scholarly journals A T-type Ca2+ current underlies low-threshold Ca2+ potentials in cells of the cat and rat lateral geniculate nucleus.

1989 ◽  
Vol 413 (1) ◽  
pp. 543-561 ◽  
Author(s):  
V Crunelli ◽  
S Lightowler ◽  
C E Pollard
Keyword(s):  
Lateral Geniculate Nucleus ◽  
Lateral Geniculate ◽  
Low Threshold ◽  
In Cells

Current Clamp and Modeling Studies of Low-Threshold Calcium Spikes in Cells of the Cat’s Lateral Geniculate Nucleus

1999 ◽  
Vol 81 (5) ◽  
pp. 2360-2373 ◽  
Author(s):  
X. J. Zhan ◽  
C. L. Cox ◽  
J. Rinzel ◽  
S. Murray Sherman
Keyword(s):  
Membrane Potential ◽  
Lateral Geniculate Nucleus ◽  
Current Clamp ◽  
Calcium Spikes ◽  
Modeling Studies ◽  
Lateral Geniculate ◽  
Voltage Dependent ◽  
Low Threshold ◽  
Variable Latency ◽  
In Cells

Current clamp and modeling studies of low-threshold calcium spikes in cells of the cat’s lateral geniculate nucleus. All thalamic relay cells display a voltage-dependent low-threshold Ca2+ spike that plays an important role in relay of information to cortex. We investigated activation properties of this spike in relay cells of the cat’s lateral geniculate nucleus using the combined approach of current-clamp intracellular recording from thalamic slices and simulations with a reduced model based on voltage-clamp data. Our experimental data from 42 relay cells showed that the actual Ca2+ spike activates in a nearly all-or-none manner and in this regard is similar to the conventional Na+/K+ action potential except that its voltage dependency is more hyperpolarized and its kinetics are slower. When the cell’s membrane potential was hyperpolarized sufficiently to deinactivate much of the low-threshold Ca2+ current ( I T) underlying the Ca2+ spike, depolarizing current injections typically produced a purely ohmic response when subthreshold and a full-blown Ca2+ spike of nearly invariant amplitude when suprathreshold. The transition between the ohmic response and activated Ca2+ spikes was abrupt and reflected a difference in depolarizing inputs of <1 mV. However, activation of a full-blown Ca2+ spike was preceded by a slower period of depolarization that was graded with the amplitude of current injection, and the full-blown Ca2+ spike activated when this slower depolarization reached a sufficient membrane potential, a quasithreshold. As a result, the latency of the evoked Ca2+ spike became less with stronger activating inputs because a stronger input produced a stronger depolarization that reached the critical membrane potential earlier. Although Ca2+ spikes were activated in a nearly all-or-none manner from a given holding potential, their actual amplitudes were related to these holding potentials, which, in turn, determined the level of I T deinactivation. Our simulations could reproduce all of the main experimental observations. They further suggest that the voltage-dependent K+ conductance underlying I A, which is known to delay firing in many cells, does not seem to contribute to the variable latency seen in activation of Ca2+ spikes. Instead the simulations indicate that the activation of I T starts initially with a slow and graded depolarization until enough of the underling transient (or T) Ca2+ channels are recruited to produce a fast, “autocatalytic” depolarization seen as the Ca2+spike. This can produce variable latency dependent on the strength of the initial activation of T channels. The nearly all-or-none nature of Ca2+ spike activation suggests that when a burst of action potentials normally is evoked as a result of a Ca2+ spike and transmitted to cortex, this signal is largely invariant with the amplitude of the input activating the relay cell.

Oscillations and Long-Lasting Correlations in a Model of the Lateral Geniculate Nucleus and Visual Cortex

2000 ◽  
Vol 84 (4) ◽  
pp. 1863-1868 ◽  
Author(s):  
Kyle L. Kirkland ◽  
Adam M. Sillito ◽  
Helen E. Jones ◽  
David C. West ◽  
George L. Gerstein
Keyword(s):  
Experimental Data ◽  
Visual Cortex ◽  
Cell Membrane ◽  
Lateral Geniculate Nucleus ◽  
Feedback Inhibition ◽  
Frequency Range ◽  
Lateral Geniculate ◽  
Low Threshold ◽  
Thalamocortical System

We have previously developed a model of the corticogeniculate system to explore cortically induced synchronization of lateral geniculate nucleus (LGN) neurons. Our model was based on the experiments of Sillito et al. Recently Brody discovered that the LGN events found by Sillito et al. correlate over a much longer period of time than expected from the stimulus-driven responses and proposed a cortically induced slow covariation in LGN cell membrane potentials to account for this phenomenon. We have examined the data from our model, and we found, to our surprise, that the model shows the same long-term correlation. The model's behavior was the result of a previously unsuspected oscillatory effect, not a slow covariation. The oscillations were in the same frequency range as the well-known spindle oscillations of the thalamocortical system. In the model, the strength of feedback inhibition from the cortex and the presence of low-threshold calcium channels in LGN cells were important. We also found that by making the oscillations more pronounced, we could get a better fit to the experimental data.

Response latencies of cells in the cat's lateral geniculate nucleus are less variable during burst than tonic firing

1998 ◽  
Vol 15 (2) ◽  
pp. 231-237 ◽  
Author(s):  
W. GUIDO ◽  
S. MURRAY SHERMAN
Keyword(s):  
Signal Detection ◽  
Lateral Geniculate Nucleus ◽  
Visual Stimulus ◽  
Burst Firing ◽  
Signal To Noise ◽  
Response Latencies ◽  
Tonic Firing ◽  
Lateral Geniculate ◽  
In Cells

We measured the variability in latency of the first spike seen in cells of the cat's lateral geniculate nucleus following the onset of a visual stimulus. We found that, in each of the 11 cells tested, this variability was significantly lower during burst than during tonic firing. We suggest that this difference confers an advantage in signal detection during burst compared to tonic firing. This complements other reported advantages of burst firing for signal detection seen in signal-to-noise ratios and in the ability to efficiently drive postsynaptic cells.

scholarly journals Dynamics of Low-Threshold Spike Activation in Relay Neurons of the Cat Lateral Geniculate Nucleus

2001 ◽  
Vol 21 (3) ◽  
pp. 1022-1032 ◽  
Author(s):  
Carolina Gutierrez ◽  
Charles L. Cox ◽  
John Rinzel ◽  
S. Murray Sherman
Keyword(s):  
Lateral Geniculate Nucleus ◽  
Lateral Geniculate ◽  
Low Threshold Spike ◽  
Low Threshold ◽  
Relay Neurons
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