Dendritic organization in
thalamocortical neurons and state-dependent functions of inhibitory synaptic
inputs
Mike Neubig and Alain Destexhe
Thalamus and Related Systems 1: 39-52, 2001
Abstract:
GABA-ergic thalamic reticular neurons function generically or
singularly in a state-dependent manner: during quiet sleep they
synchronously and rhythmically inhibit thalamocortical neurons (TCNs) via
bursts, thereby eliciting the low-threshold Ca2+ potentials in TCNs
that are crucial to oscillatory network behavior in the
thalamo-reticulo-cortical system; during wakefulness they shape the flux of
ascending sensory information by inhibiting TCNs with asynchronous and
arrhythmic single-spikes. To investigate how the reticulo-thalamic synapses,
which occur throughout TCN dendrites, are able to effect such disparate
functions, we have: (1) used a 1416 compartment model of a 3D reconstructed
TCN; (2) triggered dendritic miniature (TTX-independent) and unitary
(single-afferent) conductance-based synaptic events, and (3) recorded axial
currents and voltage transients in all 1416 compartments simultaneously. For
synapses at all dendritic locations, more than 79% of the charge transfer
reached the soma, where it dispersed into other dendritic trees to return to
the extracellular space. In accord, dendritic synapses in 80% of the arbor
induced voltage responses that were severely attenuated at the soma (>75%
loss). Spatio-temporal aspects of distributed postsynaptic responses were
examined as well. Except for synapses in the 13 most proximal compartments,
the amplitude and phase of the voltage responses degraded rapidly within a
focal region that did not extend beyond the host tree, and was limited most
often to a subtree. The bulk response (outside the focal region) was highly
synchronous and uniform. Interestingly, there were not 1403 different focal
regions, but only 20, each clearly distinct from the rest and sharply
delineated. Structural attributes of the arbor determined their boundaries.
Boundaries were invariant when the analysis was repeated on rescaled versions
(length, diameter) of the reconstructed arbor. Unitary events also induced
focal/bulk structures for both burst and single-spike triggers - paradigms
that correspond to single-afferent drives during quiet sleep and arousal,
respectively. Such qualities differ dramatically from previously proposed
motifs of dendritic clustering, each of which carried nonlinear sensitivities
to parameter values. We propose that dendritic clustering underlies the role
of reticulo-thalamic synapses in the early processing of ascending sensory
information and that bulk responses contribute robustness to the induction and
maintenance oscillations in the thalamo-reticulo-cortical network.
return to
publication list
return to main page