Mechanism of inhibition following reflex discharge in spinal cord interneurons

Using the method of microelectrode (intracellular and extracellular) recording, the mechanism of inhibition following reflex discharge in interneurons of the lumbosacral section of the spinal cord of cats on activation of cutaneous and high-threshold muscle afferents was studied. It was shown that the postdischarge depression of the reflex responses 10–20 msec after the moment of activation of the neuron is due to afterprocesses in the same neuron and presynaptic pathways. The depression of spike potentials from the 20th to the 100th msec is produced by inhibitory postsynaptic potentials (IPSP). During the development of IPSP the inhibition of spike potentials can be due to both a decrease of the depolarization of the postsynaptic membrane below the critical threshold and a decrease of sensitivity of the cell membrane to the depolarizing action of the excitatory postsynaptic potential (EPSP). At intervals between the stimuli of 30–100 msec the duration of EPSP after the first stimulus does not differ from that after the second stimulus. Hence, it is suggested that the presynaptic mechanisms do not play an essential part in this type of inhibition of interneurons. The inhibition following the excitation favors the formation of a discrete message to the neurons of higher orders.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 3–9, January–February, 1970.     

Action potential generation by turtle cortical neurons. Dendritic and somatic spikes

Action potentials of neurons of the turtle general cortex and the pattern of their generation were studied by an intracellular recording method. Besides the complete action potential, the cells also generate partial spikes of varied amplitude which compose the complete action potential. The threshold of generation and the discrete amplitude of each partial spike are not strictly constant but they fluctuate gradually and spontaneously within certain limits without any change in membrane potential of the cell. Somatic and dendritic spikes are distinguished. The trigger zones of the latter are located at various distances from the soma. During orthodromic activation of cortical neurons dendritic spikes are generated consecutively and spread to the some electrotonically with a decrement. They are the immediate cause of generation of the somatic spike.M. V. Lomonovsov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 237–242, May–June, 1976.     

Characteristics of poststimulus and lateral inhibition in neurons of cat primary auditory cortex

Experiments using intracellular recording of potentials from neurons of the primary auditory cortex of cats anesthetized with pentobarbital showed that under the influence of tones of characteristic frequency for the neuron under test, or of electrical stimulation of nerve fibers of the spiral ganglion, innervating the center of the receptive field of the neuron, transient excitation of the latter is followed by the development of prolonged (20–250 msec) inhibition. The cause of this inhibition is an IPSP arising in the neuron after the action potential. On the basis of data showing a close connection between inhibition and the preceding spike it is concluded that it arises through the participation of a mechanism of recurrent inhibition. During the action of tones of uncharacteristic frequency or electrical stimulation of the peripheral part of the receptive field of the neuron, a response consisting of EPSP-IPSP arises in the neuron. This IPSP is accompanied by inhibition of spontaneous activity of the neuron and its responses to testing stimulation. It has been shown that this inhibition is lateral in its genesis. Characteristics of these two types of inhibition are given.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 194–201, March–April, 1984.     

Effect of intracellular injection of cyclic amp on electrical characteristics of identified neurons in Helix pomatia

The effect of intracellular iontophoretic injection of cyclic AMP on electrical activity of neurons RPa1, RPa3, LPa2, LPa3, and LPl1 in the corresponding ganglia ofHelix pomatia was investigated. Injection of cyclic AMP into neuron LPl1 was found to cause the appearance of rhythmic activity (if the neuron was originally "silent"), an increase in the frequency of spike generation (if the neuron had rhythmic activity), and a decrease in amplitude of waves of membrane potential, in the duration of the interval between bursts, and in the number of action potentials in the burst (if the neuron demonstrated bursting activity). In the remaining "silent" neurons injection of cyclic AMP led to membrane depolarization. Injection of cyclic AMP into neurons whose membrane potential was clamped at the resting potential level evoked the development of an inward transmembrane current (cyclic AMP current), the rate of rise and duration of which increased proportionally to the size and duration of the injection. Theophylline in a concentration of 1 mM led to an increase in the amplitude and duration of the cyclic AMP current by about 50%. It is concluded that a change in the cyclic AMP concentration within the nerve cell may modify the ionic permeability of its membrane and, correspondingly, its electrical activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 517–525, September–October, 1980.     

Generation of spike activity by dendrites of secondary neurons of the rat olfactory bulb

Experiments on secondary neurons of the rat olfactory bulb showed the existence of a third region of action potential generation. It evidently consists of dendrites. This is shown by the distance from the soma of the point where action potentials arise initially and by the recording of spontaneous action potentials of comparatively low amplitude, not spreading into the axon. Action potentials are generated by apical dendrites and also, perhaps, by basal dendrites. Besides partial action potentials with stable amplitude, partial action potentials with, for practical purposes, a stepwise changing amplitude also were recorded. It is suggested that the amplitude of the partial action potentials is modified by IPSPs in the spike-generating zones.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 282–290, May–June, 1976.     

Possible mechanisms of dendritic potential habituation in the cat association cortex

The effect of application of strychnine and calcium and of post-tetanic potentiation on the dynamics of gradual decay of dendritic potentials in the association cortex, which is regarded as monosynaptic habituation, was studied in acute experiments on cats anesthetized with pentobarbital. Despire a significant increase in amplitude of dendritic potentials after strychnine application or calcium enrichment of the physiological saline, the time course of habituation was unchanged. The course of habituation also remained unchanged during post-tetanic potentiation. It is concluded that habituation of dendritic potentials is due to processes taking place in the postsynaptic dendrite membrane itself and is independent of postsynaptic inhibition or transmitter exhaustion in presynaptic endings.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 208–213, March–April, 1984.     

Mathematical analysis of the possibility of detecting correlation between spike trains of weakly interacting neurons

The number of spikes which must be recorded in order to detect significant correlation between spike trains of two synaptically connected neurons was estimated by a mathematical model. Dependence of this number of spikes on importance of interneuronal connection (measured as the amplitude of the EPSP evoked by a single spike of the input neuron in the output cell) and on the intensity of total spontaneous excitatory influences on the output neuron and on its own parameters was studied. For cells which corresponded in the weight of connections between them, their intrinsic parameters, and characteristics of spontaneous activity to real spinal neurons, the necessary number of spikes was 10⁷–10⁸. An increase in amplitude of the single EPSP and also a decrease in the intensity of the input spontaneous spike train and parameters of after-hyperpolarization of the postsynaptic neuron led to a decrease in the number of spikes necessary for the detection of significant correlation. On the basis of the results of this and previous investigations the possible principles for construction of a spinal locomotor generator are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 290–296, May–June, 1980.     

Functional development of hippocampal mossy fiber synapses in rabbits

The course of functional maturation with age of mossy fiber synapses on pyramidal cells in areas CA_3,4 of the dorsal hippocampus was investigated by extracellular recording of focal potentials and single unit responses of the hippocampus to electrical stimulation of the dentate fascia in waking, unimmobilized rabbits aged from 1 to 14 days. After the 4th day of postnatal life focal potentials appeared in response to single stimulation, in the form of a biphasic short-latency wave, characteristic of responses of the mature hippocampus, accompanied by spike discharges with a latent period of 3 to 10 msec and inhibitory responses of the hippocampal neurons. During the next 10 days the amplitude of the focal potentials increased from several hundred millivolts, with the sharpest increase observed from the 4th through the 7th days. In early age periods global and unitary responses were shown to be capable of frequency potentiation and also of short-term after-potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 246–254, May–June, 1980.     

Electrophysiological properties of neurons and neuronal organization of the crayfish somatogastric ganglion

Experiments with intracellular recording from neurons of the isolated crayfish somatogastric ganglion established that the membrane potential of the neurons is 53±3 mV. Single stimulation of the central branches of the ganglion evoked EPSP and a spike in the neurons. The spike amplitude was 7.5±0.6 mV. The small amplitude of the spike is explained by the fact that it arises at some distance from the body of the neuron and propagates electrotonically in it. Summation of several EPSP is necessary in most cases for initiation of the spike. When the orthodromic stimulus was strong enough, and IPSP occurred in some cells in addition to the EPSP and spike. Stimulation of the peripheral nerves of the ganglion induced in most neurons antidromic excitation and in some neurons orthodromic excitation. Some neurons spontaneously discharged rhythmically with an unstable frequency (11–27 impulses/sec). An investigation of the effect on neurons of chemical agents [acetylcholine, adrenalin, noradrenalin, gamma-aminobutyric acid (GABA), glutamic acid, and dopamine] showed that acetylcholine has the strongest and most stable depolarizing action and apparently is a synaptic transmitter in the ganglion. The other agents excited some neurons — depolarized them and evoked rhythmic discharges — and, coversely, hyperpolarized and suppressed the rhythmic activity of other neurons. A scheme of neuronal organization of the somatogastric ganglion of the crayfish is proposed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 307–313, May–June, 1970.     

Posttetanic changes in hippocampal minimal evoked potentials

Changes in the EEG induced by a single spike were recorded in the hippocampus of an unanesthetized rabbit. Summation of focal electrical activity synchronous with spontaneous single unit discharges at the symmetrical point of contralateral hemisphere revealed no stable potentials which could reflect these changes. In two cases discharges identified as activity of Shaffer's collaterals were recorded in area CA₁. Summation of post-spike changes in evoked activity recorded by the same microelectrode showed stable negative waves with an amplitute of 40–60 µV, which could have been evoked by single spikes. The curve of amplitude of the averaged evoked potentials versus near-threshold current strength stimulating the intrahippocampal pathways was not smooth in most experiments but stepwise in character. It is suggested that the minimal evoked potential corresponding to the first step (amplitude 40–80 µV) reflects a response to stimulation of one fiber. After above-threshold tetanization prolonged posttetanic potentiation of the minimal evoked potentials did not arise in CA₁ in response to stimulation of Shaffer's collaterals. Minimal evoked potentials recorded in area CA₃ in response to stimulation of the dentate fascia showed clear potentiation. The results are in agreement with the hypothesis of the synaptic localization of the mechanisms responsible for prolonged posttetanic potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 124–134, March–April, 1977.     

Sodium- and Calcium-Dependent Spike Potentials in the Secretory Neuron Soma of the X-Organ of the Crayfish

Membrane characteristics of neuron somata in the medulla terminalis ganglionic X-organ of crayfish have been investigated with intracellular glass microelectrodes. The soma membrane developed action potentials with 10–20 mv of overshoot. Delayed rectification appeared at 10–20 mv above resting membrane potential. In 50% of the neuron somata examined, action potentials were observed in Na-free medium or TTX medium. The peak potential level of the spike in these media depended on the extracellular concentration of Ca ion. It increased with the Ca concentration. In low calcium media, the peak potential level of the spike varied with Na concentration. Action potentials of the X-organ-sinus gland tract disappeared after bathing in Na-free or TTX medium, suggesting that the conductive action potential was dependent on Na ions. From these results, it is concluded that there are two systems in the neuron soma, one of which responds to the Na ion and the other, to the Ca ion. Inhibitory innervation of the X-organ by the cerebral ganglion was manifested by IPSP's when the optic peduncle was stimulated. A postulated connection between the Ca-dependent spike and the release of hormone in X-organ neuron somata is discussed.     

Modulation of electrical activity of neuron RPa2 ofHelix pomatia

Neuron RPa2 ofHelix pomatia can generate rhythmic (beating) or periodic (bursting) activity. A spontaneous switch from beating to bursting activity takes place in the course of tens of minutes. Similar changes in electrical activity can be induced by the addition of the water-soluble fraction obtained from a homogenate of snail ganglia to the experimental chamber. Artificial polarization of the membrane of neuron RPa2 by asteady inward current leads to an increase in the duration of intervals between bursts and to a decrease in the number of action potentials in the burst. With an increase in amplitude of the polarizing current, action potential generation ceases completely, but generation of waves of membrane potential persists. If the voltage on the neuron membrane is clamped, periodic fluctuations of membrane current disappear. It is suggested that action potential generation by neurons RPa2 is determined by the properties of the potential-dependent conductance of its membrane, i.e., that it is endogenous in origin and can be regulated by compounds acting on the membrane. These compounds, secreted by other neurons, resemble neurotransmitters or neurohormones.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 406–412, July–August, 1981.     

Various forms of potentials recorded from caudate nucleus neurons

Spontaneous and evoked activity of caudate nucleus neurons was recorded extracellularly in acute experiments on cats. Different forms of potentials were found by analysis of the results. The potentials recorded belong to three types: ordinary action potentials; prepotentials or incomplete spikes differing from ordinary action potentials in their lower amplitude and slower decline, and complex discharges in which a spike of somewhat reduced amplitude is followed by a slow positive-negative wave. In the spontaneous activity prepotentials were observed both in complete action potentials and in isolation. The frequency of the complex discharges was 0.5–1 per second. The slow wave of these discharges blocked prepotential and action potential formation. The origin of these forms of potentials in neurons of the caudate nucleus is discussed and they are compared with analogous forms of potentials described for the Purkinje cells of the cerebellum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 149–156, March–April, 1977.     

Possible role of voltage-sensitive potassium channels in generation of response in Pacinian corpuscles

The effects of 20 mM tetraethylammonium (TEA) and 5 mM 4-aminopyridine (4-AP) on mechanically and electrically excitable membranes of Pacinian corpuscles were investigated using the air gap technique for producing constant superfusion and recording electrical response at the receptor. The effects of TEA led to a 150% rise in the duration of receptor potential, the amplitude of which declined by 40%. No statistically significant changes in response to mechanical stimulation could be detected after applying 4-AP to the receptor membrane. The two blockers mentioned did modify the membrane of the first nodes of Ranvier, producing a 2–3-fold increase in the duration of action potentials. Computations based on the Dodge model would indicate that the observed effects may be explained by inhibition of voltage-dependent potassium channels which help to transform receptor current into spike response in the intact receptor.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 5, pp. 623–630, September–October, 1988.     

Electrotonic interaction between secondary neurons of the carp olfactory bulb

Responses of secondary neurons of the carp olfactory bulb evoked by electrical stimulation of the olfactory tract were investigated by intracellular recording. In most neurons spike responses were identified as antidromic. Their latent periods varied from 2.5 to 55 msec. Two other types of responses of secondary neurons had constant latent periods: the pseudo-antidromic spike and a fast low-amplitude depolarization potential. It is concluded that these responses are generated by the antidromic spike of a neighboring neuron, connected electrotonically with the recorded neuron.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 490–496, September–October, 1976.     

Electrophysiological investigation of the cat ciliary ganglion

Electrical responses of some nerves of the ciliary ganglion to stimulation of its other nerves were recorded, and intracellular recordings were also made from neurons of the ganglion (in situ). The overwhelming majority of preganglionic fibers terminate synaptically on neurons of the ganglion. Postganglionic fibers leave in the lateral and medial ciliary nerves, in which the velocity of conduction of excitation ranges from 1.9 to 9.0 m/sec. A few preganglionic fibers pass through the ciliary ganglion into the lateral ciliary nerve, giving off collaterals to neurons of the ganglion, so that stimulation of the lateral ciliary nerve evokes a response in the medial ciliary nerve (preganglionic axon reflex). The resting potential of neurons of the ciliary ganglion is 57±2.8 mV, and their action potential 68±3.6 mV. Single orthodromic stimulation usually evokes a single action potential in a neuron. The amplitude of the EPSP is increased during hyperpolarization of the postsynaptic membrane, confirming the chemical nature of synaptic transmission in the ganglion. The antidromic response consists of an IS-component and spike. The spike is followed by after-hyperpolarization, with a mean amplitude equal to 31% of the spike amplitude, and the time taken for it to fall to one–third of its initial amplitude is 75–135 msec.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 101–108, July–August, 1969.     

Comparison of structural and functional age changes in identified neurons of molluscLymnaea stagnalis

Experiments on adult (aged 10–12 months) and old (aged 20–22 months) molluscsLymnaea stagnalis were aimed at comparison of functional and structural changes in identified neurons of the lesser parietal ganglion. No age changes were observed in the membrane potential of a neuron, in the resistance of its membrane, or in the amplitude, duration, and rate of rise of the leading edge of the action potential. With age, thresholds for direct stimulation of a neuron increased substantially, the repolarization phase of the action potential slowed down, and the amplitude of the afterhyperpolarization decreased. The most pronounced age changes were revealed in the characteristics of background neuronal activity. A distinct correlation was observed between the frequency of background spikes in a neuron and the state of its structures, both in adult and in old individuals. In the molluscs of both age groups the neurons with a high frequency of spike generation featured high activity of the protein-biosynthesizing system. In contrast, the structure of cells with a low firing frequency in old molluscs differed significantly from that of the neurons with similar activity in adult individuals, first of all, by substantially pronounced morphological manifestations of the suppression of protein-synthesizing processes, as well as by catabolic and destructive-dystrophic changes.Neirofiziologiya/Neurophysiology, Vol. 25, No. 6, pp. 409–417, November–December, 1993.     

Dynamics of auditory cortical unit responses of the waking cat during defensive conditioning to acoustic stimulation

In chronic experiments on cats unit responses of the primary auditory cortex (area 50) were studied by microelectrode recording during defensive conditioning to sound. During formation of the reflex biphasic responses with relatively short-latency (50–100 msec) and longer-latency (400–500 and 800–900 msec) activation predominated. Neighboring neurons, whose activity was recorded by the same microelectrode, also were involved more intensively in activity. Application of a differential stimulus in 70% of cases produced definite changes in unit activity, among which responses of activation type predominated. Analysis of the course of spike responses of the same neuron during the period of action of a large number of combinations and its comparison with the formation of the conditioned-reflex motor response revealed no direct correlation between these events.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 99–108, March–April, 1979.     

The effect of pentylenetetrazol on the metacerebral neuron of Helix pomatia

The effects of Pentylenetetrazol (PTZ) on the metacerebral giant cell (MCC) of the snail, Helix pomatia were studied. Actions on membrane resistance, time constant, resting and action potentials, outward and inward ionic currents were examined. Superfusion with PTZ in concentrations of 25 to 50 mmol/l, induced a gradually evolving convulsive state, which could be studied by intracellular recording from the MCCs. In the pre-convulsive state an acceleration of the spontaneous activity developed and was followed by paroxysmal depolarization shifts (PDSs), in the convulsive phase. PTZ prolonged the membrane time constant by about 10 percent, but this could not be traced back to alterations in membrane resistance or capacity. The resting membrane potential was not significantly altered; the action potentials were prolonged by slowing down of both the rising and decaying phases. The outward potassium currents were repressed by PTZ in a voltage dependent manner. The decrease of the IA current became more pronounced at increasingly positive command pulses, while IK was relieved from depression especially at longer pulse durations. Inward currents were isolated with the aid of suppression of outward currents by 50 mmol/l TEA. Under these conditions sodium currents, measured in calcium deficient Ringer solution were moderately depressed, while the calcium currents, examined during sodium-free superfusion, were mildly enhanced by PTZ. It is concluded that PTZ effects on ionic conductances, on membrane parameters, on the resting potential and ionic currents explain only modifications of spike potentials occurring in the convulsive state and do not account for the PDS, the central phenomenon of the convulsive electrographic activity, at least in this thoroughly examined type of neuron.     

The ionic requirements for the production of action potential in Achatina fulica Ferussac neuron

The ionic requirement for the production of directly elicited action potentials of a tonically auto-active neuron (TAN) in the subesophageal ganglia of the giant African snail, Achatina fulica Ferussac, was studied electrophysiologically. Calcium free Ringer solution containing 1 mM EDTA reversibly abolished the directly elicited action potential. Verapamil (10 micrograms/ml) or cocaine (4 mg/ml) decreased both amplitude and Vmax of the action potentials. The amplitude of the action potential was also slightly decreased in sodium free choline Ringer. However, tetrodotoxin did not significantly affect either the amplitude or Vmax of the directly elicited action potentials. The results suggest that the ionic requirement for generating action potential in snail neuron is not an ordinary sodium spike. Both calcium and sodium ions may participate in carrying charges across the membrane of the action potential.