IBOTENATE STIMULATES GLUTAMATE RELEASE FROM GUINEA-PIG CEREBROCORTICAL SYNAPTOSOMES - INHIBITION BY L-2-AMINO-4-PHOSPHONOBUTYRATE (L-AP4)

Ibotenate induced a concentration- and largely calcium-dependent release of endogenous glutamate from guinea pig cerebro-cortical synaptosomes. In the absence of Mg2+, the response to ibotenate was enhanced through a mechanism involving N-methyl-d-aspartate (NMDA) receptors; this component was sensitive to the NMDA antagonist 2-amino-7-phosphonoheptanoate (AP7). In the presence of Mg2+, the ibotenate-induced Ca2+-dependent release was abolished by l-2-amino-4-phosphonobutyrate (l-AP4). It is suggested that presynaptic 'l-AP4 receptors' exist in guinea pig cerebral cortex, at which ibotenate acts to facilitate glutamate release. l-AP4 may act as an antagonist, or partial agonist of weak intrinsic activity. © 1990.