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. 2000 Nov 7;97(23):12864-8.
doi: 10.1073/pnas.230175697.

Sensory deprivation without competition yields modest alterations of short-term synaptic dynamics

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Sensory deprivation without competition yields modest alterations of short-term synaptic dynamics

G T Finnerty et al. Proc Natl Acad Sci U S A. .

Abstract

Cortical maps express experience-dependent plasticity. However, the underlying cellular mechanisms remain unclear. We have recently shown that sensory deprivation results in large changes of the short-term dynamics of excitatory synapses at the junction of deprived and spared somatosensory (barrel) cortex, which may contribute to map reorganization. A key issue is whether the alterations in short-term synaptic dynamics are driven by a loss of sensory input or by competition between deprived and spared inputs. Here, we report that short-term dynamics of horizontal pathways in the middle of uniformly deprived cortex change only modestly. Vertical intracortical pathways were unaffected by deprivation. Our results suggest that uniform loss of sensory activity has a limited effect on short-term synaptic dynamics. We concluded that competition between sensory inputs is necessary to produce large-scale changes in synaptic dynamics after sensory deprivation.

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Figures

Figure 1
Figure 1
Short-term synaptic dynamics in the thalamocortical slice. (A) Schematic diagram of the position of the recording and stimulating electrodes positions in primary somatosensory cortex. The gray band represents layer 4 of the barrel field. A field electrode was used to apply bicuculline methiodide focally. (B) Average responses (3 trials) evoked by stimulation of the horizontal layer 2–2 pathway at 20 Hz in one slice from deprived cortex. (C) Single exponential fit to the responses in B. (D) Single exponential fit to the responses evoked by 20-Hz stimulus trains averaged across all recordings in deprived cortex (open circles, n = 14 neurons from 10 slices) and spared cortex (filled circles, n = 12 neurons from 10 slices) of rats trimmed for 5 days.
Figure 2
Figure 2
Horizontal layer 2 to layer 2 pathway. (A) Normalized steady-state EPSP amplitudes evoked by stimulation of layer 2–2 pathways in deprived (open circles, n = 10) or spared cortex (filled circles, n = 10) with brief stimulus trains of varying frequencies after 5 days of deprivation. (B) Time constant of EPSP amplitude depression calculated from single exponential fits to normalized EPSP amplitudes evoked by stimulation of layer 2–2 pathways in deprived (open circles, n = 10) or spared cortex (filled circles, n = 10) at varying frequencies after 5 days of deprivation. (C) Normalized steady-state EPSP amplitudes evoked by stimulation of layer 2–2 pathways in deprived (open circles, n = 7) or spared cortex (filled circles, n = 7) with brief stimulus trains of varying frequencies after 10–14 days of deprivation. (D) Time constant of EPSP amplitude depression calculated from single exponential fits to normalized EPSP amplitudes evoked by stimulation of layer 2–2 pathways in deprived (open circles, n = 7) or spared cortex (filled circles, n = 7) at varying frequencies after 10–14 days of deprivation. (E) Pooled differences in normalized steady state after 5- and 10-day trims. (F) Pooled differences in time constant of EPSP amplitude depression after 5- and 10-day trims.
Figure 3
Figure 3
Vertical layer 4 to layer 2 pathway. (A) Normalized steady-state EPSP amplitudes evoked by stimulation of layer 4–2 pathways in deprived (open circles, n = 10) or spared cortex (filled circles, n = 10) with brief stimulus trains of varying frequencies after 5 days of deprivation. (B) Time constant of EPSP amplitude depression calculated from single exponential fits to normalized EPSP amplitudes evoked by stimulation of layer 4–2 pathways in deprived (open circles, n = 10) or spared cortex (filled circles, n = 10) at varying frequencies after 5 days of deprivation. (C) Normalized steady-state EPSP amplitudes evoked by stimulation of layer 4–2 pathways in deprived (open circles, n = 7) or spared cortex (filled circles, n = 7) with brief stimulus trains of varying frequencies after 10–14 days of deprivation. (D) Time constant of EPSP amplitude depression calculated from single exponential fits to normalized EPSP amplitudes evoked by stimulation of layer 4–2 pathways in deprived (open circles, n = 7) or spared cortex (filled circles, n = 7) at varying frequencies after 10–14 days of deprivation. (E) Pooled differences in normalized steady state after 5- and 10-day trims. (F) Pooled differences in time constant of EPSP amplitude depression after 5- and 10-day trims.

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