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At least 19 recordsLinked to original sources
PubMed1989

Bistable firing properties of soleus motor units in unrestrained rats.

EMG recordings from single motor units in the soleus muscle were performed in alert unrestrained rats. A cuff electrode around the tibial nerve and subcutaneously placed electrodes in the foot permitted stimulation of afferent fibres. The movements of the rat and the simultaneous EMG activity were displayed together on a video monitor. Most motor units were tonically active for extended periods during quiet standing. During tonic discharge, maintained shifts between stable low (8-12 Hz; quartiles) and high (16-22.8 Hz) frequency ranges were initiated by short-lasting synaptic excitation of the motoneuron pool by stimulation of Ia afferents, or inhibition by stimulation of skin afferents. The shifts were not related to gross limb movements. This phenomenon is referred to as a bistable firing pattern. Bistable firing also occurred spontaneously during quiet standing. Typically the firing frequency shifted between a low (9-12.5 Hz) and a high (20-24.5 Hz) mode. During recordings of simultaneous activity in two units, spontaneous and stimulus-induced frequency jumps causing maintained changes in firing frequency were regularly seen to occur in one unit, while the frequency in the second unit was unchanged or only phasically influenced. These results demonstrate for the first time a bistable firing pattern during postural activity in the intact animal. The firing pattern closely resembles the bistable behaviour described in spinal motoneurons in reduced preparations, where it is due to the presence of a plateau potential. This suggests that the bistable firing is unexplained by plateau potentials also in the intact animal.

Action Potentials↗
PubMed1986

The role of visual pattern persistence in bistable stroboscopic motion.

Two alternating frames, each consisting of three square elements, were used to study bistable stroboscopic motion percepts. Bistable percepts were obtained which depend on the interstimulus interval (ISI) between the alternating frames. At short ISIs only end-to-end element motion was observed; and at higher ISIs only group motion was perceived. It was found that the progressive ISI-dependent transitions from element to group motion depended on element size and frame duration. These dependencies are predictable from the systematic influence which these variables are known also to exert on visual pattern persistence, indicating that such persistence contributes to determining which precept dominates during bistable stroboscopic motion sequences. These findings bear relevantly on recent attempts to conceptually relate bistable motion percepts to short-range stroboscopic motion processes.

Form Perception↗
PubMed1990

Bistabilities and annihilation phenomena in electrophysiological cardiac models.

We have investigated the oscillatory behavior of cardiac cellular elements simulated by two electrophysiological models: the van Capelle and Durrer (VCD) model and the sinoatrial node cell model of Yanagihara, Noma, and Irisawa (YNI). The VCD model behavior was examined systematically by using continuation-bifurcation analysis. Bifurcation diagrams were constructed as a function of Qit1, an intrinsic parameter of the model, which sets both maximum diastolic potential and depolarization threshold of the cell. The existence of stable high amplitude oscillations was evidenced between two Hopf bifurcation points (HB). Near each HB, a zone of bistability was detected. Close to the HB that corresponded to high values of Qit1, a high amplitude periodic stable state coexisted with a stable steady state. Close to the other HB, in a narrow range of lower Qit1 values, a relatively high amplitude periodic stable state coexisted with a low amplitude periodic stable state. There was no stable steady state in the latter bistability zone. Through the use of phase-plane representations and the determination of separatrices between the different attractor basins, we could deduce the conditions of timing, polarity, and strength needed for a pulse perturbation to send the system from one state to another and vice versa. The YNI model was analyzed by numerical simulation, and the oscillatory behavior of the sinoatrial node cell was explored while applying a depolarizing bias current of various strengths. Results were similar to those obtained from the VCD model in that there were two bistability regions for two different ranges of applied bias current. Depending on current intensity, annihilation of pacemaker activity could be achieved in both zones. However, the coexistence of two oscillatory stable states was never observed in the YNI model. From the behavioral similarities of these different models, we can conclude that bistabilities and annihilation phenomena can be found in transitional zones between quiescence and rhythmic activity.

Animals↗
PubMed1985

Ca++ dependent bistability induced by serotonin in spinal motoneurons.

The plateau potential, responsible for the bistable state of spinal motoneurons, recently described in the decerebrate cat, was suggested to depend on serotonin (Hounsgaard et al. 1984). In an in vitro preparation of the spinal cord of the turtle we now show that serotonin, applied directly to the bath, transforms the intrinsic response properties of motoneurons, uncovering a plateau potential and voltage sensitive bistability. The changes induced by serotonin were blocked by Mn++, while the plateau potential and the bistability remained after application of tetrodotoxin. We conclude that serotonin controls the expression of a Ca++ dependent plateau potential in motoneurons.

Animals↗
PubMed1989

pH-induced bistable dynamic behaviour in the reaction catalysed by glucose-6-phosphate dehydrogenase and conformational hysteresis of the enzyme.

1. Bistable (multiple stationary states) dynamic behaviour in the activity of glucose-6-phosphate dehydrogenase that was subjected to successive pH change was demonstrated in an open continuously stirred tank reactor. Although the enzyme under study did not exhibit an autocatalytic effect and was homogeneously distributed, bistability was shown to occur. 2. The successive pH changes of the enzyme solution corresponded to a pH transition (8.3 in equilibrium 2), i.e. an acidification (forward direction) and an alkalinization (reverse direction). By use of intrinsic protein fluorescence methods, a glucose-6-phosphate dehydrogenase conformational hysteresis was shown to exist concomitant with the pH transition before and after enzyme injection into the reactor. 3. The results obtained suggest that the enzyme behaves, conformationally, as a memory device that stores information about its pH history (i.e. the enzyme records information in its structure about the environment to which it was previously exposed) and transduces it in a non-linear dynamic fashion, producing the bistable behaviour observed in the open reactor.

Catalysis↗
PubMed2025

Bistable Mutation-Selection Equilibria and Violations of Fisher's Theorem in Tetraploids: Insights from Nonlinear Dynamics.

Polyploidy and whole genome duplication (WGD) are widespread biological phenomena with substantial cellular, meiotic, and genetic effects. Despite their prevalence and significance across the tree of life, population genetics theory for polyploids is not well developed. The lack of theoretical models limits our understanding of polyploid evolution and restricts our ability to harness polyploidy for crop improvement amidst increasing environmental stress. To address this gap, we developed and analyzed deterministic models of mutation-selection balance for tetraploids under polysomic (autotetraploid) and disomic (allotetraploid) inheritance patterns and arbitrary dominance relationships. We also introduced a new mathematical framework based on ordinary differential equations and nonlinear dynamics for analyzing the models. We find that autotetraploids approach Hardy-Weinberg Equilibrium 33% faster than allotetraploids, but the different tetraploid inheritance models show little differences in mutation load and allele frequency at mutation-selection balance. Our model also reveals two bistable points of mutation-selection balance for dominant alleles with biased mutation rates over a wide range of selection coefficients in the tetraploid models compared to bistability in only a narrow range for diploids. Finally, using discrete time simulations, we explore the temporal dynamics of allele frequency and fitness change and compare these dynamics to the predictions of Fisher's Fundamental Theorem of Natural Selection. While Fisher's predictions generally hold, we show that the bistable dynamics for dominant mutations fundamentally alter the associated temporal dynamics. Overall, this work develops foundational theoretical models that will facilitate the development of population genetic models and methodologies to study evolution in empirical tetraploid populations.

Fisher’s Fundamental Theorem↗
PubMed1978

A comparison of the "phrygian cap" deformity with bistable and gray scale ultrasound.

Sixteen patients with a "phrygian cap" deformity of the gall bladder seen with oral cholecystography were further evaluated with both bistable and gray scale ultrasound. The bistable technique produced internal echoes that were suspicious of gall stones. When this same area was reevaluated with the more accurate gray scale technique, the folded-fundus deformity was clearly visualized.

Cholelithiasis↗
PubMed1977

[Bistability of pyruvate production by E. coli ML30 in continuous culture].

The pyruvate production of E. coli ML30 in continuous cultures was investigated. In a glucose mineralsalt medium with ammonium as the limiting substrate two stable stationary states (bistability) of pyruvate concentration were obtained. The bistability was limited to dilution rates lower than 0.3 h-1 and connected with a decrease of the yield coefficient (Y Glc) from approximately 0.45 to approximately 0.1.

Culture Media↗
PubMed1977

[Bistability in the activity of glutamine synthetase in ammonium-limiting chemostat cultures of Escherichia coli ML 30].

The approximative estimation of the function micron([NH+4]) in cultures of E. coli ML 30 had shown that bistability of the ammonium concentration in ammonium limited continuous cultures could be possible (BERGTER et al. 1977). This phenomenon suggested a bistability in the regulation of ammonia assimilation. Therefore, the activity of one key enzyme of the two ammonia assimilation systems was measured. The distribution of the activity of glutamine synthetase in ammonia limited continuous cultures after different transition states confirmed this suggestion.

Ammonia↗
PubMed1990

Usefulness of information in bistable system and Dyson model for the origin of metabolism.

Useful or meaningful information for the transition between disordered and ordered states occurring in a chemical system, which organizes itself out of molecular chaos, is stochastically discussed from the viewpoint of dynamical system theory. To make the discussion perspicuous it is helpful to assume that the time evolution of the chemical system proceeds by a univariate, bistable one-step process of birth-and-death type. The model for the evolution of primordial metabolism proposed by Dyson is a bistable system, and hence this model answers the purpose of illustrating the usefulness of information.

Biological Evolution↗
PubMed1987

Bistability and irreversible transitions in a simple substrate cycle.

The dynamic properties of a simple substrate cycle involving two antagonist enzymes are investigated. One of these enzymes exhibits a non-linearity through inhibition by excess substrate. Depending either on the interconverted substrate pool concentration or the maximal activity of the non-inhibited enzyme, monostability, bistability and irreversible transitions may occur. A reversible bistable cycle is shown to present interesting features for regulatory purposes as it can respond to external (and/or internal) modulations in two different ways: A buffering effect by efficient stabilization of the steady-states, or, an increase in sensitivity by switching the system from one regime to the opposite one. The plausible biochemical and biological implications of irreversible transitions are discussed and emphasized in terms of "metabolic transitions".

Enzymes↗
PubMed1988

Bistability of alpha-motoneurones in the decerebrate cat and in the acute spinal cat after intravenous 5-hydroxytryptophan.

1. In the preceding paper (Crone, Hultborn, Kiehn, Mazieres & Wigström, 1988) it was shown that a short-lasting synaptic excitation ('on' stimulus) of extensor motoneurones (primarily triceps surae) in the decerebrate cat often resulted in a maintained excitability increase, which could be reset by a short-lasting inhibitory stimulus train ('off' stimulus). In the present experiments intracellular recording from triceps surae motoneurones and the electroneurogram (ENG activity) from triceps surae nerve branches were performed in parallel. 2. Sustained firing of individual triceps surae motoneurones was most often recorded in parallel with the maintained ENG activity following a synaptic 'on' stimulus. When the motoneurone was silenced, by a hyperpolarizing current through the microelectrode, there was no sign of on-going synaptic excitation during the maintained ENG activity following an 'on' stimulus. It was therefore suggested that voltage-dependent intrinsic properties of the motoneurones themselves could be responsible for the maintained firing. 3. In confirmation of this hypothesis it was found that short-lasting depolarizing current pulses through the recording microelectrode could trigger a self-sustained firing in the motoneurone provided that the bias current (i.e. the holding potential) was kept within certain limits. Hyperpolarizing current pulses terminated the firing. When the spike-generating mechanism was inactivated (by long-lasting excessive depolarization) similar depolarizing and hyperpolarizing current pulses could initiate and terminate plateau potentials in the motoneurones. By grading the depolarizing current pulses it was found that the plateau potentials were of all-or-none character, typically around 10 mV in amplitude. The two levels of excitability which can be triggered by short-lasting excitation and inhibition of the motoneurones is referred to as 'bistable' behaviour of the motoneurones. 4. After an acute spinal transection, in the unanaesthetized cat, the bistable behaviour of the motoneurones disappeared. However, it reappears following intravenous injection of the serotonin precursor 5-hydroxytryptophan (50-120 mg/kg). 5. Individual triceps surae motor units were recorded by selective EMG electrodes during tonic stretch reflexes in the decerebrate preparations. Based on an analysis of their firing pattern during lengthening and shortening (or vibration) of the muscle it is suggested that plateau potentials in motoneurones are recruited during the tonic stretch reflex. Furthermore, it is argued that a quantitatively important part of the depolarization of motoneurones during the tonic stretch reflex indeed originates from these plateau potentials.(ABSTRACT TRUNCATED AT 400 WORDS)

5-Hydroxytryptophan↗
PubMed1992

Contribution of Ca and Ca-activated Cl channels to regenerative depolarization and membrane bistability of cone photoreceptors.

1. Cone photoreceptors in several vertebrate species generate Ca-dependent regenerative depolarizations (e.g., Ca spikes lasting up to 2 s) in response to current injection or surround illumination and may remain in a state of prolonged depolarization (e.g., a permanent plateau near 0 mV) after these stimuli. This paper, while confirming the role of Ca channels in the regenerative depolarization, demonstrates that Ca-activated Cl channels either enhance or hinder prolonged depolarization, depending on the value of the chloride equilibrium potential (ECl). 2. Current- and voltage-clamp recordings obtained with the whole-cell patch-clamp technique were compared in 158 isolated tiger salamander cones to determine the contribution of specific ion channel types to the two forms of depolarizing response. Cones dialyzed with CsCl or KCl intracellular solution (such that ECl = 0 mV) that had sustained negative slope regions in their current-voltage (I-V) relations recorded under voltage clamp, were, under current clamp, bistable with respect to their resting potential. Injection of approximately 20-pA steps of depolarizing current resulted in transitions from the negative stable membrane potential (near -50 mV) to a long lasting plateau around 0 mV. Injection of 200-300 pA of hyperpolarizing current could then force a return to the negative stable resting potential, although once repolarization occurred, current injection had to be reduced or terminated to prevent damaging hyperpolarization of the cell. 3. The inward currents accounting for the negative slope region of the I-V relation were carried in Ca and Ca-activated Cl channels. Specific block of Ca-activated Cl current (ICl(Ca)) by 100 microM niflumic acid (NFA) eliminated the prolonged depolarization, even though the negative slope conductance region in the I-V persisted and the cone could still produce the briefer Ca-dependent regenerative depolarizations. Application of 100 microM Cd2+ blocked both forms of depolarization. 4. Substitution of Ba2+, which among other actions did not activate ICl(Ca), usually supported regenerative depolarizations of shortened duration, demonstrating the role of Ca channels in the initial phase of these responses. 5. A difference was observed in the regenerative depolarization when ECl was shifted away from 0 mV, where it had been in the experiments described above. With ECl set to -40 or -60 mV by reduction of [Cl-] in the pipette, steady-state membrane bistability was eliminated and prolonged depolarization did not occur. Under these conditions, application of the Cl channel blocker NFA showed that ICl(Ca) contributes to membrane hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Bistability and control for ATP synthase and adenylate cyclase is obtained by the removal of substrate inhibition.

The thesis of this article is that the raison d'être of the electron transfer chain and the receptor system is to remove 'substrate inhibition' of the enzymes ATP synthase and adenylate cyclase respectively. Activation by energization or hormone is analogous and presents the features of ideal control system; bistability, hysteresis, sensitivity and amplification, and rapid transitions between resting and active states. In the first part of the article, the simplest nontrivial model conforming with the experimental results is put forward. After the system is described, nonlinear and linear models are developed. An important aspect captured by the model is that the enzyme is structurally asymmetric corresponding to the assumption of regulatory site(s) distinct from catalytic site(s). The structural distinction between a regulatory site and a catalytic site entails different binding and specificity properties of the two types of sites with respect to the nucleotides. In the second part, the experimental evidence for the theory is discussed. It is shown that energization and hormone indeed reduce 'substrate inhibition' and that the properties of time lag and criticality predicted by the theory are indeed verified in experiment and are in turn explained by the theory. The theory can explain and correlate various hitherto unexplained experimental phenomena such as the irreversibility of ATP synthesis and the functional role of the ATP synthase asymmetry. The property of hysteresis predicted by the nonlinear model, is indicated by postillumination ATP synthesis, and preactivation of chloroplasts with reduced dithiols indeed display 'hysteresis loops'. In Aplysia memory for short term sensitization may reside in the hysteretic prolonged elevation of cAMP in sensory neurons.

ATP Synthetase Complexes↗
PubMed1989

The effects of dichoptic and binocular viewing on bistable motion percepts.

Two competitive percepts are produced from a bistable stroboscopic motion display. In this display two frames, each containing three horizontally arrayed elements are presented alternately for several cycles. At short interstimulus intervals (ISIs) element or end-to-end motion responses are obtained when the two inner, spatially overlapping elements are seen as stationary and the third element moves back and forth from one end to the other end. Group motion responses are obtained at longer ISIs when the three elements are seen to move back and forth as a group. The dominance of these two percepts across ISIs was controlled by the manipulation of (1) element size, (2) frame duration, and (3) viewing conditions. Under both binocular and dichoptic viewing, element motion responses increase as element size and frame duration decrease. By maximizing pattern persistence substantial element motion responses were obtained dichoptically as well as binocularly. Instead of supporting the existence of two separate, low-level and high-level, motion systems, our data suggest that there is a single, high-level mechanism for motion whose output can be modulated by pattern persistence.

Afterimage↗
PubMed1986

Conductivity-mediated regulation in a compartmental enzyme system. Superactivation and conductance bistability.

This paper deals with the 'conductivity effect' which results from the action of an electric current in a compartmental system involving a chemical reaction producing ionic species. This effect, due to the difference between internal and external conductivities, leads to the accumulation of ionic species inside the reactive compartment. Different results are obtained depending on the considered kinetics: amplification of reaction rate increase, and chemical and conductance bistabilities.

Biological Transport↗
PubMed1991

Cramps: a sign of motoneurone 'bistability' in a human patient.

In a patient suffering from severe long-lasting cramps, cramps were triggered in the triceps surae by volleys in homonymous Ia afferents (elicited by electrical stimulation or by tendon taps) and were interrupted by antidromic invasion and Renshaw inhibition of triceps surae motoneurones (evoked by a single maximal stimulation of motor axons). This result suggests that the mechanisms which generate the cramps are intrinsic to alpha-motoneurone somata. A similar on-off switching of a self-sustained motor discharge has been observed in the decerebrate cat and recognized to depend on 'bistability' of the motoneuronal membrane. We propose that the same mechanism may be at the origin of the cramp discharge.

Adult↗
PubMed1990

The relationship between visual persistence and event perception in bistable motion display.

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.

Attention↗