  The investigation of the neuronal environment allows us to better understand
the activity of a cerebral region as a whole. The recent experimental evidences
of the presence of transporters for glutamate and GABA in both neuronal and
astrocyte compartments raise the question of the functional importance of the
astrocytes in the regulation of the neuronal activity. We propose a new
computational model at the mesoscopic scale embedding the recent knowledge on
the physiology of neuron and astrocyte coupled activities. The neural
compartment is a neural mass model with double excitatory feedback, and the
glial compartment focus on the dynamics of glutamate and GABA concentrations.
Using the proposed model, we first study the impact of a deficiency in the
reuptake of GABA by astrocytes, which implies an increase in GABA concentration
in the extracellular space. A decrease in the frequency of neural activity is
observed and explained from the dynamics analysis. Second, we investigate the
neuronal response to a deficiency in the reuptake of Glutamate by the
astrocytes. In this case, we identify three behaviors : the neural activity may
either be reduced, or enhanced or, alternatively, may experience a transient of
high activity before stabilizing around a new activity regime with a frequency
close to the nominal one. After translating theoretically the neuronal
excitability modulation using the bifurcation structure of the neural mass
model, we state the conditions on the glial feedback parameters corresponding
to each behavior.
