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
Abstract
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.
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