MEMORY OF INHIBITORY AVOIDANCE IN THE RAT IS REGULATED BY GLUTAMATE METABOTROPIC RECEPTORS IN THE HIPPOCAMPUS

This experiment investigated the effect on memory, in rats, of the bil ateral intrahippocampal post-training infusion of the glutamate metabo tropic receptor (mGLUR) agonist, ACPD (1S, 2R-aminocyclopentane dicarb oxylate) and of the mGLUR antagonist, MCPG ([RS]-alpha-methyl-4-carbox yphenyl glycine). Male Wistar rats were implanted bilaterally with can nulae in the CA1 region of the dorsal hippocampus. After recovery from surgery they were trained in a step-down inhibitory avoidance task an d tested for retention 24 h later. Immediately or 180 min after traini ng they received a bilateral intrahippocampal infusion of saline (0.5 mu l), ACPD (1.0 or 2.5 mu g/side), MCPG (2.5 mu g/side) or ACPD plus MCPG, in 0.5 yl saline. Upon immediate posttraining infusion, ACPD cau sed a dose-dependent enhancement of memory and MCPG was amnestic. The effect of MCPG was antagonized by the simultaneous administration of A CPD. When given 180 min after training, the drugs had no effect on mem ory. The results indicate that the early phase of memory is regulated by mGLURs in the hippocampus, and support the suggestion that memory i nvolves long-term potentiation initiated at the time of training in th e hippocampus.