Glial modulation of synaptic transmission in the retina.

Glial modulation of synaptic transmission and neuronal excitability in the mammalian retina is mediated by several mechanisms. Stimulation of glial cells evokes Ca(2+) waves, which propagate through the network of retinal astrocytes and Müller cells and result in the modulation of the activity of neighboring ganglion cells. Light-evoked spiking is enhanced in some ganglion cells and depressed in others. A facilitation or depression of light-evoked excitatory postsynaptic currents is also seen in ganglion cells following glial stimulation. In addition, stimulation of glial cells evokes a sustained hyperpolarizing current in ganglion cells which is mediated by ATP release from Müller cells and activation of neuronal A(1) adenosine receptors. Recent studies reveal that light-evoked activity in retinal neurons results in an increase in the frequency of Ca(2+) transients in Müller cells. Thus, there is two-way communication between neurons and glial cells, suggesting that glia contribute to information processing in the retina.