Ionic mechanisms underlying synchronized oscillations and propagating waves in a model of ferret thalamic slices
Journal of Neurophysiology
AND CONCLUSIONS cells, leading to waves of spindle activity as observed in experimerits. 1. A network model of thalamocortical (TC) and thalamic retic-8. The spatiotemporal properties of propagating waves in the ular (RE) neurons was developed based on electrophysiological model were highly dependent on the intrinsic properties of TC measurements in ferret thalamic slices. Single-compartment TC cells. The spatial pattern of spiking activity was markedly different and RE cells included
... included voltage-and calcium-sensitive currents defor spindles compared with bicuculline-induced oscillations and scribed by Hodgkin-Huxley type of kinetics. Synaptic currents depended on the rebound burst behavior of TC cells. The upregulawere modeled by kinetic models of cr-amino-3-hydroxy-5-methyltion of Ih produced a refractory period so that colliding spindle 4-isoxazolepropionic acid (AMPA), y-aminobutyric acid-A (GAwaves merged into a single oscillation and extinguished. Finally, BAA) and GABAB receptors. reducing the Ih conductance led to sustained oscillations. 2. The model reproduced successfully the characteristics of spindle and slow bicuculline-induced oscillations observed in vitro. The characteristics of these two types of oscillations depended on both the intrinsic properties of TC and RE cells and their pattern of interconnectivity. 3. The oscillations were organized by the reciprocal recruitment between TC and RE cells, due to their mutual connectivity and bursting properties. TC cells elicited AMPA-mediated excitatory postsynaptic potentials (EPSPs) in RE cells, whereas RE cells elicited a mixture of GABA* and GABAB inhibitory postsynaptic potentials (IPSPs) in TC cells. Because of the presence of a T current, sufficiently strong EPSPs could elicit a burst in RE cells, and TC cells could generate a rebound burst following GABAergic IPSPs. Under these conditions, interaction between the TC and RE cells produced sustained oscillations. 9. Two key properties of cells in the thalamic network may account for the initiation, propagation, and termination of spindle oscillations, the activity-dependent upregulation of Ih in TC cells, and the localized axonal projections between TC and RE cells. In addition, the model predicts that a nonlinear stimulus dependency of GABAB responses accounts for the genesis of prolonged synchronized discharges following block of GABA* receptors.