Mixed-mode Oscillations in Pyramidal Neurons Under Antiepileptic Drug Conditions

Subthreshold oscillations in combination with large-amplitude oscillations generate mixedmode oscillations (MMOs), which mediate various spatial and temporal cognition and memory processes and behavioral motor tasks. Although many studies have shown that canard theory is a reliable method to investigate the properties underlying the MMOs phenomena, the relationship between the results obtained by applying canard theory and conductancebased models of neurons and their electrophysiological mechanisms are still not well understood. The goal of this study was to apply canard theory to the conductance-based model of pyramidal neurons in layer V of the Entorhinal Cortex to investigate the properties of MMOs under antiepileptic drug conditions (i.e., when persistent sodium current is inhibited). We investigated not only the mathematical properties of MMOs in these neurons, but also the electrophysiological mechanisms that shape spike clustering. Our results show that pyramidal neurons can display two types of MMOs and the magnitude of the slow potassium current determines whether MMOs of type I or type II would emerge. Our results also indicate that slow potassium currents with large time constant have significant impact on generating the MMOs, as opposed to fast inward currents. Our results provide complete characterization of the subthreshold activities in MMOs in pyramidal neurons and provide explanation to experimental studies that showed MMOs of type I or type II in pyramidal neurons under antiepileptic drug conditions

Vesicular glutamatergic transmission in noise-induced loss and repair of cochlear ribbon synapses

Noise-induced excitotoxicity is thought to depend on glutamate. However, the excitotoxic mechanisms are unknown, and the necessity of glutamate for synapse loss or regeneration is unclear. Despite absence of glutamatergic transmission from cochlear inner hair cells in mice lacking the vesicular glutamate transporter-3

Mixed-mode oscillations in pyramidal neurons under antiepileptic drug conditions

<div><p>Subthreshold oscillations in combination with large-amplitude oscillations generate mixed-mode oscillations (MMOs), which mediate various spatial and temporal cognition and memory processes and behavioral motor tasks. Although many studies have shown that canard theory is a reliable method to investigate the properties underlying the MMOs phenomena, the relationship between the results obtained by applying canard theory and conductance-based models of neurons and their electrophysiological mechanisms are still not well understood. The goal of this study was to apply canard theory to the conductance-based model of pyramidal neurons in layer V of the Entorhinal Cortex to investigate the properties of MMOs under antiepileptic drug conditions (i.e., when persistent sodium current is inhibited). We investigated not only the mathematical properties of MMOs in these neurons, but also the electrophysiological mechanisms that shape spike clustering. Our results show that pyramidal neurons can display two types of MMOs and the magnitude of the slow potassium current determines whether MMOs of type I or type II would emerge. Our results also indicate that slow potassium currents with large time constant have significant impact on generating the MMOs, as opposed to fast inward currents. Our results provide complete characterization of the subthreshold activities in MMOs in pyramidal neurons and provide explanation to experimental studies that showed MMOs of type I or type II in pyramidal neurons under antiepileptic drug conditions.</p></div

Carbonaceous Materials and Their Advances as a Counter Electrode in Dye-Sensitized Solar Cells: Challenges and Prospects

Dye-sensitized solar cells (DSSCs) serve as low-costing alternatives to silicon solar cells because of their low material and fabrication costs. Usually, they utilize Pt as the counter electrode (CE) to catalyze the iodine redox couple and to complete the electric circuit. Given that Pt is a rare and expensive metal, various carbon materials have been intensively investigated because of their low costs, high surface areas, excellent electrochemical stabilities, reasonable electrochemical activities, and high corrosion resistances. In this feature article, we provide an overview of recent studies on the electrochemical properties and photovoltaic performances of carbon-based CEs (e.g., activated carbon, nanosized carbon, carbon black, graphene, graphite, carbon nanotubes, and composite carbon). We focus on scientific challenges associated with each material and highlight recent advances achieved in overcoming these obstacles. Finally, we discuss possible future directions for this field of research aimed at obtaining highly efficient DSSCs

Conductance-based model of pyramidal neurons.

<p>The model composed of a capacitor and five parallel resistors. The constant resistor represents the passive leakage current, <i>g</i>_<i>leak</i>. Four other resistors correspond to the active conductances, <i>g</i>_<i>ks</i>, <i>g</i>_<i>nap</i>, <i>g</i>_<i>k</i>, <i>g</i>_<i>na</i>. The <i>g</i>_<i>k</i> and <i>g</i>_<i>na</i> are conductances of Hodgkin-Huxley model for generating fast action potentials. <i>E</i>_<i>k</i>, <i>E</i>_<i>na</i> and <i>E</i>_<i>L</i> are the reversal potentials of potassium, sodium and leak currents respectively.</p

The evolutions of dynamics of the pyramidal cells in layer V of EC.

<p><b>a)</b> Steady-state (in)activation functions. <b>b)</b> Voltage-dependent time constant functions (<i>τ</i>_<i>mKS</i> = 90 msec).</p

In control condition, the singularities, <i>V</i>-nullcline (red) and <i>n</i>-nullcline (green) for <i>I</i> = 17.5 (μA/cm²).

<p>In the Region of interest (ROI), the existence of folded node on <i>L</i>^- (filled blue cycle, d) indicates the occurrence of type I MMOs (left-trace and right-lower-trace). In this model, there is also a folded node on <i>L</i>⁺ (filled blue cycle, b), which shows there is also the type II MMOs in this model (right-upper-trace). In control condition, there is also a stable folded focus on <i>L</i>⁺ (a), folded saddle on <i>L</i>^-(c) and saddle point on <i>NN</i> (e).</p

The evolution of variables in the reduced model of pyramidal neurons for <i>I</i>_<i>inp</i> = 17.2 (μA/cm²).

<p><b>a)</b> For <i>g</i>_<i>ks</i> = 2 (μS/cm²), the membrane potential displays the type I MMO (<i>upper</i> trace), activation variable of <i>K</i>⁺-channel, <i>n</i> (<i>middle</i> trace), and activation variable of <i>KS</i>-channel, <i>m</i>_<i>ks</i> (<i>lower</i> trace). <b>b)</b> For <i>g</i>_<i>ks</i> = 1 (μS/cm²), the membrane potential shows the type II MMO (<i>upper</i> trace), activation variable of <i>K</i>⁺-channel, <i>n</i> (<i>middle</i> trace), and activation variable of <i>KS</i>-channel, <i>m</i>_<i>ks</i> (<i>lower</i> trace).</p

The folded and ordinary singularities on nullclines for changing <i>g</i>_<i>na</i> (μS/cm²).

<p><b>a)</b><i>g</i>_<i>na</i> = 1 (μS/cm²), <b>b)</b> <i>g</i>_<i>na</i> = 3.36 (μS/cm²), <b>c)</b> <i>g</i>_<i>na</i> = 20 (μS/cm²), and <b>d)</b> <i>g</i>_<i>na</i> = 40.86 (μS/cm²). The phase space of this system contains a single branch <i>V</i>-nullcline (red line) and three branches n-nullcline (green line) including <i>L</i>⁺ (upper horizontal line), <i>L</i>^- (lower horizontal line) and <i>NN</i> (vertical curve). The color convention for equilibria is similar to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178244#pone.0178244.g005" target="_blank">Fig 5</a>.</p