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Using potassium currents to solve signal-to-noise problems in inhibitory feedforward networks of the striatum
Journal article   Peer reviewed

Using potassium currents to solve signal-to-noise problems in inhibitory feedforward networks of the striatum

Jeanette Hellgren Kotaleski, D. Plenz and K. T. Blackwell
Journal of neurophysiology, Vol.95(1), pp.331-341
01/01/2006
DOI: 10.1152/jn.00063.2005
PMCID: PMC4107364
PMID: 16192340

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Abstract

Using potassium currents to solve signal-to-noise problems in inhibitory feedforward networks of the striatum. J Neurophysiol 95: 331 - 341, 2006. First published September 28, 2005; doi: 10.1152/jn. 00063.2005. Fast-spiking (FS) interneurons provide the main route of feedforward inhibition from cortex to spiny projection neurons in the striatum. A steep current-firing frequency curve and a dense local axonal arbor suggest that even small excitatory inputs could translate into powerful feedforward inhibition, although such an arrangement is also sensitive to amplification of spurious synaptic inputs. We show that a transient potassium (KA) current allows the FS interneuron to strike a balance between sensitivity to correlated input and robustness to noise, thereby increasing its signal-to-noise ratio (SNR). First, a compartmental FS neuron model was created to match experimental data from striatal FS interneurons in cortex - striatum - substantia nigra organotypic cultures. Densities of sodium, delayed rectifier, and KA channels were optimized to replicate responses to somatic current injection. Spontaneous alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and gamma-aminobutyric acid ( GABA) synaptic currents were adjusted to the experimentally measured amplitude, rise time, and interevent interval histograms. Second, two additional adjustments were required to emulate the remaining experimental observations. GABA channels were localized closer to the soma than AMPA channels to match the synaptic population reversal potential. Correlation among inputs was required to produce the observed firing rate during up-states. In this final model, KA channels were essential for suppressing down-state spikes while allowing reliable spike generation during up-states. This mechanism was particularly important under conditions of high dopamine. Our results suggest that KA channels allow FS interneurons to operate without a decrease in SNR during conditions of increased dopamine, as occurs in response to reward or anticipated reward.
 basal ganglia dendritic calcium dopaminergic modulation fast-spiking interneurons neocortical pyramidal neurons neostriatal neurons nmda receptors nucleus-accumbens spiny projection neurons synaptic input

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