Fig. 3.
The effects of priming are expressed heterosynaptically. As in Figure 1, the data are normalized to the 5 min period immediately preceding the first LFS episode, and the period from 25 to 30 min after the second LFS was used to evaluate LTD magnitude. A, A summary plot (n = 7) of normalized field EPSP measurements from two independent pathways. Priming of one pathway (asterisks) was performed as in Figure 1, except in the absence of dl-APV, resulting in LTP of the primed pathway (solid squares). At 30 min after priming, LFS of the unprimed pathway (1 Hz) was performed, resulting in homosynaptic LTD (open squares). B, Summary quantitation from the experiment above (right set ofof bars) and from a similar experiment (data not shown), in which dl-APV was present during the priming protocol (left set of bars,n = 8). The open bars illustrate the effects of LFS performed in one pathway when the second pathway had been primed previously (i.e., heterosynaptic priming). The solid bars illustrate the data from the primed pathways (which did not experience LFS). Error bars indicate the mean ± SEM, andasterisks indicate a significant depression compared with both the other pathway (p < 0.01,t test) and when compared with the data for Figure 1A and C (p < 0.05, ANOVA followed by Student–Newman–Keuls post hoctests).