THE DEMONSTRATION OF LONG-LATENCY POTENTIALS IN THE CA1 REGION OF THERAT HIPPOCAMPAL SLICE

Shaffer collateral evoked extracellular DC potentials with latencies g reater than 100 ms are demonstrated in the CA1 region of the rat hippo campal slice preparation. The most prominent potential following the p opulation spike is a positive potential peaking between 150 and 400 ms after the stimulus. The amplitude of the potential is approximately t wo orders of magnitude smaller than the population spike. This potenti al shares several characteristics with the P300 from electroencephalog ram studies of evoked potentials. Thus, it was dubbed the in vitro P3. One of the most distinguishing characteristics of the in vitro P3 is a negative potential that immediately follows it. The negative potenti al is smaller in amplitude than the in vitro P3, but lasts for several seconds. A similar potential also follows the P300 in electroencephal ogram studies. These data suggest that the in vitro P3 is an in vitro version of the long latency evoked potential known as the P300 in elec troencephalogram studies.