Induction of stable long-term depression in vivo in the hippocampal-prefrontal cortex pathway

We studied excitatory field potentials in the medial prefrontal cortex (mPF C, prelimbic area) to electrostimulation of the ventral hippocampus (CA1/su bicular region) in the anaesthetized rat. Nine hundred stimulus trains (5 p ulses at 250 Hz) applied at 1 Hz to the ventral hippocampus significantly a nd persistently depressed the amplitude and maximal slope (similar to 55% f or each index) of the prelimbic field potentials, but did not change the la tency of the maximal slope or peak negativity. Twelve stimulus trains (50 p ulses at 250 Hz) applied subsequently at 0.1 Hz restored the depression bac k to control level, and this reversible depression was maintained for at le ast 13 h. Cumulative depressive effects on the prelimbic field potential am plitude and maximal slope were observed upon addition of stimulus trains in the hippocampus. An important implication of the results is that the direc t pathway from the hippocampus to the mPFC in the rat retains long-term dep ression (LTD) as a neuroplastic form in vivo. This form could cooperate wit h long-term potentiation (LTP) and such a bi-directional synaptic plasticit y in the prefrontal cortex contributes to how cortical neural networks stor e information.