Submitted on February 22, 2008
Revised on April 18, 2008
Accepted on May 12, 2008
High threshold, proximal initiation, and slow conduction velocity of action potentials in dentate granule neuron mossy fibers
Geraldine J Kress1, Margaret J Dowling1, Julian P Meeks1, and Steven Mennerick1*
1 Washington University School of Med
* To whom correspondence should be addressed. E-mail: menneris{at}psychiatry.wustl.edu.
Dentate granule neurons give rise to some of the smallest unmyelinated fibers in the mammalian central nervous system, the hippocampal mossy fibers. These neurons are also key regulators of physiological and pathophysiological information flow through the hippocampus. We took a comparative approach to studying mossy fiber action potential initiation and propagation in hippocampal slices from juvenile rats. Dentate granule neurons exhibited axonal action potential initiation significantly more proximal than CA3 pyramidal neurons. This conclusion was suggested by phase plot analysis of somatic action potentials and by local tetrodotoxin application to the axon and somatodendritic compartments. This conclusion was also verified by immunostaining for voltage-gated sodium channel alpha subunits, and by direct dual soma/axonal recordings. Dentate neurons exhibited a significantly higher action potential threshold and slower axonal conduction velocity than CA3 neurons. We conclude that while the electrotonically proximal axon location of action potential initiation allows granule neurons to sensitively detect and integrate synaptic inputs, the neurons are sluggish to initiate and propagate an action potential.
