Conductance Mechanism Responsible for Long-Term Potentiation in Monosynaptic and Isolated Excitatory Synaptic Inputs to Hippocampus

摘要

1) The biophysical mechanisms underlying long term potentiation (LTP) were investigated in indentifiable and monosynaptic excitatory inputs to hippocampal neurons. The results provide the first insights into the conductance changes that are responsible for the expression of LTP. 2) Both current- and voltage-clamp measurements of the mossy fiber synaptic response in pyramidal neurons of region CA3 were made with a single-electrode-clamp system. The excitatory postsynaptic response was pharmacologically isolated by bathing hippocampal slices in saline containing picrotoxin, which blocks the synaptic inhibition that normally accompanies the experimentally evoked mossy fiber response. LTP was induced by tetanically stimulating the mossy fiber input of 1 s at 100 Hz. Before and 20 min to 1 h after inducing LTP, we attempted to measure the mean excitatory postsynaptic potential (EPSP) amplitude, intrasomatic current-voltage relationship to a step current waveform, membrane time constant spike threshold peak excitatory postsynaptic current amplitude synaptic conductance increase and synaptic reversal potential but adequate assessments of all eight of these were not always obtained for every cell that was studied.