Figure 5.

Effects of theta burst stimulation on labeling after topical application of rhodamine-phalloidin. A, Field EPSPs recorded at a single site in s. radiatum of CA1b and elicited by stimulating electrodes in CA1a (S1) or CA1c (S2). Theta bursts were delivered to S1 and then 2 min later to S2. The induction of short-term potentiation in S1 had no evident effect on the response in S2 recorded 2 min later. Calibration bars: 0.5 mV, 5 ms. B, D, Labeling in the standard-sized sampling zone placed over areas of afferent stimulation in the proximals. radiatum of two control slices. C, E, Labeling in fields comparable with those shown in B and D in two slices that had received theta burst stimulation. A fine dendritic segment is labeled in C; similar processes are very faint or not labeled in E. F, Number of labeled spines and dendritic branches in the sampling zone in slices given control (C; n = 4) or theta burst (T; n = 5) stimulation. Note that the large increase (∼14-fold; p < 0.002) in phalloidin-positive spines was elicited by the latter treatment without any evident increase in labeled dendritic segments. Magnification, 20×. Scale bar: B-E, 50 μm. Error bars represent SEM.