A MODEL OF SPINDLE RHYTHMICITY IN THE ISOLATED THALAMIC RETICULAR NUCLEUS

1. The oscillatory properties of the isolated reticular (RE) thalamus were modeled with the use of compartmental models of RE cells. Hodgkin -Huxley type kinetic models of ionic channels were derived from voltag e- and current-damp data from RE cells. Interactions between interconn ected RE cells were simulated with the use of a kinetic model of gamma -aminobutyric acid (GABA) inhibitory synapses. 2. The intrinsic bursti ng properties of RE cells in the model were due to the presence of a l ow-threshold Ca2+ current and two Ca2+-activated currents. The propert ies of these model RE cells were compared with RE neurons recorded int racellularly in vivo in cats. 3. Model RE cells densely interconnected with GABA(A) synapses produced synchronous oscillations at a frequenc y close to that of spindles (7-14 Hz). Networks of RE neurons organize d in a two-dimensional array with only proximal connectivity also exhi bited synchronized oscillations in the spindle range. In addition, the proximally connected network showed periods of high and low synchroni city, giving rise to waxing and waning oscillations in the population of RE cells. 4. The spatiotemporal behavior of the network was investi gated during waxing and waning oscillations. The waxing and waning eme rged as an alternation between periods of desynchronized and synchroni zed activity, corresponding to periods of irregular and coherent spati al activity. During synchronized periods, the network displayed propag ating coherent waves of synchronous activity that had a tendency to fo rm spirals. 5. Networks of model RE neurons fully connected through GA BA(B) synapses exhibited perfectly synchronous oscillations at lower f requencies (0.5-1 Hz), but two-dimensional networks with proximal GABA (B) connectivity failed to synchronize. 6. These simulations demonstra te that networks of model neurons that include the main intrinsic curr ents found in RE cells can generate waxing and waning oscillatory acti vity similar to the spindle rhythmicity observed in the isolated RE nu cleus in vivo. The model reveals the interplay between the intrinsic r hythmic properties of RE cells and the fast synaptic interactions in o rganizing synchronized rhythmicity.