The Journal of Neuroscience, March 11, 2009, 29(10):3233-3241; doi:10.1523/JNEUROSCI.6000-08.2009
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Development/Plasticity/Repair
Synaptic Depolarization Is More Effective than Back-Propagating Action Potentials during Induction of Associative Long-Term Potentiation in Hippocampal Pyramidal Neurons
Jason Hardie and
Nelson Spruston
Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208
Correspondence should be addressed to Dr. Nelson Spruston, Department of Neurobiology and Physiology, Northwestern University, 2205 Tech Drive, M213, EV3520, Evanston, Il 60208. Email: spruston{at}northwestern.edu
Long-term potentiation (LTP) requires postsynaptic depolarization that can result from EPSPs paired with action potentials or larger EPSPs that trigger dendritic spikes. We explored the relative contribution of these sources of depolarization to LTP induction during synaptically driven action potential firing in hippocampal CA1 pyramidal neurons. Pairing of a weak test input with a strong input resulted in large LTP (
75% increase) when the weak and strong inputs were both located in the apical dendrites. This form of LTP did not require somatic action potentials. When the strong input was located in the basal dendrites, the resulting LTP was smaller (
25% increase). Pairing the test input with somatically evoked action potentials mimicked this form of LTP. Thus, back-propagating action potentials may contribute to modest LTP, but local synaptic depolarization and/or dendritic spikes mediate a stronger form of LTP that requires spatial proximity of the associated synaptic inputs.
Received Dec. 17, 2008;
accepted Jan. 15, 2009.
Correspondence should be addressed to Dr. Nelson Spruston, Department of Neurobiology and Physiology, Northwestern University, 2205 Tech Drive, M213, EV3520, Evanston, Il 60208. Email: spruston{at}northwestern.edu