Figure 3

Induction of spine shrinkage in vivo. (A) Representative images of spine shrinkage. We stimulated, on average, 2.8 spines per dendrite using the same method as was used for enlargement but with a perfusion solution containing 1 mM magnesium (Mg²⁺). Spines (S1, magenta arrowheads) stimulated with low-frequency two-photon glutamate uncaging (1 Hz, 15 min) exhibited significant shrinkage. Some neighboring spines also shrunk (e.g., n1, yellow arrowheads), while others did not (e.g., n2, white arrowheads). The uncaging point is indicated by a small magenta dot. (B) Time-courses for spine head volume changes in panel (A). The magenta, yellow, and white circles indicate spine S1, n1, and n2 traces, respectively. (C) Average time courses for stimulated spines without (red circles) or with the NMDA receptor antagonist APV (blue diamonds). Forty-three spines were not exposed to APV while 12 were. Average time courses for spine neighbors located <3 μm (black circle) or 3–10 μm (gray circle) from the stimulated spines are also plotted (56 spines for <3 μm and 59 spines for 3–10 μm).