Dendritic Low-Threshold Calcium Currents in Thalamic Relay Cells

Abstract

The low-threshold calcium current (IT) underlies burst generation in thalamocortical (TC) relay cells and plays a central role in the genesis of synchronized oscillations by thalamic circuits. Here we have combined in vitro recordings and computational modeling techniques to investigate the consequences of dendritically located IT in TC cells. Simulations of a reconstructed TC cell were compared with the recordings obtained in the same cell 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 with dissociated cells. Comparison of the model with 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 three-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.

Characterization of Rebound Depolarization in Neurons of the Rat Medial Geniculate Body In Vitro

“…The robustness of RD could partly be attributed to the high density of expression of T-type Ca 2? channels in the soma and dendrites of thalamic relay neurons [37][38][39]. Third, RD can be recorded in most MGB neurons in young animals (P15-22).…”

The initiation of bursts in thalamic neurons and the cortical control of thalamic sensitivity

“…The computational models were based on those in several previously published papers, in which the details of those models have been described (Destexhe et al 1994(Destexhe et al , 1996(Destexhe et al , 1998b. All the models were simulated using the Neuron simulation environment (Hines & Carnevale 1997).…”

“…Computational models of thalamic relay and reticular neurons were based on cellular morphologies obtained in two previous studies (Destexhe et al 1996(Destexhe et al , 1998b. These neurons (illustrated respectively in gures 1 and 3) were intracellularly recorded in slices from rat ventrobasal nucleus and stained with biocytin (Huguenard & Prince 1992).…”

“…Active currents (I Na , I K d , I T ) were based on Hodgkin & Huxley (1952) type kinetic models (see equations and parameters in Destexhe et al 1996Destexhe et al , 1998b. The density of T-current in the dendrites of relay cells was estimated based on voltage-clamp recordings of the T-current in intact and dissociated cells (Destexhe et al 1998b), as well as from direct measurements of channel activity in dendrites (Williams & Stuart 2000).…”

NPY signaling through Y1 receptors modulates thalamic oscillations

“…1C) or might cause the rate of relay cell depolarization to be too low for T-type calcium channel activation [10]. Low threshold calcium channels are concentrated on relay cell dendrites [5], and nRt axons synapse onto relay cell dendrites [32], which could allow for effective T-type calcium channel modulation.…”