Astrocytes put down the broom and pick up the baton.

In this issue of Cell, Panatier et al. (2006) show that D-serine released by astrocytes, a type of glial cell in the brain, promotes NMDA receptor activity at synapses in the hypothalamus. These results confirm that glial cells participate in synaptic signaling and show that they can dictate the tenor of synaptic plasticity.