Figure 6.

Theta stimulation-induced increases in rhodamine-phalloidin labeling persist for at least 30 min and are blocked by the NMDA receptor antagonist APV in slices from young adult rats. Photomicrographs of labeling within the sampling zone in stratum radiatum after topical application of rhodamine-phalloidin are shown; stimulating and recording electrodes were located as described in Figure 5. Top panels (from left to right) show the sampling zone in a control slice, in three slices (a, b, c) that received TBS, and in a fourth slice in which TBS was delivered in the presence of 100 μm APV. The slices were fixed 30 min after theta burst or (for control) low-frequency stimulation. As shown, relative to control, there was a large increase in punctate labeling with TBS stimulation but not with TBS plus APV. The graph at the bottom describes the effects of theta burst stimulation on the group mean ± SEM of the initial slopes of fEPSPs recorded from the proximal s. radiatum and elicited by stimulation of the Schaffer-commissural projections. Traces are representative fEPSP recordings from ACSF- and APV-infused slices that were collected during the period of baseline recordings (a) and 30 min after theta burst stimulation (b). Both the graph and traces demonstrate that APV completely blocked the induction of LTP.