Journal of neurophysiology
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The excitability properties of turtle olfactory nerve (o.n.) were studied in vitro using potassium-sensitive microelectrodes (KSM), a modified sucrose gap chamber, and a standard nerve chamber to measure conduction velocity. A pronounced supernormal period (SNP), as indicated by increased conduction velocity of the o.n. fiber volley, lasting up to several seconds, was observed following a single stimulus. The compound action potential recorded in the sucrose gap chamber showed a prolonged depolarization with a similar time course to the SNP. ⋯ The excitability of these neighboring nonactivated fibers was increased, further indicating the importance of activity-dependent changes in [K+]o in modulating axonal excitability. These results demonstrate the importance of activity-dependent increases in extracellular potassium in modulating nonmyelinated o.n. fiber excitability. They also indicate that increases in [K+]o and an associated membrane depolarization contribute to the increased excitability observed during fiber recruitment and the supernormal period.