Ionic Mechanisms Underlying Synchronized Oscillations And Propagating Waves In A Model Of Ferret Thalamic Slices

this paper, we investigated model networks of TC and RE cells, endowed with intrinsic properties and topographic connectivity specific to the thalamus. The model reproduced the propagating properties of spindle waves, in agreement with another modeling study (Golomb et al., 1996) that used simpler models of thalamic neurons (no action potentials and graded synaptic transmission). The focus of Golomb et al. model was the parameters Destexhe et al., J. Neurophysiol. 76: 2049-2070, 1996 4 that influence propagation of activity but mechanisms for the initiation and termination of spindle oscillations were not included. We investigated the hypothesis that the termination, or waning, of spindles depends on an activity-dependent process in TC cells. Based on recent experiments by Bal and McCormick (1995), we assume that the calcium-dependent upregulation of a hyperpolarization-activated current, I h , is the biophysical basis of the waning. We show that this mechanism, together with other known intrinsic and synaptic properties of the thalamic circuitry, accounts for the initiation, propagation and termination of spindle waves. We also show that the same model exhibits the patterns of oscillation observed following application of bicuculline, a GABAA receptor antagonist. This convulsant transforms spindles into a slower and more synchronized oscillations (von Krosigk et al., 1993; Bal et al., 1995a, 1995b; Kim et al., 1995), similar to the pattern seen in thalamic neurons during some types of epileptic discharges. In agreement with previous models (Destexhe and Sejnowski, 1995; Golomb et al., 1996), lateral inhibition in the RE nucleus was essential in developing such patterns of discharges. Some of the results presented here were reported previously in an abstract (Destexhe..