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Y Yarom

Publications and source records attributed to Y Yarom.

63 records · Page 4Linked to original sources
PubMed1981

Properties and distribution of ionic conductances generating electroresponsiveness of mammalian inferior olivary neurones in vitro.

The electrophysiological properties of the high- and low-threshold Ca spikes described in inferior olivary neurones were analysed in detail. 1. During hyperpolarization the low- and high-threshold Ca action potentials can coexist as two distinct spikes, demonstrating non-mutual exclusion. 2. The high-threshold Ca spike shows a lack of refractoriness, is generated remotely from the site of recording and is composed of several all-or-none components, the last two properties suggesting a dendritic origin. 3. Hyperpolarization of the neurones allows the activation of the low-threshold Ca spike, which has activation properties resembling those of the early K conductance described in invertebrates. This low-threshold Ca spike shows refractoriness. 4. The relation between membrane polarization and low-threshold Ca spike is S-shaped. Low-threshold Ca spikes become apparent at -70 mV and have a maximum rate of rise (saturation) at polarization levels more negative than -85 mV. Thus, hyperpolarization removes a voltage-dependent Ca inactivation which is present at normal resting membrane potential (-65 mV). 5. Replacement of extracellular Ca by Ba or addition of tetraethylammonium to the bath corroborates the lack of fast inactivation for the high-threshold Ca spike and the inactivation properties of the low-threshold Ca conductance. It also demonstrates that the duration of the after-depolarization is determined by an interplay between inward Ca current and both voltage-dependent and Ca-dependent K currents. 6. Extracellular recordings from single cells indicate that the Na-dependent spike and the low-threshold Ca action potential are somatic in origin, while the high-threshold Ca spike (after-depolarization) and the hyperpolarization that follows are apparently located in the dendrites. 7. The ionic conductances comprise the main components of the oscillatory behaviour of these cells. The sequence of events leading to oscillation entails initially a low-threshold Ca spike or Na spike, followed by an after-depolarization/after-hyperpolarization sequence and then a post-anodal exaltation product by a rebound low-threshold Ca spike.

Action Potentials↗
PubMed1981

Isolated mammalian brain in vitro: new technique for analysis of electrical activity of neuronal circuit function.

A new technique is described that allows neurobiological research in mammalian brain in vitro. The approach utilizes the vascular system to irrigate portions of the brain-in this case the brain stem and cerebellum "en block." The preparation, which can survive for about 10 hours, demonstrates normal field potentials following stimulation of either the surface or the underlying white matter at both cerebellar and brain stem levels. Intracellular studies at both these levels indicate cellular activity in every way similar to the in vivo or the slice preparation from the same regions. This new technique offers potential for the study of ionic mechanisms underlying electrical activity as well as neurochemistry, neuroanatomy, neuropharmacology, and neuroendocrinology.

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PubMed1976

Modulation of spike frequency by regions of special axonal geometry and by synaptic inputs.

1. Spike propagation across the nonhomogeneous section of the giant axon in ganglion T3 of the cockroach was analyzed by intracellular microelectrodes recording at the posterior and anterior ends of T3. Ascending and descending potentials were evoked by stimulation of A5-A6 and T2-T3 connectives. 2. At high frequencies, descending and ascending impulses exhibit the following: a) consecutive reduction in the spike amplitude, b) a decrease in the afterhyperpolarization; c) gradual appearance of a prepotential together with an increase in delay of spike initiation; d) failure of full spike invasion into the recording area, showing only a decremental potential. 3. The duration of a train required to block spike propagation when the whole connective is stimulated is much shorter (about 6 times) than that required when a single giant axon is stimulated. 4. The conduction block is associated with a marked decrease in effective membrane resistance, greater than that expected from depolarization and delayed rectification. 5. Synaptic potentials could be recorded in the giant axons in the caudal base of ganglion T3 after stimulation of either the ipsilateral or contralateral connectives at both ends of the ganglion. These synaptic potentials could be blocked by d-tubocurarine (d-TC) or low Ca2+-high Mg2+. 6. Activation of these synapses produces a marked increase in membrane conductance, blocking propagation of spike trains through the ganglion. 7. After these synapses are blocked by d-TC or low Ca2+-high Mg2+, high-frequency stimulation still produces a conduction block. 8. It seems that conduction of spike during repetitive stimulation is affected both by accumulation of extracellular potassium, which depolarizes the membrane and causes sodium inactivation, and by activation of synaptic inputs to shunt the membrane in this region. 8. Each of these two mechanisms by itself can produce conduction block along the giant axons in ganglion T3.

Action Potentials↗
PubMed1976

Ultrastructure of region of a low safety factor in inhomogeneous giant axon of the cockroach.

1. The structure of the ventral giant axons of the cockroach at the level of ganglion T3 was studied by means of light and electron microscopy. 2. From serial sections and cobalt injections, the axons diameter was found to range between 40 and 60 mum at the caudal end of ganglion T3; toward the center of T3 they narrow to 20-40 mum, and again expand to 30-45 mum anteriorly in ganglion T3. 3. Each giant axon sends off several branches, 1-15 mum in diameter, into the neuropil. The giant axons and the bases of their branches are enveloped by cytoplasmic processes of glial cells. The periaxonal space is about 100-200 A. 4. Distally the branches are devoid of glial envelopes and the extracellular space between the branches and other axonal profiles is about 200 A. Terminals with presumptive chemical synapses on the giant axon branches were found. Clear vesicles, 300-400 A in diameter, are seen clustered together. The width of the supposedly synaptic gap is about 100 A. 5. In some areas the branches and other axonal profiles form close appositions.

Animals↗
PubMedDate not supplied

To beat or not to beat: a decision taken at the network level.

The cells of the inferior olivary nucleus, the sole source of the cerebellar climbing fibers, form a network of electrically coupled neurons. Experimental observations show that these neurons produce a large repertoire of electrical signals, among which sub-threshold oscillations of the membrane potential. Simultaneous recordings from pairs of neurons and optical imaging of voltage sensitive dyes show that sub-threshold activity occurs in synchrony throughout the network. The mechanism underlying the generation of the sub-threshold oscillations is not fully understood. Experimental observations suggest that the electrical coupling is essential but insufficient for their generation. Several theoretical mechanisms have been suggested to explain these observations. Up-to-date, the most realistic model is the heterogeneity model, that assumes a certain degree of heterogeneity among olivary neurons. The heterogeneity model proposes that sub-threshold oscillations are produced by electrical coupling of neurons with the same types of ionic conductances, but with different densities. The variability in channel densities yield neurons of different functional types. The main prediction of the model is that different functional types of neurons should be found in the inferior olive. Dynamic clamp experiments support this prediction.

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PubMedDate not supplied

Immunospecific inhibition of nerve conduction by T lymphocytes reactive to basic protein of myelin.

Experimental autoimmune encephalomyelitis (EAE) induced by immunization to the basic protein of central nervous system myelin (BP) is a paralytic disease in which T lymphocytes attack the individual's own central nervous system. As the target is in white matter, EAE has been considered an experimental model of some aspects of human disease such as multiple sclerosis. To investigate whether autoimmune T lymphocytes could produce paralysis, we studied the effects on the electrophysiology of isolated nerves produced by T-lymphocyte lines reactive specifically to BP or other antigens. We now report that propagation of action potentials evoked by electrical stimulation was blocked by incubating optic nerves with specific anti-BP T cells. This blockade could be reversed for up to two hours by removing the anti-BP line cells from the optic nerve. The anti-BP line cells had no effect on conduction along allogeneic optic nerves or syngeneic peripheral nerves. This indicates that disruption of the function of myelin in neuroimmunological disease may result from an immunologically specific interaction between autoimmune T lymphocytes and myelin antigens.

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PubMedDate not supplied

Physiological synaptic interactions mediated by potassium ions.

We present experiments indicating that specific and efficient interactions among neurons can be mediated by the increase in extracellular potassium ion concentration as a consequence of a single action potential in one neuron. Intracellular recording and stimulation from adjacent giant interneurons (GIN) of the cockroach Periplaneta americana reveals reciprocal synaptic interactions at the level of the metathoracic ganglion (T3). The reciprocal synaptic interaction (GGSP) is characterized by: a short synaptic delay (1 ms), fast rise time (1-1.5 ms), an amplitude of 5-8 mV and a long decay time (60-100 ms). The GGSP is not blocked by the addition of 5 mM cobalt ions and is insensitive to trans membrane voltage. The possibility that the GGSP is mediated by an electrotonic synapse was ruled out by experiments which showed that no direct current spread takes place between adjacent giant axons. Intracellular injection of TEA caused prolongation of the action potential of the injected fiber. The rate of rise and amplitude of the GGSP in the second fiber was significantly reduced. These results are consistent with the interpretation that the GGSP is mediated by the accumulation of potassium ions in the extracellular space. Serial cross sections for electron microscope reveal that the plasma membrane of adjacent GINS comes into close proximity (7-10 nm). These regions may serve as the site for the potassium mediated interactions.

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