Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 6, Pages 2187-2192Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0710628105
Keywords
barrel cortex; dendrites; neocortex; somatostatin; feedforward inhibition
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Funding
- NCRR NIH HHS [P20 RR015574, RR15574] Funding Source: Medline
- NINDS NIH HHS [NS050437, R01 NS050437] Funding Source: Medline
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GABA-releasing cortical interneurons are crucial for the neural transformations underlying sensory perception, providing feedforward inhibition that constrains the temporal window for synaptic integration. To mediate feedforward inhibition, inhibitory interneurons need to fire in response to ascending thalamocortical inputs, and most previous studies concluded that ascending inputs activate mainly or solely proximally targeting, parvalbumin-containing fast-spiking interneurons. However, when thalamocortical axons fire at frequencies that are likely to occur during natural exploratory behavior, activation of fast-spiking interneurons is rapidly and strongly depressed, implying the paradoxical conclusion that feedforward inhibition is absent when it is most needed. To address this issue, we took advantage of lines of transgenic mice in which either parvalbumin- or somatostatin-containing interneurons express GFP and recorded the responses of interneurons from both subtypes to thalamocortical stimulation in vitro. We report that during thalamocortical activation at behaviorally expected frequencies, fast-spiking interneurons were indeed activated only transiently because of rapid depression of their thalamocortical inputs, but a subset of layer 5 somatostatin-containing interneurons were robustly and persistently activated after a delay, due to the facilitation and temporal summation of their thalamocortical excitatory postsynaptic potentials. Somatostatin-containing interneurons are considered distally targeting. Thus, they are likely to provide delayed dendritic inhibition during exploratory behavior, contributing to the maintenance of a balance between cortical excitation and inhibition while leaving a wide temporal window open for synaptic integration and plasticity in distal dendrites.
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