A novel role of dendritic gap junction and mechanisms underlying its interaction with thalamocortical conductance in fast spiking inhibitory neurons.
BACKGROUND
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.


RESULTS
Under 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.


CONCLUSIONS
Dendritic 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.
Sun
Qian-Quan
QQ
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA. neuron@uwyo.edu
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D048430:Cell Shape / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D003198:Computer Simulation; D003712:Dendrites / Q000502:physiology*; D017629:Gap Junctions / Q000502:physiology*; D005968:Glutamate Decarboxylase / Q000235:genetics; D007395:Interneurons / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D008959:Models, Neurological; D009431:Neural Conduction / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000502:physiology; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000502:physiology; D013787:Thalamic Nuclei / Q000502:physiology*
D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2