Self-sustained rhythmic spike and wave activity and response of glial and nerve cells in the cat sensorimotor cortex

During acute experiments on unanesthetized cats, immobilized with myorelaxants, it was found that during rhythmic stimulation (8–14 Hz, duration: 10 sec) of the ventroposterolateral thalamic nucleus brief hyperpolarization is succeeded by depolarization in the pyramidal neurons of the sensorimotor cortex. Following this depolarization, rhythmic (approximately 3 Hz) paroxysmal depolarizing shifts in membrane potential are produced by ending stimulation, succeeded by protracted hyperpolarization and termination of rhythmic wave activity. Depolarization only is observed in glial cells, however, while hyperpolarization sets in after hyperpolarization is completed in the neurons. It is suggested that long-term changes in the membrane potential of cortical cells could make some contribution to the setting up and termination of rhythmic spike and wave activity.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 319–325, May–June, 1986.     

Neuronal response in a strychninized cortical slab isolated from the cat

Intracellular response in neurons and glial cells of an isolated cortical slab to direct electrical stimulation of the slab following surface application of strychnine was investigated during experiments on immobilized unanesthetized cats. Strychnine induced single epileptiform discharges and after-discharges in the slab and in the neurons it contained in the form of large-scale paroxysmal depolarization shifts (PDS) in membrane potential (MP). Spontaneous summated epileptiform discharges and neuronal activity in the units examined were not very synchronized. Electrical stimulation induced generalized paroxysmal activity in the isolated slab. Neuronal PDS were accompanied by refractory periods, onset of which did not depend on MP level. Strychnine increased the number of neurons manifesting background activity in which action potentials were generated by rhythmic depolarizing MP waves of extrasynaptic origin. Epileptiform response in strychninized cortical isolated slabs to presentation of single stimuli is accompanied by major depolarization shifts in the MP of glial cells. Paroxysmal excitation is thought to be triggered in strychninized isolated cortical slabs by extrasynaptic factors and closely linked to altered concentration of extracellular potassium.I. I. Mechnikov University, Odessa. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 23–29, January–February, 1990.     

Protracted depolarizing potentials of neurons in a strychninized cortical slab isolated from the cat

Neuronal response in a cortical slab isolated from the cat during surface application of strychnine was investigated in experiments on immobilized unanesthetized animals by means of intracellular recording techniques. Protracted depolarizing potentials (PDP) were found to occur spontaneously and in response to a single intracortical electrical stimulus in a proportion of the neurons. These potentials could be triggered by transformation of response along the lines of "paroxysmal depolarizing shift" (PDS) — hyperpolarization, with hyperpolarization replaced by depolarizing potentials. A further increase in depolarizing after-potentials resulted in the generation of PDP. These changes were normally accompanied by enhanced summated epileptiform activity in the isolated cortical slab. It is postulated that PDP were triggered by increased calcium conductance at the neuronal membrane during intensification of paroxysmal response in the isolated cortical slab.I. I. Mechnikov University, Odessa. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 19–23, January–February, 1990.     

Unit activity in an epileptic focus formed in the cat motor cortex with tetanus toxin

Single unit activity was recorded intracellularly in the zone of an epileptic focus produced by injection of tetanus toxin into the cerebral cortex of cats. Epileptic activity of all neurons tested correlated with cortical discharges between fits. A group of neurons with continuous spontaneous activity, in which a steady fall of membrane potential and cyclic changes in the frequency of the spike discharges were observed was distinguished. In these neurons paroxysmal depolarization changes of membrane potential were found in the discharges between fits, without subsequent hyperpolarization of the membrane. Hyperpolarization potentials after paroxysmal depolarization shifts could be observed in neurons of other groups. The role of neurons of the different groups in the formation of an "epileptic aggregate," the main generator of pathologically enhanced excitation, is discussed.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Institute of Clinical and Experimental Neurology, Ministry of Health of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 582–589, November–December, 1978.     

Brain oscillations,medium spiny neurons,and dopamine

1. The striatum is part of a multisynaptic loop involved in translating higher order cognitive activity into action. The main striatal computational unit is the medium spiny neuron, which integrates inputs arriving from widely distributed cortical neurons and provides the sole striatal output.2. The membrane potential of medium spiny neurons' displays shifts between a very negative resting state (down state) and depolarizing plateaus (up states) which are driven by the excitatory cortical inputs.3. Because striatal spiny neurons fire action potentials only during the up state, these plateau depolarizations are perceived as enabling events that allow information processing through cerebral cortex – basal ganglia circuits. In vivo intracellular recording techniques allow to investigate simultaneously the subthreshold behavior of the medium spiny neuron membrane potential (which is a reading of distributed patterns of cortical activity) and medium spiny neuron firing (which is an index of striatal output).4. Recent studies combining intracellular recordings of striatal neurons with field potential recordings of the cerebral cortex illustrate how the analysis of the input–output transformations performed by medium spiny neurons may help to unveil some aspects of information processing in cerebral cortex – basal ganglia circuits, and to understand the origin of the clinical manifestations of Parkinson's disease and other neurologic and neuropsychiatric disorders that result from alterations in dopamine-dependent information processing in the cerebral cortex – basal ganglia circuits.     

Neuronal electrical activity in the epileptic focus produced by electrical stimulation in an isolated cortical slab

Characteristics of neuronal activity in an isolated cortical slab were investigated during the onset of seizure spikes induced by frequent and powerful stimulation of the slab during experiments on unanesthetized immobilized cats. A high degree of coordination between the activity of cellular elements was found in the focus of epileptiform activity studied: convulsive shifts in membrane potential exactly corresponding to electrocorticograms of convulsive activity waves were observed in all neurons studied using intracellular techniques. No action potentials occurred in the soma of any of these neurons, moreover. Bursting spike discharges were recorded from neurons of the isolated slab at the same time. Findings from extra- and intracellular recordings of activity in the same neurons showed that action potentials are generated during convulsive activity at certain trigger zones remote from the cell in question without involving the soma, from which convulsive shifts in membrane potentials were recorded simultaneously. Mechanisms possibly underlying the generation of spike activity in neurons of the isolated slab undergoing development of generalized convulsive state are discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 357–365, May–June, 1988.     

Spike generation by spinal neurons evoked by sinusoidal depolarization in cats

Dynamic characteristics of transformation of cell membrane depolarization by spinal neurons into spike discharge frequency were investigated in anesthetized cats. Neurons were activated by sinusoidally modulated currents passed through an intracellular microelectrode. Frequency analysis of this transformation for motoneurons was carried out within a modulation frequency range of 0.2–10 Hz. Frequency characteristics were determined with respect to parameters of the first harmonic of the evoked firing rate; the region of values of current fluctuations was chosen on the linear part of the current intensity versus firing rate characteristic curve. Changes in amplitude characteristics did not exceed 5 dB in absolute terms; at the same time the phase lead of the output signal increased with a rise of frequency. At a frequency of 0.2 Hz phase shifts were virtually absent, but at frequencies of 1, 5, and 10 Hz they amounted to 32, 50, and 83° on average respectively. Transformation of membrane depolarization by neurons into spike discharge frequency is characterized by essentially nonlinear properties, due in particular to the absence of a dynamic component of the response to a negative rate of change of depolarizing current. The frequency characteristics of spike activity of neurons of the motor system are discussed from the standpoint of possible correction of dynamic properties of the whole system at the single unit level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 35–42, January–February, 1982.     

Stimulation of the thalamus and its effect on electrographic manifestations of the brain in unrestrained rats.

The thalamus was electrically stimulated in unrestrained rats with implanted cortical and subcortical electrodes. Single pulses often triggered rhythmic cortical activity identical with the 8--9/sec spike episodes which occur spontaneously in rats in the walking state. In rhythmic stimulation of the thalamus, self-sustained 3/sec spike-wave paroxysmal activity, with partial clonic jerks, was observed. Specific and non-specific thalamic nuclei participated in the production of these activities.     

Postsynaptic components of paroxysmal neuronal response in the strychninized neocortex

Neuronal response in the strychninized cortical suprasylvian gyrus was investigated in experiments on immobilized and unanesthetized cats using intracellular techniques. Paroxysmal depolarizing shifts (PDS) in neuronal membrane potential were recorded, consisting of a bursting discharge and slow depolarization wave. It was found when using intracortical stimulation that PDS can accumulate and change in shape and size. Bursting discharges in PDS were induced by large-scale EPSP which could be distinguished from paroxysmal response. Data from presumably intradendritic readings demonstrated the presence of large-scale EPSP during the generation of epileptiform discharges in the cortex. In a proportion of cells, PDS were accompanied by hyperpolarizing potentials — apparently IPSP, since they undergo reversal with intercellular administration of Cl^–. The contribution of excitatory and inhibitory synaptic influences to paroxysmal neuronal response is discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiologiya, Vol. 22, No. 5, pp. 642–649, September–October, 1990.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 435–443, July–August, 1986.     

Effects of systemic injection of neuroleptics on neuronal background activity in the cat ventrolateral thalamic nucleus

Background activity was recorded in 272 neurons of the ventrolateral thalamic nucleus before and after systemic haloperidol and droperidol injection at a cataleptic dose using intracellular techniques during chronic experiments on cats in a drowsy condition. Brief burster discharges lasting 5–50 msec and following on at a high intraburst spike rate (of 200–450 Hz) were characteristic of neuronal activity in intact animals. Regular discharges occurred at the rate of 2–2.5 Hz or occasionally 3–4 Hz in 15% of cells. Numbers of neurons with the latter activity pattern rose to 22 and 30%, respectively, following haloperidol and droperidol injection. Both irregular and prolonged (80–300 msec) regular discharges were recorded in one third of the total. A relatively low intraburst spike rate (of 60–170 Hz) was observed in 37% of cells following 10 days' haloperidol injection. These changes are thought to be produced by intensified inhibitory effects on neurons of the thalamic ventrolateral nucleus from the substantia nigra and reticular thalamic nucleus following blockade of dopaminergic and -adrenergic receptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 675–685, September–October, 1989.     

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.     

Changes in membrane potential and postsynaptic potentials evoked by strychnine in neocortical neurons

Intracellular responses of neurons of the suprasylvian fissure to intracortical stimulation before and during topical cortical strychnine application was studied in experiments on immobilized, unanesthetized cats (a local anesthetic was used). Untreated cortical neurons responded to intracortical stimulation with a monosynaptic excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP). Application of strychnine evoked epileptiform population activity and paroxysmal depolarizations of neuronal membrane potentials (MPs), followed by hyperpolarization. Increased hyperpolarizations, and the prolonged duration of their summation were responsible for an increased MP and reduced or abolished tonic spike activity. Intracellular application (as a result of diffusion from the microelectrode) of ethyleneglycoltetraacetate (EGTA) that blocked the calcium-dependent potassium membrane conductance (gK(Ca)) abolished the hyperpolarization. The development of epileptiform activity was accompanied by reduction of the IPSP, and an increase in the monosynaptic EPSP. The role of gK(Ca) and postsynaptic inhibition in epileptogenesis is discussed.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 24, No. 6, pp. 684–691, November–December, 1992.     

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.     

Two patterns of bulbar neuronal response to microstimulation of locomotor and inhibitory brain stem sites

Synaptic responses (postsynaptic potentials and action potentials) were evoked in mesencephalic decerebellated cats by stimulating pontine bulbar locomotor and inhibitory sites (LS and IS, respectively) with a current of not more than 20 µA in "medial" and "lateral" neurons of the medulla. Some neurons even produced a response to presentation of single (actually low — 2–5 Hz — frequency) stimuli. The remaining cells responded to stimulation at a steady rate of 30–60 Hz only. Both groups of medial neurons were more receptive to input from LS. Lateral neurons responding to even single stimuli reacted more commonly to input from LS and those responding to steady stimulation only to input from IS. Many neurons with background activity (whether lateral or medial) produced no stimulus-bound response, but rhythmic stimulation either intensified or inhibited such activity. This response occurs most commonly with LS stimulation. Partial redistribution of target neurons in step with increasing rate of presynaptic input may play a major part in control of motor activity.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 257–266, March–April, 1990.     

Neuronal response in an epileptically excited isolated cortical slab to single electrical stimuli

Neuronal response to single stimuli was investigated in a cortical slab isolated from immobilized cats before, during, and after onset of induced epileptic states. Neurons of the isolated cortical slab were found to generate EPSP and paroxysmal depolarizing shifts (PDS) in membrane potential (MP) during the development of generalized epileptoid activity; these occurred together with refractory periods. Duration of the latter corresponds with the PDS plateau and repolarizing shifts in MP. Single electrical stimuli induced gradual alteration in PDS as these shifts developed. Neurons still maintain their ability to generate PDS arising in response to presentation of single stimuli once ictal activity has ceased. Postsynaptic response is not thought to play a decisive role in the genesis of epileptoid activity. Nonspecific factors and especially alterations in the concentration of electrogenic ions apparently contribute to this phenomenon.I. I. Mechnikov State University, Odessa. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 198–204, March–April, 1989.     

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.     

Spontaneous unit activity in anterior (limbic) nuclei of rabbit thalamus

Spontaneous spike activity in three anterior (limbic) neurons of the thalamic nucleus was studied by means of extracellular recording during chronic experiments on anesthetized rabbits. Neurons of the anteroventral nucleus showed high mean rate (24.8±5.8 spikes/sec) and varying structure of spike discharges ("inactivating" bursts of discharges, modulations in delta- and theta-rhythms, and bursts of discharges with a spindle rhythm of 12–14 Hz). "Inactivating" bursts of discharges alternating with single discharges predominated in the activity of neurons of the anteromedial nucleus (mean rate 10.0±1.4 spikes/sec). Activity of the anterodorsal nucleus could be clearly distinguished by the predominance of high-frequency groups of spikes (mean group frequency 67±5 spikes/sec) with prolonged intervals between groups.Institute of Biological Physics, Academy of Sciences of the USSR, Puschino, Moscow Province. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 579–586, September–October, 1985.