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Review
, 26 (4), 179-185

Spike Frequency Adaptation in Neurons of the Central Nervous System

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Review

Spike Frequency Adaptation in Neurons of the Central Nervous System

Go Eun Ha et al. Exp Neurobiol.

Abstract

Neuronal firing patterns and frequencies determine the nature of encoded information of the neurons. Here we discuss the molecular identity and cellular mechanisms of spike-frequency adaptation in central nervous system (CNS) neurons. Calcium-activated potassium (KCa) channels such as BKCa and SKCa channels have long been known to be important mediators of spike adaptation via generation of a large afterhyperpolarization when neurons are hyper-activated. However, it has been shown that a strong hyperpolarization via these KCa channels would cease action potential generation rather than reducing the frequency of spike generation. In some types of neurons, the strong hyperpolarization is followed by oscillatory activity in these neurons. Recently, spike-frequency adaptation in thalamocortical (TC) and CA1 hippocampal neurons is shown to be mediated by the Ca2+-activated Cl- channel (CACC), anoctamin-2 (ANO2). Knockdown of ANO2 in these neurons results in significantly reduced spike-frequency adaptation accompanied by increased number of spikes without shifting the firing mode, which suggests that ANO2 mediates a genuine form of spike adaptation, finely tuning the frequency of spikes in these neurons. Based on the finding of a broad expression of this new class of CACC in the brain, it can be proposed that the ANO2-mediated spike-frequency adaptation may be a general mechanism to control information transmission in the CNS neurons.

Keywords: afterhyperpolarization; anoctamin-2; calcium-activated chloride channel; calcium-activated potassium channel; spike-frequency adaptation; thalamocortical neuron.

Figures

Fig. 1
Fig. 1. Ca2+-dependent spike frequency adaptation and adaptation index. (A) TC neuron with a depolarizing current injection to induce tonic firing in 2.4 mM Ca2+ buffer displays the prolongation of inter-spike intervals (ISI). Adaptation index can be obtained from the ration of 1st ISI over nth ISI. (B) Replacement of extracellular buffer to Ca2+-free buffer abolishes the spike-frequency adaptation.
Fig. 2
Fig. 2. Ca2+-activated potassium channels mediate afterhyperpolarization. Ca2+-activated potassium channels such as BKCa and SKCa channels mediates afterhyperpolarization. BKCa channels are directly activated by Ca2+ binding where SKCa channels are activated by Ca2+-calmodulin. They are functionally linked to various voltage-gated Ca2+ channels depending on neuronal types.
Fig. 3
Fig. 3. Ca2+-dependent spike frequency adaptation mediated by Ca2+-activated chloride channels in TC and CA1 neurons. When a neuron is highly activated, Ca2+influx via voltage gated Ca2+ channel would increase the local [Ca2+]in in turn activate ANO2. The influx of Cl- caused by the low [Cl-]in in CNS neurons would hyperpolarize membrane potential, which would decrease the spike generation probability.

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