QUANTITATIVE-ANALYSIS OF LONG-TERM POTENTIATION IN THE HIPPOCAMPAL DENTATE GYRUS OF THE FREELY-MOVING 15-DAY-OLD RAT

The magnitude and duration of long-term potentiation (LTP) of perforan t path/dentate granule cell synapses was examined in freely moving rat s beginning at 15 days of age. Measures of dentate granule cell popula tion EPSP slope and population spike amplitude (PSA) obtained before a nd after tetanization were used to evaluate the level of LTP, Tetaniza tion resulted in significant enhancement of both the population EPSP s lope (approximate to +75%) and PSA (approximate to +40%) measures, Thi s enhancement was maintained without significant change for 18 h, afte r which both measures began a steady and continuous rise. Daily input/ output response measures from age-matched nontetanized animals were us ed to factor out enhancement related to normal development, Under this schema, tetanization-induced enhancement of both EPSP slope and PSA m easures decayed slowly, beginning 18-24 h after tetanization, returnin g to baseline 5 days after tetanization. Enhancement obtained from 90- day-old animals decayed to baseline 24 h after tetanization. The longe r duration of LTP obtained from preweanlings is discussed with regard to the development of inhibitory systems modulating granule cell excit ability.