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 Ca2+ waves, which propagate through the network of retinal astrocytes and Muller 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 Muller cells and activation of neuronal A, adenosine receptors. Recent studies reveal that light-evoked activity in retinal neurons results in an increase in the frequency of Ca2+ transients in Muller cells. Thus, there is two-way communication between neurons and glial cells, suggesting that glia contribute to information processing in the retina. (C) 2004 Wiley-Liss, Inc.