Occurrence Of Action Potentials Research Articles

Effect of denervation and colchicine treatment of the nerve on electrical and chemical excitability of frog tonic muscle fibre

In order to investigate the role of axoplasmic transport in controlling the acetylcholine sensitivity and action potential generation in frog tonic muscle fibres, a comparison of changes produced in these fibres by denervation or by application of colchicine to the nerve was performed. Extrajunctional cholinergic sensitivity appeared both after colchicine treatment and after denervation. However, action potential generation appeared after denervation but not after colchicine treatment. Insensitivity of the factor controlling action potential generation to colchicine, which is known to interrupt fast axonal flow, and the low rate of its transport (determined by the time difference in action potential occurrence at various lengths of the nerve stump after denervation and coming to about 1.6 mm/day) suggest that the tropic factor responsible for the suppression of action potentials in tonic fibres is moved by slow axonal transport. It is concluded that the action potential mechanism in tonic fibres is controlled by the axonal flow of substances which differ from these controlling the acetylcholine receptors.

The spectro-temporal receptive field. A functional characteristic of auditory neurons.

The Spectro-Temporal Receptive Field (STRF) of an auditory neuron has been introduced experimentally on the base of the average spectro-temporal structure of the acoustic stimuli which precede the occurrence of action potentials (Aertsen et al., 1980, 1981). In the present paper the STRF is considered in the general framework of nonlinear system theory, especially in the form of the Volterra integral representation. The STRF is proposed to be formally identified with a linear functional of the second order Volterra kernel. The experimental determination of the STRF leads to a formulation in terms of the Wiener expansion where the kernels can be identified by evaluation of the system's input-output correlations. For a Gaussian stimulus ensemble and a nonlinear system with no even order contributions of order higher than two, it is shown that the second order cross correlation of stimulus and response, normalized with respect to the spectral contents of the stimulus ensemble, leads to the stimulus-invariant spectro-temporal receptive field. The investigation of stimulus-invariance of the STRF for more general nonlinear systems and for stimulus ensembles which can be generated by nonlinear transformations of Gaussian noise involve the evaluation of higher order stimulus-response correlation functions.

A comparison of the spectro-temporal sensitivity of auditory neurons to tonal and natural stimuli.

The spectro-temporal sensitivity of auditory neurons has been investigated experimentally by averaging the spectrograms of stimuli preceding the occurrence of action potentials or neural events ( the APES : Aertsen et al., 1980, 1981). The properties of the stimulus ensemble are contained in this measure of neural selectivity. The spectro-temporal receptive field (STRF) has been proposed as a theoretical concept which should give a stimulus-invariant representation of the second order characteristics of the neuron's system function (Aertsen and Johannesma, 1981). The present paper investigates the relation between the experimental and the theoretical description of the neuron's spectro-temporal sensitivity for sound. The aim is to derive a formally based stimulus-normalization procedure for the results of the experimental averaging procedure. Under particular assumptions, regarding both the neuron and the stimulus ensemble, an integral equation connecting the APES and the STRF is derived. This integral expression enables to calculate the APES from the STRF by taking into account the stimulus spectral composition and the characteristics of the spectrogram analysis. The inverse relation, i.e. starting from the experimental results and by application of a formal normalization procedure arriving at the theoretical STRF, is effectively hindered by the nature of the spectrogram analysis. An approximative "normalization" procedure, based on intuitive manipulation of the integral equation, has been applied to a number of single unit recordings from the grassfrog's auditory midbrain area to tonal and natural stimulus ensembles. The results indicate tha spectrogram analysis, while being a useful real-time tool in investigating the spectro-temporal transfer properties of auditory neurons, shows fundamental shortcomings for a theoretical treatment of the questions of interest.

Sensory transduction in an insect mechanoreceptor: extended bandwidth measurements and sensitivity to simulus strenght

The dynamic properties of sensory transduction in an insect mechanoreceptor, the femoral tactile spine of the cockroach, Periplaneta americana, have been studied by measurement of the frequency response function between randomly varying movement of the tactile spine and afferent action potentials from the sensory neuron which innervates it. The frequency response function of the mechanoreceptor has been characterized over a frequency range which is more than ten times larger than has previously been used for this preparation. Also the effects of varying the amplitude of the stimulating signal have been studied by the use of a range of input signal strengths from about 0.5 to 10 μm R.M.S. displacement. The measured frequency response functions can all be well fitted by a theoretical relationship which is a fractional exponent of complex frequency, provided that the time delay caused by conduction of the action potentials from the sensory dendrite to the recording electrodes is taken into account. Under small signal conditions the exponent of complex frequency is close to 0.5 but with larger displacements its value decreases to about half this value. The overall sensitivity of the receptor, as measured by the gain of the frequency response function at a natural frequency of 1 radian/s, is not significantly altered by changes in the input movement amplitude, so that the receptor behaves linearly in this respect. However, the mean rate of action potential occurrence is not linearly related to input movement amplitude. These results are discussed in terms of current theories of sensory transduction and the possible role of tubular bodies in the dynamic behaviour of insect cuticular mechanoreceptors.

Perturbations of membrane structure by optical probes: I. Location and structural sensitivity of merocyanine 540 bound to phospholipid membranes.

The maximum monomer absorption wavelength of a frequently used external membrane probe, Merocyanine 540, can be related to the location of the binding site for the dye within lipid membranes. Solvent studies indicate the occurrence of very specific and mutual perturbances between the probe and its microenvironment, that are of relevance, when investigating structural and functional events in biomembranes with the aid of this dye. Merocyanine 540 (MC 540) is an excellent probe for structural altions in the lipids including phase transitions. The extinction coefficient and λmax place the location of the dye-chromophore slightly above the domain of the glycerol of backbone of neutral and charged phospholipids. This explains the sensitivity of MC 540 to structural variations in the head-group region of several synthetic dipalmitoyl-lecithin analogues. The major physical parameters involved in variations of the optical signals associated with changes in the membrane structure are the dye/lipid partition coefficient and the monomer-dimer dissociation constant of the dye bound to the lipids. A temperature dependent transition from the liquid-crystalline to the crystalline state leads mainly to an exclusion of the dye from the lipid phase with a concomitant dimerization of the dye molecules still in contact with the polarhead group region of the lipid. The relevance of this finding for the mechanism of transient optical signals in connection with the occurrence of action potentials in excitable membranes is discussed. Our findings underline the necessary caution when applying external optical probes and analyzing membrane features from the spectral data, because of inevitable perturbances in the microenvironment of every probe molecule.

Electrical activity of lymphatic smooth muscles.

SummaryMembrane action potentials of bovine mesenteric lymphatics were recorded simultaneously with isometric contractions by the use of the sucrose gap method. The action potentials, about 3 sec in duration, always had one-to-one correspondence to the contraction waves. Each action potential consisted of three phases, i.e., initial slow depolarization, spike, and slow repolarization. The application of nor-adrenalin elicited a slight but long-lasting depolarization superimposed by frequent discharges of action potentials. The administration of acetylcholine in a relatively high concentration to the preparations induced a transient depolarization followed by the occurrence of action potentials. From the effects of tetrodotoxin, manganese, calcium-free environment, and barium chloride on the spontaneous contractions, it was suggested that calcium current may probably play a major role in producing spike discharge in bovine lymphatic smooth muscles.

Correlations between aerodynamic output, electrical activity in the indirect flight muscles and wing positions of bees flying in a servomechanically controlled wind tunnel

1) Bees hanging on an aerodynamic two component balance were placed in front of a laminar wind tunnel. They controlled the wind velocity in the tunnel through a servo-mechanism that held the wind velocity to exactly the opposite of the flight speed, thus selecting lift and thrust freely. The parameters lift, wind velocity, occurrence of action potentials in the indirect dorsoventral flight muscles (DV) and indirect dorsolongitudinal flight muscles (DL) and body temperature were measured. The correlations were analysed (Fig. 1). 2) The lift is positively correlated to the body angle (angle between body length axis and wind tunnel length axis), the flight speed is negatively correlated to the body angle (Fig. 2). 3) Action potential frequencies in both muscle groups exhibit a strong positive correlation to the lift (Fig. 3). Changes in action potential frequencies and lift run parallel with a delay of less than 200 msec (limitation imposed by measuring system). Different motor units in a given muscle have different absolute discharge frequencies (Fig. 4). 4) A pronounced synchronization between wingbeats and action potentials in the indirect dorsoventral muscles can always be found. 5) Randomly triggered photographic pictures show the wings most frequently at the lower turning point. Exposures that were triggered by action potentials in the dorsoventral indirect flight muscles display this wing position significantly more frequently (Fig. 5).

?Action potentials? in nematode-induced plant transfer cells

In a study of membrane potential properties of giant cells induced in the roots ofImpatiens balsamina by a rootknot nematode, trains of action potential-like fluctuations were recorded. Giant cells are multinucleate transfer cells, and it is suggested that the occurrence of action potentials may be characteristic of transfer cells.

Receptor potentials and action potentials in Drosera tentacles

Voltage fluctuations identified as receptor potentials can be detected with electrodes applied to the mucilage surrounding the head of a tentacle of Drosera intermedia if the head is stimulated by contact with a live insect, by the touch of a clean, inert object, or by application of salt solutions. Associated with a low receptor potential are action potentials, which occur at a frequency dependent on the magnitude of the receptor potential. These action potentials can be detected with electrodes applied to any region of the stalk of the tentacle. Inflection of the lower stalk follows the occurrence of action potentials. Inflection is minute for isolated action potentials but large and rapid when several occur within a brief interval.The apparent amplitude of action potentials recorded from the stalk is independent of receptor potential amplitude, but that of action potentials recorded from the mucilage commonly decreases as the receptor potential deviates from the baseline and increases as it returns. It is suggested that variation of apparent amplitude of the action potentials may result from postulated variation in the resistance of receptor membranes.

The Pharmacology of Smooth Muscle Tissue

Publisher Summary This chapter discusses the pharmacology of smooth muscle tissue. There has been a growing interest in the mechanism of action of pharmacological drugs on smooth muscle at the cellular level. A great step in the study of drugs was the detection of the relation between tonus, spontaneous activity and phase shifts in the electric activity of smooth muscle fibers. Increase of the tonus of smooth muscle evoked by acetylcholine, physostigmine, pilocarpine and choline, is accompanied by depolarization of the cell membrane, an increase in frequency of the spikes and a steeper rise of the prepotentials. A dissociation between the excitatory process and contraction itself may also arise during inhibition of carbohydrate-phosphate exchange in the muscle fiber by 2, 4-dinitrophenol. The influence of acetylcholine on the biochemical state of the smooth muscle is also suggested by investigations showing that an increase in tonus under the influence of acetylcholine leads to an increased oxygen consumption by the smooth muscle fibers. It is observed that 2, 4-dinitrophenol interferes with the normal linkage of tonus alterations in smooth muscle and its electrical activity, whereas the occurrence of action potentials is not coupled with an increase in tonus.

Micro-electrode studies on mammalian vascular muscle.

1. Transmembrane potentials were measured in smooth muscle cells in the walls of small arteries in the frog tongue and skin of the lateral abdomen. Resting potentials had mean values of 64.7 and 43.6 mV respectively, and action potentials of up to 60 mV amplitude and 100-200 msec duration could be elicited by electrical stimulation in the tongue vessels.2. Micro-electrodes were inserted into smooth muscle cells in the walls of small arteries and arterioles of the rat mesenteric circulation. Intracellular potentials varied continually and maximum polarization averaged 39.4 mV.3. Rhythmic slow waves with a period varying from 4.5 to 7.8 sec were observed, and their amplitude but not their frequency was affected by the level of anaesthesia.4. Spike potentials were recorded, amplitude up to 35 mV, with occasional overshoot, and duration 40-50 msec; these were followed by a positive after-potential, 100-150 msec duration and amplitude up to 8 mV.5. Experiments using chemical and surgical means of interfering with the autonomic nervous system showed that the amplitude, but not the frequency, of the slow waves and the occurrence of action potentials were markedly affected by nervous influences.6. Stimulation of the smooth muscle by asphyxia, electrical stimulation of the splanchnic nerves, and local application of adrenaline, noradrenaline and vasopressin increased the frequency of action potentials and the amplitude of the slow waves, and inhibiting agents such as acetylcholine and removal of the nerve supply depressed the electrical activity.

THE RELATIONSHIP BETWEEN ELECTRICAL AND MECHANICAL ACTIVITY OF THE SMALL INTESTINE OF DOG AND MAN

Electrical activity of the small intestine of man and of dogs has been studied using monopolar recording techniques and spread of electrical activity in the small intestine of the dog using a bipolar recording technique. Motility was studied simultaneously. Electrical activity consisted of slow waves and action potentials which occurred when contractions were present. Action potentials were not conducted but slow waves sometimes spread aborally for short distances. Particular attention was paid to the relation of slow waves to action potentials and to motility. No consistent alteration in the frequency or configuration of slow waves was found associated with the occurrence of action potentials and motility, although serotonin or epinephrine altered slow wave frequency slightly. Slow waves usually were increased in amplitude during periods when motility and action potentials were occurring (during eating or balloon propulsion; after the administration of serotonin, neostigmine, physostigmine, or morphine). Slow wave amplitudes usually were diminished when motility was inhibited (by balloon distention; after administration of epinephrine, etc.). Action potentials tended to occur in phase with the slow waves, when the muscle electrode was positive relative to the indifferent electrode, but this was not always so during nonpropulsive contractions. There was also a correlation between the occurrence of distal spread of slow waves over the duodenum and upper jejunum and the ability of the intestine in this region to respond to balloon distention by propulsion.In the dog, body temperature consistently affected slow waves. A decrease of 10 °C diminished their frequencies to less than one-half and diminished their amplitude. Slow waves occurred at similar frequencies and with regular conduction after large doses of nicotine or atropine. Dibenzyline, dichloroisopropyl-norepinephrine, and vagotomy did not markedly alter slow wave frequencies. These findings and those in our studies with microelectrodes indicate that the slow waves are myogenic in origin, and represent electrical currents in the extracellular fluid initiated by periodic depolarizations of muscle cells of the small intestine.

THE RELATIONSHIP BETWEEN ELECTRICAL AND MECHANICAL ACTIVITY OF THE SMALL INTESTINE OF DOG AND MAN

Electrical activity of the small intestine of man and of dogs has been studied using monopolar recording techniques and spread of electrical activity in the small intestine of the dog using a bipolar recording technique. Motility was studied simultaneously. Electrical activity consisted of slow waves and action potentials which occurred when contractions were present. Action potentials were not conducted but slow waves sometimes spread aborally for short distances. Particular attention was paid to the relation of slow waves to action potentials and to motility. No consistent alteration in the frequency or configuration of slow waves was found associated with the occurrence of action potentials and motility, although serotonin or epinephrine altered slow wave frequency slightly. Slow waves usually were increased in amplitude during periods when motility and action potentials were occurring (during eating or balloon propulsion; after the administration of serotonin, neostigmine, physostigmine, or morphine). Slow wave amplitudes usually were diminished when motility was inhibited (by balloon distention; after administration of epinephrine, etc.). Action potentials tended to occur in phase with the slow waves, when the muscle electrode was positive relative to the indifferent electrode, but this was not always so during nonpropulsive contractions. There was also a correlation between the occurrence of distal spread of slow waves over the duodenum and upper jejunum and the ability of the intestine in this region to respond to balloon distention by propulsion.In the dog, body temperature consistently affected slow waves. A decrease of 10 °C diminished their frequencies to less than one-half and diminished their amplitude. Slow waves occurred at similar frequencies and with regular conduction after large doses of nicotine or atropine. Dibenzyline, dichloroisopropyl-norepinephrine, and vagotomy did not markedly alter slow wave frequencies. These findings and those in our studies with microelectrodes indicate that the slow waves are myogenic in origin, and represent electrical currents in the extracellular fluid initiated by periodic depolarizations of muscle cells of the small intestine.

Researches on the influence of catalytic agents in ester formation; on the esterification of cyanacetic acid

<h3>Abstract</h3> Dynamic calcium imaging is a major technique of neuroscientists. It can reveal information about the location of various calcium channels and calcium permeable receptors, the time course, magnitude, and location of intracellular calcium concentration ([Ca²⁺]_i) changes, and indirectly, the occurrence of action potentials. Dynamic sodium imaging, a less exploited technique, can reveal analogous information related to sodium signaling. In some cases, like the examination of AMPA and NMDA receptor signaling, measurements of both [Ca²⁺]_i and [Na⁺]_i changes in the same preparation may provide more information than separate measurements. To this end, we developed a technique to simultaneously measure both signals at high speed and sufficient sensitivity to detect localized physiologic events. This approach has advantages over sequential imaging because the preparation may not respond identically in different trials. We designed custom dichroic and emission filters to allow the separate detection of the fluorescence of sodium and calcium indicators loaded together into a single neuron in a brain slice from the hippocampus of Sprague-Dawley rats. We then used high-intensity light emitting diodes (LEDs) to alternately excite the two indicators at the appropriate wavelengths. These pulses were synchronized with the frames of a CCD camera running at 500 Hz. Software then separated the data streams to provide independent sodium and calcium signals. With this system we could detect [Ca²⁺]_i and [Na⁺]_i changes from single action potentials in axons and synaptically evoked signals in dendrites, both with submicron resolution and a good signal-to-noise ratio (S/N).