Figure 3.
Theta burst stimulation causes actin polymerization in dendritic segments. A, A primary (apical) dendritic branch from a cell with potentiated synapses. Note the numerous fine oblique dendritic branches. SP, Stratum pyramidale; SRp, proximal stratum radiatum; SRd, distal stratum radiatum; SM, stratum lacunosum-moleculare. B, A cluster of labeled segments from a theta burst slice in which multiple cells had been clamped. Note that the labeled segments are restricted to the inner half of the s. radiatum, the area innervated by the fibers that had received theta bursts. C, Mean number of labeled dendritic segments in control (cont) and theta-stimulated (theta) slices; the difference between groups is highly significant (p = 0.001). Error bars represent SEM. D, Distribution of numbers of stained segments across control and theta burst slices (bars represent numbers of segments per slice sample field, in nonoverlapping categories). Slightly <40% of the potentiated slices did not have more labeled branches than found in controls; this value is higher than that for labeled spines (Fig. 2G). E, F, Labeled basal dendrites in two cells expressing LTP; s. pyramidale is at the bottom of each micrograph. Photographs were taken at 10× objective magnification. Scale bar: (in A) A, B, E, F, 20 μm.