FIGURE 4.

Cellular events driving propagation of the wave of spreading depression in the neuron-astrocyte network of Fig. 1 B. Shown are the changes in ATP concentration at seven successive astrocytes (A) after initiation of the purinergic wave at the first astrocyte in the chain (see Fig. 1 B), together with the accompanying changes in intracellular IP₃ (B) and intracellular Ca²⁺ (C) within the astrocytes. The concentration of glutamate released from these astrocytes onto successive neurons (Glu_A in Fig. 1 B) and of glutamate released from the neurons onto successive astrocytes (Glu_B in Fig. 1 B) is given in D and E, respectively. The effect of these transmitters on the transmembrane potential of successive neurons (F) and astrocytes (G) is given together with that of the extracellular potential change at successive sites along the network chain of Fig. 1 B, indicating the wave of propagating SD (H); increasing D_K by a factor of 4 gives the larger potential shown in (I). The propagation speed of the ATP wave is now ∼41 μm s⁻¹, double that of Fig. 3 A where no neurons are present.