Characteristics of cortical responses to electrostimulation of the internal geniculate body during formation of a defensive conditioned reflex]

During elaboration of a classical defensive conditioned reflex the dogs exhibited a dependence of the changes in amplitude and configuration of evoked potentials (EP) to electrical stimulation of the medial geniculate body (MGB), a conditioned stimulus, on the nature of effector manifestation of the conditioned reflex: the late components were the most depressed at multiple phasic reactions and not infrequently increased and became complicated at single and short motor reactions as well as at their incidental absence. The primary oscillations, while mostly remaining unchanged, were depressed in the case of conditioned reactions attended with a general motor restlessness. A difference has been revealed during conditioning in the EP changes to electrical stimulation of MGB and to an adequate peripheral stimulation. It has been assumed that EP changes during conditioned activity are determined by the relationship between the levels of tonic and phasic cortical activation.     

Strychnine decreases the voltage-dependent Ca2+ current of bothAplysia and frog ganglion neurons

1. The effects of strychnine on the voltage-dependent Ca2+ current (ICa) were studied in physically isolated Aplysia neurons and enzymatically dissociated frog sensory neurons of the dorsal root ganglion. Neurons were studied under the internal perfusion and the voltage clamp condition. 2. Strychnine decreased the ICa with threshold concentrations for effect at 1 to 10 microM. The depression of ICa increased with strychnine dose without effects on the current-voltage relation of ICa. The effects of low concentrations of strychnine were reversible, but recovery was incomplete at higher concentrations. The potency of strychnine was about 10 times less than that of diltiazem, an organic Ca2+ antagonist. At 100 microM the ICa of Aplysia neurons was reduced to about half of the control. This concentration of strychnine also reduced the peak amplitude of ICa of frog sensory neurons. 3. These results indicate that, in addition to its actions on transmitter responses and on Na+ and K+ currents, strychnine has effects on ICa that have not previously been appreciated.     

The mescaline or strychnine spikes as a tool for physiological and pharmacological studies

The all-or-nothing spikes elicited by antidromic, afferent, or direct electrical stimulation of a cortical area treated with mescaline or strychnine were studied. These potentials are most probably originated in nonsynaptic dentritic membranes and their changes in amplitude and latency can be an index of the excitability of these structures. Several factors are considered as sources of error when measurements of such parameters are made to follow their changes in different experimental conditions. When these sources of error can be eliminated, the frequency, amplitude and latency of those spikes can be taken as an index of the variations in cortical excitability under some physiological conditions. Another use of these giant potentials can be for the study of humoral and pharmacological agents.     

Analysis of evoked potentials of the cerebellar cortex

Evoked potentials (EP) of the cerebellar cortex in response to stimulation of peripheral nerves are characterized by a two-phase positive-negative oscillation of the potential having a latent period of 10–25 msec. The electropositive phase can contain up to three components. The latent period of component I comprises 3–9 msec. The latent period and amplitude of this component are distinguished by considerable stability, which indicates the predominant significance of presynaptic processes in its formation. The sign of component II changes at a depth of 500 µ (and more), which corresponds to the position of the granular cell layer. At this level there arises in the neurons a response with a latent period of 4–10 msec in the form of a group (3–10) of impulses with a frequency of up to 200 per sec. It is concluded that the granular cells participate in the formation of component II and partially participate in the formation of components I and III of the EP. Responses to stimulation of the nerves appear synchronously with the EP in 24% of responding Purkinje cells; they fall on the maximum electropositive deviation or component III of the EP. Microinjections of 1% strychnine into the cerebellar cortex cause an increase of EP amplitude; impulse activity of the neurons is intensified. This indicates participation of postsynaptic processes in the formation of EP. No shifts in the EP of the cerebellar cortex were observed after intracortical injection of 0.1% atropine.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 429–433, July–August, 1970.     

Effect of transection of afferent pathways on evoked potentials,theta rhythm,and neuronal activity in the hippocampus

The effect of destruction of septo-hippocampal and subiculo-hippocampal connections on the electrical activity in the hippocampus was studied in tubocurarized rabbits. The theta rhythm and the so-called "intracellular theta rhythm" [7] were found to disappear on destruction of the septo-hippocampal connections, other consequences being the loss of neuronal capacity for responding to sciatic nerve stimulation, loss of neuronal inhibitory responses, and total or partial suppression of the negative phase of the evoked potential (EP). Destruction of subiculo-hippocampal connections entails a decrease in amplitude of the theta rhythm recorded from the hippocampal surface, retention of the "intracellular theta rhythm," and a slight decrease in amplitude of both EP phases. The number of neurons failing to respond to sciatic stimulation is increased; the character of cellular response remains unchanged. It is hypothesized that hyperpolarization of hippocampal pyramidal neurons may be responsible for generating the negative phase of the EP, and that this phase and the hippocampal theta rhythm may be of a common origin.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 439–444, July–August, 1970.     

Correlation of subjective assessments with somatosensory evoked potentials to electrical stimulation of the finger in man

The relationship between 5 positive components of somatosensory evoked potentials (EPs) and subjective response to electrical stimuli, which were recorded in the same human subjects, was assessed in the present study. Five levels of tactile stimuli and 6 levels of noxious stimuli were applied to the tip of the right index finger. The relationship between the magnitude of subjective response and stimulus intensity was well expressed by a power function. Of 5 major positive components in an EP, P30 and P50 were localized at contralateral primary somatic projection area, while P90, P190 and P270 were at the vertex area. The amplitude of the 5 components systematically increased as increasing stimulus intensity, and also increased with the magnitude of subjective response. A significant correlation between the amplitude of P30 or P50 and stimulus intensity was found when the effect of subjective response was partially out. By contrast, the amplitudes of P190 and P270 were associated with subjective response when the effect of stimulus intensity was partially out. These results suggest that the earlier EP components reflect sensory signal processing, while the latter ones concern the subjective evaluating system.     

Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp

Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.     

Effect of local surface cooling of the rat cortex on the impulse activity of neurons assumed to be the sources of corticofugal influences

In an experiment on albino rats with electrodermal stimulation of the forepaw evoked potentials (EP) in the neostriatum (NS), the cortical primary response (PR), and impulse reactions of neurons (mainly of layers V and VI of the cortex) were recorded. The zone of leading-off of the potentials in the cortex was subjected to local surface cooling, which led to an increase in the PR amplitude. This facilitation was accompanied by a change in the time parameters of the impulse reactions of the cortical neurons: the latency and duration increased, and a rhythmic organization of activity appeared or intensified (if it was already present). The increase in the PR amplitude and number of spikes in the response of the cortical neurons to stimulus presentation was far less intensive than the sharp increase in EP amplitude in the NS, and did not correspond to it fully in time. The data suggest that the activating influence of the corticofugal signal on EP in the NS is determined not so much by the intensity of the descending signal as by its temporal organization.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 181–189, March–April, 1991.     

Evoked potentials in the reticular formation of the rabbit midbrain during formation of a dominant focus in it

During creation of a dominant focus in the midbrain reticular formation (RF) by its multiple stimulation with a high-frequency current (stimulation frequency 200 Hz, pulse duration 0.1-0.5 ms, voltage 1-3 V, duration 5 s) a statistically significant increase of the amplitude of the evoked potential (EP) in RF to light flashes was revealed in comparison with background data. Significant increase of EP amplitude was also observed in RF in response to the same stimuli applied in successive experiments without RF stimulation, which pointed to the existence of a latent dominant focus in the CNS.     

Synaptic Integration in Electrically Coupled Neurons

Interactions among chemical and electrical synapses regulate the patterns of electrical activity of vertebrate and invertebrate neurons. In this investigation we studied how electrical coupling influences the integration of excitatory postsynaptic potentials (EPSPs). Pairs of Retzius neurons of the leech are coupled by a nonrectifying electrical synapse by which chemically induced synaptic currents flow from one neuron to the other. Results from electrophysiology and modeling suggest that chemical synaptic inputs are located on the coupled neurites, at 7.5 μm from the electrical synapses. We also showed that the space constant of the coupled neurites was 100 μm, approximately twice their length, allowing the efficient spread of synaptic currents all along both coupled neurites. Based on this cytoarchitecture, our main finding was that the degree of electrical coupling modulates the amplitude of EPSPs in the driving neurite by regulating the leak of synaptic current to the coupled neurite, so that the amplitude of EPSPs in the driving neurite was proportional to the value of the coupling resistance. In contrast, synaptic currents arriving at the coupled neurite through the electrical synapse produced EPSPs of constant amplitude. This was because the coupling resistance value had inverse effects on the amount of current arriving and on the impedance of the neurite. We propose that by modulating the amplitude of EPSPs, electrical synapses could regulate the firing frequency of neurons.     

An analysis of the relationship between the current and potential generated by a quantum of acetylcholine in muscle fibers without transverse tubules

Summary Miniature end plate potentials (MEPPs) were recorded in glyceroltreated muscle fibers with four microelectrodes which were used to determine the passive electrical characteristics of the same fibers. Voltage responses which were computed from miniature end plate currents (MEPCs) and the passive cable properties of a fiber, agreed very closely with experimentally recorded MEPPs confirming the hypothesis that MEPPs spread passively along a muscle fiber. The model was used to analyze the effect of variations in synaptic current and the properties of a muscle fiber on the postsynaptic response. The decrement of MEPPs was exponential for distances up to 1 to 2 mm from an origin but then deviated from the initial exponential. Variations in the growth time of the input current up to 1 msec had little effect on computed MEPPs whereas an increase in the decay time constant caused a significant increase in MEPP amplitude and effective space constant. An increase in the internal resistivity of a muscle fiber increased MEPP amplitude at the origin but decreased the effective space constant. The amplitude of MEPPs was inversely proportional to the 1.5 power of the diameter of a muscle fiber, and the MEPP space constant increased as the square root of the diameter. The amplitude of MEPPs is not necessarily determined by the input resistance of the muscle fiber. Changes in input resistance caused by changes in membrane resistance would have little effect on te amplitude or decrement of MEPPs.     

Correlation between electrical activity and ACTH/beta-endorphin secretion in mouse pituitary tumor cells

The electrical and secretory activities of mouse pituitary tumor cells (AtT-20/D-16v), which contain and release the ACTH/beta-endorphin family of peptides, were studied by means of intracellular recordings and radioimmunoassays. Injection of depolarizing current pulses evoked action potentials in all cells and the majority (82%) displayed spontaneous action potential activity. Action potentials were found to be calcium-dependent. Barium increased membrane resistance, action potential amplitude and duration, and release of ACTH and beta- endorphin immunoactivity. Isoproterenol increased both action potential frequency and hormone secretion. Raising the external calcium concentration increased the frequency and amplitude of the action potentials and stimulated secretion of ACTH and beta-endorphin immunoactivity. Thus, stimulation of secretory activity in AtT-20 cells was closely correlated with increased electrical activity. However, a complete blockade of action potential activity had no effect on basal hormone secretion in these cells. These results suggest that the mechanisms underlying stimulated hormone secretion are different from those responsible for basal secretory activity. It is proposed that the increased influx of calcium due to the increased action potential frequency initiates the stimulated release of hormone from these cells.     

Action of an enkephalinase blocker on the effect of acupuncture in acupuncture sensitive and resistant rabbits]

In unanaesthetized acupuncture-sensitive rabbit d-phenylalanine injection didn't change the EP in response to tooth pulp electrostimulation, but prolonged the analgetic effect of auriculo-acupuncture stimulation 15 Hz expressed by decreasing of the amplitude of N1P2 component EP. In acupuncture-resistant rabbit d-phenylalanine injection induced analgetic effect which was enhanced and prolonged by auriculo-acupuncture stimulation. It's suggested that the recovery of pain sensibility after acupuncture analgesia is determined by enkephalinase's mechanism activation which is activated permanently in acupuncture-resistant rabbits.     

Changes in somatosensory evoked potentials in patients with vertebrogenic pain syndromes treated by electroacupuncture

Application of electroacupuncture (EAP) of the segmental points to patients with vertebrogenic algesic syndromes decreased amplitude of N150 and P240 waves recorded from vertex to painful electrocutaneous stimulation in the region innervated by an affected root. As distinct from EAP of segmental point auricular EAP not only decreased the amplitude of late components of evoked potentials (EP), but also increased it, direction of EP changes depending on the character of sensitivity disorders. It is suggested that effect of EAP-evoked EP changes in patients with hypalgesia is determined by two oppositively acting factors: by a decrease of nociceptive afferent impulsation intensity as a result of the antinociceptive system activation and by an increase of the afferent impulsation intensity due to recovery of function of central terminals in primary sensory neurons.     

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.     

Formation of epileptic activity complexes in the cerebral cortex as a result of a determinant focus induced by acetylcholine]

Foci of increased excitability were created by means of weak strychnine and penicillin dilutions in experiments on cats. These foci worked at individual regimens. Creation with acetylcholine and proserine of a hyperactive focus led to increase of the amplitude and frequency of convulsive discharges at first in the nearest activity foci, and then in the ones remote from the hyperactive focus. The next stage was attended by qualitative changes in the activity pattern of strychnine and penicillin foci (the appearance of acetylcholine activity in them) and by the formation of a single functional focal complex working in the regimen of acetylcholine focus. Thus, the latter played the role of a determinant structure. Suppression of the determinant focus activity led to disappearance of the acetylcholine activity in all the other foci, restoration of the initial (penicillin and strychnine) activity, and to the epileptic complex decay.     

Dynamical mechanisms of pacemaker generation in IK1-downregulated human ventricular myocytes: insights from bifurcation analyses of a mathematical model

Dynamical mechanisms of the biological pacemaker (BP) generation in human ventricular myocytes were investigated by bifurcation analyses of a mathematical model. Equilibrium points (EPs), periodic orbits, stability of EPs, and bifurcation points were determined as functions of bifurcation parameters, such as the maximum conductance of inward-rectifier K+ current (I(K1)), for constructing bifurcation diagrams. Stable limit cycles (BP activity) abruptly appeared around an unstable EP via a saddle-node bifurcation when I(K1) was suppressed by 84.6%. After the bifurcation at which a stable EP disappears, the I(K1)-reduced system has an unstable EP only, which is essentially important for stable pacemaking. To elucidate how individual sarcolemmal currents contribute to EP instability and BP generation, we further explored the bifurcation structures of the system during changes in L-type Ca2+ channel current (I(Ca,L)), delayed-rectifier K+ currents (I(K)), or Na(+)/Ca2+ exchanger current (I(NaCa)). Our results suggest that 1), I(Ca,L) is, but I(K) or I(NaCa) is not, responsible for EP instability as a requisite to stable BP generation; 2), I(K) is indispensable for robust pacemaking with large amplitude, high upstroke velocity, and stable frequency; and 3), I(NaCa) is the dominant pacemaker current but is not necessarily required for the generation of spontaneous oscillations.     

Sulfhydryl Groups Modulate the Allosteric Interaction Between Glycine Binding Sites at the Inhibitory Glycine Receptor

We have investigated the effect of chemical reagents that modify sulfhydryl groups on the ligand binding properties of the glycine receptor (GlyR). The Hill coefficient (nH) for the displacement of [3H]strychnine binding by glycine was increased from approximately 0.8 to values significantly above 1 (approximately 1.2-1.4) in membranes pretreated with the disulfide-reducing agent dithiothreitol or glutathione. However, the affinity of strychnine or glycine for the GlyR was not affected by these treatments. This indicates that several glycine binding sites interact cooperatively for displacing bound strychnine under such experimental circumstances. A similar increase in the nH for glycine has been observed when the temperature of the binding assay was increased to 37 degrees C. Combination of dithiothreitol pretreatment and increased binding temperature led to nH variations similar to those observed with either of these treatments alone, a finding suggesting that their mechanisms of action are not independent. Conversely, modification of rat spinal cord membranes or of purified and reconstituted GlyR preparations with the sulfhydryl-alkylating agent N-ethylmaleimide or fluorescein-maleimide decreased nH values to approximately 0.5, without affecting glycine or strychnine affinities. This effect may be caused by an increased heterogeneity of GlyR populations. It is interesting that occupancy of the receptor by glycine or beta-alanine (but not by antagonists) specifically protects from the effects of the different sulfhydryl reagents. Moreover, the presence of some of the Eccles' anions, i.e., anions that permeate through the channels associated with GlyRs and gamma-aminobutyric acidA receptors, seems to be required for the action of both dithiothreitol and N-ethylmaleimide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of tetraethylammonium and 4-aminopyridine on the plateau potential of circular myometrium from the pregnant rat

In the pregnant rat, spontaneous electrical activity of circular muscle (CM) changes from single, plateau-type action potentials at early and mid-term to repetitive spike trains at term. To examine mechanisms underlying the plateau, we studied the effects of potassium channel blockers tetraethylammonium (TEA) and 4-aminopyridine (4-AP) on membrane potentials in CM from rats on gestation Days 14, 15, 16, 21 (term). Apparent membrane conductance was measured at rest and during the plateau in Day 14 muscles with and without TEA. 4-AP depolarized the resting membrane on all gestation days. Therefore, a direct action of 4-AP on plateau configuration could not be separated from an indirect effect of depolarization. TEA did not affect the resting potential but increased action potential size and depolarization rate on all gestation days. On Day 16, TEA reduced plateau amplitude, unmasking small, repetitive depolarizations. D-600 decreased plateau amplitude and duration and attenuated these effects of TEA. Plateau conductance increased initially then decreased before membrane repolarization. Membrane conductance and outward rectification during the plateau were reduced by TEA. The plateau potential may result from an outwardly rectifying TEA-sensitive current combined with a slow inward current, the plateau magnitude being determined by the relative intensity of each current.