1 We have investigated increases in cytosolic Ca 2+ in response to nucleotides in mixed rat cerebrocortical cultures (neurons and glia in similar numbers) and in essentially neuron-free glial cultures. 2 In both cultures, the agonist-response profile was 2-methylthioADP(2MeSADP)42-methylthioATP(2MeSATP)4ADP4ATP4adenosine 5 0 -O-(3-thiotriphosphate), consistent with a P2Y 1 receptor. The maximal responses to 2MeSADP, 2MeSATP and ADP were identical, but that to ATP was higher. 3 Suramin, pyridoxal-phosphate-6-azophenyl-2 0 ,4 0 -disulphonic acid, reactive blue 2 (RB2), and adenosine biphosphate (A3P5P) were antagonists with apparent pA 2 values of 5.5 for suramin, 6.4 for RB2, and 4.7 for A3P5P. . This further indicated that the 2MeSADP response was not in the neurons. 6 Reverse transcriptase -polymerase chain reaction studies detected transcripts for P2Y 1 , P2Y 4 and P2Y 6 in RNA preparations from embryonic rat cortex, and from both mixed and glial cultures. P2Y 2 transcripts were not detected in the embryonic cortex. 7 Based on this and previous work, it is proposed that the principal P2Y influences in the brain are on cytosolic Ca 2+ in glial cells and presynaptic sites on neurons.

1 Evidence has previously been presented that P1 receptors for adenosine, and P2 receptors for nucleotides such as ATP, regulate stimulus-evoked release of biogenic amines from nerve terminals in the brain. Here we investigated whether adenosine and nucleotides exert presynaptic control over depolarisation-elicited glutamate release. 2 Slices of rat brain cortex were perfused and stimulated with pulses of 46 mM K + in the presence of the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (0.2 mM). High K + substantially increased eux of glutamate from the slices. 3 Basal glutamate release was unchanged by the presence of nucleotides or adenosine at concentrations of 300 mM. 4 Adenosine, ATP, ADP and adenosine 5'-O-(3-thiotriphoshate) at 300 mM attenuated depolarisation-evoked release of glutamate. However UTP, 2-methylthio ATP, 2-methylthio ADP, and a,bmethylene ATP at 300 mM had no eect on stimulated glutamate eux. 5 Adenosine deaminase blocked the eect of adenosine, but left the response to ATP unchanged. 6 The A 1 antagonist 8-cyclopentyl-1,3-dipropylxanthine antagonised the inhibitory eect of both adenosine and ATP. 7 Cibacron blue 3GA inhibited stimulus-evoked glutamate release when applied alone. When cibacron blue 3GA was present with ATP, stimulus-evoked glutamate release was almost eliminated. However, this P2 antagonist had no eect on the inhibition by adenosine. 8 These results show that the release of glutamate from depolarised nerve terminals of the rat cerebral cortex is inhibited by adenosine and ATP. ATP appears to act directly and not through conversion to adenosine.