Central Synaptic Integration: Linear After All?

Physiology ◽  
2002 ◽  
Vol 17 (4) ◽  
pp. 138-143
Author(s):  
C. Stricker
Keyword(s):  
Experimental Evidence ◽  
Time Course ◽  
Synaptic Integration ◽  
Synaptic Currents ◽  
Unitary Events

Unitary synaptic currents in hippocampus show small variability. Experimental evidence suggests that the neuron is endowed with mechanisms to reduce location-dependent differences in amplitude and time course of synaptic events, contributing to small variability. These mechanisms may allow the neuron to count individual quanta and thereby linearize integration of unitary events.

NMDA-Dependent Currents in Granule Cells of the Dentate Gyrus Contribute to Induction but Not Permanence of Kindling

1999 ◽  
Vol 81 (2) ◽  
pp. 564-574 ◽  
Author(s):  
Ümit Sayin ◽  
Paul Rutecki ◽  
Thomas Sutula
Keyword(s):  
Nmda Receptor ◽  
Dentate Gyrus ◽  
Time Course ◽  
Granule Cells ◽  
Receptor Activation ◽  
Perforant Path ◽  
Synaptic Current ◽  
Synaptic Currents ◽  
Class V ◽  
Dependent Component

NMDA-dependent currents in granule cells of the dentate gyrus contribute to induction but not permanence of kindling. Single-electrode voltage-clamp techniques and bath application of the N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovaleric acid (APV) were used to study the time course of seizure-induced alterations in NMDA-dependent synaptic currents in granule cells of the dentate gyrus in hippocampal slices from kindled and normal rats. In agreement with previous studies, granule cells from kindled rats examined within 1 wk after the last of 3 or 30–35 generalized tonic-clonic (class V) seizures demonstrated an increase in the NMDA receptor–dependent component of the perforant path–evoked synaptic current. Within 1 wk of the last kindled seizure, NMDA-dependent charge transfer underlying the perforant path–evoked current was increased by 63–111% at a holding potential of −30 mV. In contrast, the NMDA-dependent component of the perforant-evoked current in granule cells examined at 2.5–3 mo after the last of 3 or 90–120 class V seizures did not differ from age-matched controls. Because the seizure-induced increases in NMDA-dependent synaptic currents declined toward control values during a time course of 2.5–3 mo, increases in NMDA-dependent synaptic transmission cannot account for the permanent susceptibility to evoked and spontaneous seizures induced by kindling. The increase in NMDA receptor–dependent transmission was associated with the induction of kindling but was not responsible for the maintenance of the kindled state. The time course of alterations in NMDA-dependent synaptic current and the dependence of the progression of kindling and kindling-induced mossy fiber sprouting on repeated NMDA receptor activation are consistent with the possibility that the NMDA receptor is part of a transmembrane signaling pathway that induces long-term cellular alterations and circuit remodeling in response to repeated seizures, but is not required for permanent seizure susceptibility in circuitry altered by kindling.

Encoding of Visual Information by LGN Bursts

1999 ◽  
Vol 81 (5) ◽  
pp. 2558-2569 ◽  
Author(s):  
Pamela Reinagel ◽  
Dwayne Godwin ◽  
S. Murray Sherman ◽  
Christof Koch
Keyword(s):  
Action Potential ◽  
Visual Information ◽  
Neural Coding ◽  
Time Course ◽  
Visual Stimuli ◽  
Reconstruction Method ◽  
Stimulus Information ◽  
Coding Efficiency ◽  
Response Modes ◽  
Unitary Events

Encoding of visual information by LGN bursts. Thalamic relay cells respond to visual stimuli either in burst mode, as a result of activation of a low-threshold Ca2+ conductance, or in tonic mode, when this conductance is inactive. We investigated the role of these two response modes for the encoding of the time course of dynamic visual stimuli, based on extracellular recordings of 35 relay cells from the lateral geniculate nucleus of anesthetized cats. We presented a spatially optimized visual stimulus whose contrast fluctuated randomly in time with frequencies of up to 32 Hz. We estimated the visual information in the neural responses using a linear stimulus reconstruction method. Both burst and tonic spikes carried information about stimulus contrast, exceeding one bit per action potential for the highest variance stimuli. The “meaning” of an action potential, i.e., the optimal estimate of the stimulus at times preceding a spike, was similar for burst and tonic spikes. In within-trial comparisons, tonic spikes carried about twice as much information per action potential as bursts, but bursts as unitary events encoded about three times more information per event than tonic spikes. The coding efficiency of a neuron for a particular stimulus is defined as the fraction of the neural coding capacity that carries stimulus information. Based on a lower bound estimate of coding efficiency, bursts had ∼1.5-fold higher efficiency than tonic spikes, or 3-fold if bursts were considered unitary events. Our main conclusion is that both bursts and tonic spikes encode stimulus information efficiently, which rules out the hypothesis that bursts are nonvisual responses.

scholarly journals An acetylcholine receptor lacking both γ and ε subunits mediates transmission in zebrafish slow muscle synapses

2011 ◽  
Vol 138 (3) ◽  
pp. 353-366 ◽  
Author(s):  
Rebecca Mongeon ◽  
Michael Walogorsky ◽  
Jason Urban ◽  
Gail Mandel ◽  
Fumihito Ono ◽  
...  
Keyword(s):  
Acetylcholine Receptor ◽  
Time Course ◽  
Single Channel ◽  
Slow Muscle ◽  
Synaptic Function ◽  
Fast Muscle ◽  
Xenopus Laevis Oocytes ◽  
Synaptic Currents ◽  
Functional Features ◽  
Single Channel Currents

Fast and slow skeletal muscle types in larval zebrafish can be distinguished by a fivefold difference in the time course of their synaptic decay. Single-channel recordings indicate that this difference is conferred through kinetically distinct nicotinic acetylcholine receptor (AChR) isoforms. The underlying basis for this distinction was explored by cloning zebrafish muscle AChR subunit cDNAs and expressing them in Xenopus laevis oocytes. Measurements of single-channel conductance and mean open burst duration assigned α2βδε to fast muscle synaptic current. Contrary to expectations, receptors composed of only αβδ subunits (presumed to be α2βδ2 receptors) recapitulated the kinetics and conductance of slow muscle single-channel currents. Additional evidence in support of γ/ε-less receptors as mediators of slow muscle synapses was reflected in the inward current rectification of heterologously expressed α2βδ2 receptors, a property normally associated with neuronal-type nicotinic receptors. Similar rectification was reflected in both single-channel and synaptic currents in slow muscle, distinguishing them from fast muscle. The final evidence for α2βδ2 receptors in slow muscle was provided by our ability to convert fast muscle synaptic currents to those of slow muscle by knocking down ε subunit expression in vivo. Thus, for the first time, muscle synaptic function can be ascribed to a receptor isoform that is composed of only three different subunits. The unique functional features offered by the α2βδ2 receptor likely play a central role in mediating the persistent contractions characteristic to this muscle type.

Channel kinetics determine the time course of NMDA receptor-mediated synaptic currents

Nature ◽  
1990 ◽  
Vol 346 (6284) ◽  
pp. 565-567 ◽  
Author(s):  
Robin A. J. Lester ◽  
John D. Clements ◽  
Gary L. Westbrook ◽  
Craig E. Jahr
Keyword(s):  
Nmda Receptor ◽  
Time Course ◽  
Channel Kinetics ◽  
Synaptic Currents

The time course of NMDA receptor-mediated synaptic currents

1995 ◽  
pp. 206-218 ◽  
Author(s):  
ROBIN A. J. LESTER ◽  
JOHN D. CLEMENTS ◽  
GANG TONG ◽  
GARY L. WESTBROOK ◽  
CRAIG E. JAHR
Keyword(s):  
Nmda Receptor ◽  
Time Course ◽  
Synaptic Currents

scholarly journals Comparison of excitatory currents activated by different transmitters on crustacean muscle. I. Acetylcholine-activated channels.

1983 ◽  
Vol 81 (4) ◽  
pp. 547-569 ◽  
Author(s):  
C Lingle ◽  
A Auerbach
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Voltage Dependence ◽  
Single Channel ◽  
Noise Analysis ◽  
Synaptic Currents ◽  
Cancer Borealis ◽  
Open Time ◽  
Conductance Increase ◽  
Channel Open Time

The properties of acetylcholine-activated excitatory currents on the gm1 muscle of three marine decapod crustaceans, the spiny lobsters Panulirus argus and interruptus, and the crab Cancer borealis, were examined using either noise analysis, analysis of synaptic current decays, or analysis of the voltage dependence of ionophoretically activated cholinergic conductance increases. The apparent mean channel open time (tau n) obtained from noise analysis at -80 mV and 12 degrees C was approximately 13 ms; tau n was prolonged e-fold for about every 100-mV hyperpolarization in membrane potential; tau n was prolonged e-fold for every 10 degrees C decrease in temperature. Gamma, the single-channel conductance, at 12 degrees C was approximately 18 pS and was not affected by voltage; gamma was increased approximately 2.5-fold for every 10 degrees C increase in temperature. Synaptic currents decayed with a single exponential time course, and at -80 mV and 12 degrees C, the time constant of decay of synaptic currents, tau ejc, was approximately 14-15 ms and was prolonged e-fold about every 140-mV hyperpolarization; tau ejc was prolonged about e-fold for every 10 degrees C decrease in temperature. The voltage dependence of the amplitude of steady-state cholinergic currents suggests that the total conductance increase produced by cholinergic agonists is increased with hyperpolarization. Compared with glutamate channels found on similar decapod muscles (see the following article), the acetylcholine channels stay open longer, conduct ions more slowly, and are more sensitive to changes in the membrane potential.

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