Long-term potentiation in hippocampal CA3 neurons: tetanized input regulates heterosynaptic efficacy.

Three excitatory synaptic inputs to hippocampal CA3 neurons--the mossy fibers, Schaffer collateral/commissural fibers, and fimbrial fibers--were determined to be separate and independent in the pharmacologically disinhibited in vitro slice. Long-term synaptic potentiation (LTP) was induced in one of these three synaptic inputs, and subsequent synaptic efficacy changes in the other two nontetanized inputs were characterized using current and voltage clamp techniques. LTP in the mossy fiber input was accompanied by potentiation of Schaffer and fimbrial responses, whereas the induction of LTP in the Schaffer pathway was associated with the potentiation of fimbria responses and a depression of mossy fiber responses. LTP induced in the fimbrial response was confined to that input alone.