Reversible depression of postsynaptic responses of molluscan neurons after strong direct hyperpolarizing stimulation

The effect of strong repetitive hyperpolarizing electrical stimulation (through an intracellular microelectrode) on postsynaptic unit responses to tactile stimulation of part of the mantle ofHelix pomatia was studied. Strong electrical stimulation (electro-convulsive shock) led to temporary disappearance of the responses to tactile stimulation. Depression of the responses was not connected with any change in the membrane potential level. The responses gradually returned to their initial form during the next 30 min. Habituation of responses to tactile stimulation was accelerated after electro-convulsive shock. An effect of electro-convulsive shock on postsynaptic structures is postulated.     

Hyperpolarizing and depolarizing mechanoreceptor potentials inStylonychia

Summary The surface ofStylonychia was mechanically stimulated with a piezo-crystal driven microneedle of 0.5-2 m distal diameter and maximal amplitudes of 13 m. Stimulation of the anterior surface of the cell produced a membrane depolarization, while stimulation of the posterior surface elicited a hyperpolarizing response. The analysis of electric responses to mechanical stimuli, driven by pulses varied in duration, amplitude, rate and acceleration, revealed that the hyperpolarizing receptor potential (hRP) rose in parallel with the stimulus velocity. Stimulus amplitudes beyond 12 m and at rates larger than 4 mm/s did not increase the amplitude of the membrane response. Sustained stimuli slowed down the repolarization to the resting level. Adaptation of the receptor response was seen with small and sustained velocities of the stimulating probe. The depolarizing receptor response (dRP) triggered an action potential consisting of two regenerative components, one graded, the other all-or-none. Positive conditioning current pulses reversed the polarity of the dRP which was primarily Ca-dependent (22.4 mV/log [Ca]₀).The dRP was isolated from the action potential by negative membrane conditioning. The reversal potential of the hyperpolarizing receptor response was negative of the resting potential and completely K-dependent (58.5 mV/log [K]_o).Submaximal hyperpolarizing and subthreshold depolarizing receptor potentials showed summation. No refractoriness of the hRP was detected. Summation of depolarizing responses beyond the threshold activated a regenerative membrane depolarization.Abbreviations hRP Hyperpolarizing receptor potential - dRP Depolarizing receptor potential Dedicated to Professor J. Schwartzkopff on the occasion of his sixtieth birthdaySupported by the Deutsche Forschungsgemeinschaft (SFB 114, TP A5)     

Photoreceptor Potentials of Opposite Polarity in the Eye of the Scallop, Pecten irradians

Intracellular recordings were obtained from single visual cells of the scallop, Pecten irradians. Two types of units are found. One type gives a graded, depolarizing response to light and the other a graded, hyperpolarizing response. The depolarizing cells are 2–3 log units more sensitive to light and have a longer latency than the hyperpolarizing type. At high light intensities the depolarizing cells are inactivated while the hyperpolarizing cells maintain their responses. When action potentials are seen they occur during illumination in depolarizing cells ("on" response) and after illumination in hyperpolarizing cells ("off" response). The evidence suggests that the depolarizing responses are from the microvilli-brearing proximal cells, and the hyperpolarizing responses from the ciliary-type distal cells of the retina, and that both responses are directly produced by light.     

Systemic circulatory reaction in the initial period of Cannon's traumatic shock

In experiments on dogs it was shown that on the basis of the dynamics of circulatory parameters it is possible to divide the erectile phase of traumatic shock into two periods. The first period, similar to "defence reactions" in dangerous situations and under the action of potent non-specific stimuli, is characterized by an increased blood inflow to the myocardium, rise in the cardiac output and reduction of the tonus in peripheral vessels. The second period is characterized by the beginning of decompensation of the cardiovascular system. It is completed by the development of the torpid phase of shock.     

Action potentials of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cats

In cats anesthetized with chloralose and pentobarbital stimulation of the infraorbital nerve by a volley of 3 or 4 stimuli 1.2 times stronger than the threshold for excitation of A-fibers caused the generation of action potentials in motoneurons of the masseter muscle if the frequency of stimuli in the volley exceeded 300/sec. Paired stimuli with a strength of 2.0 thresholds, and with an interval of 1.3–4.0 msec between stimuli, led to generation of an action potential by the motoneurons. If the interval exceeded 4 msec stimulation with a strength of 1.2–2.0 thresholds caused biphasic facilitation of the second EPSP with a facilitation factor of between 0.2 and 1.0. The small number of stimuli, combined with their high frequency in the volley, required for action potential generation by masseter motoneurons suggests that they are due to activation of A-fibers of the infraorbital nerve connected with fast-adapted receptors of the vibrissae.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 4 pp. 385–389, July–August, 1978.     

Rapid exocytosis of stenotele nematocysts in Hydra vulgaris

Each cnidarian nematocyte includes a vesicular organelle, called nematocyst, which discharges its content when the cell receives appropriate stimuli. Extracellular electrical stimuli induced discharge of in situ stenoteletype nematocysts in Hydra vulgaris when the apical membrane of nematocytes was depolarized by about 25 mV or more (threshold). Stimuli hyperpolarizing the apical membrane induced discharge only at high amplitudes, adding about 80 mV or more to the resting membrane potential of the nematocyte (resulting in a voltage that may permeabilize the apical membrane). In order to determine the speed of the initiating (exocytotic) process, the delay between stimulus and a clearly visible sign of discharge (i.e., protrusion of the nematocyst's stylets) was measured using video microscopy with triggered flash illumination. The minimal delay was 330–450 s and 230–350 s for depolarizing and large hyperpolarizing stimuli, respectively. With depolarizing stimuli, all discharges of stenoteles occurred between 330 and 950 s after the stimulus. The deviation was caused by differences in the physiological state of the animals tested rather than by variance in the responsiveness of different stenoteles in the same tentacle.Voltage dependence, short latency and Ca/Mg-antagonism are similar to those characterizing exocytosis of synaptic vesicles. This correspondence suggests that discharge of nematocysts is initiated by a similar exocytotic process preceding the ejection of the nematocyst's content.     

Different effects of blocked potassium channels on action potentials, accommodation, adaptation and anode break excitation in human motor and sensory myelinated nerve fibres: computer simulations

 Action potentials and electrotonic responses to 300-ms depolarizing and hyperpolarizing currents for human motor and sensory myelinated nerve fibres have been simulated on the basis of double cable models. The effects of blocked nodal or internodal potassium (fast or slow) channels on the fibre action potentials, early and late adaptations to 30-ms suprathreshold slowly increasing depolarizing stimuli have been examined. The effects of the same channels on accommodation after the termination of a prolonged (100 ms) hyperpolarizing current pulse have also been investigated. By removing the nodal fast potassium conductance the action potentials of the sensory fibres are considerably broader than those of the motor neurons. For both types of fibres, the blocked nodal slow potassium channels have a substantially smaller effect on the action potential repolarization. When the suprathreshold depolarizing current intensity is increased, the onset of the spike burst occurs sooner, which is common in the behaviour of the fibres. The most striking differences in the burst activity during early adaptation have been found between the fibres when the nodal fast potassium channels are blocked. The results obtained confirm the fact that the motor fibres adapt more quickly to sustained depolarizing current pulses than the sensory ones. The results also show that normal human motor and sensory fibres cannot be excited by a 100-ms hyperpolarizing current pulse, even at the threshold level. When removing the potassium channels in the nodal or internodal axolemma, the posthyperpolarization increase in excitability is small, which is common in the behaviour of the fibres. However, anode break excitation can be simulated in the fibres with simultaneous removal of the potassium channels under the myelin sheath, and this is more pronounced in the human sensory fibres than in motor fibres. This phenomenon can also be found when the internodal and some of the nodal (fast or slow) potassium channels are simultaneously blocked. Received: 8 November 1999 / Accepted in revised form: 29 February 2000     

Dissociation of reproduction of conditioned vegetative and motor reactions during retrograde electroconvulsive amnesia]

It has been shown in chronic experiments on rats that electro-convulsive action applied in five to ten seconds after one-session conditioning completely precludes the reproduction of conditioned motor reactions, while conditioned bradycardiac reactions are clearly reproduced in tests one hour and 24 hours after elaboration. Unconditioned stimulus presented in another experimental situation six to seven days after elaboration and amnesic action, leads to a stable reproduction of the previously non-achieved conditioned motor reactions. The results obtained suggest that electrical seizures influence the reproduction of motor reactions, rather than fixation of temporary connection.     

The effect of opiate receptor ligands on emotional cardiovascular reactions in lower primates

Intravenous naloxone injection (0.1 mg/kg) facilitated blood pressure increase in response to conditioned sound stimulus followed by electrocutaneous shock in conscious chair-restrained baboons (Papio hamadryas). Naloxone at a dose of 1.0 mg/kg had an opposite effect and led to the decrease in blood pressure and heart rate in conditioned fear reflex. Naloxone microinjections (50 microM) into the periventricular hypothalamus led to a significant diminution of blood pressure and heart rate increment in response to electrocutaneous shock; naloxone microinjections into tractus solitarius nuclei suppressed blood pressure and heart rate reactions both to conditioned (sound) and unconditioned (electrocutaneous shock) stimuli. Microinjections of equimolar morphine quantities in these brain regions facilitated such reactions. It is concluded that endogenous opioid system participates in the formation of cardiovascular reactions to emotional stimuli in monkeys, with multiple opioid receptors of periventricular hypothalamus and tractus solitarius nuclei involved in the generation of such reactions.     

Role of calcium ions and spike activity in the neurotrophic control of membrane potential in rat muscle fibers

Blockade of calcium permeability produced an increase in postdenervation depolarization of rat diaphragm muscle fibers during in vitro experiments, while increased Ca²⁺ concentration in the sarcoplasm induced by caffeine led to hyperpolarization of the muscle membrane. Direct stimulation of the muscles or carbamylcholine application retarded the reduction of membrane potential in the muscle fibers. Verapamil and d-tubocurarine eliminated the hyperpolarizing effect of stimulation. The hyperpolarizing effects of carbamylcholine applied in conjunction with stimulation did not produce an accumulated action on the membrane. It is deduced that the factors governing membrane potential in the muscle fibers are acetylcholine and Ca²⁺ reaching the sarcoplasm mainly through the acetylcholine-sensitive ionic channels during the process of nerve impulse fluxes.S. V. Kurashov Medical Institute, Kazan', Ministry of Public Health of the RSFSR. Translated from Neirofiziologiya, Vol. 19, No. 4, pp. 449–456, July–August, 1987.     

Reproduction of the electrophysiologic correlates of a conditioned defense reflex following electroconvulsive activity]

Acute and chronic experiments on cats have shown the possibility of obtaining in one session conditioned EEG-responses and vegetative changes as well as conditioned motor reactions time-locked to the moment of the unconditioned pain stimulation omitted during testing. Electro-convulsive stimulation directly after elaboration prevents the appearance of conditioned motor reactions, while conditioned EEG and vegetative changes are retained after electric seizures. A conclusion has been drawn that the emotional component of conditioned reactions is not subjected to the amnestic effect of electro-convulsive action.     

Ultrasound elicits tonic responses and diminishes the phasic responses to adequate stimuli in thread-hair mechanoreceptors of Acheta domesticus

Single mechanoreceptor cells in filiform hair sensilla on the cercus of Acheta domesticus were stimulated adequately by steplike deflections in their plane of least restraint and inadequately by ultrasound. Ultrasound was fed either into the cercus or into the thread-hair as substrate-borne sound of 110–120 kHz. The receptor responds to deflections of the thread-hair (adequate stimuli) with phasic receptor potentials which can be picked up transepithelially. These responses can be either depolarizing (excitatory responses) or hyperpolarizing (inhibitory responses). Ultrasound applied simultaneously or shortly preceding the adequate stimulus reduces both kinds of responses in a graded way. The receptor can respond to ultrasound alone. At small intensities the responses are predominantly inhibitory; with increasing intensity they may become excitatory. In both cases the responses to ultrasound are tonic and do not reach the peak responses to saturating adequate stimuli. The off-effect, which follows adequate stimuli and leads to inhibitory responses after excitatory stimuli and vice versa, typically does not occur or is exitatory at the end of sonication. The observed effects of sonication are totally reversible. The correlation between transepithelial voltage, spike frequencies and spike amplitudes in the unsonicated and sonicated sensilla allows the responses to be attributed to sonication to the same conductance, which is also modulated by adequate stimuli. A model is discussed, according to which ultrasound exerts its effects by facilitating dissipative relaxation in the dendritic membrane, which is assumed to be involved in stimulus-energy transfer.     

Effect of a volatile anesthetic upon presynaptic excitability in mammalian hippocampus

Changes in presynaptic terminal axon excitability produced by enflurane in the rat hippocampal slice preparation were investigated by stimulation of Schaeffer collateral terminal axons and by recording single unit antidromic action potentials. Stimulating pulses were preceded by conditioning hyperpolarizing or depolarizing current pulses. A plot of net threshold for action potential generation against the conditioning pulse yields an "accommodation curve;" changes in this curve can be used to assess the mechanism by which changes in excitability are produced. Enflurane, at a concentration equivalent to approximately equal to 1.3 times the minimum alveolar concentration, reduced excitability of terminal axons and increased accommodation in a manner consistent with a possible change in the inactivation of gNa.     

Oscillations of membrane potential in L cells

Summary Effects of divalent cations on oscillations of membrane potentials (i.e., spontaneous repetitive hyperpolarizing responses) and on hyperpolarizing responses induced by electrical stimuli as well as on resting potentials were studied in large nondividing L cells. Deprivation of Ca²⁺ from the external medium inhibited these hyperpolarizing responses accompanying slight depolarization of the resting potential. Sr²⁺ or Mn²⁺ applied to the external medium in place of Ca²⁺ was able to substitute for Ca²⁺ in the generation of hyperpolarizing responses, while Mg²⁺, Ba²⁺ or La³⁺ suppressed hyperpolarizing responses. The addition of A23187 to the bathing medium or intracellular injection of Ca²⁺, Sr²⁺, Mn²⁺ or La³⁺ induced membrane hyperpolarization. When the external Ca²⁺, Sr²⁺ or Mn²⁺ concentration was increased, the resting potential also hyperpolarized, in a saturating manner. The amplitude of maximum hyperpolarization produced by high external Ca²⁺ was of the same order of magnitude as those of hyperpolarizing responses and was dependent on the external K⁺ concentration. In the light of these experimental observations, it was deduced that the K⁺ conductance increase associated with the hyperpolarizing excitation is the result of an increase in the intracellular concentration of free Ca²⁺ mainly derived from the external solution.     

Calcium currents modulated by adrenergic receptors in sympathetic neurons

The superior cervical sympathetic ganglion is currently being used as a model neuronal system for the study of Ca2+-dependent processes in the mammalian nervous system. We have characterized a regenerative calcium conductance in postganglionic neurons. This Ca2+ current contributes to the shoulder of the action potential. In addition, Ca2+ influx during the spike activates a K+ conductance, which generates a hyperpolarizing afterpotential. These Ca2+-dependent potentials are antagonized by catecholamines. Pharmacologic studies suggest that alpha 2-adrenergic receptors inhibit the regenerative voltage-dependent Ca2+ influx that occurs during the action potential. Alpha-adrenergic agonists were also found to reduce the depression of the compound action potential following a train of preganglionic stimuli. We hypothesize that alpha 2-receptors function primarily to antagonize Ca2+ influx and thereby exert significant control over neuronal excitability and release of neurotransmitters.     

Suppression of pacemaker activity by rapid repetitive phase delay

Spontaneous activity of pacemaker cells or structures may be suppressed by rapid repetitive stimulation. Conditions are that the oscillator's phase reset curve, characterizing the phase resetting effect of single stimuli, has a phase delay part and that the interval between the stimuli falls within a range of values, determined by the form oo the phase reset curve. Under these conditions, which appeared the same as those for stable underdrive pacing, the pacemaker becomes stably entrained to the stimuli without firing, i.e. it is kept within a certian part of its limit cycle because the pulses repeatedly delay the next coming action potential. This rapid stimulation suppression of pacemaker activity is demonstrated experimentally on a simple electronic pacemaker cell model for two types of phase reset curves, a biphasic one for depolarizing and a monophasic one for hyperpolarizing pulses. Computer simulations of coupled pacemaker cells, interacting by phase reset curves, illustrate how this type of pacemaker suppression may protect a population of pacemaker cells like the sinus node in the heart against arrhythmias.Supported by the Netherlands Foundation for Medical Research FUNGOSupported by the Netherlands Organization for the Advancement of Pure Research ZWO     

The Intrinsic Electrophysiological Characteristics of Fly Lobula Plate Tangential Cells: III. Visual Response Properties

In this last paper in a series (Borst and Haag, 1996; Haag et al., 1997) about the lobula plate tangential cells of the fly visual system (CH, HS, and VS cells), the visual response properties were examined using intracellular recordings and computer simulations. In response to visual motion stimuli, all cells responded mainly by a graded shift of their axonal membrane potential. While ipsilateral motion resulted in a graded membrane potential shift, contralateral motion led to distinct EPSPs. For HS cells, simultaneous extracellular recorded action potentials of a spiking interneuron, presumably the H2 cell, corresponded to the EPSPs in the HS cell in a one-to-one fashion. When HS cells were hyperpolarized during ipsilateral motion, they mainly produced action potentials, but when they were hyperpolarized during contralateral motion only a slight increase of EPSP amplitude, could be observed. Intracellular application of the sodium channel blocker QX 314 abolished action potentials of HS cells while having little effect on the graded membrane response to ipsilateral motion. HS and CH cells were also studied with respect to their spatial integration properties. For both cell types, their graded membrane response was found to increase less than linearly with the size of the ipsilateral motion pattern. However, while for HS cells various amounts of hyperpolarizing current injected during motion stimulation led to different saturation levels, this was not the case for CH cells. In response to a sinusoidal velocity modulation, CH cells followed pattern motion only up to 10 Hz modulation frequency, but HS cells still revealed significant membrane depolarizations up to about 40 Hz.In the computer simulations, the compartmental models of tangential cells, as derived in the previous papers, were linked to an array of local motion detectors. The model cells revealed the same basic response features as their natural counterparts. They showed a response saturation as a function of stimulus size. In CH-models, however, the saturation was less pronounced than in real CH-cells, indicating spatially nonuniform membrane resistances with higher values in the dendrite. As in the experiments, HS models responded to high-frequency velocity modulation with a higher amplitude than did CH models.     

Effect of amiloride on bulk flow and iontophoretic taste stimuli in the hamster

Summary This investigation 1) demonstrates the effect of amiloride on various taste responses in the hamster, and 2) tests the hypothesis that its action on iontophoretic application of taste stimuli parallels its action on bulk flow delivery. Amiloride has not previously been tested in the hamster nor has its effect on iontophoretic stimuli (socalled electric taste), which is thought to behave similarly to bulk flow stimuli, been examined. Amiloride treatment (4 min of 0.0001M) of the hamster's tongue effectively inhibited chorda tympani responses to NaCl and LiCl solutions. Bulk flow (0.1M) and iontophoretic (+7 A through 0.001M) presentations of NaCl and LiCl, which had unequal response magnitudes pre-treatment, were inhibited to the same residual response magnitude post-treatment. Recovery then proceeded along two distinct curves asymptotically returning to pre-treatment response levels. These curves could be adequately described by a simple exponential relationship. KCl responses were unaffected when presented via bulk flow techniques but significantly reduced when presented iontophoretically. HCl responses via either method were only slightly diminished. No decrement in response level was observed for the sweet stimuli sucrose (0.5M) or saccharin (–9 A through 0.001M Na-saccharin) nor for potassium picrate, a bitter stimulus, (0.01M or –10 A through 0.001M). Amiloride treatment of the hamster tongue was as specific in its action for sodium and lithium as reported in other species, and with the exception of KCl the action of amiloride on iontophoretic stimulation paralleled its action on bulk flow stimulation.     

Suppression of "fast" IPSP,superposed on "slow", as a possible cause of priming in murine hippocampus

Intra- and extracellular response in area CA1 to stimulation of two independent afferent inputs, one a priming or conditioned and the other a test or primed input (C1 and C2, respectively) were recorded in surviving murine hippocampal slices. Duration and amplitude of test field potentials (FP) and of excitatory postsynaptic potentials (EPSP), were measured, as well as amplitude of "fast" and "slow" components of inhibitory postsynaptic potentials or stimulation varying between 0 and 1 sec. Conditioning brought about an increase in the duration of FP, in duration and amplitude of EPSP, and suppression of IPSP at intervals of between 50 and 500 msec peaking at 200 msec (i.e., priming effect). These changes correlated with level of IPSP_b in response to conditioned stimuli. The most pronounced effect could be seen in neurons manifesting hyperpolarizing IPSP in response to test stimuli. Suppression of test IPSP_a after superposition on IPSP_b is thought to bring about the increase in test FP and EPSP seen during priming.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 730–739, November–December, 1990.     

Changes in the configuration of conditioned reactions of visual cortex neurons during changes in reinforcement parameters]

In order to study the influences of controlled changes of defensive integration on the activity of visual cortical units their responses to a conditioned light flash and electric cutaneous stimulation with a 600 msec interval between them were recorded in experiments on alert rabbits. It has been shown that in a third of the neurones the types of reaction to light flashes and electric stimuli coincide. The changes in parameters of the reinforcing shock led to a changed response of most cells to the conditioned photic stimulus and electric stimulation. The changes may have affected units which produce any activation phase, including cells with activity characteristic of detectory ("simple" and "complex") visual neurones. The data obtained suggest that the special function of the visual cortex is used in different ways in systemic mechanisms of conditioned and unconditioned defensive acts and that the integrated system of a behavioral act exerts control both on the use of the unit in a certain systemic process and on its receptive field.