Sensitive control of heart rate in monkeys using burst stimulation of the vagus nerve

Burst vagus stimulation led to synchronization of the cardiac and vagal rhythms at certain frequency ranges. The increase of the number of impulses in a burst from 1 to 16 extended the range of synchronization and shifted it towards lower frequencies forming a total range of exact regulation of the heart rate within 85--40% of the initial rate. It was suggested that vagal effect consists of tonic and synchronizing components.     

Effect of the sympathetic nervous system in regulating heart rhythm during burst stimulation of the vagus nerve

In cat experiments, the right inferior cardiac nerve was stimulated at a frequency of 2 and 4 Hz and the right vagus by bursts of 1, 2, 4, 8 and 16 impulses. Stimulation of the inferior cardiac nerve shifted the ranges of the heart rate control up the frequency scale. The shift of the range boundaries was mainly determined by the intensity of sympathetic regulation and by the number of impulses in a burst which stimulates the vagus nerve.     

Further investigations of the transient kinetics of alcohol oxidation catalysed by horse liver alcohol dehydrogenase

Due to the controversy over the half-of-the-sites reactivity of horse liver alcohol dehydrogenase during benzyl alcohol oxidation, we have re-investigated the transient kinetics, stoichiometry and rate parameters over a wide range of substrate concentrations (0.05 mm to 40 mm) at pH 7.0 and 8.5 and using newly determined extinction coefficients. Data were elaborated by computer analysis in order to separate the initial rapid step (burst) from the whole time-course of the reaction. It has been found that: (1) the dependence of the burst amplitude upon benzyl alcohol concentration is distinctly biphasic. In the range from 0.05 mm up to approximately 1 mm the burst amplitude is rather insensitive to changes in alcohol concentration and corresponds to 50% of the active sites of the enzyme; for alcohol concentrations greater than 1 mm this amplitude increases and reaches a value of approximately 90% when benzyl alcohol is 40 mm. (2) The steady-state initial rate is also biphasic with respect to alcohol concentration, indicative of substrate inhibition, which begins in the concentration range at which deviation from the half-burst also appears. In other words, burst amplitudes larger than 50% are concomitant with inhibition of the rate of enzyme turnover. (3) In the presence of isobutyramide the burst is larger than 50% for the whole range of concentration of the substrate and extrapolates at infinite substrate concentration to approximately 90% of the enzyme sites. (4) With deuteroethanol as substrate, the burst is larger than 50%, with or without isobutyramide, and extrapolates to approximately 95% of the enzyme sites at infinite substrate concentration. These data explain the discrepancy of results in the literature concerning the transient kinetics of alcohol oxidation. Mechanistic implications of the results (particularly the deviation from the halfof-the-sites behaviour of benzyl alcohol under inhibition conditions) are discussed.     

Electrophysiological Studies of a Water Receptor Associated With the Taste Sensilla of the Blowfly

Electrophysiological evidence is given that water is the specific stimulus for a fourth sensory cell associated with the taste sensilla of the blowfly. Water elicited impulses from a single cell which responded in two distinct phases: an initial rapid rate of discharge followed by a lesser, sustained steady rate. The latter, in the case of sucrose solutions, was inhibited in direct proportion to the log of the osmotic pressure over a 10⁴ range of pressures. Other non-electrolytes inhibited, but the effect could not be simply correlated with parameters of the solutions. Electrolytes inhibited the water response more sharply and at lower concentrations. The inhibition in all cases was not dependent on impulses in the other sensory cells of the taste sensillum.     

Staurosporine, a protein kinase inhibitor, up-regulates the stimulation of human neutrophil respiratory burst by N-formyl peptides and platelet activating factor

Staurosporine (STAR), a potent protein kinase C (PKC) antagonist, was found to modulate the chemoattractant-induced respiratory burst of human polymorphonuclear leukocytes (PMNs) according to drug concentration. Low STAR concentrations from 10 to 200 nM potentiated the N-formyl-methionyl-leucyl-phenylalanine (fMLP) and platelet activating factor (Paf)-induced respiratory burst, affecting both the initial rate and the total amount of superoxide anion generated. The maximal increase occurred in the presence of 100 nM STAR and optimal fMLP concentration and reached 60-100% of control values. Above 250 nM, STAR inhibited the respiratory burst with an IC50 of 360 and 320 nM for fMLP and Paf, respectively. The respiratory burst induced by PKC activators such as phorbol myristate acetate or phorbol 12, 13 dibutyrate was inhibited effectively by STAR, with a low IC50 (25 nM) for both stimuli. Thus, the use of low STAR concentrations points to two possible roles of PKC in the regulation of NADPH oxidase activity, i.e. a positive regulation in phorbol ester-treated cells and a negative regulation in chemoattractant-stimulated PMNs.     

Studies on the initial phase of dynein ATPase activity.

Kinetic measurement of the reaction of dynein ATPase (ATP phosphohydrolase, EC 3.6.1.3) extracted from the gills of Mytilus edulis shows that in the presence of Mg2+ there is a very rapid initial liberation of Pi from the dynein-ATP system, followed by a slower liberation in the steady state. In view of following results, we have confirmed that this phenomenon is not due to the accumulation of end products, a fall in substrate concentration, nor to the presence of labile impurities in ATP but is due to the catalytic activity of dynein ATPase. 1. The replacement of native dynein by heat denatured dynein or other kinds of Mg2+-ATPase could not produce such a burst phenomenon under the same condition. 2. Both the rate of initial burst and that of steady state were proportional to enzyme content over a wide range under our standard condition. 3. Initial burst was also observed under the constant ATP level by using a ATP generate system. 4. Preincubation of dynein with Pi prior to initiation of the reaction did not eliminate the initial burst. Some properties of the initial rapid liberation of dynein ATPase were also examined. These are shown below. 5. The free ADP liberation did not show any initial burst though the Pi liberation did in the initial phase and the rate of free ADP liberation was almost equal to that of Pi liberation of the steady state. 6. Mg2+ was more effective than Ca2+ for the appearance of the initial burst while the liberation of Pi in the steady state was activated more by Ca2+ than by Mg2+. The addition of K+ in the presence of Mg2+ resulted in a marked increase of Pi liberation in the steady state but not in the initial state. 7. The activation energy of the initial burst was 9.7 kcal, which is slightly smaller than that of myosin ATPase.     

Rhythmic swimming activity in neurones of the isolated nerve cord of the leech.

1. Repeating bursts of motor neurone impulses have been recorded from the nerves of completely isolated nerve cords of the medicinal leech. The salient features of this burst rhythm are similar to those obtained in the semi-intact preparation during swimming. Hence the basic swimming rhythm is generated by a central oscillator. 2. Quantitative comparisons between the impulse patterns obtained from the isolated nerve cord and those obtained from a semi-intact preparation show that the variation in both dorsal to ventral motor neurone phasing and burst duration with swim cycle period differ in these two preparations. 3. The increase of intersegmental delay with period, which is a prominent feature of swimming behaviour of the intact animal, is not seen in either the semi-intact or isolated cord preparations. 4. In the semi-intact preparation, stretching the body wall or depolarizing an inhibitory motor neurone changes the burst duration of excitatory motor neurones in the same segment. In the isolated nerve cord, these manipulations also change the period of the swim cycle in the entire cord. 5. These comparisons suggest that sensory input stabilizes the centrally generated swimming rhythm, determines the phasing of the bursts of impulses from dorsal and ventral motor neurones, and matches the intersegmental delay to the cycle period so as to maintain a constant body shape at all rates of swimming.     

Integrative Neurophysiology of the Lobster Cardiac Ganglion

The synchronized bursts of impulses produced by the nine neuronsof the isolated Homarus cardiac ganglion are usually initiatedby Cell 7. Activity in all other cells commences with very shortlatency thereafter. Impulses in most cells originate in triggerzones located 1–2 mm from the cell body, but the firstseveral impulses in Cells 8 and 9 frequently originate in distaltrigger zones some distance from the somata. Large cells fireat a high initial frequency, dropping rapidly to a low frequencyplateau. Small cells exhibit a more tonic behavior and fireat intermediate rates. More anterior small cells tend to firefaster than more posterior ones. The major synaptic interactionsare the impulse-mediated excitatory ones from small cells tolarge cells, and possibly to more anterior small cells. Thereare weak interactions from large cells back onto small cells,and very specific interactions from Cells 1 and 2 onto 3_A, 4_A,5_A, and 3_B 4_B 5_B respectively. The large discrete EPSPs generatedin large cells by small cell impulses appear to be the explanationfor "discrete positioning" in large-cell firing patterns. Inthis situation, large-cell impulses only fire at discrete timesduring the burst, regardless of the actual large-cell pattern. The overall view is of a two-layered neural system in whichthe small cells possess an endogenous oscillatory driver potential,synchronized by synaptic and electrotonic interactions, anddriving a train of impulses in each cell. This activates excitatorysynapses on the large cells, which combined with a triggereddriver potential in each large cell, produces synchronized trainsof motor impulses which activate the heart muscle, causing theheartbeat.     

Neurohormonal alteration of integrative properties of the cardiac ganglion of the lobster Homarus americanus.

The spontaneous burst discharges of isolated lobster (Homarus americanus) cardiac ganglia were recorded with a spaced array of electrodes. Small regions (less than 1 mm) of the ganglion were exposed to the cardioexcitor neurohormone in extracts of pericardial organs (XPO) or to 10(-5) M 5-hydroxytryptamine (5HT). All axons were excited (increased mean firing frequency, f) by both substances, but only by applications in the region between the soma (but excluding it) and proximal site of impulse initiation. Units not so exposed changed their f relatively little despite f increases of as much as threefold in exposed units and changes in burst rate and overall length. Regularity and grouping of all impulse activity into bursts was never disturbed. 5HT increases burst rate at any point of application. The increases are larger if small cells are affected than if only large cells are exposed. Burst length decreases except when the pacemaker is affected. In contrast, XPO affects neither burst rate or length unless small cells are affected. Length is increased if non-pacemaker small cells are affected; both rate and length increase if the pacemaker is affected. The pacemaker usually exhibits an f of intermediate value. Rate changes are not simply related to its f. A small cell can "burst" in the absence of impulses from any other cells. XPO may enhance endogenous "driver potentials," while 5HT may excite by depolarizing at limited sites.     

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.     

The mechanism of the skeletal muscle myosin ATPase. II. Relationship between the fluorescence enhancement induced by ATP and the initial Pi burst.

A major question about the mechanism of the myosin ATPase is how much of the fluorescence change which accompanies the binding of ATP to myosin is due to the conformational change induced by ATP and how much is due to the subsequent hydrolysis of ATP in the initial Pi burst. Several laboratories have suggested that the maximal rate of the fluorescence change represents the rate of the irreversible conformational change induced by ATP. In the present study, the rate of irreversible ATP binding, the rate of the initial Pi burst, and the rate of the fluorescence enhancement were compared under varied conditions. The results show that: 1) the fluorescence enhancement is mainly due to the hydrolysis of ATP in the initial Pi burst rather than to the conformational change induced by the binding of ATP; 2) the rate of the initial Pi burst is considerably slower than the rate of irreversible ATP binding at high ATP concentration; 3) the rate of the initial Pi burst is almost the same as the rate of the fluorescence enhancement. Therefore, the maximum rate of the fluorescence enhancement represents the rate of the initial Pi burst rather than the rate of the conformational change induced by ATP binding.     

Arterial baroreflex control of muscle sympathetic nerve activity in the transition from rest to steady-state dynamic exercise in humans

We sought to investigate arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) in the transition from rest to steady-state dynamic exercise. This was accomplished by assessing the relationship between spontaneous variations in diastolic blood pressure (DBP) and MSNA at rest and during the time course of reaching steady-state arm cycling at 50% peak oxygen uptake (VO(2peak)). Specifically, DBP-MSNA relations were examined in eight subjects (25 +/- 1 yr) at the start of unloaded arm cycling and then during the initial and a later period of arm cycling once the 50% VO(2peak) work rate was achieved. Heart rate and arterial blood pressure were progressively increased throughout exercise. Although resting MSNA [16 +/- 2 burst/min; 181 +/- 36 arbitrary units (au) total activity] was unchanged during unloaded cycling, MSNA burst frequency and total activity were significantly elevated during the initial (27 +/- 4 burst/min; 367 +/- 76 au; P < 0.05) and later (36 +/- 7 burst/min; 444 +/- 91 au; P < 0.05) periods of exercise. The relationships between DBP and burst incidence, burst strength, and total MSNA were progressively shifted rightward from unloaded to the initial to the later period of 50% VO(2peak) arm cycling without any changes in the slopes of the linear regressions (i.e., ABR sensitivity). Thus a continuous and dynamic resetting of the ABR control of MSNA occurred during the transition from rest to steady-state dynamic exercise. These findings indicate that the ABR control of MSNA was well maintained throughout dynamic exercise in humans, progressively being reset to operate around the exercise-induced elevations in blood pressure and MSNA without any changes in reflex sensitivity.     

Modeling the activity burst in the initial phase of cellulose hydrolysis by the processive cellobiohydrolase Cel7A

The hydrolysis of cellulose by processive cellulases, such as exocellulase TrCel7A from Trichoderma reesei, is typically characterized by an initial burst of high activity followed by a slowdown, often leading to incomplete hydrolysis of the substrate. The origins of these limitations to cellulose hydrolysis are not yet fully understood. Here, we propose a new model for the initial phase of cellulose hydrolysis by processive cellulases, incorporating a bound but inactive enzyme state. The model, based on ordinary differential equations, accurately reproduces the activity burst and the subsequent slowdown of the cellulose hydrolysis and describes the experimental data equally well or better than the previously suggested model. We also derive steady-state expressions that can be used to describe the pseudo-steady state reached after the initial activity burst. Importantly, we show that the new model predicts the existence of an optimal enzyme-substrate affinity at which the pseudo-steady state hydrolysis rate is maximized. The model further allows the calculation of glucose production rate from the first cut in the processive run and reproduces the second activity burst commonly observed upon new enzyme addition. These results are expected to be applicable also to other processive enzymes.     

Processing of calling songs by an L-shaped neuron in the prothoracic ganglion of the female cricket, Acheta domesticus

ABSTRACT. An L-shaped auditory intemeuron (LI) has been recorded from extracellularly and intracellularly, and identified morphologically (by Lucifer yellow or cobalt injection) in the prothoracic ganglion of mature female Acheta domesticus. The morphology of the LI is very similar to ascending, prothoracic acoustic interneurons that are most sensitive to higher carrier frequencies in both A. domesticus and other gryllid species. Its terminations in the brain are similar to ascending acoustic interneurons found in other gryllids. The LI neuron is most sensitive to 4–5 kHz model calling songs (CSs), the main carrier frequency of the natural call. Thresholds to high frequencies (8–15 kHz) are 15–20 dB higher. Increasing CS intensities of up to 15 dB above threshold at 4–5 kHz result in increased firing rates by the LI. More than 15 dB increase in intensity causes saturation with little increase in spiking rate until the intensity surpasses 80 dB. In response to 70 dB or higher stimulus intensities, the LI responds to the second and third CS syllables with one or two spikes, pauses, and then produces a burst of nerve impulses with the same or greater latency than for lower intensity stimuli. In response to CS syllables of changing duration (10–30 ms) this neuron responds with a rather constant duration burst of impulses. Syllable periods of the CS stimuli were accurately encoded by the LI. Progressively stronger injection of hyperpolarizing current reduces, and ultimately stops spiking of the LI in response to CS stimuli. More intense stimulation with reduced hyperpolarization shows an initial spike, pause and burst of spikes. Intracellular recording from axonal regions of the neuron shows large spikes, small EPSPs and a developing hyperpolarization through the response to a CS chirp. Inhibitory input to the LI is demonstrated at 4.5, 8 and 16 kHz. This probably explains the specialized response characteristics of the LI which enhanced its encoding of CS syllable period.     

Coupling between muscle activities and muscle torques during horizontal-planar arm movements with direction reversal.

In this study we investigated the hypothesis that the simple set of rules used to explain the modulation of muscle activities during single-joint movements could also be applied for reversal movements of the shoulder and elbow joints. The muscle torques of both joints were characterized by a triphasic impulse. The first impulse of each joint accelerated the limb to the target and was generated by an initial burst of the muscles activated first (primary mover). The second impulse decelerated the limb to the target, reversed movement direction and accelerated the limb back to the initial position, and was generated by an initial burst of the muscles activated second (secondary movers). A third impulse, in each joint, decelerated the limb to the initial position due to the generation of a second burst of the primary movers. The first burst of the primary mover decreased abruptly, and the latency between the activation of the primary and secondary movers varied in proportion with target distances for the elbow, but not for the shoulder muscles. All impulses and bursts increased with target distances and were well coupled. Therefore, as predicted, the bursts of muscle activities were modulated to generate the appropriate level of muscle torque.     

Dependence of the efficacy of transfecting muscle fibers in vivo on electroporation conditions

This study is a survey of in vivo experiments on transfection of laboratory mouse muscle fibers by electroporation using an original device generating electric impulses. Transfection efficiency proved to depend on DNA dose and the number of electric impulses. It can be increased significantly by electroporation at varying pulse burst polarity. At both direct electrode application to muscles and electroporation through the skin, the muscle fiber transfection was more efficient under electroporation conditions much milder than those usually reported. The use of electroporation method for gene therapy of Duchenne muscular dystrophy is discussed.     

Synchronization effects in the pacemaker during high-frequency atrial stimulation

The succession of intra-impulse intervals in venous sinus of isolated frog heart was studied during suprathreshold atrial stimulation at a frequency exceeding the initial pacemaker rate by l5-200%. Near to the initial and multiple frequency pacemaker synchronization takes place with the stimulator rhythm. With the stimulation of frequency increase atrial impulses begin to conduct retrogradely and regular ectopic rhythm is established. A unilateral pacemaker acceleration with the unilateral frequency drawing together is revealed in intermediate areas. Different effects appear to accompany it including asymptotic and cyclic synchronization proving in the form of arrhythmias.     

The transient kinetics of uptake of galactosides into Escherichia coli.

The uptake of galactosides into Escherichia coli via the lactose permease was studied in the time range 0.01-10s by rapid mixing and quenched flow. An initial transient was observed under two conditions. Firstly, a lag in the approach to the steady state was observed at low galactoside concentrations (less than Km). Secondly, a burst of uptake was observed when anaerobic cell suspensions were mixed with aerobic substrate solutions. However, the cause of the burst of uptake appears to be a burst in the rate of respiration. The rate of galactoside uptake during this phase is 10-fold greater than during the steady state.     

Use of the principles of computer statistical analysis for investigating the background impulse activity of neurons

A program for complex statistical analysis of the background impulse activity of neurons on a computer is proposed. The program includes: determination of the portion of the recording having a stable statistical structure; calculation of histograms of the probability density function of the interspike intervals (ISI) and statistical indexes related with them; correlation-spectral analysis of the ISI sequence; correlation-spectral analysis of the instants of appearance of impulses (from the frequency graph and graph of the function of recovery of impulse activity); and determination of the type and degree of relation of the lengths of adjacent ISI's and entropy analysis of this connection. A method is described for determining the portion of burst and group activity of the investigated neuron in the recording. The effectiveness of using the proposed program was checked by analyzing the background activity of pyramidal cells of the cat cortex. An analysis of neurons equal in frequency of background activity and rate of conduction of impulses in axons showed that the differences in the internal statistical structure of their impulses are very substantial.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 6, pp. 587–600, November–December, 1970.     

Electrophysiology of the Insect Dorsal Ocellus : I. Origin of the components of the electroretinogram

Dorsal ocelli are small cup-like organs containing a layer of photoreceptor cells, the short axons of which synapse at the base of the cup with dendritic terminals of ocellar nerve fibers. The ocellar ERG of dragonflies, recorded from the surface of the receptor cell layer and from the long lateral ocellar nerve, contains four components. Component 1 is a depolarizing sensory generator potential which originates in the distal ends of the receptor cells and evokes component 2. Component 2 is believed to be a depolarizing response of the receptor axons. It evokes a hyperpolarizing postsynaptic potential, component 3, which originates in the dendritic terminals of the ocellar nerve fibers. Ocellar nerve fibers in dragonflies are spontaneously active, discharging afferent nerve impulses (component 4) in the dark-adapted state. Component 3 inhibits this discharge. The ERG of the cockroach ocellus is similar. The main differences are that component 3 is not as conspicuous as in the dragonflies and that in most cases ocellar nerve impulses appear only as a brief burst at "off." In one preparation a spontaneous discharge of nerve impulses was observed. As in the dragonflies, this was inhibited by illumination.