Fig. 4.

AP-LTD interaction with synaptically induced L-LTP. (A) L-LTP expression was not affected by transient blockade of glutamatergic transmission (OS/NS, 92.2 ± 6.5%), but was depotentiated by AS (OS/AS, 62.8 ± 7.4%; P < 0.05). (B) Weak TBS delivered to NS slices after washout of glutamatergic antagonists induced an early form of LTP, which decayed within 3 h to prestimulated level (NS/OS, 95.1 ± 3.8%). In contrast, if the same stimulation was delivered to antidromically stimulated slices, robust LTP developed in the stratum radiatum (AS/OS, 148.7 ± 19.0%; P < 0.05). OS, orthodromic stimulation of Schaffer collaterals; AS, antidromic stimulation of axons in the alveus; NS, no stimulation was delivered. The mean slopes of fEPSPs were normalized to pre-TBS level and renormalized to 100% before the second stimulus. The insets show stimulation electrode placement. Representative synaptic responses evoked and recorded in the stratum radiatum before (black) and after (gray) stimulation are shown at the indicated time points. (Calibration, 0.5 mV, 5 ms.) Perfusion with glutamatergic antagonists marked with dashed vertical bar.