IN order to examine the relationship between long-term potentiation (LTP) and phosphoinositide (PI) turnover, we evaluated these throughout anesthetized rat brain using carbon-11-labeled diacylglycerol (11C-DAG). High-frequency tetanic stimulation (400 pulses at 40 0Hz) to the perforant pathway induced LTP in rat dentate gyrus. In autoradiograms of rat brains, LTP was associated with the occurrence of multiple highly radioactive spots in many regions distant from the stimulated site. Following i.v. administration of an NMDA receptor antagonist prior to stimulation, however, no high-density spots were found. These findings directly demonstrate that potentiation of phosphoinositide-derived signaling was induced during LTP, and the finding of multiple location suggests the occurrence of polysynaptic neurotransmission through neural networks pertaining to learning and memory.