FIGURE 1.

(A) Lane of model astrocytes, represented by cubes of side 25 μm, separated by spaces of width 25 μm. The cubes have their centers in the x, y plane (z = 0) and are aligned parallel to the x axis. ATP diffuses in the extracellular space and binds to receptors that are uniformly distributed on the surfaces of the cubes. The neurons are not shown; although there is a one-to-one correspondence with the astrocytes, their interaction is via glutamate and, as explained in the text, it is not necessary to explicitly include glutamate diffusion in the model. Thus their spatial position is not needed for the calculations. (B) Neuron-astrocyte model network in which astrocytic transmission is effected by ATP and neuronal transmission by glutamate, as follows: from neuron to neuron, glutamate (Glu_C) acting on AMPA receptors; from astrocyte to neuron, glutamate (Glu_A) acting on NMDA receptors; from neuron to astrocyte, glutamate (Glu_B) acting on metabotropic receptors; from astrocyte to astrocyte, ATP acting on P2Y receptors. (C) Neuron-astrocyte model network in which astrocytic transmission is principally effected by GJs, together with a small component due to released ATP. (The ATP production rate is reduced to one-tenth of that in the model of part A.) The remainder of the network is as in part A.