Fig. 1.
Nifedipine blocks the induction of LTD in aged rat slices. A, Plot of normalized field CA3/CA1 EPSP slopes (percentage of baseline ± SEM) obtained in stratum radiatum from three slices in response to stimulation of Schaffer collateral fibers (0.033 Hz). After an initial baseline period, 900 pulses of continuous 1 Hz stimulation (bar) induced a significant depression of the synaptic response. B1, An experiment conducted on an individual slice from an aged rat in which 1 Hz stimulation (1 Hz 1) was delivered in the presence of 10 μm nifedipine (thick bar) and did not depress the synaptic response. After the first 1 Hz train, nifedipine was washed from the recording medium, and a second episode of 1 Hz stimulation (1 Hz 2) was delivered in a drug-free medium. This second train of 1 Hz stimulation induced a marked depression that could be reversed to baseline by 100 Hz stimulus bursts (arrow). Insets for A andB1 display the averaged field EPSP waveforms from 10 successive responses collected immediately before and 30 min after (arrowheads) the delivery of 1 Hz stimulation. Calibration: 1 mV, 5 msec. B2,B3, Average data from aged rat slices (B2, n = 8;B3, n = 7) that were treated identically to the individual case inB1. Note that responses inB3 are normalized to the average of responses in B2 collected between 25 and 30 min after the termination of the first 1 Hz train.