TRAINING IN THE MORRIS WATER MAZE OCCLUDES THE SYNERGISM BETWEEN ACPDAND ARACHIDONIC-ACID ON GLUTAMATE RELEASE IN SYNAPTOSOMES PREPARED FROM RAT HIPPOCAMPUS

We report here that release of glutamate, inositol phospholipid metabo lism, and protein kinase C (PKC) activity are increased in synaptosome s prepared from hippocampi of rats that had been trained in a spatial learning task. In hippocampi obtained from animals that were untrained , activation of the metabotropic glutamate receptor by the specific ag onist trans-1-amino-cyclopentyl-1,3-dicarboxylate (ACPD) increased rel ease of glutamate but only in the presence of a low concentration of a rachidonic acid. A similar Interaction between arachidonic acid and AC PD was observed on inositol phospholipid turnover and on PKC activity. However, the synergistic effect of arachidonic acid and ACPD on gluta mate release was occluded in hippocampal synaptosomes prepared from tr ained rats. Occlusion of the effect on inositol phospholipid turnover and PKC activation was also observed. These data suggest that the mole cular changes that underlie spatial learning may include activation of metabotropic glutamate receptors in the presence of arachidonic acid and that the interaction between arachidonic acid and ACPD triggers th e presynaptic changes that accompany learning.