Optogenetics Used to Show That Axon Initial Segments (AIS’s) Can Change Length and Influence Repetitive Spike Firing Much More Rapidly Than Previously Thought

Neurons communicate by passing electrical messages, known as action potentials, between each other. Each neuron has a highly specialized structural region, the so-called “axon initial segment” (AIS), whose primary role is in the generation and sending of these messages. The AIS can undergo changes in size, length, and location in response to alterations of a neuron's ongoing electrical activity. However, until now, all such “AIS plasticity” has been believed to be exceptionally slow, occurring over a timescale of days. Work by researchers from the MRC Centre for Developmental Neurobiology (MRC CDN), part of the Institute of Psychiatry, Psychology & Neuroscience at King's College London at King’s College London, has now shown that AIS changes can occur much more quickly, influencing the way cells fire action potentials. These results were published online on October 29, 2015 in an open-access article in the journal Cell Reports. The article is titled “Rapid Modulation of Axon Initial Segment Length Influences Repetitive Spike Firing.” Located near the beginning of the axon, which is the neuron's major output structure, the AIS has a crucial role in kick-starting communication between brain cells. However, for AIS plasticity to play a more prominent role in the brain's responses to altered activity, the structure needs to be able to change far more quickly than has previously been shown. For this reason, Dr. Mark Evans (now at the Gladstone Institute of Neurological Disease in San Francisco), Dr. Adna Dumitrescu, Dr. Dennis Kruijssen, Dr. Samuel Taylor, and Dr. Matthew Grubb decided to investigate how rapidly an AIS can be altered.