Associative spike timing-dependent potentiation of the basal dendritic excitatory synapses in the hippocampus in vivo.

Spike timing-dependent plasticity in the hippocampus has rarely been studied in vivo. Using extracellular potential and current source density analysis in urethane-anesthetized adult rats, we studied synaptic plasticity at the basal dendritic excitatory synapse in CA1 after excitation-spike (ES) pairing; E was a weak basal dendritic excitation evoked by stratum oriens stimulation, and S was a population spike evoked by stratum radiatum apical dendritic excitation. We hypothesize that positive ES pairing-generating synaptic excitation before a spike-results in long-term potentiation (LTP) while negative ES pairing results in long-term depression (LTD).

Differential long-term depression in CA3 but not in dentate gyrus following low-frequency stimulation of the medial perforant path.

Synaptic plasticity may depend not only on the afferent fibers but also on the recipient structure. The medial perforant path (MPP) from the entorhinalcortex projects to both the dentate gyrus (DG) and CA3, resulting in excitatory postsynaptic potentials (EPSPs) in both areas. In this study, we showed that long-term depression (LTD) following low-frequency stimulation of MPP was found only in CA3a, a CA3 subfield, but not in DG.