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Propagating Activity in Neocortex, Mediated by Gap Junctions and Modulated by Extracellular Potassium.

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Elevated extracellular potassium (K+) enables synchronized parvalbumin-expressing interneuron activity to propagate in the cortex. This intercellular communication, mediated by gap junctions, occurs naturally during intense brain activity and influences seizure dynamics.

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Area of Science:

  • Neuroscience
  • Computational Neuroscience
  • Cellular Neuroscience

Background:

  • Parvalbumin-expressing interneurons form gap junction-coupled networks.
  • These networks support synchronized activity, but propagation in natural states is unclear.
  • Extracellular potassium ([K+]o) increases during intense neural activity, like seizures.

Purpose of the Study:

  • To investigate if parvalbumin-expressing interneuron activity propagates under elevated [K+]o.
  • To determine the mechanisms underlying activity propagation.
  • To compare propagation under elevated [K+]o with 4-aminopyridine-induced activity.

Main Methods:

  • Optogenetic activation of parvalbumin-expressing interneurons in mouse visual cortex.
  • Recording neural activity with a linear electrode array.
  • Manipulating [K+]o and using pharmacological blockers (GABAergic, glutamatergic, gap junction inhibitors).
  • Computational modeling of network dynamics.

Main Results:

  • At baseline [K+]o, activity was confined to the activated area.
  • Elevated [K+]o (>8.0 mm) enabled propagation of interneuron activity (59.1 mm/s).
  • Propagation was independent of GABAergic transmission but modulated by glutamatergic blockers.
  • Gap junction blockade (quinine, mefloquine, carbenoxolone) prevented propagation.

Conclusions:

  • Elevated [K+]o facilitates gap junction-dependent propagation of parvalbumin-expressing interneuron activity.
  • This syncytial propagation mechanism may influence seizure dynamics.
  • Propagation differs qualitatively between high [K+]o and 4-aminopyridine conditions.