Spread of dendritic excitation in layer 2/3 pyramidal neurons in rat barrel cortex in vivo
Karel Svoboda1, 2, Fritjof Helmchen2, Winfried Denk2
& David W. Tank2
1
Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
2
Biological Computation Research Department, Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974, USA
Correspondence should be addressed to Karel Svoboda svoboda@cshl.org
In layer 2/3 pyramidal neurons of barrel cortex in vivo, calcium ion concentration ([Ca2+]) 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 [Ca2+] 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 [Ca2+] transients. The restricted pattern of dendritic [Ca2+] 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 [Ca2+] influx induced by a sensory stimulus by increasing cellular excitability, consistent with the importance of these systems in plasticity and learning.
