BIOPHYSICAL THEORY AND MODELING |
Bidirectional modulation of neuronal responses by depolarizing GABAergic inputs
Kenji Morita 1*, Kunichika Tsumoto 2 and Kazuyuki Aihara 1
1 Institute of Industrial Science, The University of Tokyo
2 ERATO Aihara Complexity Modeling Project, JST
* To whom correspondence should be addressed. E-mail: morita{at}sat.t.u-tokyo.ac.jp.
Submitted on March 18, 2005
Revised on April 30, 2005
Accepted on 30 November 2005
 |
Abstract |
|---|
The reversal potential of GABAA receptor-channels is known to be less negative than the resting potential under some cases. Recent electrophysiological experiments revealed that GABAergic unitary conductance with such a depolarized reversal potential could not only prevent but also facilitate action potential generation depending on the timing of its application relative to excitatory unitary conductance. Using a two-dimensional model of neocortical neurons, we simulate the experiments regarding integration of unitary conductances, and execute bifurcation analysis. Then we extend analysis to the case in which the neuron receives two kinds of periodic input trains - an excitatory glutamatergic one and a GABAergic one. We show that the periodic depolarizing GABAergic input train can modulate the output time-averaged firing rate bi-directionally, namely as an increase or a decrease, in a devil's-staircase-like manner depending on the phase difference with the glutamatergic input train. Bifurcation analysis reveals the existence of a wide variety of phase-locked solutions underlying such a graded bidirectional response characteristic of the neuron. We examine how the input time-width and the value of the GABAA reversal potential affect the response. Moreover, considering a population of neurons, we show that depolarizing GABAergic inputs bi-directionally modulate the amplitude of the oscillatory population activity.
Key Words:
GABA, bifurcation, devil's-staircase, firing rate, gamma oscillations, neural coding
