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Audio versions of bioRxiv paper abstracts

    Obesity promotes glucocorticoid-dependent muscle atrophy in male C57BL6J mice.

    Obesity promotes glucocorticoid-dependent muscle atrophy in male C57BL6J mice.

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.11.247106v1?rss=1

    Authors: Gunder, L. C., Harvey, I., Redd, J. R., Davis, C. S., AL-Tamimi, A., Brooks, S. V., Bridges, D.

    Abstract:
    Glucocorticoids promote muscle atrophy by inducing a class of proteins called atrogenes, resulting in reductions in muscle size and strength. In this work, we evaluated whether a mouse model with pre-existing diet-induced obesity had altered glucocorticoid responsiveness. We observed that all animals treated with the synthetic glucocorticoid dexamethasone had reduced strength, but that obesity exacerbated this effect. These changes were concordant with more pronounced reductions in muscle size, particularly in Type II muscle fibers, and potentiated induction of atrogene expression in the obese mice relative to lean mice. Furthermore, we show that the reductions in lean mass do not fully account for the dexamethasone-induced insulin resistance observed in these mice. Together these data suggest that obesity potentiates glucocorticoid-induced muscle atrophy.

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    The luteinizing hormone receptor knock-out mouse as a tool to probe the in vivo actions of gonadotropic hormonesreceptors in females

    The luteinizing hormone receptor knock-out mouse as a tool to probe the in vivo actions of gonadotropic hormonesreceptors in females

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.11.244467v1?rss=1

    Authors: Jonas, K. C., Rivero Muller, A., Oduwole, O., Peltoketo, H., Huhtaniemi, I. T.

    Abstract:
    Mouse models with altered gonadotropin functions have provided invaluable insight into the functions of these hormones/receptors. Here we describe the repurposing of the infertile and hypogonadal LHR knockout mouse model (LuRKO), to address outstanding questions in reproductive physiology. Using crossbreeding strategies and physiological and histological analyses, we first addressed the physiological relevance of forced LHR homomerization in female mice using BAC expression of two mutant LHR, that have previously shown to undergo functional complementation and rescue the hypogonadal phenotype of male LuRKO mice. In female LuRKO mice, co-expression of signal and binding deficient LHR mutants failed to rescue the hypogonadal and anovulatory phenotype. This was apparently due to the low-level expression of the two mutant LHR and potential lack of LH/LHR-dependent pleiotropic signaling that has previously been shown to be essential for ovulation. Next, we utilized a mouse model overexpressing human chorionic gonadotropin (hCG) with increased circulating LH/hCG-like bioactivity to ~40 fold higher than WT females, to determine if high circulating hCG could reveal putative LHR-independent actions. No effects were found, thus, suggesting that LH/hCG mediate their gonadal and non-gonadal effects solely via LHR. Finally, targeted expression of a constitutively active FSHR progressed antral follicles to pre-ovulatory follicles and displayed phenotypic markers of enhanced estrogenic activity but failed to induce ovulation in LuRKO mice. This study highlights the critical importance and precise control of LHR and FSHR for mediating ovarian functions and of the potential re-purposing existing genetically modified mouse models in answering outstanding physiological questions.

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    At-level allodynia after mid-thoracic contusion in the rat

    At-level allodynia after mid-thoracic contusion in the rat

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.10.240499v1?rss=1

    Authors: Blumenthal, G. H., Nandakumar, B., Schnider, A. K., Detloff, M. R., Ricard, J., Bethea, J. R., Moxon, K. A.

    Abstract:
    The rat mid-thoracic contusion model has been used to study at-level tactile allodynia after spinal cord injury (SCI), one of the more common types of allodynia. An important advantage of this model is that not all animals develop allodynia and, therefore, it could be used to more clearly examine mechanisms that are strictly related to pain development separately from mechanisms related to the injury itself. However, how to separate those that develop allodynia from those that do not is unclear. The aims of the current study were to identify where allodynia and spasticity develop and use this information to identify metrics that separate animals that develop allodynia from those that do not in order study difference in their behavior. To accomplish these aims, a standardized grid was used to localize pain on the dorsal trunk and map it to thoracic dermatomes, providing for the development of a pain score that relied on supraspinal responses and separated subgroups of animals. Similar to human studies, the development of allodynia often occurred with the development of spasticity or hyperreflexia. Moreover, the time course and prevalence of pain phenotypes (at-, above-, or below level) produced by this model were similar to that observed in humans who have sustained an SCI. However, the amount of spared spinal matter in the injured cord did not explain the development of allodynia, as was previously reported. This approach can be used to study the mechanism underlying the development of allodynia separately from mechanisms related to the injury alone.

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    Varying intestinal absorption curves of glucose and fat with different plasma insulin curves in different positions

    Varying intestinal absorption curves of glucose and fat with different plasma insulin curves in different positions

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.10.243063v1?rss=1

    Authors: Yang, J., Wang, L., Song, L., Li, G., Jin, X., Tian, S.

    Abstract:
    It has been shown that posture could affect the rehabilitation of some diseases, and even affect the physiological metabolism and function of certain systems of the human body, including gastrointestinal absorption of glucose. Studies attributed the different gastrointestinal absorption rate in different positions to the varying rate of gastric emptying in different positions. However, it is still unknown whether the absorption rate of nutrients from the intestine varies in different positions. To verify this hypothesis, the present study was conducted using rats as subjects. After injection of glucose or chyme of safflower oil into the upper segment of jejunum of rats, curves of plasma glucose or triglyceride were drawed to evaluate and compare the potential influences on intestinal absorption by postures. We found varying intestinal absorption curves of glucose and fat with different plasma insulin curves in different positions. To be specific, the right lateral decubitus resulted in the most sharp curves, whereas the supine position the most obtuse curves with a delayed peak, both in case of glucose and fat absorption. These findings contribute to understand the position-related absorption kinetics of substances in the intestinal tract. According to this study, posture may be important for the prevention and nursing intervention of some diseases related to metabolic kinetics of glucose and lipids. It may also be important for the absorption and transport of lipophilic drugs through the mesentery lymphatic vessels.

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    A Uropathogenic E. coli UTI89 model of prostatic inflammation and collagen accumulation for use in studying aberrant collagen production in the prostate

    A Uropathogenic E. coli UTI89 model of prostatic inflammation and collagen accumulation for use in studying aberrant collagen production in the prostate

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.10.238196v1?rss=1

    Authors: RUETTEN, H. M., Sandhu, J., Mueller, B., Wang, P., Zhang, H. L., Wegner, K. A., Cadena, M., Sandhu, S., Abler, L., Zhu, J., O'Driscoll, C. A., Chelgren, B., Wang, Z., Shen, T., Barasch, J., Bjorling, D. E., Vezina, C. M.

    Abstract:
    Bacterial infection is one known etiology of prostatic inflammation. Prostatic inflammation is associated with prostatic collagen accumulation and both are linked to progressive lower urinary tract symptoms in men. We characterized a model of prostatic inflammation utilizing transurethral instillations of E. coli UTI89 in C57BL/6J male mice with the goal of determining the optimal instillation conditions, understanding the impact of instillation conditions on urinary physiology, and identifying ideal prostatic lobes and collagen 1a1 prostatic cell types for further analysis. The smallest instillation volume tested (50 L) distributesd exclusively to bladder, 100 and 200 L volumes distributes to bladder and prostate, and a 500 L volume distributes to bladder, prostate and ureter. A threshold optical density (OD) of 0.4 E. coli UTI89 in the instillation fluid is necessary for significant (p 0.05) prostate colonization. E. coli UTI89 infection results in a low frequency, high volume spontaneous voiding pattern. This phenotype is due to exposure to E. coli UTI89, not catheterization alone, and is minimally altered by a 50 L increase in instillation volume and doubling of E. coli concentration. Prostate inflammation is isolated to the dorsal prostate and is accompanied by increased collagen density. This is partnered with increased density of PTPRC+, ProCOL1A1+ co-positive cells and decreased density of ACTA2+, ProCOL1A1+ co-positive cells. Overall, we determined that this model is effective in altering urinary phenotype and producing prostatic inflammation and collagen accumulation in mice.

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    Mechanical stimulation of endocardial Purkinje fibres can trigger ventricular arrhythmias

    Mechanical stimulation of endocardial Purkinje fibres can trigger ventricular arrhythmias

    Link to bioRxiv paper:
    http://biorxiv.org/cgi/content/short/2020.08.10.234195v1?rss=1

    Authors: c, E., Walton, R. D., Kaur, S., Power, A., Haissaguerre, M., Bernus, O., Ward, M.-L.

    Abstract:
    Acute ventricular dilation can evoke mechanically-induced arrhythmias, our study investigated whether Purkinje fibres (PFs) may play a role. Changes in left ventricular (LV) pressure and pseudo-ECGs were measured in isolated, Langendorff-perfused, male Wistar rat hearts in sinus rhythm. The LV endocardial surface was irrigated with experimental agents, via an indwelling catheter. Mechanically-induced arrhythmias were triggered by LV lumen inflation (100ul in 2s) via an indwelling balloon. Arrhythmias occurred as the LV volume was increased and spontaneously ceased within 20s of the onset of LV inflation. Arrhythmias were indexed as an increase in the standard deviation of all R-R intervals (SDRR), the number of ectopic activations and the period of these activations. Following 10s LV endocardial irrigation with Lugol solution (IK/I2) to chemically ablate surface PFs or with 0 Na+ Tyrode, there was a statistically significant attenuation of mechanically-induced arrhythmias. Lugol reduced the mechanically-induced increase in SDRR (Tyrode pre-stretch 3.5 {+/-} 1.7ms to 113.8 {+/-} 15.1ms during stretch vs Lugol pre-stretch 3.3 {+/-} 0.5ms to 39.9 {+/-} 14.5ms during stretch n=8, P less than 0.05). There was also a reduction in the number (21.2 {+/-} 2.0 to 1.5 {+/-} 0.7, P less than 0.001) and period (5.9 {+/-} 0.71s to 1.7 {+/-} 0.85s, P less than 0.01) of ectopic activations. The experiment was repeated using LV lumen irrigation with either 1uM GsMTx4, a peptide that blocks stretch-activated channels or 50uM 9-Phenanthrol (9-Phen), a blocker of TRPM4 channels. GsMTx4 did not attenuate mechanically-activated arrhythmias while 9-Phen had a partial effect. 9-Phen statistically reduced the number and period of ectopic activations but did not attenuate the mechanically-induced increase in SDRR (n=6-11 for each intervention). In further studies, in situ focal mechanical stimulation of individual PFs, caused ectopic activations, in each of 4 sheep LV preparations (0.2 {+/-} 0.1 ectopics in 10s pre-mechanical stimulation vs 2.1 {+/-} 0.2 ectopics in 10s during mechanical stimulation, P less than 0.001). We interpret our observations in rat and sheep hearts as evidence for a role of PFs in the generation of some mechanically-induced arrhythmia.

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