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The Reversal Potential of Inhibitory Synapses
Strongly Impacts the Dynamics of Neural
Networks
Santi Chillemi, Michele Barbi, and Angelo Di Garbo
Istituto di Biofisica CNR, Sezione di Pisa,
Via G. Moruzzi 1, 56124 Pisa, Italy
{
santi.chillemi,michele.barbi,angelo.digarbo
}
@pi.ibf.cnr.it
http://www.pi.ibf.cnr.it
Abstract.
The balance between inhibition and excitation is at the basis
of the maintenance of stable and normal brain electrical activity. Exper-
imental results revealed that inhibitory synapses can become depolariz-
ing as the intracellular concentration of
Cl
−
1 of the postsynaptic cells
increases. In this work the dynamical behaviour of a network of pyrami-
dal cells coupled to inhibitory Fast-Spiking interneurons was studied by
simulations. In particular, in agreement to the experimental data, it was
found that the increase of the reversal potential of inhibitory synapses
strongly impacts the network dynamics.
1
Introduction
The brain is populated by excitatory neurons and inhibitory interneurons. Among
interneurons the most prominent class is that of Fast-Spiking (FS) cells: they
are coupled by inhibitory and electrical synapses and are capable of generating
synchronous oscillations [1,2]. These cells exert a powerful control of the firing
activity of pyramidal neurons by means of somatic and perisomatic synaptic
GABAergic contacts [3]. Interneurons receive excitatory inputs from pyramidal
cells and then feedback inhibition to them by modulating their firing activities
[4]. This mechanism is at the core of the existence of an excitatory-inhibitory
feedback loop between pyramidal cells and interneurons [1,2,3,5]. When the cel-
lular mechanisms regulating these processes are compromised (like in epilepsy)
the dynamics of this network becomes more complex and not well known. For
instance recently it was shown that FS interneurons are the drivers of seizure like
phenomena by activating directly pyramidal cells through excitatory GABAer-
gic transmission [6,7]. In fact it was shown that in particular conditions (for
instance when an accumulation of
Cl
−
occurs) inhibitory GABAergic synapses
can be converted to excitatory. However at present is still unresolved whether
interneurons are actively capable of promoting seizure like activity by means
of this mechanisms. Motivated by the previous remarks in the present paper we
studied the synchronization phenomena occurring in a network of interconnected
FS interneurons and pyramidal neurons. To gain realistic results the cells and
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