In vivo, in vitro and computational analysis of dendritic calcium currents in thalamic reticular neurons

Alain Destexhe, Diego Contreras, Mircea Steriade, Terrence J. Sejnowski and John R. Huguenard

Journal of Neuroscience 16: 169-185, 1996

Abstract:

Thalamic reticular (RE) neurons are involved in the genesis of synchronized thalamocortical oscillations, which depend in part on their complex bursting properties. We have investigated the intrinsic properties of RE cells using computational models based on morphological and electrophysiological data. Simulations of a reconstructed RE cell were compared directly to recordings from the same cell to obtain precise values for the passive parameters. In a first series of experiments, the low-threshold calcium current (IT) was studied with voltage-clamp in acutely dissociated RE cells which lack most of their dendrites. Simulations based on a cell with truncated dendrites and Hodgkin-Huxley kinetics reproduced these recordings with a relatively low density of IT. In a second series of experiments, voltage-clamp recordings obtained in intact RE cells in slices showed a higher amplitude and slower kinetics of IT. These properties could be reproduced from the reconstructed cell model assuming higher densities of IT in distal dendrites. In a third series of experiments, current-clamp recordings were obtained in RE cells in vivo. The marked differences with in vitro recordings could be reconciled by simulating synaptic bombardment in the dendrites of RE cells, but only if they contained high distal densities of IT. In addition, simpler models with as few as three compartments could reproduce the same behavior assuming dendritic IT. These models and experiments show how intrinsic bursting properties of RE cells, as recorded in vivo and in vitro, may be explained by dendritic calcium currents.

Movies:

Several movie files illustrate the dynamics of membrane potential in soma and dendrites of thalamic reticular neurons. They are an excellent complement to the figures of the paper. The somatodendritic distribution of membrane potential is shown by colors during a burst of action potentials. In particular, see how distal dendrites are maintained at a depolarized level, "feeding" the soma with current during the burst.

dendritRE_full.mpg (large size movie, also contains a plot of the membrane potential at the soma)

dendritRE.mpg (medium size)

dendritRE_short.mpg (small size)

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.

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