 ± 6 vs. LA: 335 ± 6 b/min) without change in MAP, as well as greater pressor response (ΔPAM: C: 17 ± 2 vs. LA: 26 ± 3 mmHg) and tachycardia (ΔFC: C: 86 ± 6 vs. LA: 129 ± 13 b/min) to n‐propyl in the PVN. At baseline the spectral analysis of rats of LA group showed: lower sympathetic modulation for systolic blood pressure (LF: C: 4.6 ± 0.6 vs. LA: 2.1 ± 0.4 mmHg2) smaller variance in pulse interval (C: 42.4 ± 3.2 vs. LA: 24.6 ± 5.1 ms2), lower sympathovagal index (LF/HF: C: 0.8 ± 0.1 vs. LA: 0.3 ± 12:07) and increase of spontaneous baroreflex gain: (Gain full baroreflex: C: 1.3 ± 0.1 vs. LA: 2.2 ± 0.2 ms/mm Hg; Gain Up: C: 1.4 ± 0.1 vs. LA: 2.5 ± 0.3 ms/mm Hg; Gain Down: C: 1.2 ± 0.1 vs. LA: 1.8 ± 0.2 ms/mmHg). In addition, LA animals showed higher concentrations of nitrite in the PVN (C: 3.3 ± 0.7 vs. LA: 5.5 ± 0.7 uM/mg/PVN), kidneys (C: 7 ± 1 vs. LA: 18 ± 3 uM) and thoracic aorta (C: 4 ± 0.6; LA: 12 ± 3 .mu.M). Therefore, supplementation with L‐arginine modified the baseline autonomic control, increase in nitregirc tonus by NO in the PVN via nNOS, and an increase in NO bioavailability, leading to similar effects obtain after exercise training.

Support or Funding Information

CNPq (fellowship program)
Postnatal Developmental Changes of Orexin in Spontaneously Hypertensive Rats
Authors: Dunn Savannah , Moushey Alexander , Dong Ruhong , Li Aihua
Published: November 2023

Orexins are involved in the regulation of cardiorespiratory functions and neurogenic hypertension. Using spontaneously hypertensive rats (SHRs), we have reported that 1) SHRs have more orexin neurons in the hypothalamus at young (postnatal days (P) 30–58) and adult ages than age‐matched, normotensive Wistar‐Kyoto (WKY) rats, 2) blocking orexin receptors (OXRs) with a dual OXR antagonist, almorexant, can normalize high blood pressure (BP) in young SHRs and significantly lower high BP in adult SHRs, and 3) hypercapnia (stress) activates more orexin neurons in the hypothalamus of SHRs than in normotensive WKY rats.

Our study objective is to establish a developmental pattern of the orexinergic system in SHRs and WKYs and to better understand the role of the orexin system in hypertension. Specifically, we aim to define at which postnatal age the total number of orexin neurons starts to diverge between SHRs and normotensive rats, and to determine whether the increased number of orexin neurons in SHRs is due to an increase in the number of newly proliferated orexin neurons in the hypothalamus postnatally.

To evaluate the total number and dispersion of orexin neurons in SHRs and WKY rats at P7–P25, we used immunohistochemical (IHC) staining of orexin A peptide. To evaluate new postnatal proliferation of orexin neurons, bromodeoxyuridine (BrdU) was injected (50 mg kg−1, i.p.) in SHR and WKY pups for 5 consecutive days beginning at P5, P10, P15, or P25. Up to 7 days after the final injection, brains were harvested and the hypothalamus isolated. To assess the proliferation and maturity of orexinergic neurons in the hypothalamus, orexin positive neurons were double labelled with antibodies for BrdU, which incorporates as a thymidine into the genome of dividing cells and their progeny, doublecortin (DCX), which labels the cytoplasm of immature neurons (< 2 weeks old), or neuronal nuclear antigen (NeuN), which labels the nucleus of mature neurons (> 2 weeks old).

Our early results show that 1) SHRs have significantly more orexin A‐immunoreactive (ir) neurons in the hypothalamus than age‐matched WKYs at P10–20, but not at P7, 2) SHRs have more BrdU/orexin‐ir neurons in the hypothalamus at P7–11 than at P25–29, and 3) SHRs have more DCX/orexin‐ir neurons in the hypothalamus at P14–20 than at P35 and later. Our data suggest that the divergence in number of orexin neurons between SHRs and normotensive rats can be seen as early as P10 and that this difference may be mediated by increased postnatal proliferation in the orexin system. This early divergence may imply a causal or upstream role in the development of neurogenic hypertension. These studies are essential in the determination of the mechanistic development of hypertension and thereby treatment of the origin of disease in the future.

Support or Funding Information

NIH HL28066
Ventilation Inhibits Sympathetic Neural Recruitment During Severe Chemoreflex Stress
Authors: Badrov Mark B , Barak Otto F , Mijacika Tanja , Drvis Ivan , Dujic Zeljko , Shoemaker J Kevin
Published: November 2023

The current study investigated the effects of ventilation on sympathetic neural recruitment during severe chemoreflex stress. We measured, in six trained breath‐hold divers (one female; 35±11 yrs, 181±11 cm, 74±13 kg), muscle sympathetic nerve activity (MSNA; microneurography), heart rate (HR; electrocardiogram), blood pressure (BP; Finometer), and arterial hemoglobin saturation (HbSat; pulse oximetry) at baseline (2 mins) and during alternating periods (30 s) of functional residual capacity (FRC) apnea and asphyxic rebreathing, a protocol designed to elicit severe chemoreflex activation in the absence and presence of ventilation, respectively. Subjects were instructed to stop when they achieved ~85% of their self‐perceived ‘maximal’ tolerance for the protocol. The final FRC apnea and rebreathe periods were used for analysis. Sympathetic action potential (AP) discharge patterns were studied using a novel AP detection and analysis technique. This technique quantifies not only the number and morphology of APs within the integrated burst at rest, but also the emergence of latent (and larger) APs as stress develops. Compared to baseline, HbSat decreased to similar levels during FRC apnea and rebreathe (80±3 and 78±11%, respectively; P>0.05). Compared to baseline (18±7 bursts/min), MSNA burst frequency increased during FRC apnea (Δ35±6 bursts/min; P<0.01), but not rebreathe (Δ1±4 bursts/min; P>0.05), whereas burst amplitude (54±12 AU) increased during both FRC apnea (Δ82±30 AU) and rebreathe (Δ26±16 AU; both P<0.05), although the increase was greater during FRC apnea (P<0.01). Compared to baseline (9±3 APs/burst), the mean AP content per integrated burst increased during both FRC apnea (Δ20±6 APs/burst) and rebreathe (Δ7±5 APs/burst; both P<0.01). Similarly, the number of active AP clusters per integrated burst (5±1 clusters/burst) increased during both FRC apnea (Δ4±1 clusters/burst) and rebreathe (Δ2±1 clusters/burst; both P<0.01). However, in both cases, the magnitude of increase was greater during FRC apnea (both P<0.01). Finally, when APs were binned according to peak‐to‐peak amplitude (i.e., into clusters), the number of total AP clusters detected (12±2 total clusters) increased during FRC apnea (Δ6±1 total clusters; P<0.01), but not rebreathe (Δ0±1 total clusters; P>0.05). As such, ventilation restrains sympathetic neural recruitment during severe chemoreflex stimulation. While the increased within‐burst firing frequency of previously active, lower‐threshold sympathetic axons appears preserved, but diminished, in the presence of ventilation (i.e., rebreathe), the recruitment of previously silent, higher‐threshold sub‐populations of larger‐sized sympathetic axons appears specific to apnea, and inhibited by ventilation.

Support or Funding Information

Supported by Natural Sciences and Engineering Research Council of Canada.