Spread of dendritic excitation in layer 2/3 pyramidal neurons in rat barrel cortex in vivo


In layer 2/3 pyramidal neurons of barrel cortex in vivo , calcium ion concentration ([Ca 2+ ]) transients in apical dendrites evoked by sodium action potentials are limited to regions close to the soma. To study the mechanisms underlying this restricted pattern of calcium influx, we combined two–photon imaging of dendritic [Ca 2+ ] dynamics with dendritic membrane potential measurements. We found that sodium action potentials attenuated and broadened rapidly with distance from the soma. However, dendrites of layer 2/3 cells were electrically excitable, and direct current injections could evoke large [Ca 2+ ] transients. The restricted pattern of dendritic [Ca 2+ ] transients is therefore due to a failure of sodium action–potential propagation into dendrites. Also, stimulating subcortical activating systems by tail pinch can enhance dendritic [Ca 2+ ] influx induced by a sensory stimulus by increasing cellular excitability, consistent with the importance of these systems in plasticity and learning.

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Figure 1: In vivo electrophysiology and two–photon laser scanning microscopy.
Figure 2: Dendritic [Ca2+] transients evoked by sodium action potentials.
Figure 3: Properties of dendritic sodium action potentials.
Figure 6: Modulation of dendritic [Ca2+] transients by tail pinch.
Figure 5: Dendritic Ca2+ spikes evoked by current injection.
Figure 4: Dendritic [Ca2+] transients evoked by sodium action potential bursts.


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We thank G. Buzsaki for suggestions, B. Burbach for help with histology, and G. Major, Z. Mainen and E. Stern for comments on the manuscript. This work was supported by Lucent Technologies and the Klingenstein, Pew, and Whitaker Foundations (K.S.), and the Max–Planck Society (F.H.).

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Correspondence to Karel Svoboda.

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Svoboda, K., Helmchen, F., Denk, W. et al. Spread of dendritic excitation in layer 2/3 pyramidal neurons in rat barrel cortex in vivo. Nat Neurosci 2, 65–73 (1999). https://doi.org/10.1038/4569

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