Sexual dichromatism of the Blue-throated Starfrontlet, <i>Coeligena helianthea</i>, hummingbird plumage

Among the many richly coloured birds, hummingbirds with their brilliant colouration are outstanding. We studied the plumage of male and female Blue-throated Starfrontlet, Coeligena helianthea, which exhibits a marked sexual dichromatism. The wide diversity of coloured feathers (blue, purple, golden, green, red) makes it an attractive species to investigate the structural basis of the colouration and to study the connection between the displayed colours and the perception by conspecifics. We analysed the optical properties of the feather barbules, applying spectrophotometry, scatterometry, and electron microscopy. Using the anatomical results, the spectral data can be interpreted by optical modelling. The reflectance spectra of the feathers of male C. helianthea strikingly overlap with the spectral sensitivities of bird photoreceptors, which suggests that the feather and photoreceptor spectra are tuned

Iridescent colouration of male Anna's hummingbird (<i>Calypte anna</i>) caused by multilayered barbules

The male Anna's hummingbird features a brightly reddish-pink reflecting gorget, due to large stacks of melanosomes in the feather barbules, arranged in layers separated by keratin. Direct observations together with detailed scatterometry demonstrated that the barbules reflect incident light in an approximately specular manner. The structural colouration is iridescent, i.e. varies with a changing angle of light incidence. Spectrophotometrical measurements of the barbule reflectance and absorbance can be well interpreted with calculated spectra obtained with a transfer matrix method for optical multilayers, using anatomical data and measured refractive index spectra. The organization of the reflectors as a Venetian blind presumably functions to create a high spectral contrast of the male's plumage during courtship

Visual 3-D SLAM from UAVs

The aim of the paper is to present, test and discuss the implementation of Visual SLAM techniques to images taken from Unmanned Aerial Vehicles (UAVs) outdoors, in partially structured environments. Every issue of the whole process is discussed in order to obtain more accurate localization and mapping from UAVs flights. Firstly, the issues related to the visual features of objects in the scene, their distance to the UAV, and the related image acquisition system and their calibration are evaluated for improving the whole process. Other important, considered issues are related to the image processing techniques, such as interest point detection, the matching procedure and the scaling factor. The whole system has been tested using the COLIBRI mini UAV in partially structured environments. The results that have been obtained for localization, tested against the GPS information of the flights, show that Visual SLAM delivers reliable localization and mapping that makes it suitable for some outdoors applications when flying UAVs

The training-induced changes on automatism, conduction and myocardial refractoriness are not mediated by parasympathetic postganglionic neurons activity

The purpose of this study is to test the role that parasympathetic postganglionic neurons could play on the adaptive electrophysiological changes produced by physical training on intrinsic myocardial automatism, conduction and refractoriness. Trained rabbits were submitted to aphysical training protocol on treadmill during 6 weeks. The electrophysiological study was performed in an isolated heart preparation. The investigated myocardial properties were: (a) sinus automatism, (b) atrioventricular and ventriculoatrial conduction, (c) atrial, conduction system and ventricular refractoriness. The parameters to study the refractoriness were obtained by means of extrastimulus test at four diVerent pacing cycle lengths (10% shorter than spontaneous sinus cycle length, 250, 200 and 150 ms) and (d) mean dominant frequency (DF) of the induced ventricular Wbrillation (VF), using a spectral method. The electrophysiological protocol was performed before and during continuous atropine administration (1 ¿M), in order to block cholinergic receptors. Cholinergic receptor blockade did not modify either the increase in sinus cycle length, atrioventricular conduction and refractoriness (left ventricular and atrioventricular conduction system functional refractory periods) or the decrease of DF of VF. These Wndings reveal that the myocardial electrophysiological modiWcations produced by physical training are not mediated by intrinsic cardiac parasympathetic activity.The authors thank Carmen Rams, Ana Diaz, Pilar Navarro and Cesar Avellaneda for their excellent technical assistance. This work has been supported by grants from the Spanish Ministry of Education and Science (DEP2007-73234-C03-01) and Generalitat Valenciana (PROMETEO 2010/093). M Zarzoso was supported by a research scholarship from Generalitat Valenciana (BFPI/2008/003).Zarzoso Muñoz, M.; Such Miquel, L.; Parra Giraldo, G.; Brines Ferrando, L.; Such, L.; Chorro, F.; Guerrero, J.... (2012). The training-induced changes on automatism, conduction and myocardial refractoriness are not mediated by parasympathetic postganglionic neurons activity. European Journal of Applied Physiology. 112(6):2185-2193. https://doi.org/10.1007/s00421-011-2189-4S218521931126Armour JA, Hopkins DA (1990a) Activity of in vivo canine ventricular neurons. Am J Physiol Heart Circ Physiol 258:H326–H336. doi: 10.1152/ajpregu.00183.2004Armour JA, Hopkins DA (1990b) Activity of canine in situ left atrial ganglion neurons. Am J Physiol Heart Circ Physiol 259:H1207–H1215Armour JA (2004) Cardiac neuronal hierarchy in health and disease. Am J Physiol Regul Integr Comp Physiol 287:R262–R271Armour JA, Murphy DA, Yuan BX, Macdonald S, Hopkins DA (1997) Gross and microscopic anatomy of the human intrinsic cardiac nervous system. Anat Rec 247:289–298Bedford TG, Tipton CM (1987) Exercise training and the arterial baroreflex. J Appl Physiol 63:1926–1932Bonaduce D, Petretta M, Cavallaro V, Apicella C, Ianniciello A, Romano M, Breglio R, Marciano F (1998) Intensive training and cardiac autonomic control in high level athletes. Med Sci Sports Exerc 30:691–696Brack KE, Coote JH, Ng GA (2011) Vagus nerve stimulation protects against ventricular fibrillation independent of muscarinic receptor activation. Cardiovasc Res 91:437–446. doi: 10.1093/cvr/cvr105Brorson L, Conradson TB, Olsson B, Varnauskas E (1976) Right atrial monophasic action potential and effective refractory periods in relation to physical training and maximal heart rate. Cardiovasc Res 10:160–168Carmeliet E, Mubagwa K (1998) Antiarrhythmic drugs and cardiac ion channels: mechanisms of action. Prog Biophys Mol Biol 70:1–72Chorro FJ, Cánoves J, Guerrero J, Mainar L, Sanchis J, Such L, López-Merino V (2000) Alteration of ventricular fibrillation by flecainide, verapamil, and sotalol: an experimental study. Circulation 101:1606–1615Di Carlo SE, Bishop VS (1990) Exercise training enhances cardiac afferent inhibition of baroreflex function. Am J Physiol 258:212–220Gagliardi M, Randall WC, Bieger D, Wurster RD, Hopkins DA, Armour JA (1988) Activity of in vivo canine cardiac plexus neurons. Am J Physiol Heart Circ Physiol 255:H789–H800Gao L, Wang W, Liu D, Zucker IH (2007) Exercise training normalizes sympathetic outflow by central antioxidant mechanisms in rabbits with pacing-induced chronic heart failure. Circulation 115:3095–3102. doi: 10.1161/CIRCULATIONAHA.106.677989Gaustad SE, Rolim N, Wisløff U (2010) A valid and reproducible protocol for testing maximal oxygen uptake in rabbits. Eur J Cardiovasc Prev Rehabil 17:83–88. doi: 10.1097/HJR.0b013e32833090c4Gómez-Cabrera MC, Borrás C, Pallardó FV, Sastre J, Ji LL, Viña J (2005) Decreasing xanthine oxidase-mediated oxidative stress prevents useful cellular adaptations to exercise in rats. J Physiol 567:113–120. doi: 10.1113/jphysiol.2004.080564Gray AL, Johnson TA, Ardell JL, Massari VJ (2004) Parasympathetic control of the heart II. A novel interganglionic intrinsic cardiac circuit mediates neural control of heart rate. J Appl Physiol 96:2273–2278. doi: 10.1152/japplphysiolHamilton KL, Powers SK, Sugiura T, Kim S, Lennon S, Tumer N, Mehta JL (2001) Short-term exercise training can improve myocardial tolerance to I/R without elevation in heat shock proteins. Am J Physiol Heart Circ Physiol 281:1346–1352Inoue H, Zipes DP (1987) Changes in atrial and ventricular refractoriness and atrioventricular nodal conduction produced by combinations of vagal and sympathetic stimulation that result in a constant spontaneous sinus cycle length. Circ Res 60:942–951Jew KN, Olsson MC, Mokelke EA, Palmer BM, Moore RL (2001) Endurance training alters outward K+ current characteristics in rat cardiocytes. J Appl Physiol 90:1327–1333Johnson TA, Gray AL, Lauenstein JM, Newton SS, Massari VJ (2004) Parasympathetic control of the heart I. An interventriculo-septal ganglion is the major source of the vagal intracardiac innervation of the ventricles. J Appl Physiol 96:2265–2272. doi: 10.1152/japplphysiol.00620.2003Katona PG, McLean M, Dighton DH, Guz A (1982) Sympathetic and parasympathetic cardiac control in athletes and nonathletes at rest. J Appl Physiol 52:1652–1657Lewis SF, Nylander E, Gad P, Areskog N (1980) Non-autonomic component in bradycardia of endurance trained men at rest and during exercise. Acta Physiol Scand 109:297–305Litovsky SH, Antzelevitch C (1990) Differences in the electrophysiological response of canine ventricular subendocardium and subepicardium to acetylcholine and isoproterenol. A direct effect of acetylcholine in ventricular myocardium. Circ Res 67:615–627Löffelholz K (1981) Release of acetylcholine in the isolated heart. Am J Physiol 240(4):H431–H440Lopatin AN, Nichols CG (2001) Inward rectifiers in the heart: an update on I(K1). J Mol Cell Cardiol 33:625–638. doi: 10.1006/jmcc.2001.1344Mace LC, Palmer BM, Brown DA, Jew KN, Lynch JM, Glunt JM, Parsons TA, Cheung JY, Moore RL (2003) Influence of age and run training on cardiac Na+/Ca2+ exchange. J Appl Physiol 95:1994–2003. doi: 10.1152/japplphysiol.00551.2003Martins JB, Zipes DP (1980) Effects of sympathetic and vagal nerves on recovery properties of the endocardium and epicardium of the canine left ventricle. Circ Res 46:100–110Mezzani A, Giovannini T, Michelucci A, Padeletti L, Resina A, Cupelli V, Musante R (1990) Effects of training on the electrophysiologic properties of atrium and accessory pathway in athletes with Wolff–Parkinson–White syndrome. Cardiology 77:295–302Mokelke EA, Palmer BM, Cheung JY, Moore RL (1997) Endurance training does not affect intrinsic calcium current characteristics in rat myocardium. Am J Physiol Heart Circ Physiol 273:H1193–H1197Mont L, Elosua R, Brugada J (2009) Endurance sport practice as a risk factor for atrial fibrillation and atrial flutter. Europace 11:11–17. doi: 10.1093/europace/eun289Moore RL, Korzick DH (1995) Cellular adaptations of the myocardium to chronic exercise. Prog Cardiovasc Dis 37:371–396Negrao CE, Moreira ED, Santos MC, Farah VM, Krieger EM (1992) Vagal function impairment after exercise training. J Appl Physiol 72:1749–1753Ng GA, Brack KE, Coote JH (2001) Effects of direct sympathetic and vagus nerve stimulation on the physiology of the whole heart—a novel model of isolated Langendorff perfused rabbit heart with intact dual autonomic innervation. Exp Physiol 86:319–329Nylander E, Sigvardsson K, Kilbom A (1982) Training-induced bradycardia and intrinsic heart rate in rats. Eur J Appl Physiol Occup Physiol 48:189–199Panfilov AV (2006) Is heart size a factor in ventricular fibrillation? Or how close are rabbit and human hearts? Heart Rhythm 3:862–864. doi: 10.1016/j.hrthm.2005.12.022Papka RE (1976) Studies of cardiac ganglia in pre- and postnatal rabbits. Cell Tissue Res 175:17–35Pardini BJ, Patel KP, Schmid PG, Lund DD (1987) Location, distribution and projections of intracardiac ganglion cells in the rat. J Auton Nerv Syst 20:91–101Scott AS, Eberhard A, Ofir D, Benchetrit G, Dinh TP, Calabrese P, Lesiuk V, Perrault H (2004) Enhanced cardiac vagal efferent activity does not explain training-induced bradycardia. Auton Neurosci 112:60–68. doi: 10.1016/j.autneu.2004.04.006Seals DR, Chase PB (1989) Influence of physical training on HR variability and baroreflex circulatory control. J Appl Physiol 66:1886–1895Shi X, Stevens GHJ, Foresman BH, Stern SA, Raven PB (1995) Autonomic nervous system control of the heart: endurance exercise training. Med Sci Sports Exerc 27:1406–1413Snyders DJ (1999) Structure and function of cardiac potassium channels. Cardiovasc Res 42:377–390Stein R, Moraes RS, Cavalcanti AV, Ferlin EL, Zimerman LI, Ribeiro JP (2000) Atrial automaticity and atrioventricular conduction in athletes: contribution of autonomic regulation. 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Characterization of a Mo/Au thermometer for ATHENA

The first dark characterization of a thermometer fabricated with our Mo/Au bilayers to be used as a transition edge sensor is presented. High-quality, stress-free Mo layers, whose thickness is used to tune the critical temperature (TC ) down to 100 mK, are deposited by sputtering at room temperature (RT ) on Si3N4 bulk and membranes, and protected from degradation with a 15-nm sputtered Au layer. An extra layer of high-quality Au is deposited by ex situ e-beam to ensure low residual resistance. The thermometer is patterned on a membrane using standard photolithographic techniques and wet etching processes, and is contacted through Mo paths, displaying a sharp superconducting transition (α ≈ 600). Results show a good coupling between Mo and Au layers and excellent TC reproducibility, allowing to accurately correlate dM o and TC . Since dAu is bigger than ξM for all analyzed samples, bilayer residual resistance can be modified without affecting TC . Finally, first current to voltage measurements at different temperatures are measured and analyzed, obtaining the corresponding characterization parameters

Sequential Loading of Cohesin Subunits during the First Meiotic Prophase of Grasshoppers

The cohesin complexes play a key role in chromosome segregation during both mitosis and meiosis. They establish sister chromatid cohesion between duplicating DNA molecules during S-phase, but they also have an important role during postreplicative double-strand break repair in mitosis, as well as during recombination between homologous chromosomes in meiosis. An additional function in meiosis is related to the sister kinetochore cohesion, so they can be pulled by microtubules to the same pole at anaphase I. Data about the dynamics of cohesin subunits during meiosis are scarce; therefore, it is of great interest to characterize how the formation of the cohesin complexes is achieved in order to understand the roles of the different subunits within them. We have investigated the spatio-temporal distribution of three different cohesin subunits in prophase I grasshopper spermatocytes. We found that structural maintenance of chromosome protein 3 (SMC3) appears as early as preleptotene, and its localization resembles the location of the unsynapsed axial elements, whereas radiation-sensitive mutant 21 (RAD21) (sister chromatid cohesion protein 1, SCC1) and stromal antigen protein 1 (SA1) (sister chromatid cohesion protein 3, SCC3) are not visualized until zygotene, since they are located in the synapsed regions of the bivalents. During pachytene, the distribution of the three cohesin subunits is very similar and all appear along the trajectories of the lateral elements of the autosomal synaptonemal complexes. However, whereas SMC3 also appears over the single and unsynapsed X chromosome, RAD21 and SA1 do not. We conclude that the loading of SMC3 and the non-SMC subunits, RAD21 and SA1, occurs in different steps throughout prophase I grasshopper meiosis. These results strongly suggest the participation of SMC3 in the initial cohesin axis formation as early as preleptotene, thus contributing to sister chromatid cohesion, with a later association of both RAD21 and SA1 subunits at zygotene to reinforce and stabilize the bivalent structure. Therefore, we speculate that more than one cohesin complex participates in the sister chromatid cohesion at prophase I

Sequential Loading of Cohesin Subunits during the First Meiotic Prophase of Grasshoppers

A previous version of this article appeared as an Early Online Release on January 2, 2007 (doi:10.1371/journal.pgen.0030028.eor).The cohesin complexes play a key role in chromosome segregation during both mitosis and meiosis. They establish sister chromatid cohesion between duplicating DNA molecules during S-phase, but they also have an important role during postreplicative double-strand break repair in mitosis, as well as during recombination between homologous chromosomes in meiosis. An additional function in meiosis is related to the sister kinetochore cohesion, so they can be pulled by microtubules to the same pole at anaphase I. Data about the dynamics of cohesin subunits during meiosis are scarce; therefore, it is of great interest to characterize how the formation of the cohesin complexes is achieved in order to understand the roles of the different subunits within them. We have investigated the spatio-temporal distribution of three different cohesin subunits in prophase I grasshopper spermatocytes. We found that structural maintenance of chromosome protein 3 (SMC3) appears as early as preleptotene, and its localization resembles the location of the unsynapsed axial elements, whereas radiation-sensitive mutant 21 (RAD21) (sister chromatid cohesion protein 1, SCC1) and stromal antigen protein 1 (SA1) (sister chromatid cohesion protein 3, SCC3) are not visualized until zygotene, since they are located in the synapsed regions of the bivalents. During pachytene, the distribution of the three cohesin subunits is very similar and all appear along the trajectories of the lateral elements of the autosomal synaptonemal complexes. However, whereas SMC3 also appears over the single and unsynapsed X chromosome, RAD21 and SA1 do not. We conclude that the loading of SMC3 and the non-SMC subunits, RAD21 and SA1, occurs in different steps throughout prophase I grasshopper meiosis. These results strongly suggest the participation of SMC3 in the initial cohesin axis formation as early as preleptotene, thus contributing to sister chromatid cohesion, with a later association of both RAD21 and SA1 subunits at zygotene to reinforce and stabilize the bivalent structure. Therefore, we speculate that more than one cohesin complex participates in the sister chromatid cohesion at prophase I.This work was supported by grants BFU2005–05668-C03–01, BFU2006–06655, BFU2005–01266, BFU2005–02431, and BFU2006–04406 from Ministerio de Educación y Ciencia, España, and grants 1001160016 and 11/BCB/013 from Universidad Autónoma de Madrid and Comunidad de Madrid. The Department of Immunology and Oncology was founded and is supported by the Spanish Council for Scientific Research (CSIC).Peer reviewe

Effect of chronic exercise on myocardial electrophysiological heterogeneity and stability. Role of intrinsic cholinergic neurons: A study in the isolated rabbit heart

[EN] A study has been made of the effect of chronic exercise on myocardial electrophysiological heterogeneity and stability, as well as of the role of cholinergic neurons in these changes. Determinations in hearts from untrained and trained rabbits on a treadmill were performed. The hearts were isolated and perfused. A pacing electrode and a recording multielectrode were located in the left ventricle. The parameters determined during induced VF, before and after atropine (1 mu M), were: fibrillatory cycle length (VV), ventricular functional refractory period (FRPVF), normalized energy (NE) of the fibrillatory signal and its coefficient of variation (CV), and electrical ventricular activation complexity, as an approach to myocardial heterogeneity and stability. The VV interval was longer in the trained group than in the control group both prior to atropine (78 +/- 10 vs. 68 +/- 10 ms) and after atropine (76 +/- 8 vs. 67 +/- 10 ms). Likewise, FRPVF was longer in the trained group than in the control group both prior to and after atropine (53 +/- 8 vs. 42 +/- 7 ms and 50 +/- 6 vs. 40 +/- 6 ms, respectively), and atropine did not modify FRPVF. The CV of FRPVF was lower in the trained group than in the control group prior to atropine (12.5 +/- 1.5% vs. 15.1 +/- 3.8%) and, decreased after atropine (15.1 +/- 3.8% vs. 12.2 +/- 2.4%) in the control group. The trained group showed higher NE values before (0.40 +/- 0.04 vs. 0.36 +/- 0.05) and after atropine (0.37 +/- 0.04 vs. 0.34 +/- 0.06; p = 0.08). Training decreased the CV of NE both before (23.3 +/- 2% vs. 25.2 +/- 4%; p = 0.08) and after parasympathetic blockade (22.6 +/- 1% vs. 26.1 +/- 5%). Cholinergic blockade did not modify these parameters within the control and trained groups. Activation complexity was lower in the trained than in the control animals before atropine (34 +/- 8 vs. 41 +/- 5), and increased after atropine in the control group (41 +/- 5 vs. 48 +/- 9, respectively). Thus, training decreases the intrinsic heterogeneity of the myocardium, increases electrophysiological stability, and prevents some modifications due to muscarinic block.This research was supported by the Spanish Ministry of Education and Science, (DEP2007-73234-C03-01 to AMA), http://www.mecd.gob.es/portada-mecd/; and the Generalitat Valenciana (PROMETEO 2010/093 to FJC, and FPI/2008/003 to MZ), http://www.gva.es/va/inicio/presentacion; jsessionid=ydprbDQZTsCTz85W1Such-Miquel, L.; Brines-Ferrando, L.; Alberola, A.; Zarzoso Muñoz, M.; Chorro Gasco, FJ.; Guerrero-Martínez, JF.; Parra-Giraldo, G.... (2018). Effect of chronic exercise on myocardial electrophysiological heterogeneity and stability. Role of intrinsic cholinergic neurons: A study in the isolated rabbit heart. PLoS ONE. 13(12). https://doi.org/10.1371/journal.pone.0209085S1312Billman, G. E. (2002). Aerobic exercise conditioning: a nonpharmacological antiarrhythmic intervention. Journal of Applied Physiology, 92(2), 446-454. doi:10.1152/japplphysiol.00874.2001Billman, G. E. (2006). A comprehensive review and analysis of 25 years of data from an in vivo canine model of sudden cardiac death: Implications for future anti-arrhythmic drug development. Pharmacology & Therapeutics, 111(3), 808-835. doi:10.1016/j.pharmthera.2006.01.002Dor-Haim, H., Berenfeld, O., Horowitz, M., Lotan, C., & Swissa, M. (2013). Reduced Ventricular Arrhythmogeneity and Increased Electrical Complexity in Normal Exercised Rats. PLoS ONE, 8(6), e66658. doi:10.1371/journal.pone.0066658Hamer, M., & Stamatakis, E. (2008). Physical Activity and Cardiovascular Disease: Directions for Future Research. The Open Sports Sciences Journal, 1(1), 1-2. doi:10.2174/1875399x00801010001Powers, S. K., Smuder, A. J., Kavazis, A. N., & Quindry, J. C. (2014). Mechanisms of Exercise-Induced Cardioprotection. Physiology, 29(1), 27-38. doi:10.1152/physiol.00030.2013Hull, S. S., Vanoli, E., Adamson, P. B., Verrier, R. L., Foreman, R. D., & Schwartz, P. J. (1994). Exercise training confers anticipatory protection from sudden death during acute myocardial ischemia. Circulation, 89(2), 548-552. doi:10.1161/01.cir.89.2.548Hajnal, Á., Nagy, O., Litvai, Á., Papp, J., Parratt, J. R., & Végh, Á. (2005). Nitric oxide involvement in the delayed antiarrhythmic effect of treadmill exercise in dogs. Life Sciences, 77(16), 1960-1971. doi:10.1016/j.lfs.2005.02.015Such, L., Alberola, A. M., Such-Miquel, L., López, L., Trapero, I., Pelechano, F., … Chorro, F. J. (2008). Effects of chronic exercise on myocardial refractoriness: a study on isolated rabbit heart. Acta Physiologica, 193(4), 331-339. doi:10.1111/j.1748-1716.2008.01851.xZarzoso, M., Such-Miquel, L., Parra, G., Brines-Ferrando, L., Such, L., Chorro, F. J., … Alberola, A. (2011). The training-induced changes on automatism, conduction and myocardial refractoriness are not mediated by parasympathetic postganglionic neurons activity. European Journal of Applied Physiology, 112(6), 2185-2193. doi:10.1007/s00421-011-2189-4Billman, G. E. (2009). Cardiac autonomic neural remodeling and susceptibility to sudden cardiac death: effect of endurance exercise training. American Journal of Physiology-Heart and Circulatory Physiology, 297(4), H1171-H1193. doi:10.1152/ajpheart.00534.2009HAN, J., & MOE, G. K. (1964). Nonuniform Recovery of Excitability in Ventricular Muscle. Circulation Research, 14(1), 44-60. doi:10.1161/01.res.14.1.44Beaumont, E., Salavatian, S., Southerland, E. M., Vinet, A., Jacquemet, V., Armour, J. A., & Ardell, J. L. (2013). Network interactions within the canine intrinsic cardiac nervous system: implications for reflex control of regional cardiac function. The Journal of Physiology, 591(18), 4515-4533. doi:10.1113/jphysiol.2013.259382Armour, J. A. (2008). Potential clinical relevance of the ‘little brain’ on the mammalian heart. Experimental Physiology, 93(2), 165-176. doi:10.1113/expphysiol.2007.041178Abramochkin, D. V., Nurullin, L. F., Borodinova, A. A., Tarasova, N. V., Sukhova, G. S., Nikolsky, E. E., & Rosenshtraukh, L. V. (2009). Non-quantal release of acetylcholine from parasympathetic nerve terminals in the right atrium of rats. Experimental Physiology, 95(2), 265-273. doi:10.1113/expphysiol.2009.050302CHORRO, F. J., CANOVES, J., GUERRERO, J., MAINAR, L., SANCHIS, J., SORIA, E., … LOPEZ-MERINO, V. (2000). Opposite Effects of Myocardial Stretch and Verapamil on the Complexity of the Ventricular Fibrillatory Pattern: An Experimental Study. Pacing and Clinical Electrophysiology, 23(11), 1594-1603. doi:10.1046/j.1460-9592.2000.01594.xSuch, L., Rodriguez, A., Alberola, A., Lopez, L., Ruiz, R., Artal, L., … Chorro, F. J. (2002). Intrinsic changes on automatism, conduction, and refractoriness by exercise in isolated rabbit heart. Journal of Applied Physiology, 92(1), 225-229. doi:10.1152/jappl.2002.92.1.225Duytschaever, M., Mast, F., Killian, M., Blaauw, Y., Wijffels, M., & Allessie, M. (2001). Methods for Determining the Refractory Period and Excitable Gap During Persistent Atrial Fibrillation in the Goat. Circulation, 104(8), 957-962. doi:10.1161/hc3401.093156Wijffels, M. C. E. F., Kirchhof, C. J. H. J., Dorland, R., & Allessie, M. A. (1995). Atrial Fibrillation Begets Atrial Fibrillation. Circulation, 92(7), 1954-1968. doi:10.1161/01.cir.92.7.1954Zaitsev, A. V., Berenfeld, O., Mironov, S. F., Jalife, J., & Pertsov, A. M. (2000). Distribution of Excitation Frequencies on the Epicardial and Endocardial Surfaces of Fibrillating Ventricular Wall of the Sheep Heart. Circulation Research, 86(4), 408-417. doi:10.1161/01.res.86.4.408Armour, J. A., Collier, K., Kember, G., & Ardell, J. L. (1998). Differential selectivity of cardiac neurons in separate intrathoracic autonomic ganglia. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 274(4), R939-R949. doi:10.1152/ajpregu.1998.274.4.r939Armour, J. A., & Hopkins, D. A. (1990). Activity of in vivo canine ventricular neurons. American Journal of Physiology-Heart and Circulatory Physiology, 258(2), H326-H336. doi:10.1152/ajpheart.1990.258.2.h326D’Souza, A., Bucchi, A., Johnsen, A. B., Logantha, S. J. R. J., Monfredi, O., Yanni, J., … Boyett, M. R. (2014). Exercise training reduces resting heart rate via downregulation of the funny channel HCN4. Nature Communications, 5(1). doi:10.1038/ncomms4775Sartiani, L., Romanelli, M., Mugelli, A., & Cerbai, E. (2015). Updates on HCN Channels in the Heart: Function, Dysfunction and Pharmacology. Current Drug Targets, 16(8), 868-876. doi:10.2174/1389450116666150531152047Herrmann, S., Layh, B., & Ludwig, A. (2011). 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Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder

We present results from a new incoherent-beam Fast Radio Burst (FRB) search on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its large instantaneous field of view (FoV) and relative thermal insensitivity allow us to probe the ultra-bright tail of the FRB distribution, and to test a recent claim that this distribution's slope, $\alpha\equiv-\frac{\partial \log N}{\partial \log S}$, is quite small. A 256-input incoherent beamformer was deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were described by a single power-law with $\alpha=0.7$, we would expect an FRB detection every few days, making this the fastest survey on sky at present. We collected 1268 hours of data, amounting to one of the largest exposures of any FRB survey, with over 2.4\,$\times$\,10$^5$\,deg$^2$\,hrs. Having seen no bursts, we have constrained the rate of extremely bright events to $<\!13$\,sky$^{-1}$\,day$^{-1}$ above $\sim$\,220$\sqrt{(\tau/\rm ms)}$ Jy\,ms for $\tau$ between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also allows us to rule out $\alpha\lesssim0.9$ with 95$\%$ confidence, after marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we show that for a cosmological population and a large dynamic range in flux density, $\alpha$ is brightness-dependent. Since FRBs now extend to large enough distances that non-Euclidean effects are significant, there is still expected to be a dearth of faint events and relative excess of bright events. Nevertheless we have constrained the allowed number of ultra-intense FRBs. While this does not have significant implications for deeper, large-FoV surveys like full CHIME and APERTIF, it does have important consequences for other wide-field, small dish experiments