scholarly journals CHANGES IN THE DURATION OF THE ELECTRIC RESPONSE OF SINGLE NERVE FIBERS FOLLOWING REPETITIVE STIMULATION

1956 ◽  
Vol 40 (1) ◽  
pp. 19-25 ◽  
Author(s):  
Constantine S. Spyropoulos
Keyword(s):  
Nerve Fiber ◽  
Nerve Fibers ◽  
Repetitive Stimulation ◽  
Bufo Marinus ◽  
Electric Response ◽  
Rapid Rate ◽  
Semitendinosus Muscle ◽  
Single Nerve ◽  
Toad Bufo

Single nerve fibers were isolated from the nerve innervating the sartorius or semitendinosus muscle of the toad (Bufo marinus). Single nerve fiber responses were recorded with three arrangements of the "bridge insulator" method. During stimulation at 50 to 150 pulses per second for 20 to 140 minutes the spike duration was progressively increased. After tetanization the spike duration usually continued to increase at a more rapid rate. Within 5 to 60 minutes further prolongation stopped and within 1 to 10 hours the spike duration was normal. The duration of the response of tetanized fibers was from 2.5 to more than 10 times the spike duration of untetanized fibers. Prolongation was observed in nerve fibers isolated from nerves tetanized in vivo.

Initiation and abolition of electric response of nerve fiber by thermal and chemical means

1961 ◽  
Vol 200 (2) ◽  
pp. 203-208 ◽  
Author(s):  
C. S. Spyropoulos
Keyword(s):  
Chemical Composition ◽  
Nerve Fiber ◽  
Temperature Variation ◽  
Temperature Rise ◽  
Nerve Fibers ◽  
Bufo Marinus ◽  
Ion Concentration ◽  
Electric Response ◽  
Sudden Rise ◽  
Toad Bufo

Techniques were developed to produce brief pulses of temperature variation or pulses of variation in the chemical composition of the medium surrounding the node of nerve fibers of the toad ( Bufo marinus). The effect of such changes were studied upon the nodal response. The response was prolonged by addition of a small amount of Ni ion to the medium and/or by making the Ringer's hypertonic by addition of NaCl. Application of a pulse of temperature rise during the plateau of a response resulted in abolition of the response. A pulse of rise in the concentration of Ca ion in the medium also brought about abolition. Sudden cooling, sudden removal of Ca ion from the medium or a sudden rise in the K-ion concentration during the plateau of the response resulted in prolongation of the response; in some instances, the process of repolarization was completely prevented by these procedures. In the node at rest, sudden cooling or a sudden rise in the K-ion concentration in the medium initiated a full-sized response in an all-or-none manner.

Response of Single Nerve Fibers at Different Hydrostatic Pressures

1957 ◽  
Vol 189 (1) ◽  
pp. 214-218 ◽  
Author(s):  
Constantine S. Spyropoulos
Keyword(s):  
Hydrostatic Pressure ◽  
High Pressures ◽  
Nerve Fibers ◽  
Hydraulic Pump ◽  
Semitendinosus Muscle ◽  
Response Interval ◽  
Shock Response ◽  
Single Nerve ◽  
Toad Bufo ◽  
Striking Effect

The effects of high hydrostatic pressure upon isolated single nerve fibers were investigated. Single nerve fibers were isolated from the nerve innervating the sartorius or semitendinosus muscle of the toad ( Bufo marinus). The responses of single nerve fibers were recorded using the ‘bridge-insulator,’ the ‘interface’ and the ‘three-compartment’ methods. Hydrostatic pressures up to 16,000 psi were developed with a hand operated hydraulic pump. The most striking effect of high pressures was the prolongation of the duration of the response. At 10,000 psi the duration was 4.5–5.0 times the duration at atmospheric pressures. The duration of prolonged responses (by previous tetanization) was not appreciably altered by high pressures. The amplitude, rheobase and shock-response interval were only slightly affected. At 5000 psi the shock-response interval increased by 5–15% and the rheobase by 10–15%.

scholarly journals CONTINUOUS CONDUCTION OF IMPULSES IN PERIPHERAL MYELINATED NERVE FIBERS

1951 ◽  
Vol 35 (2) ◽  
pp. 343-360 ◽  
Author(s):  
Y. Laporte
Keyword(s):  
Nerve Fiber ◽  
Continuous Process ◽  
Conduction Block ◽  
Nerve Fibers ◽  
Nerve Trunk ◽  
Conduction Time ◽  
Myelinated Nerve ◽  
Myelinated Nerve Fibers ◽  
Single Nerve ◽  
Internodal Segment

1. Conduction of impulses in peripheral myelinated fibers of a nerve trunk is a continuous process, since with uninjured nerve fibers: (a) within each internodal segment the conduction time increases continuously and linearly with increasing conduction distance; (b) the presence of nodes of Ranvier does not result in any detectable discontinuity in the conduction of the impulse; (c) the ascending phase of the spike always has an S shape and never presents signs of fractionation; (d) the shape and magnitude of the spike are constant at all points of each internodal segment. 2. Records have been presented of the external logitudinal current that flows during propagation of an impulse in undissected single nerve fiber (Fig. 6). 3. Propagation of impulses across a conduction block occurs with a readily demonstrable discontinuity.

scholarly journals Metabolic costs induced by lactate in the toad Bufo marinus: new mechanism behind oxygen debt?

2003 ◽  
Vol 94 (3) ◽  
pp. 1177-1185 ◽  
Author(s):  
Ilka Pinz ◽  
Hans-O. Pörtner
Keyword(s):  
Metabolic Rate ◽  
Energy Demand ◽  
Isolated Hepatocytes ◽  
Ringer Solution ◽  
Bufo Marinus ◽  
Proton Exchange ◽  
Plasma Catecholamine ◽  
Proton Symport ◽  
Toad Bufo

The mechanism of an increase in metabolic rate induced by lactate was investigated in the toad Bufo marinus. Oxygen consumption (V˙o 2) was analyzed in fully aerobic animals under hypoxic conditions (7% O2 in air), accompanied by measurements of catecholamines in the plasma, and was measured in isolated hepatocytes in vitro under normoxia by using specific inhibitors of lactate proton symport [α-cyano-4-hydroxycinnamate (CHC)] and sodium proton exchange (EIPA). The rise in metabolic rate in vivo can be elicited by infusions of hyperosmotic (previous findings) or isosmotic sodium lactate solutions (this study). Despite previous findings of reduced metabolic stimulation under the effect of adrenergic blockers, the increase inV˙o 2 in vivo was not associated with elevated plasma catecholamine levels, suggesting local release and effect. In addition to the possible in vivo effect via catecholamines, lactate induced a rise in V˙o 2 of isolated hepatocytes, depending on the concentration present in a weakly buffered Ringer solution at pH 7.0. No increase was found at higher pH values (7.4 or 7.8) or in HEPES-buffered Ringer solution. Inhibition of the Lac−-H+ transporter with α-CHC or of the Na+/H+ exchanger with EIPA prevented the increase in metabolic rate. We conclude that increasedV˙o 2 at an elevated systemic lactate level may involve catecholamine action, but it is also caused by an increased energy demand of cellular acid-base regulation via stimulation of Na+/H+ exchange and thereby Na+-K+-ATPase. The effect depends on entry of lactic acid into the cells via lactate proton symport, which is likely favored by low cellular surface pH. We suggest that these energetic costs should also be considered in other physiological phenomena, e.g., when lactate is present during excess, postexerciseV˙o 2.

Heterogeneity and lability of endogenous digitalis-like substances in the plasma of the toad, Bufo marinus

1996 ◽  
Vol 271 (2) ◽  
pp. R325-R332
Author(s):  
V. P. Butler ◽  
J. F. Morris ◽  
T. Akizawa ◽  
M. Matsukawa ◽  
P. Keating ◽  
...  
Keyword(s):  
Inhibitory Activity ◽  
Bufo Marinus ◽  
The Third ◽  
In Vitro Incubation ◽  
Low Concentrations ◽  
Atpase Inhibitors ◽  
Fresh Plasma ◽  
Toad Bufo

Three major groups of endogenous digitalis-like substances (EDLS) have been identified in the plasma of the toad, Bufo marinus. One group of compounds, present in fresh plasma, is composed of chromatographically homogeneous polar conjugates, principally bufadienolide 3-sulfates, which exhibit relatively weak Na(+)-K(+)-adenosinetriphosphatase (ATPase) inhibitory activity. A second and larger group of compounds, also found in fresh plasma, includes chromatographically heterogeneous conjugates, which are effective inhibitors of Na(+)-K(+)-ATPase; these compounds possess properties similar to those of bufotoxins. The third group of EDLS consists of free unconjugated bufadienolides, which are also effective Na(+)-K(+)-ATPase inhibitors. These unconjugated bufadienolides are present in relatively low concentrations in fresh toad plasma, but appreciable quantities are enzymatically generated from conjugates (believed to consist principally of bufotoxins) during the in vitro incubation of plasma. We suggest that the extent to which circulating polar EDLS are enzymatically deconjugated in vivo may be important in the regulation of the digitalis-sensitive Na(+)-K(+)-ATPase of toad brain, the only known digitalis-sensitive Na(+)-K(+)-ATPase in the toad.

scholarly journals Deep Learning-Based Analysis of Macaque Corneal Sub-Basal Nerve Fibers in Confocal Microscopy Images

2019 ◽  
Author(s):  
Jonathan D. Oakley ◽  
Daniel B. Russakoff ◽  
Megan E. McCarron ◽  
Rachel L. Weinberg ◽  
Jessica M. Izzi ◽  
...  
Keyword(s):  
Deep Learning ◽  
Confocal Microscopy ◽  
Nerve Fiber ◽  
Ground Truth ◽  
Automated Analysis ◽  
Nerve Fibers ◽  
Fiber Analysis ◽  
Quantitative Measurements ◽  
Nerve Fiber Analysis

AbstractPurposeTo describe and assess different deep learning-based methods for automated measurement of macaque corneal sub-basal nerves using in vivo confocal microscopy (IVCM).MethodsThe automated assessment of corneal nerve fiber length (CNFL) in IVCM images is of increasing clinical interest. These measurements are important biomarkers in a number of diseases including diabetes mellitus, human immunodeficiency virus, Parkinson’s disease and multiple sclerosis. Animal models of these and other diseases play an important role in understanding the disease processes as efforts toward developing new and effective therapeutics are made. And while automated methods exist for nerve fiber analysis in clinical data, differences in anatomy and image quality make the macaque data more challenging and has motivated the work reported here.Toward this goal, nerves in macaque corneal IVCM images were manually labelled using an ImageJ plugin (NeuronJ). Different deep convolutional neural network (CNN) architectures were evaluated for accuracy relative to the ground truth manual tracings. The best performing model was used on separately acquired macaque ICVM images to additionally compare inter-reader variability.ConclusionsDeep learning-based segmentation of sub-basal nerves in IVCM images shows excellent correlation to manual segmentations in macaque data. The technique is indistinguishable across readers and paves the way for more widespread adoption of objective automated analysis of sub-basal nerves in IVCM.Translational RelevanceQuantitative measurements of corneal sub-basal nerves are important biomarkers for disease screening and management. This work reports on different approaches that, in using deep learning-based techniques, leverage state of the art analysis methods to demonstrate performance akin to human graders. In application, the approach is robust, rapid and objective, offering utility to a variety of clinical studies using IVCM.

Neurally-derived nitric oxide regulates vascular tone in pulmonary and cutaneous arteries of the toad, Bufo marinus

2008 ◽  
Vol 295 (5) ◽  
pp. R1640-R1646 ◽  
Author(s):  
Brett L. Jennings ◽  
John A. Donald
Keyword(s):  
Nitric Oxide ◽  
Pulmonary Artery ◽  
Specific Inhibitor ◽  
Nerve Fibers ◽  
Bufo Marinus ◽  
Physiological Data ◽  
No Donor ◽  
Signaling Mechanism ◽  
Toad Bufo

In this study, the role of nitric oxide (NO) in regulation of the pulmocutaneous vasculature of the toad, Bufo marinus was investigated. In vitro myography demonstrated the presence of a neural NO signaling mechanism in both arteries. Vasodilation induced by nicotine was inhibited by the soluble guanylyl cyclase (GC) inhibitor, 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one, and the NO synthase (NOS) inhibitor, Nω-nitro-l-arginine (l-NNA). Removal of the endothelium had no significant effect on the vasodilation. Furthermore, pretreatment with N5-(1-imino-3-butenyl)-l-ornithine (vinyl-l-NIO), a more specific inhibitor of neural NOS, caused a significant decrease in the nicotine-induced dilation. In the pulmonary artery only, a combination of l-NNA and the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37), completely blocked the nicotine-induced dilation. In both arteries, the vasodilation was also significantly decreased by glibenclamide, an ATP-sensitive K+ (K+ATP) channel inhibitor. Levcromakalim, a K+ATP channel opener, caused a dilation that was blocked by glibenclamide in both arteries. In the pulmonary artery, NO donor-mediated dilation was significantly decreased by pretreatment with glibenclamide. The physiological data were supported by NADPH-diaphorase histochemistry and immunohistochemistry, which demonstrated NOS in perivascular nerve fibers but not the endothelium of the arteries. These results indicate that the pulmonary and cutaneous arteries of B. marinus are regulated by NO from nitrergic nerves rather than NO released from the endothelium. The nitrergic vasodilation in the arteries appears to be caused, in part, via activation of K+ATP channels. Thus, NO could play an important role in determining pulmocutaneous blood flow and the magnitude of cardiac shunting.

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