TY - JOUR
T1 - A computational model for how the fast afterhyperpolarization paradoxically increases gain in regularly firing neurons
AU - Jaffe, David B.
AU - Brenner, Robert
N1 - Funding Information:
This project was supported by National Science Foundation Grant 1456862.
Publisher Copyright:
© 2018 the American Physiological Society. All rights reserved.
PY - 2018/4
Y1 - 2018/4
N2 - The gain of a neuron, the number and frequency of action potentials triggered in response to a given amount of depolarizing injection, is an important behavior underlying a neuron’s function. Variations in action potential waveform can influence neuronal discharges by the differential activation of voltage- and ion-gated channels long after the end of a spike. One component of the action potential waveform, the afterhyperpolarization (AHP), is generally considered an inhibitory mechanism for limiting firing rates. In dentate gyrus granule cells (DGCs) expressing fast-gated BK channels, large fast AHPs (fAHP) are paradoxically associated with increased gain. In this article, we describe a mechanism for this behavior using a computational model. Hyperpolarization provided by the fAHP enhances activation of a dendritic inward current (a T-type Ca 2+ channel is suggested) that, in turn, boosts rebound depolarization at the soma. The model suggests that the fAHP may both reduce Ca 2+ channel inactivation and, counterintuitively, enhance its activation. The magnitude of the rebound depolarization, in turn, determines the activation of a subsequent, slower inward current (a persistent Na + current is suggested) limiting the interspike interval. Simulations also show that the effect of AHP on gain is also effective for physiologically relevant stimulation; varying AHP amplitude affects interspike interval across a range of “noisy” stimulus frequency and amplitudes. The mechanism proposed suggests that small fAHPs in DGCs may contribute to their limited excitability. NEW & NOTEWORTHY The afterhyperpolarization (AHP) is canonically viewed as a major factor underlying the refractory period, serving to limit neuronal firing rate. We recently reported that enhancing the amplitude of the fast AHP (fAHP) in a relatively slowly firing neuron (vs. fast spiking neurons) expressing fast-gated BK channels augments neuronal excitability. In this computational study, we present a novel, quantitative hypothesis for how varying the amplitude of the fAHP can, paradoxically, influence a subsequent spike tens of milliseconds later.
AB - The gain of a neuron, the number and frequency of action potentials triggered in response to a given amount of depolarizing injection, is an important behavior underlying a neuron’s function. Variations in action potential waveform can influence neuronal discharges by the differential activation of voltage- and ion-gated channels long after the end of a spike. One component of the action potential waveform, the afterhyperpolarization (AHP), is generally considered an inhibitory mechanism for limiting firing rates. In dentate gyrus granule cells (DGCs) expressing fast-gated BK channels, large fast AHPs (fAHP) are paradoxically associated with increased gain. In this article, we describe a mechanism for this behavior using a computational model. Hyperpolarization provided by the fAHP enhances activation of a dendritic inward current (a T-type Ca 2+ channel is suggested) that, in turn, boosts rebound depolarization at the soma. The model suggests that the fAHP may both reduce Ca 2+ channel inactivation and, counterintuitively, enhance its activation. The magnitude of the rebound depolarization, in turn, determines the activation of a subsequent, slower inward current (a persistent Na + current is suggested) limiting the interspike interval. Simulations also show that the effect of AHP on gain is also effective for physiologically relevant stimulation; varying AHP amplitude affects interspike interval across a range of “noisy” stimulus frequency and amplitudes. The mechanism proposed suggests that small fAHPs in DGCs may contribute to their limited excitability. NEW & NOTEWORTHY The afterhyperpolarization (AHP) is canonically viewed as a major factor underlying the refractory period, serving to limit neuronal firing rate. We recently reported that enhancing the amplitude of the fast AHP (fAHP) in a relatively slowly firing neuron (vs. fast spiking neurons) expressing fast-gated BK channels augments neuronal excitability. In this computational study, we present a novel, quantitative hypothesis for how varying the amplitude of the fAHP can, paradoxically, influence a subsequent spike tens of milliseconds later.
KW - Afterhyperpolarization
KW - BK channels
KW - Computational model
KW - Dentate gyrus granule cell
KW - Depolarizing afterpotential
KW - Excitability
KW - Rebound
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U2 - 10.1152/jn.00385.2017
DO - 10.1152/jn.00385.2017
M3 - Article
C2 - 29357445
AN - SCOPUS:85045399206
VL - 119
SP - 1506
EP - 1520
JO - Journal of Neurophysiology
JF - Journal of Neurophysiology
SN - 0022-3077
IS - 4
ER -