Intracellular and computational characterization of the intracortical inhibitory control of synchronized thalamic inputs in vivo.
Diego Contreras, Alain Destexhe and Mircea Steriade

Journal of Neurophysiology 77: 335-350, 1997.

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We investigated the presence and role of the local inhibitory cortical control over synchronized thalamic inputs during spindle oscillations (7-14 Hz) by combining intracellular recordings of pyramidal cells in barbiturate-anesthetized cats and computational models. The recordings showed that (a) similar EPSP/IPSP sequences occurred during either spindles or following thalamic stimulation; (b) reversed IPSPs with chloride-filled pipettes transformed spindle-related EPSP/IPSP sequences into robust bursts with spike inactivation, resembling paroxysmal depolarizing shifts during seizures; and (c) dual simultaneous impalements showed that inhibition associated with synchronized thalamic inputs is local. Computational models were based on reconstructed pyramidal cells constrained by recordings from the same cells. These models showed that the transformation of EPSP/IPSP sequences into fully developed spike-bursts critically needs a relatively high density of inhibitory currents in the soma and proximal dendrites. In addition, models predict significant Ca2+ transients in dendrites due to synchronized thalamic inputs. We conclude that synchronized thalamic inputs are subject to strong inhibitory control within the cortex and propose that (1) local impairment of inhibition contributes to transform spindles into spike-wave type of discharges, and (2) spindle-related inputs trigger Ca2+ events in cortical dendrites that may subserve plasticity phenomena during sleep.