Figure 4.

Partial reversal of the impairment of LTP maintenance by AAIs. After recording at least 20 min, LTP was induced. Immediately afterward, AAIs were superfused for 5 and 10 min, respectively (solid bars). After an 80 min washout, the stimulation intensity was adjusted to the new 30–50% of maximal amplitude and responses recorded for an additional 10 min to reestablish control conditions. Tetani were delivered a second time and pEPSPs recorded for an additional 80 min. The ghostline indicates the level of LTP (mean ± SEM) from control slices in Fig. 3C. (A) Effects of cytochalasin D. Eighty minutes after LTP induction, both concentrations superfused for either 5 min or 10 min reduced LTP magnitude to about 150% of control. A second set of tetani delivered after washout could not induce stable LTP. (B) Effects of cytochalasin D compared with latrunculin A. As for cytochalasin D, latrunculin A superfused for 5 or 10 min irreversibly blocked LTP maintenance. (C) Effects of cytochalasin B. Although cytochalasin B superfused at low concentrations and for only 5 min reduced LTP magnitude as significantly as with higher concentrations and longer superfusion times, this effect was reversible, and the second set of tetani induced normal PTP and LTP magnitudes. LTP appeared stable.