ACTIVATION OF METABOTROPIC GLUTAMATE RECEPTORS INDUCE DIFFERENTIAL-EFFECTS ON SYNAPTIC TRANSMISSION IN THE DENTATE GYRUS AND CA1 OF THE HIPPOCAMPUS IN THE ANESTHETIZED RAT

Activation of ACPD-sensitive metabotropic receptors induced differenti al effects on synaptic transmission and the induction of LTP in CA1 an d the dentate gyrus of the hippocampus i.c.v. injections of (1S,3R)-1- aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD] induced endurin g potentiation of the fEPSP in CA1, which occluded tetanically induced LTP. In contrast, ACPD induced a dose-dependent biphasic effect on th e fEPSP in the dentate gyrus, consisting of an initial short lasting p otentiation, followed by enduring depression of the response, and bloc kade of LTP. These two effects are likely to be mediated by two differ ent classes of the receptor as in the dentate gyrus the selective clas s I agonist, (RS)-3,5-dihydroxyphenylglycine (DHPG) induced sustained potentiation of the fEPSP, whereas the mixed mGluR2 agonist-mGluR1 ant agonist, (S)-4-carboxy-3-hydrophenylglycine((S)-4C3H-PG) induced only depression. Increasing the concentration of calcium directly in the de ntate gyrus prior to, and in conjunction with, injections of ACPD indu ced sustained potentiation rather than depression. The differential ef fects indicate that the second messenger cascades the subtypes of rece ptors are linked with, mediate different forms of synaptic plasticity within the hippocampus and have important implications for their role in learning. Copyright (C) 1996 Elsevier Science Ltd.