Figure 1.

Inhibition of protein synthesis blocks early maintenance of MF LTP but not of C/A LTP. A, Control experiments. Left panel, Group data (n = 5; mean ± SEM; circles) of the amplitude of MF fEPSPs evoked by stimulation of MF before and after delivery of HFS (upward arrows). After PTP the amplitude of the response decayed gradually to a stable LTP. Right panel, Single traces of MF fEPSPs recorded during baseline and 120 min after the induction of LTP (asterisk). B, Left panel, Group data (n = 3; mean ± SEM; squares) of the effect of emetine (20 μm; applied 60 min after delivery of HFS; upward arrow) on MF LTP. Right panel, Traces are single MF fEPSPs recorded during baseline and at the end of emetine perfusion (asterisk). C, Left panel, Group data (n = 5; mean ± SEM; triangles) of effect of cycloheximide (60 μm; applied 60 min after HFS; upward arrow) on MF LTP. Right traces are single MF fEPSPs recorded during baseline and at the end of cycloheximide perfusion (asterisk). Cycloheximide and emetine significantly reduced MF LTP (fEPSP amplitude before drug application vs during drug application: p < 0.01). All experiments were performed in the presence of MK-801 (15 μm). D, Left panel, Group data of the amplitude of C/A fEPSPs evoked by stimulation of s. radiatum in area CA2. Emetine application (20 μm; rhombus; n = 3) 60 min after the induction of LTP by HFS delivered to C/A fibers (upward arrow) did not affect the potentiated responses. Right panel, Representative traces of C/A fEPSPs before and at the end of emetine perfusion (asterisk). The horizontal bar indicates duration of drug perfusion (60 min). Calibration: 0.2 mV, 10 msec.