Axon Segments May Form Distinct Processing Units

A paper we examined last year showed that spikelet activity in CA1 hippocampal pyramidal cells displayed a preference for place (like action potentials in place cells; see blog post “Spikelets and Place Cells“). They also saw evidence that spikelets sometimes induced full action potentials as recorded in the soma of pyramidal cells.

A new paper “Slow integration leads to persistent action potential firing in distal axons of coupled interneurons” (published February 2011 in Nature Neuroscience) describes a previously unknown slow integration of action potentials that results in the abrupt appearance of action potentials in the distant segments of CA1 hippocampal interneuron axons that may persist in firing for tens of seconds to minutes. Perhaps most important, natural firing patterns of action potentials elicited persistent firing in the distal axons of these interneurons.

The authors showed that the persistent spiking activity in or near the distal axon could be shared by multiple neurons without a requirement for somatic or dendritic depolarization or synaptic interactions through excitatory or inhibitory receptors. In fact, they show that spikelets seem to be reflections of action potentials in distant axon branches that never interact with the interneuron’s cell body or dendrites.

Note: The authors present some preliminary evidence that the persistent firing of action potentials in distant axon segments may depend on gap junctions. This is particularly interesting given the recent report on the role played by gap junctions in learning and memory (see my blog post “Electrical Synapses are Important for Learning and Memory“).

Other related blog posts:

Spikelets and Place Cells

Electrical Synapses are Important for Learning and Memory