Working Together to Fire Neurons Rapidly?

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Science's STKE  25 Apr 2006:
Vol. 2006, Issue 332, pp. tw137
DOI: 10.1126/stke.3322006tw137

Neurons encode information by means of the conducted nerve impulse, or action potential, a rapidly propagating electrical signal. During an action potential, the potential difference across the neuronal membrane transiently reverses so that the inside of the neuron becomes positive relative to the outside. Hodgkin and Huxley, whose groundbreaking research forms the basis for modern electrophysiology, showed that action potentials in the squid giant axon entail a rapid voltage-dependent increase in inward current, carried by sodium ions, and a slower voltage-dependent increase in outward current, carried by potassium ions. They developed a model to explain action potential generation based on the voltage-dependent gating of populations of ion channels, in which individual channels act independently of each other (see Gutkin and Ermentrout). Naundorf et al. analyzed action potentials recorded from cat cortical neurons in vivo and rat, mouse, and cat cortical neurons in vitro and found that action potential initiation occurred more abruptly, with a more rapid depolarizing phase, than predicted by the Hodgkin and Huxley model. Moreover, threshold (the voltage at which the action potential is triggered) varied more than predicted. To account for their observations, Naundorf et al. developed a model for action potential initiation in which neighboring sodium channels are activated cooperatively rather than independently of each other. When they applied the sodium channel blocker tetrodotoxin (to effectively reduce channel density), they saw action potentials more like those predicted by the Hodgkin and Huxley model. Thus, the authors propose that, in cortical neurons, action potential initiation depends on cooperative activation of sodium channels and that this may facilitate encoding of rapidly varying signals.

B. Naundorf, F. Wolf, M. Volgushev, Unique features of action potential initiation in cortical neurons. Nature 440, 1060-1063 (2006). [PubMed]

B. Gutkin, G. B. Ermentrout, Spikes too kinky in the cortex? Nature 440, 999-1000 (2006). [PubMed]