HEBBIAN INDUCTION OF LTP IN VISUAL-CORTEX - PERFORATED PATCH-CLAMP STUDY IN CULTURED NEURONS

1. To see whether presynaptic activation paired with postsynaptic depo larization is necessary for the induction of long-term potentiation (L TP) in visual cortex or whether an activation of postsynaptic receptor s in conjunction with depolarization is sufficient, we carried out per forated patch-clamp recordings with nystatin from cultured cortical ne urons of rats. 2. Recorded neurons were monosynaptically activated eit her by electrical stimulation of an adjacent neuron or by direct activ ation of glutamate on ''hot spots'' of dendrites through iontophoresis or pressure ejection. In experiments in which cultured neurons were s tained immunocytochemically with antibody against synaptophysin after electrophysiological recordings, hot spots were found to correspond to probable synaptic sites. 3. Excitatory postsynaptic currents (EPSCs) evoked by test stimulation applied to the adjacent neuron at 0.1 Hz we re recorded at a holding potential of -60 or -70 mV for 5-10 min after an establishment of the whole cell recording configuration. Then, sti mulation was paired with postsynaptic depolarization (0 mV for 200 ms) at 1 Hz for 30 or 60 s. LTP of EPSCs was induced in 7 of the 15 cells from which stable recordings were obtained for 18-30 min after pairin g. 4. When postsynaptic depolarization was paired with direct glutamat e application in the absence of presynaptic stimulation in 12 cells, o nly 1 showed LTP. Postsynaptic depolarization alone did not induce LTP in any of the six cells tested. Also, presynaptic stimulation alone d id not induce LTP in any of the five cells tested. 5. These results su ggest that the concurrent activation of presynaptic elements with post synaptic depolarization is necessary for the induction of LTP in visua l cortex.