Abstract
BackgroundLittle is known about the roles of dendritic gap junctions (GJs) of inhibitory interneurons in modulating temporal properties of sensory induced responses in sensory cortices. Electrophysiological dual patch-clamp recording and computational simulation methods were used in combination to examine a novel role of GJs in sensory mediated feed-forward inhibitory responses in barrel cortex layer IV and its underlying mechanisms.ResultsUnder physiological conditions, excitatory post-junctional potentials (EPJPs) interact with thalamocortical (TC) inputs within an unprecedented few milliseconds (i.e. over 200 Hz) to enhance the firing probability and synchrony of coupled fast-spiking (FS) cells. Dendritic GJ coupling allows fourfold increase in synchrony and a significant enhancement in spike transmission efficacy in excitatory spiny stellate cells. The model revealed the following novel mechanisms: 1) rapid capacitive current (Icap) underlies the activation of voltage-gated sodium channels; 2) there was less than 2 milliseconds in which the Icap underlying TC input and EPJP was coupled effectively; 3) cells with dendritic GJs had larger input conductance and smaller membrane response to weaker inputs; 4) synchrony in inhibitory networks by GJ coupling leads to reduced sporadic lateral inhibition and increased TC transmission efficacy.ConclusionDendritic GJs of neocortical inhibitory networks can have very powerful effects in modulating the strength and the temporal properties of sensory induced feed-forward inhibitory and excitatory responses at a very high frequency band (>200 Hz). Rapid capacitive currents are identified as main mechanisms underlying interaction between two transient synaptic conductances.
Highlights
Little is known about the roles of dendritic gap junctions (GJs) of inhibitory interneurons in modulating temporal properties of sensory induced responses in sensory cortices
The coupling coefficient reflects how much membrane voltage is generated in the postsynaptic cell via GJ coupling
I estimated the conductance of the EPJP, using input conductance of the postsynaptic cells multiplied by the coupling coefficient
Summary
Little is known about the roles of dendritic gap junctions (GJs) of inhibitory interneurons in modulating temporal properties of sensory induced responses in sensory cortices. Electrophysiological dual patch-clamp recording and computational simulation methods were used in combination to examine a novel role of GJs in sensory mediated feed-forward inhibitory responses in barrel cortex layer IV and its underlying mechanisms. I attempt to elucidate how dendritic gap junction coupling among GABAergic fast-spiking interneurons promotes sensory processing in the primary somatosensory cortex. Sensory feed-forward inhibition plays important roles in shaping the responses of principal cortical neurons, constraining runaway excitation [4,5], sharpening the contour of the receptive field [6] and improving the temporal fidelity [7]. In the somatosensory cortex, feed-forward inhibition is predominantly mediated by small clusters of GJ coupled fast-spiking (FS) interneurons No study has far tested how dendritic GJs contribute to sensory induced responses
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