Long-term potentiation in cultures of single hippocampal granule cells: a presynaptic form of plasticity.

We have explored the mechanisms of mossy fiber long-term potentiation (LTP) at autapses in single-cell cultures of guinea pig hippocampal dentate granule cells. L-AP4-sensitive, but not insensitive, cells responded to a brief tetanus with a sustained potentiation in the synaptic responses. The induction of this LTP appeared identical to that observed in hippocampal mossy fiber synapses in situ, in that it required a rise in presynaptic Ca2+ and activation of protein kinase A. Its expression also appeared to be presynaptic and was due, at least in part, to events that occurred after the entry of Ca2+ and to the switching on of previously silent release sites.