  Mounting evidence in recent years suggests that astrocytes, a sub-type of
glial cells, not only serve metabolic and structural support for neurons and
synapses but also play critical roles in regulation of proper functioning of
the nervous system. In this work, we investigate the effect of astrocyte on the
spontaneous firing activity of a neuron through a combined model which includes
a neuron-astrocyte pair. First, we show that an astrocyte may provide a kind of
multistability in neuron dynamics by inducing different firing modes such as
random and bursty spiking. Then, we identify the underlying mechanism of this
behavior and search for the astrocytic factors that may have regulatory roles
in different firing regimes. More specifically, we explore how an astrocyte can
participate in occurrence and control of spontaneous irregular spiking activity
of a neuron in random spiking mode. Additionally, we systematically investigate
the bursty firing regime dynamics of the neuron under the variation of
biophysical facts related to the intracellular environment of the astrocyte. It
is found that an astrocyte coupled to a neuron can provide a control mechanism
for both spontaneous firing irregularity and burst firing statistics, i.e.,
burst regularity and size.
