Primed-burst potentiation in adult rat visual cortex in vitro

The effectiveness of a pattern primed-bursts (PBs) on development of PB pot entiation was investigated in layer II/III of the adult rat visual cortex i n vitro. Experiments were carried out in the visual cortical slices. Popula tion excitatory postsynaptic potentials (pEPSPs) were evoked in layer II/II I by stimulation of either white matter or layer IV. To induce long-term po tentiation (LTP), eight episodes of PBs were delivered at 0.1 Hz. Regardles s of stimulation site, field potential recorded in layer II/III consisted o f two components: a short latency and high amplitude response called pEPSP1 , and a long latency and low amplitude response called pEPSP2. The incidenc e of LTP produced by PBs of layer IV was higher than that of the white matt er tetanization. In contrast, PBs of both layer TV and white matter reliabl y produced LTP of pEPSP2 in layer II/III. It is concluded that PBs, as a ty pe 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 hypo thesis is also discussed. (C) 1999 Elsevier Science B.V. All rights reserve d.