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 Ca(2+) 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 Ca(2+) 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 Ca(2+) 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.