Post-synaptic depolarization in induction of long-term potentiation in the CA1 hippocampus

The role of dendritic depolarization in the induction of long-term potentiation (LTP) was studied in the CA1 hippocampus in vitro. In Mg(2+)-free medium, conditioning stimuli of 50 pulses at 1 Hz induced LTP (1 Hz LTP). This LTP was blocked by APV. To block dendritic depolarization, GABA or muscimol was applied iontophoretically to the dendritic region in conjunction with each conditioning stimulus. This procedure blocked 1 Hz LTP, even though a larger than normal Ca2+ influx through the NMDA receptor channels was expected due to an increase in electromotive force. These results suggest that depolarization is required, in addition to unblocking Mg2+ from NMDA receptor channels, most likely to open voltage-gated calcium channels.