PMID- 16226579
OWN - NLM
STAT- MEDLINE
DCOM- 20081216
LR  - 20051017
IS  - 1875-7855 (Electronic)
IS  - 0079-6123 (Linking)
VI  - 149
DP  - 2005
TI  - Spike timing and synaptic dynamics at the awake thalamocortical synapse.
PG  - 91-105
AB  - Thalamocortical (TC) neurons form only a small percentage of the synapses onto 
      neurons of cortical layer 4, but the response properties of these cortical 
      neurons are arguably dominated by thalamic input. This discrepancy is explained, 
      in part, by studies showing that TC synapses are of high efficacy. However, TC 
      synapses display activity-dependent depression. Because of this, in vitro 
      measures of synaptic efficacy will not reflect the situation in vivo, where 
      different neuronal populations have widely varying levels of "spontaneous" 
      activity. Indeed, TC neurons of awake subjects generate high rates of spontaneous 
      activity that would be expected, in a depressing synapse, to result in a chronic 
      state of synaptic depression. Here, we review recent work in the somatosensory 
      thalamocortical system of awake rabbits in which the relationship between TC 
      spike timing and TC synaptic efficacy was examined during both thalamic "relay 
      mode" (alert state) and "burst mode" (drowsy state). Two largely independent 
      methodological approaches were used. First, we employed cross-correlation methods 
      to examine the synaptic impact of single TC "barreloid" neurons on a single 
      neuronal subtype in the topographically aligned layer 4 "barrel" - putative 
      fast-spike inhibitory interneurons. We found that the initial spike of a TC 
      burst, as well as isolated TC spikes with long preceding interspike intervals 
      (ISIs) elicited postsynaptic action potentials far more effectively than did TC 
      impulses with short ISIs. Our second approach took a broader view of the 
      postsynaptic impact of TC impulses. In these experiments we examined 
      spike-triggered extracellular field potentials and synaptic currents (using 
      current source-density analysis) generated through the depths of a cortical 
      barrel column by the impulses of single topographically aligned TC neurons. We 
      found that (a) closely neighboring TC neurons may elicit very different patterns 
      of monosynaptic activation within layers 4 and 6 of the aligned column, (b) 
      synaptic currents elicited by TC impulses with long preceding ISIs were greatly 
      enhanced in both of these layers, and (c) the degree of this enhancement differed 
      reliably among neighboring TC neurons but, for a given neuron, was very similar 
      in layers 4 and 6. Thus, results generated by both methodological approaches are 
      consistent with the presence of a chronic depression at the awake TC synapse that 
      is relieved by long ISIs. Since long ISIs necessarily precede TC "bursts", our 
      results are consistent with the notion that these events powerfully activate 
      cortical circuits.
FAU - Swadlow, Harvey A
AU  - Swadlow HA
AD  - Department of Psychology, The University of Connecticut, Storrs, CT 06269, USA. 
      Swadlow@psych.psy.uconn.edu
FAU - Bezdudnaya, Tatiana
AU  - Bezdudnaya T
FAU - Gusev, Alexander G
AU  - Gusev AG
LA  - eng
GR  - MH-64024/MH/NIMH NIH HHS/United States
PT  - Journal Article
PT  - Research Support, N.I.H., Extramural
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PT  - Review
PL  - Netherlands
TA  - Prog Brain Res
JT  - Progress in brain research
JID - 0376441
SB  - IM
MH  - Action Potentials/*physiology
MH  - Animals
MH  - Interneurons/physiology
MH  - Neural Pathways/cytology/physiology
MH  - Neurons/*physiology
MH  - Rabbits
MH  - Somatosensory Cortex/cytology/*physiology
MH  - Synapses/*physiology
MH  - Synaptic Transmission/physiology
MH  - Thalamus/cytology/*physiology
MH  - Time Factors
MH  - Ventral Thalamic Nuclei/cytology/*physiology
MH  - Wakefulness/physiology
RF  - 53
EDAT- 2005/10/18 09:00
MHDA- 2008/12/17 09:00
CRDT- 2005/10/18 09:00
PHST- 2005/10/18 09:00 [pubmed]
PHST- 2008/12/17 09:00 [medline]
PHST- 2005/10/18 09:00 [entrez]
AID - S0079-6123(05)49008-1 [pii]
AID - 10.1016/S0079-6123(05)49008-1 [doi]
PST - ppublish
SO  - Prog Brain Res. 2005;149:91-105. doi: 10.1016/S0079-6123(05)49008-1.