Astrocyte responses to neuronal activity

During the past few years, it has been established that astrocytes sense neuronal activity and are involved in signal transmission. Neuronal stimulation triggered electrophysiological and/or Ca2+ responses in astrocyte cultures and in acute brain slices. Present even within one given brain region, different pathways of neuron‐to‐astrocyte communication involving different receptor systems have been described. These mechanisms include glutamatergic and NO‐mediated signaling. Neuron‐to‐astrocyte signaling can be confined to subcellular compartments, the microdomains, or it can activate the entire cell. It can even trigger a multicellular response in astrocytes, a Ca2+ wave. This form of astrocyte long‐range signal propagation can occur independently, in pure astrocyte cultures, but it can also be triggered by neuronal activity. Astrocytes also exhibit spontaneous Ca2+ activity. Neuronal activity in acute brain slices can organize this activity into complex synchronous networks. One of the functional consequences of neuron‐to‐astrocyte signaling might be the neuronal control of microcirculation using astrocytes as a mediator. © 2004 Wiley‐Liss, Inc.