Glial cells contain metabotropic type 2 glutamate receptors (mGluR2) on their plasma membrane, which, once activated by excessive glutamate release during cerebral ischemia, results in stimulation of IP3-mediated Ca2+ release from intracellular stores and the release of 'gliotransmitters' such as TNF-α, ATP and glutamate itself [41]. Here, TNF is linked to brain ischemia.