Primed-burst potentiation in adult rat visual cortex in vitro

The effectiveness of θ pattern primed-bursts (PBs) on development of PB potentiation was investigated in layer II/III of the adult rat visual cortex in vitro. Experiments were carried out in the visual cortical slices. Population excitatory postsynaptic potentials (pEPSPs) were evoked in layer II/III by stimulation of either white matter or layer IV. To induce long-term potentiation (LTP), eight episodes of PBs were delivered at 0.1 Hz. Regardless of stimulation site, field potential recorded in layer II/III consisted of two components: a short latency and high amplitude response called pEPSP1, and a long latency and low amplitude response called pEPSP2. The incidence of LTP produced by PBs of layer IV was higher than that of the white matter tetanization. In contrast, PBs of both layer IV and white matter reliably produced LTP of pEPSP2 in layer II/III. It is concluded that PBs, as a type of activity pattern, of either white matter or layer IV can gain access to the modifiable synapses that are related to pEPSP2 in layer II/III, but accessibility of the modifiable synapses that are related to pEPSP1 depends on tetanization site. Relevancy of the results to the plasticity gate hypothesis is also discussed.