Neuroglia have multiple roles in nervous system which include the regulation of external potassium, the uptake of excitatory amino acids and releasing neurotransmitters such as glutamate and aspartate. There are three different mechanisms proposed for the release of glutamate. One of them is the calcium dependency of glutamate release; The second one is reversal of uptake of glutamate; Furosemide-sensitive release of glutamate from swelling cells is the third proposed mechanism;The objectives of this research are to determine whether neuroligand bradykinin (BK) and adenosine 5'-triphosphate (ATP) can stimulate release of excitatory amino acid (EAA) glutamate and aspartate from cultured glial cells and to identify the possible signal transduction pathways for the neuroligand-induced release of EAAs;BK caused a receptor-mediated increase in release of EAAs from cultured Schwann cells together with an increase in the cytoplasmic level of free calcium. Perturbations which inhibited bradykinin-induced calcium mobilization prevented the release of EAAs from the glia. BK did not cause cell swelling and the inhibitor of glutamate transporter did not reduce BK-induced EAA release. Therefore, BK-induced release of EAAs from Schwann cells is through the calcium-dependent mechanism;ATP can evoke release of EAAs from cultured Schwann cells. Adenosine was without effect on release of EAAs suggesting involvement of P2 receptors. ATP-evoked release of EAAs was not affected in calcium-depleted saline. However, this release was blocked by pretreatment of the cultures with both BAPTA-AM, an membrane permeant calcium chelator, and thapsigargin, an inhibitor of calcium ATPase of intracellular stores. These data confirm that ATP evokes the release of EAAs from Schwann cells by activating intracellular calcium stores;Application of the neuroligand bradykinin to cultured astrocytes elevated internal calcium and stimulated glutamate release. BK also significantly elevated calcium levels in neurons co-cultured with astrocytes, but not in solitary neurons. The glutamate receptor antagonists prevented bradykinin-induced neuronal calcium elevations. When single astrocytes were directly stimulated to increase internal calcium and release glutamate, calcium levels of adjacent neurons were increased. Thus, astrocytes regulate neuronal calcium levels through the calcium-dependent release of glutamate.