Long-term potentiation of synaptic transmission in the hippocampus of the rat; effect of calmodulin and oleoyl-acetyl-glycerol on release of [3H]glutamate.

The effect of calmodulin (CaM) and oleyl-acetyl-glycerol (OAG, a synthetic analogue of diacylglycerol, DAG) on K+-induced release of radiolabelled glutamate (Glu), was examined in synaptosomes prepared from area CA3 of control rats and rats in which long-term potentiation (LTP) had been induced in vivo by a brief train of high-frequency stimulation. Both CaM and OAG significantly enhanced release from control tissue in a dose-dependent manner. Release of preloaded L-[3H]Glu was significantly greater in synaptosomes prepared from potentiated tissue than from control tissue but neither CaM nor OAG further enhanced release in potentiated preparations. The occlusion of the two effects suggests that CaM and endogenous DAG are likely to be involved in control of Glu release and the enhancement of release associated with LTP.