An electrophysiological study of mechanisms controlling polyp retraction in colonies of the scleractinian coral Goniopora lobata.

1. Electrical or mechanical stimulation of Goniopora lobata produces coordinated retraction of polyps in the colony. With repetitive stimulation, the response spreads in linear, radial increments which become successively smaller with each stimulus. 2. Electrical activity recorded from these colonies is interpreted as originating in a conduction system responsible for effecting the colonial retraction response. The electrical activity spreads incrementally through the colony in a similar manner to the behavioural response. 3. Various hypotheses have been proposed to account for such a spread of electrical acitvity. Of these, only interneural facilitation is of appreciable importance to Goniopora. 4. Temporary termination of a pathway, by the passage of an impulse through it, was found and interpreted as being an additional and important property of the colonial conduction system.     

耳蜗电位的持续反应与其中单个脉冲的反应

研究了豚鼠耳蜗电位中持续反应与其中的单个脉冲反应的关系。由于听学系统存在着非线性,因此仅仅知道由单个短声诱发的耳蜗电位脉冲反应还无法预测一串等间隔重复短声诱发的持续反应。然而,等间隔重复短声串中第5个以后的每个短声受前面所有短声的掩蔽都相同,诱发的反应都相同,因此持续反应的稳态部分可以由掩蔽作用达到饱和时单个短声的反应通过延时相加得到。本文在时间域和频率域上定量地证明了这点。     

Lung injury risk assessment during blast exposure

Blast pulmonary trauma are common consequences of modern war and terrorism action. To better protect soldiers from that threat, the injury risk level when protected and unprotected must be assessed. Knowing from the literature that a possible amplification of the blast threat would be provided by some thoracic protective systems, the objective is to propose an original approach to correlate a measurable parameter on a manikin with a pulmonary risk level. Using a manikin whose response is correlated with the proposed tolerance limits should help in the evaluation of thoracic protective system regarding injury outcomes.A database including lung injury data from large mammals have been created, allowing the definition of iso-impulse tolerance limits from no lung injury to severe ones (∼60% of ecchymosis). As the use of this metric is not sufficient to evaluate the performance of protective systems on a manikin, the iso-impulse tolerance limits were associated with the thoracic response of post-mortem swine under blast loading. It was found that the lung injury threshold in terms of incident impulse is 58.3 kPa·ms, corresponding to a chest wall peak of acceleration/velocity/displacement of 7350 m/s², 3.7 m/s and 6.4 mm respectively. Lung injuries are considered as severe (30–60% of ecchymosis) when the incident impulse exceed 232.8 kPa·ms, leading to a chest wall peak of acceleration/velocity/displacement of 79.7 km/s², 14.7 m/s and 30.1 mm respectively.The defined lung tolerance limits are valid for a 50 kg swine (unprotected) exposed side-on to the blast threat and against a wall.     

An integral equation approach to measuring turnover in nonsteady compartmental and distributed systems

Physiological systems are often modelled by a set of compartments. Alternatively they can be described by the diffusion-convection-reaction equations governing distributed systems. The problem considered here is that of identifying a continuously changing input of some metabolite )tracee), endogenous to the system and hence inaccessible, when a nonlinear or time-varying component is also introduced into the loss parameter, as for example through feedback mechanisms. A tracer is used to determine the steady-state impulse response under time-invariant, linear conditions. A known input of tracer is also administered when the system is driven out of steady state. The integral equations developed utilize the predetermined impulse response, the measured concentrations of both tracer and tracee (output) in some region of the system to estimate the changing loss parameter and the unknown input in a continuous fashion.     

Nonlinear numerical analysis of the structural response of the intervertebral disc to impact loading

The analysis of intervertebral disc dynamics under impact loading, using computational simulation, is scarcely reported. In this study, the contribution of the characteristic structure of the disc to its dynamic response has been evaluated. The influence of several model features on the dynamic response was investigated. A hyperelastic large deformation formulation was used to describe the nonlinear behaviour of the soft tissues. The material parameters were determined by the fitting of experimental data from the literature. The model demonstrated pressure wave propagation and reflection through the disc, with a periodic oscillation of the system in response to a single impulse load, and highlighted a potential primary role played by the collagen fibre reinforcement. Their tensioning contributes to changing the stress propagation and oscillation, with a faster reduction in the internal pressure peak. The natural frequency of the disc was predicted to be approximately 9.8 Hz for the vertical oscillation.     

The Coda of the Transient Response in a Sensitive Cochlea: A Computational Modeling Study

In a sensitive cochlea, the basilar membrane response to transient excitation of any kind–normal acoustic or artificial intracochlear excitation–consists of not only a primary impulse but also a coda of delayed secondary responses with varying amplitudes but similar spectral content around the characteristic frequency of the measurement location. The coda, sometimes referred to as echoes or ringing, has been described as a form of local, short term memory which may influence the ability of the auditory system to detect gaps in an acoustic stimulus such as speech. Depending on the individual cochlea, the temporal gap between the primary impulse and the following coda ranges from once to thrice the group delay of the primary impulse (the group delay of the primary impulse is on the order of a few hundred microseconds). The coda is physiologically vulnerable, disappearing when the cochlea is compromised even slightly. The multicomponent sensitive response is not yet completely understood. We use a physiologically-based, mathematical model to investigate (i) the generation of the primary impulse response and the dependence of the group delay on the various stimulation methods, (ii) the effect of spatial perturbations in the properties of mechanically sensitive ion channels on the generation and separation of delayed secondary responses. The model suggests that the presence of the secondary responses depends on the wavenumber content of a perturbation and the activity level of the cochlea. In addition, the model shows that the varying temporal gaps between adjacent coda seen in experiments depend on the individual profiles of perturbations. Implications for non-invasive cochlear diagnosis are also discussed.     

Relation between potassium-channel kinetics and the intrinsic dynamics in isolated retinal bipolar cells

Characterization of the intrinsic dynamics of isolated retinal bipolar cells by a whole-cell patch-clamp technique combined with estimation of effective impulse responses across a range of mean injected currents reveals strikingly adaptive behavior. At resting potential, bipolar cells' effective impulse response is slow, high gain, and low pass. Depolarization speeds up response, decreases gain, and, in most cells, induces bandpass behavior.This adaptive behavior involves two K⁺ currents. The delayed-rectifier accounts for the observed gain reduction, speed increase, and bandpass behavior. The A-channel further shortens the impulse responses but suppresses bandpass features. Computer simulations of model neurons with a delayed-rectifier and varying A-channel conductances reveal that impulse responses largely reflect the flux of electrical charge through the two K⁺ channels. The A-channel broadens the frequency response and preempts the action of the delayed-rectifier, thereby reducing the associated bandpass features. Admixtures of the two K⁺ channels produce the observed variety of dynamics of retinal bipolar cells.     

Trigger regime of the functioning of a synaptic channel

It has been shown using the linear model describing the dynamics of biochemical reactions occurring in a synapse that, as periodic step-like impulses pass through a synaptic channel, it operates in the triggering regime. The transmission of an impulse through the channel is associated with the change of the stationary point of the corresponding dynamic system compared with the unexcited state of the synapse. As a result, the system periodically evolves between two stable stationary states.     

Identification of nonlinear systems using random impulse train inputs

Nonlinear systems that require discrete inputs can be characterized by using random impulse train (Poisson process) inputs. The method is analagous to the Wiener method for continuous input systems, where Gaussian white-noise is the input. In place of the Wiener functional expansion for the output of a continuous input system, a new series for discrete input systems is created by making certain restrictions on the integrals in a Volterra series. The kernels in the new series differ from the Wiener kernels, but also serve to identify a system and are simpler to compute. For systems whose impulse responses vary in amplitude but maintain a similar shape, one argument may be held fixed in each kernel. This simplifies the identification problem. As a test of the theory presented, the output of a hypothetical second order nonlinear system in response to a random impulse train stimulus was computer simulated. Kernels calculated from the simulated data agreed with theoretical predictions. The Poisson impulse train method is applicable to any system whose input can be delivered in discrete pulses. It is particularly suited to neuronal synaptic systems when the pattern of input nerve impulses can be made random.     

Effects of Polarization of the Receptor Membrane and of the First Ranvier Node in a Sense Organ

It has previously been shown that the site of production of the generator potential in Pacinian corpuscles is the receptor membrane of the non-myelinated ending, and the site of initiation of the nerve impulse, the adjacent (first) Ranvier node. Effects of membrane polarization of these sites were studied in the present work. Nerve ending and first Ranvier node were isolated by dissection, electric activity was recorded from, and polarizing currents were passed through them. All observations were done at steady levels of polarization, seconds after onset of current flow. The following results were obtained: The amount of charge transferred through the excited receptor membrane is a function of the electrical gradients across the membrane. The generator potential in response to equal mechanical stimuli increases with resting potential of the receptor membrane. The refractory state of the generator potential is not affected by polarization. The electrical threshold for impulse firing at the first Ranvier node (measured by the minimal amplitude of generator potential which elicits a nodal impulse) is nearly minimal at normal resting potential of the node. Both, hyperpolarization and depolarization lead to a rise in nodal threshold. For any level of polarization of nodal and receptor membrane, the threshold for production of impulses by adequate (mechanical) stimulation appears determined by the generator potential-stimulus strength relation and by the electrical threshold of the node.     

A minimal mechanistic model for temporal signal processing in the lateral geniculate nucleus

The receptive fields of cells in the lateral geniculate nucleus (LGN) are shaped by their diverse set of impinging inputs: feedforward synaptic inputs stemming from retina, and feedback inputs stemming from the visual cortex and the thalamic reticular nucleus. To probe the possible roles of these feedforward and feedback inputs in shaping the temporal receptive-field structure of LGN relay cells, we here present and investigate a minimal mechanistic firing-rate model tailored to elucidate their disparate features. The model for LGN relay ON cells includes feedforward excitation and inhibition (via interneurons) from retinal ON cells and excitatory and inhibitory (via thalamic reticular nucleus cells and interneurons) feedback from cortical ON and OFF cells. From a general firing-rate model formulated in terms of Volterra integral equations, we derive a single delay differential equation with absolute delay governing the dynamics of the system. A freely available and easy-to-use GUI-based MATLAB version of this minimal mechanistic LGN circuit model is provided. We particularly investigate the LGN relay-cell impulse response and find through thorough explorations of the model’s parameter space that both purely feedforward models and feedback models with feedforward excitation only, can account quantitatively for previously reported experimental results. We find, however, that the purely feedforward model predicts two impulse response measures, the time to first peak and the biphasic index (measuring the relative weight of the rebound phase) to be anticorrelated. In contrast, the models with feedback predict different correlations between these two measures. This suggests an experimental test assessing the relative importance of feedforward and feedback connections in shaping the impulse response of LGN relay cells.     

Improved pulse transit time estimation by system identification analysis of proximal and distal arterial waveforms

We investigated the system identification approach for potentially improved estimation of pulse transit time (PTT), a popular arterial stiffness marker. In this approach, proximal and distal arterial waveforms are measured and respectively regarded as the input and output of a system. Next, the system impulse response is identified from all samples of the measured input and output. Finally, the time delay of the impulse response is detected as the PTT estimate. Unlike conventional foot-to-foot detection techniques, this approach is designed to provide an artifact robust estimate of the true PTT in the absence of wave reflection. The approach is also applicable to arbitrary types of arterial waveforms. We specifically applied a parametric system identification technique to noninvasive impedance cardiography (ICG) and peripheral arterial blood pressure waveforms from 15 humans subjected to lower-body negative pressure. We assessed the technique through the correlation coefficient (r) between its 1/PTT estimates and measured diastolic pressure (DP) per subject and the root mean squared error (RMSE) of the DP predicted from these estimates and measured DP. The technique achieved average r and RMSE values of 0.81 ± 0.16 and 4.3 ± 1.3 mmHg. For comparison, the corresponding values were 0.59 ± 0.37 (P < 0.05) and 5.9 ± 2.5 (P < 0.01) mmHg for the conventional technique applied to the same waveforms and 0.28 ± 0.40 (P < 0.001) and 7.2 ± 1.8 (P < 0.001) mmHg for the conventional technique with the ECG waveform substituted for the ICG waveform. These results demonstrate, perhaps for the first time, that the system identification approach can indeed improve PTT estimation.     

Peak drug levels in linear pharmacokinetic systems—II. Conditions for a paradoxical injection rate effect with rectangular input

The preceding paper (Thorn, 1981) has shown that in a linear pharmacokinetic system with a multimodal impulse response the peak drug level may sometimes be smaller with slower rates of injection. This paper presents two theorems on this paradoxical injection rate effect where the injection is a constant infusion of finite duration. The first theorem establishes a graphical method for determining whether a given impulse response will give a paradoxical injection rate effect; and the second establishes that the maximum paradoxical increase in peak drug level is by a factor of two. It is further shown that in order to approach this maximum paradoxical increase the impulse response must contain two isolated, sharp, narrow pulses of approximately equal area. Some examples of bimodal arterial dye-dilution curves from the literature are discussed as impulse responses; and there is also a discussion of the behavior of drug level maxima and minima at different injection rates. This work was supported in part by U.S. Public Health Service Research Grant GM 21269 from the National Institute of General Medical Sciences, and in part by Biomedical Research Support Grant S07 RR 05932 from the National Institutes of Health. A portion of this work was presented at the Annual Meeting of the Society for Mathematical Biology at the Medical School of the University of Pennsylvania, Philadelphia, August 1976.     

Evidence against the involvement of a cytochrome P-450 mechanism in pulmonary hemodynamics in the newborn pig.

Control mechanisms operating through a cytochrome P-450 system have emerged lately as a possible important determinant of pulmonary hemodynamics. Their action may be expressed in the adjustment of vascular tone under both physiologic and pathophysiologic conditions. One such condition is the pulmonary constrictor response to hypoxia. The identity of the effector agent, or agents, is not known, though there are data implicating monooxygenase products of arachidonic acid. From this premise, we wanted to evaluate the effect of cytochrome P-450 inhibitors on basal pulmonary vascular tone during normoxia, and their effect upon hypoxic pulmonary vasoconstriction response. Experiments were performed in an isolated, perfused lung preparation from 1- and 7-day-old piglets, and the effects of two cytochrome P-450 inhibitors (metyrapone and ketoconazole) were tested on the perfusion pressure. At 10(-5) and 10(-4) M, metyrapone caused a modest, but significant, increase in pulmonary pressure (p less than 0.05) in 7-day-old preparations, while it was without effect in the 1-day-old preparation. Similarly, ketoconazole at concentrations from 10(-6) M upwards increased the perfusion pressure in the older animal (p less than 0.01). Responses to the inhibitors were not seen in preparations that had been pretreated with a cyclooxygenase inhibitor (indomethacin, 2.8 x 10(-6) M) or a dual cyclooxygenase-lipoxygenase inhibitor (BW755C, 10(-5) M). Hypoxic vasoconstriction was marginally enhanced by 10(-4) M metyrapone, while it was affected inconsistently by 10(-5) M ketoconazole. We conclude that vasoactive agents formed through cytochrome P-450 reactions have a minor role, or no role at all, in the control of pulmonary hemodynamics in the newborn pig.     

Spatio-Temporal Dynamics of Impulse Responses to Figure Motion in Optic Flow Neurons

White noise techniques have been used widely to investigate sensory systems in both vertebrates and invertebrates. White noise stimuli are powerful in their ability to rapidly generate data that help the experimenter decipher the spatio-temporal dynamics of neural and behavioral responses. One type of white noise stimuli, maximal length shift register sequences (m-sequences), have recently become particularly popular for extracting response kernels in insect motion vision. We here use such m-sequences to extract the impulse responses to figure motion in hoverfly lobula plate tangential cells (LPTCs). Figure motion is behaviorally important and many visually guided animals orient towards salient features in the surround. We show that LPTCs respond robustly to figure motion in the receptive field. The impulse response is scaled down in amplitude when the figure size is reduced, but its time course remains unaltered. However, a low contrast stimulus generates a slower response with a significantly longer time-to-peak and half-width. Impulse responses in females have a slower time-to-peak than males, but are otherwise similar. Finally we show that the shapes of the impulse response to a figure and a widefield stimulus are very similar, suggesting that the figure response could be coded by the same input as the widefield response.     

Characterizing and correcting for the dynamic response of a bag-in-box system

A bag-in-box system (BBS) whose volume is monitored by a mechanical spirometer tends to have a slow response if the volume of the box is large, and this may significantly affect its measurement of gas flow. We describe a device for creating reproducible gas flows with which the impulse response of a BBS may be conveniently determined. Two computational techniques for correcting a BBS flow measurement for the effects of the impulse response were investigated: 1) an exponential model method that assumes a second-order model of the BBS dynamics and 2) a Fourier transform-based method of deconvolution known as Wiener filtering. Both correction methods produced a significant increase in the accuracy of BBS flow estimations, with the Wiener filter giving superior results.     

爆炸波对生物膜微观创伤的分子动力学分析

爆炸冲击波作用到人体胸部时，肺部会出现肺出血及肺水肿等症状，这是人体爆炸创伤的主要原因，深入研究很有必要。为了更好地理解爆炸创伤的机理，应研究冲击波与微观组织作用的力学过程，但具有一定的难度，本文先从基本的生物膜做起。本文运用分子动力学研究了冲击波对DPPC膜造成的损伤，通过停止活塞来控制冲击波的冲量，观察了冲击过程中膜的恢复情况。观察了不同冲量下冲击波经过膜后磷脂分子及其周围水分子分布，发现随着冲量增大，膜越来越无序混乱，褶皱更严重，疏水区水分子越来越多。将膜冲击过程划为三个阶段，分别为冲击阶段、恢复阶段和后效阶段。发现当冲量大于153 mPa s时，在冲击过程中没有观察到膜的损伤恢复。     

Dopaminergic modulation of impulse activity of sensorymotor cortex neurons during conditioned reflex

Changes of conditioned impulse reaction of cortical neurons wer studied during microiontophoretic application of agonist and antagonists of glutamate and GABA transmission and their modulation by dopamine. It was shown paradoxal reaction of facilitation of impulse activity during iontophoretic application of ionotropic glutamate antagonist and depressive influences of metabotropic antagonist. Local iontophoretic application of dopamine increased background and evoked impulse activity of pyramidal neurons of deep layers of cortex and eliminated inhibitory influences of glutamate metabotropic antagonist MCPG. It is concluded that DA has stabilizing effects on activity of cortical neurons. It is suppose that these effects of DA realize through system of inhibitory interneurons.