LONG-TERM POTENTIATION AND FUNCTIONAL SYNAPSE INDUCTION IN DEVELOPINGHIPPOCAMPUS

LONG-TERM potentiation (LTP) is a cellular mechanism that potentially underlies learning and memory(1). To test the hypothesis that LTP is i nvolved in activity-dependent synapse formation, we combined whole-cel l recordings and confocal microscopy to investigate hippocampal glutam atergic synapses at their earliest stages of development. Here we repo rt that, during the first postnatal week, the hippocampal glutamatergi c network becomes gradually functional owing to the transformation of precursor, pure NMDA (N-methyl-D-aspartate)-receptor-based synaptic co ntacts into conducting AMPA -methylisoxazole-4-proprionate)/NMDA-recep tor-type synapses. This functional synapse induction is caused by an a ssociative form of LTP, so it is input-specific and easily triggered e xperimentally by pairing presynaptic stimulation with postsynaptic dep olarization. Our results challenge previous views that LTP occurs in t he hippocampus only at later stages of development(2-6) and that its i nduction requires dendritic spines(7). They also provide direct eviden ce that LTP is important for the activity-dependent formation of condu cting glutamatergic synapses in the developing mammalian brain.