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Persistent synchronized bursting activity in cortical tissues with low magnesium concentration: a modeling study
David Golomb1, Anat Shedmi, Rodica Curtu
1Department of Physiology, Faculty of Health Sciences, Ben-Gurion University, Be'er-Sheva, Israel. golomb@bgu.ac.il
Journal of Neurophysiology
|October 21, 2005
Summary
Synchronized bursting in cortical tissues at low extracellular magnesium is persistent and depends on slow N-methyl-D-aspartate (NMDA) conductances. This activity, crucial for epileptiform events, is influenced by NMDA and AMPA conductances and cell properties.
Area of Science:
- Neuroscience
- Computational Neuroscience
- Epilepsy Research
Background:
- Cortical tissues exhibit synchronized bursting activity (~10 Hz) at low extracellular magnesium concentration ([Mg2+]o).
- This activity is hypothesized to be persistent, coexisting with quiescence and dependent on slow N-methyl-D-aspartate (NMDA) conductances.
Purpose of the Study:
- To investigate the mechanism of persistent synchronized bursting activity in excitatory cortical networks.
- To determine the role of N-methyl-D-aspartate (NMDA) and AMPA conductances in this phenomenon.
- To explore the influence of conditional bursters and extracellular magnesium on network activity.
Main Methods:
- Construction and investigation of a conductance-based model of excitatory cortical networks.
- Analysis of a reduced single-cell model using the fast-slow method.
- Simulation of network behavior under varying NMDA and AMPA conductance values and extracellular magnesium concentrations.
Main Results:
- Population bursting activity persists for physiological NMDA decay time constants (~100 ms).
- Synchronized bursts occur with intermediate NMDA conductance (g(NMDA)) and are robust with conditional bursters.
- Increased AMPA conductance (g(AMPA)) enhances synchrony but decreases bursting frequency and can prevent activity due to adaptation.
- Higher [Mg2+]o requires increased g(NMDA) for bursting, and physiological [Mg2+]o renders the network silent.
- Inhibition weakly decreases bursting frequency when inhibitory cells receive sufficient NMDA excitation.
Conclusions:
- Persistent synchronized bursting at low [Mg2+]o is critically dependent on slow NMDA conductances and influenced by AMPA conductances.
- Conditional bursters play a significant role in supporting this epileptiform activity.
- The findings highlight the importance of specific ion channel dynamics and extracellular environment in shaping cortical network states.