Calcium action potentials restricted to distal apical dendrites of rat neocortical pyramidal neurons

J Physiol. 1997 Dec 15;505 ( Pt 3)(Pt 3):605-16. doi: 10.1111/j.1469-7793.1997.605ba.x.


1. Simultaneous whole-cell voltage and Ca2+ fluorescence measurements were made from the distal apical dendrites and the soma of thick tufted pyramidal neurons in layer 5 of 4-week-old (P28-32) rat neocortex slices to investigate whether activation of distal synaptic inputs can initiate regenerative responses in dendrites. 2. Dual whole-cell voltage recordings from the distal apical trunk and primary tuft branches (540-940 microns distal to the soma) showed that distal synaptic stimulation (upper layer 2) evoking a subthreshold depolarization at the soma could initiate regenerative potentials in distal branches of the apical tuft which were either graded or all-or-none. These regenerative potentials did not propagate actively to the soma and axon. 3. Calcium fluorescence measurements along the apical dendrites indicated that the regenerative potentials were associated with a transient increase in the concentration of intracellular free calcium ([Ca2+]i) restricted to distal dendrites. 4. Cadmium added to the bath solution blocked both the all-or-more dendritic regenerative potentials and local dendritic [Ca2+]i transients evoked by distal dendritic current injection. Thus, the regenerative potentials in distal dendrites represent local Ca2+ action potentials. 5. Initiation of distal Ca2+ action potentials by a synaptic stimulus required coactivation of AMPA- and NMDA-type glutamate receptor channels. 6. It is concluded that in neocortical layer 5 pyramidal neurons of P28-32 animals glutamatergic synaptic inputs to the distal apical dendrites can be amplified via local Ca2+ action potentials which do not reach threshold for axonal AP initiation. As amplification of distal excitatory synaptic input is associated with a localized increase in [Ca2+]i these Ca2+ action potentials could control the synaptic efficacy of the distal cortico-cortical inputs to layer 5 pyramidal neurons.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology
  • Animals
  • Axons / physiology
  • Calcium / physiology*
  • Dendrites / physiology*
  • Electric Conductivity
  • Excitatory Amino Acid Agonists / pharmacology
  • Excitatory Postsynaptic Potentials / physiology
  • Fluorescence
  • In Vitro Techniques
  • Isoxazoles / pharmacology
  • Neocortex / physiology*
  • Neocortex / ultrastructure
  • Patch-Clamp Techniques
  • Propionates / pharmacology
  • Pyramidal Cells / physiology*
  • Pyramidal Cells / ultrastructure
  • Rats
  • Receptors, N-Methyl-D-Aspartate / physiology


  • Excitatory Amino Acid Agonists
  • Isoxazoles
  • Propionates
  • Receptors, N-Methyl-D-Aspartate
  • alpha-amino-3-hydroxy-5-tert-butyl-4-isoxazolepropionate
  • Calcium