LONG-TERM POTENTIATION IN-VIVO IN LAYERS II III OF RAT BARREL CORTEX/

Long-term potentiation was studied in vivo in the rat barrel cortex. I t was found that LTP lasting several hours could be induced in layer I I/III by tetanic stimuli applied in layer IV. The probability of induc ing LTP at a given site was high (86%) provided that the electrodes we re not displaced too far horizontally. LTP was not observed if the sti mulating electrode was located on the far side of the neighbouring bar rel-column from the recording electrode. The strongest LTP was induced by stimulating layer IV septal locations or the edge of the barrel an d recording in the near half of the neighbouring barrel. However, exam ples were found of LTP from layer IV to II/III within the same barrel, within the same septum and from barrel to adjacent septum. The probab ility of inducing LTP on a particular occasion was greatly increased b y iontophoresis of bicuculline at the recording site during the tetanu s (from 20 to 55% judged by a change in peak amplitude). The average i ncrease in the peak amplitude was 29 +/- 3.2% for protocol 1 (urethane anesthesia, monopolar stimulation) and 23 +/- 7% for protocol 2 (barb iturate anesthesia, bipolar stimulation). The probability of inducing LTP was greater if the first tetanus was accompanied by BMI applicatio n (67%) than for any subsequent attempts (39%). These results suggest it should be possible to study the effect of LTP on sensory processing in defined positions within the barrel field. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.