Clusters or puncta of both postsynaptic glutamate receptors and presynaptic vesicle-associated proteins, as well as sites where the pre- and postsynaptic puncta colocalize. Within tens of minutes there is outgrowth of new pre- and postsynaptic structures, and by 0.5 to 15 hrs new synapses are formed. Homatropine Bromide Moreover, the early presynaptic alterations appear to depend on retrograde signaling from the postsynaptic cells, as occurs during the early stages of de novo synapse formation. These results suggest that the structural alterations during early-phase Catharanthine sulfate potentiation may act as tags or initial steps in a program that can lead to stable synaptic growth during late-phase potentiation. To begin to explore these ideas, we have examined changes in synaptic puncta and structures during long-lasting potentiation in hippocampal neurons. Early-phase potentiation is accompanied by rapid increases in puncta of presynaptic and postsynaptic proteins, which are due to aggregation of protein from a more diffuse background and are dependent on NMDA receptor activation and actin polymerization but not on protein synthesis. To investigate the possible contribution of these events 
to late-phase potentiation, we have now addressed three questions: Do these early changes persist and become protein synthesis dependent? What is the nature of the changes? How might they contribute to the late phase? Our results suggest that the onset of potentiation is accompanied by rapid and long-lasting increases in the number of sites where synaptic puncta and structures are assembled. These new sites are much more stable than the puncta or structures themselves, and may contribute to the transition between the early and late phase mechanisms of plasticity by serving as seeds or tags for the protein synthesis-dependent assembly and maintenance of synaptic components during the late phase. To attempt to address that question, we divided the colocalized structures into ones that overlapped and ones that were adjacent to synapsin-IR puncta. Under control conditions, both overlapping and adjacent structures continually assembled and disassembled. However, almost all of the changes in structures during potentiation were attributable to changes in the overlapping structures. There was a gradual protein synthesis-dependent increase in adjacent structures, but no difference between the glutamate and control groups.