Neuron-astrocyte cross-talk during synaptic transmission: physiological and neuropathological implications

In the central nervous system (CNS), astrocytes form an intimately connected network with neurons and their processes often closely enwrap synapses. The critical role of these cells in metabolic and trophic support to neurons, ion buffering and clearance of neurotransmitters is well established. However, recent accumulating evidence suggests that astrocytes are active partners of neurons in additional and more complex functions. In particular, astrocytes express a repertoire of neurotransmitter receptors mirroring that of neighboring synapses. Such receptors are stimulated during synaptic activity and start calcium signaling into the astrocyte network. Recent evidence indicates that intracellular oscillations and intercellular waves of calcium in astrocytes represent the start of backsignaling to neurons, as they trigger release of chemical transmitter (i.e. glutamate) via a novel process sensitive to blockers of exocytosis and involving cyclooxygenase products, the prostaglandins.