scholarly journals Feedback in the Contractile Mechanism of the Frog Heart

1972 ◽  
Vol 60 (3) ◽  
pp. 239-247 ◽  
Author(s):  
Emil Bozler
Keyword(s):  
Low Temperatures ◽  
Time Course ◽  
Low Frequency ◽  
Feedback Mechanism ◽  
Frog Heart ◽  
Contractile Mechanism ◽  
Quick Release ◽  
Rapid Changes ◽  
Frog Ventricle ◽  
Rapid Drop

Shortening causes a transient decrease, extension an increase, in activity during contractures of the frog ventricle induced by high Ca or by isosmotic K solution. This is shown by the fact that, after the immediate passive shortening, the muscle is extended under isotonic conditions when the load is diminished, and that under isometric conditions quick release causes first a rapid drop, then a further, much slower, fall of tension. Increasing the load or stretching induce the opposite effects. At low temperatures all rapid changes in length produce oscillations of low frequency. These responses are due to a sensitive feedback mechanism similar to that previously demonstrated for insect fibrillar muscle. That this mechanism comes into play in the heart under normal conditions and controls the time-course of the twitch is demonstrated by the observation that relaxation begins earlier the greater the shortening. Thus, during afterloaded isotonic twitches the onset of relaxation is advanced as the load is diminished.

Effects of Anions on Frog Ventricle

1973 ◽  
Vol 51 (10) ◽  
pp. 709-726 ◽  
Author(s):  
Esther R. Anderson ◽  
J. G. Foulks
Keyword(s):  
Mechanical Properties ◽  
Action Potential ◽  
Time Course ◽  
Frog Heart ◽  
Resting Membrane Potential ◽  
Tension Development ◽  
Action Potential Prolongation ◽  
Frog Ventricle ◽  
Slow Onset ◽  
Contractile Performance

The effects of replacement of external chloride by other anions on the electrical and mechanical properties of frog ventricular muscle have been studied.The effects of methylsulfate were similar to those expected for replacement of a permeant anion with an impermeant anion. Increased twitch tension was largely dependent on action potential prolongation. Other anions of the sulfate–sulfonate series produced similar changes, but minor differences in their actions indicated that their effects could not be explained entirely by the elimination of chloride current.Acetate and its analogues produced dramatic changes in both the electrical and mechanical properties of frog heart. All caused a marked hyperpolarization of the resting membrane potential, accompanied by characteristic changes in the shape and duration of the repolarization phase of the action potential. Enhanced contractile performance was characterized by an increased rate of tension development and a slow onset of relaxation. These effects were equally prominent upon transfer to acetate Ringer's solution after previous equilibration to a medium containing methylsulfate in place of chloride. Although similar qualitatively, the members of this series of anions also displayed marked quantitative differences in the intensity and time course of their effects.

Effects of low-frequency stimulation of the superior colliculus on spontaneous and visually guided saccades

1993 ◽  
Vol 69 (3) ◽  
pp. 953-964 ◽  
Author(s):  
P. W. Glimcher ◽  
D. L. Sparks
Keyword(s):  
Superior Colliculus ◽  
Time Course ◽  
Low Frequency ◽  
Arbitrary Point ◽  
Visually Guided ◽  
Spontaneous Movements ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation ◽  
Stimulation Current ◽  
Stimulation Of

1. The first experiment of this study determined the effects of low-frequency stimulation of the monkey superior colliculus on spontaneous saccades in the dark. Stimulation trains, subthreshold for eliciting short-latency fixed-vector saccades, were highly effective at biasing the metrics (direction and amplitude) of spontaneous movements. During low-frequency stimulation, the distribution of saccade metrics was biased toward the direction and amplitude of movements induced by suprathreshold stimulation of the same collicular location. 2. Low-frequency stimulation biased the distribution of saccade metrics but did not initiate movements. The distribution of intervals between stimulation onset and the onset of the next saccade did not differ significantly from the distribution of intervals between an arbitrary point in time and the onset of the next saccade under unstimulated conditions. 3. Results of our second experiment indicate that low-frequency stimulation also influenced the metrics of visually guided saccades. The magnitude of the stimulation-induced bias increased as stimulation current or frequency was increased. 4. The time course of these effects was analyzed by terminating stimulation immediately before, during, or after visually guided saccades. Stimulation trains terminated at the onset of a movement were as effective as stimulation trains that continued throughout the movement. No effects were observed if stimulation ended 40–60 ms before the movement began. 5. These results show that low-frequency collicular stimulation can influence the direction and amplitude of spontaneous or visually guided saccades without initiating a movement. These data are compatible with the hypothesis that the collicular activity responsible for specifying the horizontal and vertical amplitude of a saccade differs from the type of collicular activity that initiates a saccade.

scholarly journals Bidirectional in vivo structural dendritic spine plasticity revealed by two-photon glutamate uncaging in the mouse neocortex

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Jun Noguchi ◽  
Akira Nagaoka ◽  
Tatsuya Hayama ◽  
Hasan Ucar ◽  
Sho Yagishita ◽  
...  
Keyword(s):  
Dendritic Spines ◽  
Time Course ◽  
Hippocampal Slices ◽  
Low Frequency ◽  
Structural Plasticity ◽  
Experimental Conditions ◽  
Two Photon ◽  
Spine Plasticity

Abstract Most excitatory synapses in the brain form on dendritic spines. Two-photon uncaging of glutamate is widely utilized to characterize the structural plasticity of dendritic spines in brain slice preparations in vitro. In the present study, glutamate uncaging was used to investigate spine plasticity, for the first time, in vivo. A caged glutamate compound was applied to the surface of the mouse visual cortex in vivo, revealing the successful induction of spine enlargement by repetitive two-photon uncaging in a magnesium free solution. Notably, this induction occurred in a smaller fraction of spines in the neocortex in vivo (22%) than in hippocampal slices (95%). Once induced, the time course and mean long-term enlargement amplitudes were similar to those found in hippocampal slices. However, low-frequency (1–2 Hz) glutamate uncaging in the presence of magnesium caused spine shrinkage in a similar fraction (35%) of spines as in hippocampal slices, though spread to neighboring spines occurred less frequently than it did in hippocampal slices. Thus, the structural plasticity may occur similarly in the neocortex in vivo as in hippocampal slices, although it happened less frequently in our experimental conditions.

scholarly journals Southern Hemisphere Annular Mode Variability and the Role of Optimal Nonmodal Growth

2005 ◽  
Vol 62 (6) ◽  
pp. 1947-1961 ◽  
Author(s):  
Harun A. Rashid ◽  
Ian Simmonds
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Positive Feedback ◽  
General Model ◽  
Initial Perturbation ◽  
Low Frequency ◽  
Southern Annular Mode ◽  
Feedback Mechanism ◽  
Annular Mode ◽  
Positive Feedback Mechanism

Abstract The southern annular mode is the leading mode of Southern Hemisphere circulation variability, the temporal evolution of which is characterized by large amplitudes and significant persistence. Previous investigators have suggested a positive feedback mechanism that explains some of this low-frequency variance. Here, a mechanism is proposed, involving transient nonmodal growths of the anomalies, that is at least as effective as the positive feedback mechanism in increasing the low-frequency variance of the southern annular mode. Using the vector autoregressive modeling technique, a number of linear inverse models of southern annular mode variability from National Centers for Environmental Prediction–Department of Energy (NCEP–DOE) Reanalysis 2 is derived. These models are then analyzed applying the ideas of the generalized stability theory. It is found that, as a consequence of the nonnormality of the system matrices, a significant increase in the low-frequency variance of the southern annular mode occurs through optimal nonmodal growth of the zonal wind anomalies. The nonnormality arises mainly from the relative dominance of the eddy forcing, while the nonmodal growth is caused by the interference of the nonorthogonal eigenvectors of the nonnormal system matrix. These results are demonstrated first in a simple model that retains only the two leading modes of the zonally averaged zonal wind and eddy-forcing variability, and then in a more general model that includes all the important modes. Using the more general model the authors have determined, among other things, the optimal initial perturbation and the time scale over which it experiences the maximum nonmodal growth to evolve into the pattern associated with the southern annular mode.

Analysis of catecholamine effects in single atrial trabeculae of the frog heart

1977 ◽  
Vol 197 (1128) ◽  
pp. 333-362 ◽  
Keyword(s):  
Cell Membrane ◽  
Action Potential ◽  
Time Course ◽  
Drug Exposure ◽  
Drug Application ◽  
Latency Period ◽  
Frog Heart ◽  
Phosphodiesterase Activity ◽  
Inward Current ◽  
Calcium Inward Current

A study was made of the time course of the effects of adrenaline and isoprenaline on both twitch tension and the intracellular action potential of single atrial trabeculae from frog heart, under a variety of experimental conditions. Twitch tension and overshoot of action potentials rose and subsided in a parallel fashion during build-up and decline of catecholamine action. Cessation of stimulation during drug application had little effect on the tension responses to the drugs. These, and also results obtained with step changes of external calcium concentration during drug exposure, suggest that tension enhancement is a direct consequence of the increased calcium inward current produced by the catecholamines. Exceptional results from trabeculae of ‘hypodynamic’ hearts are described and interpreted on the basis of previous findings obtained in the ‘hypo-dynamic’ condition. Under suitable conditions, including the use of brief periods of drug exposure (≤20 s), three phases of ( β -catecholamine action were discernible: (1) a latency period, of up to 15 s, which preceded tension and potential rise after drug application. Results are presented suggesting that this latency mainly reflects the time which it takes for drug-combined receptors to activate adenylate cyclase in the cell membrane. (2) A sub­sequent phase was critically dependent, in both its magnitude and time course, on phosphodiesterase activity, as was shown by the application of the specific inhibitors papaverine, ICI 63 197, and Ro 20-1724. This phase is probably controlled by the build-up and decline of cAMP within the cells and the subsequent activation and deactivation of a protein kinase. (3) A third phase, associated with the final portion of the decline of catecholamine action, was relatively insensitive to moderate inhi­bition of phosphodiesterase activity. It is attributed to a change of phosphorylation of sites at the internal surface of the cell membrane, the process which, it is assumed, determines the size of calcium inward current during an action potential. Tension decline after a short staircase occurred with a time course closely similar to that of the final phase of the declining catecholamine response. A common final step in the sequential cellular processes under­ lying the two responses is proposed. In some 40% of the trabeculae examined, adrenaline responses were of ‘mixed’ origin: in addition to the relatively slow β -adrenergic action, an initial rapid tension change was present, and experimental tests suggest that this is mediated by α -type receptors.

scholarly journals Fast-to-Slow Conversion Following Chronic Low-Frequency Activation of Medial Gastrocnemius Muscle in Cats. I. Muscle and Motor Unit Properties

1997 ◽  
Vol 77 (5) ◽  
pp. 2585-2604 ◽  
Author(s):  
T. Gordon ◽  
N. Tyreman ◽  
V. F. Rafuse ◽  
J. B. Munson
Keyword(s):  
Motor Unit ◽  
Time Course ◽  
Gastrocnemius Muscle ◽  
Low Frequency ◽  
Contractile Force ◽  
Medial Gastrocnemius ◽  
Normal Range ◽  
Chronic Stimulation ◽  
Time To Peak ◽  
Medial Gastrocnemius Muscle

Gordon, T., N. Tyreman, V. F. Rafuse, and J. B. Munson. Fast-to-slow conversion following chronic low-frequency activation of medial gastrocnemius muscle in cats. I. Muscle and motor unit properties. J. Neurophysiol. 77: 2585–2604, 1997. This study of cat medial gastrocnemius (MG) muscle and motor unit (MU) properties tests the hypothesis that the normal ranges of MU contractile force, endurance, and speed are directly associated with the amount of neuromuscular activity normally experienced by each MU. We synchronously activated all MUs in the MG muscle with the same activity (20 Hz in a 50% duty cycle) and asked whether conversion of whole muscle contractile properties is associated with loss of the normal heterogeneity in MU properties. Chronically implanted cuff electrodes on the nerve to MG muscle were used for 24-h/day stimulation and for monitoring progressive changes in contractile force, endurance, and speed by periodic recording of maximal isometric twitch and tetanic contractions under halothane anesthesia. Chronic low-frequency stimulation slowed muscle contractions and made them weaker, and increased muscle endurance. The most rapid and least variable response to stimulation was a decline in force output of the muscle and constituent MUs. Fatigue resistance increased more slowly, whereas the increase in time to peak force varied most widely between animals and occurred with a longer time course than either force or endurance. Changes in contractile force, endurance, and speed of the whole MG muscle accurately reflected changes in the properties of the constituent MUs both in extent and time course. Normally there is a 100-fold range in tetanic force and a 10-fold range in fatigue indexes and twitch time to peak force. After chronic stimulation, the range in these properties was significantly reduced and, even in MU samples from single animals, the range was shown to correspond with the slow (type S) MUs of the normal MG. In no case was the range reduced to less than the type S range. The same results were obtained when the same chronic stimulation pattern of 20 Hz/50% duty cycle was imposed on paralyzed muscles after hemisection and unilateral deafferentation. The findings that the properties of MUs still varied within the normal range of type S MUs and were still heterogeneous despite a decline in the variance in any one property indicate that the neuromuscular activity can account only in part for the wide range of muscle properties. It is concluded that the normal range of properties within MU types reflects an intrinsic regulation of properties in the multinucleated muscle fibers.

Dissociating early and late visual processing via the Ebbinghaus illusion

2016 ◽  
Vol 33 ◽  
Author(s):  
FILIPP SCHMIDT ◽  
ANDREAS WEBER ◽  
ANKE HABERKAMP
Keyword(s):  
Visual Processing ◽  
High Frequency ◽  
Time Course ◽  
Temporal Dynamics ◽  
Low Frequency ◽  
Response Speed ◽  
Ebbinghaus Illusion ◽  
Priming Effects ◽  
Parvocellular Pathway ◽  
The Difference

AbstractVisual perception is not instantaneous; the perceptual representation of our environment builds up over time. This can strongly affect our responses to visual stimuli. Here, we study the temporal dynamics of visual processing by analyzing the time course of priming effects induced by the well-known Ebbinghaus illusion. In slower responses, Ebbinghaus primes produce effects in accordance with their perceptual appearance. However, in fast responses, these effects are reversed. We argue that this dissociation originates from the difference between early feedforward-mediated gist of the scene processing and later feedback-mediated more elaborate processing. Indeed, our findings are well explained by the differences between low-frequency representations mediated by the fast magnocellular pathway and high-frequency representations mediated by the slower parvocellular pathway. Our results demonstrate the potentially dramatic effect of response speed on the perception of visual illusions specifically and on our actions in response to objects in our visual environment generally.

Calcium fluxes in isolated pancreatic acini: effects of secretagogues

1981 ◽  
Vol 240 (1) ◽  
pp. G38-G49 ◽  
Author(s):  
R. L. Dormer ◽  
J. H. Poulsen ◽  
V. Licko ◽  
J. A. Williams
Keyword(s):  
Time Course ◽  
Calcium Content ◽  
Total Calcium ◽  
Good Correspondence ◽  
Amylase Release ◽  
Pancreatic Acini ◽  
Kinetic Component ◽  
Rapid Drop ◽  
Single Exponential ◽  
Stimulation Of

45Ca2+ exchange and total calcium content were measured in isolated mouse pancreatic acini. 45Ca2+ uptake could be described as the sum of a constant and a single exponential kinetic component; about 60% of total acinar calcium was exchangeable. Stimulation by bethanechol increased 45Ca2+ uptake, but the time course of uptake could be fit only by the addition of a more rapid kinetic component without any change in the total exchangeable Ca2+. 45Ca2+ washout after 1-h loading could be fit as the sum of two exponential components. Stimulation increased the rate of 45Ca2+ washout with the appearance of a third and more rapid kinetic component. There was not, however, a good correspondence between the exponential constants measured in uptake and washout protocols in unstimulated acini. Exponential constants were also affected by the concentration of calcium in the medium, further indicating the presence of nonlinearities in 45Ca2+ exchange. The dose-response relationships were similar for bethanechol stimulation of 45Ca2+ uptake and amylase release, whereas stimulation of 45Ca2+ washout reached a maximum at a higher concentration of bethanechol. Both 45Ca2+ uptake and analytical measurement of total Ca2+ showed a rapid drop in acinar Ca2+ content followed by a gradual reuptake on stimulation by bethanechol. It is concluded that the initial primary effect of secretagogues is to increase Ca2+ efflux, which is interpreted to be the result of release of sequestered calcium into the cytosol.

Rapid changes in metabolic cold defense and GDP binding to brown adipose tissue mitochondria of rat pups

1993 ◽  
Vol 264 (5) ◽  
pp. R1017-R1023 ◽  
Author(s):  
G. Kortner ◽  
K. Schildhauer ◽  
O. Petrova ◽  
I. Schmidt
Keyword(s):  
Adipose Tissue ◽  
Brown Adipose Tissue ◽  
Time Course ◽  
Developmental Changes ◽  
Whole Body ◽  
Rat Pups ◽  
Brown Adipose ◽  
Rapid Changes ◽  
Whole Body Metabolism

To determine developmental changes of brown adipose tissue (BAT) thermogenic activity at defined circadian and thermal states, we evaluated the time course of cold-induced increases of in vitro guanosine 5'-diphosphate (GDP) binding in parallel with whole body metabolism (oxygen consumption, VO2) and core temperature (Tc) in 1- to 11-day-old rat pups. During the maximum phase of the juvenile diurnal cycle, Tc of littermates was recorded continuously and VO2 alternately until 2 min before animals were killed for removal of interscapular BAT. GDP binding after 1.5 h at thermoneutrality and its increase during physiologically comparable cold loads were significantly lower in 1-day-old pups than in 5- and 11-day-old pups. Cold defense was activated more rapidly in the older pups, but GDP binding in even the 1-day-old pups was significantly increased during the second 10-min period of cold exposure. We conclude that rapid changes in thermogenic activity, in connection with the known developmental changes in the dependence of the suckling rat's metabolic cold defense on maternal and sibling contact and circadian phase, will distort longitudinal studies of any fast-changing BAT parameter when the conditions immediately before tissue removal are not thoroughly controlled.

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