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

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 cells were compared directly with recordings from the same cell to obtain precise values for the passive parameters. In a first series of experiments, the low-threshold calcium current (I(Ts)) was studied via voltage clamp in acutely dissociated RE cells that 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 I(Ts). In a second series of experiments, voltage-clamp recordings obtained in intact RE cells in slices showed a higher amplitude and slower kinetics of I(Ts). These properties could be reproduced from the reconstructed cell model assuming higher densities of I(Ts) in distal dendrites. In a third series of experiments, current-clamp recordings were obtained on 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 I(Ts). In addition, simpler models with as few as three compartments could reproduce the same behavior assuming dendritic I(Ts). 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.