Dendritic low-threshold calcium currents in thalamic relay cells

Alain Destexhe, Mike Neubig, Daniel Ulrich and John R. Huguenard

Journal of Neuroscience 18: 3574-3588, 1998

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Abstract:

The low-threshold calcium current (I_T) underlies burst generation in thalamocortical (TC) relay cells and plays a central role in the genesis of synchronized oscillations by thalamic circuits. We have here combined in vitro recordings and computational modeling techniques in order to investigate the consequences of dendritically-located I_T in TC cells. Simulations of a reconstructed TC cell were compared to the recordings obtained in the same cell in order to constrain the values of its passive parameters. T-current densities in soma and proximal dendrites were then estimated by matching the model to voltage-clamp recordings obtained in dissociated TC cells, which lack most of the dendrites. The distal dendritic T-current density was constrained by recordings in intact TC cells, which show 5-14 times larger peak T-current amplitudes compared to dissociated cells. Comparison of the model to the recordings of the same cell constrained further the T-current density in dendrites, which had to be 4.5-7.6 times higher than in the soma to reproduce all experimental results. Similar conclusions were reached using a simplified 3-compartment model. Functionally, the model shows that the same amount of T-channels can lead to different bursting behaviors if they are exclusively somatic or distributed throughout the dendrites. In conclusion, this combination of models and experiments shows that dendritic T-currents are necessary to reproduce low-threshold calcium electrogenesis in TC cells. Dendritic T-current may also have significant functional consequences, such as an efficient modulation of thalamic burst discharges by corticothalamic feedback.

Programs:

The original NEURON programs that served to simulate this model are also available. They provide a useful way to learn how to design compartmental models using NEURON.

NEURON demo:

This package creates a directory containing programs for running the compartmental model of thalamic reticular neuron using NEURON. The simulations reproduce some of the figures of the paper, in which all the details are given. There are also instructions in a README file.
See also the book chapter Neubig M, Ulrich D, Huguenard JR and Destexhe A. Dendritic calcium currents in thalamic relay cells. In: Computational Neuroscience. Trends in Research (edited by J. Bower), Plenum Press, New York, pp. 233-238, 1998.
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