Figure 5.

Effects of diffusional coupling across the spine neck on [Ca²⁺] signals. A, Example of two spines with different Δ[Ca²⁺] (1 and 2). An Alexa image of the two spines (top) and G/R images after stimulation of spine 1 (middle) or spine 2 (bottom) are shown. B, Δ[Ca²⁺] (top) and uEPSC (middle) for spines 1 and 2. FRAP measurements (bottom) for these spines indicate that diffusional coupling is unlikely to explain the observed differences in Δ[Ca²⁺]. C, Δ[Ca²⁺]/uEPSC as a function of τ_FRAP (r = 0.39; ^*p < 0.05; 41 spines; 6 cells). D, Numerical simulations of [Ca²⁺] dynamics. Top, Simulated [Ca²⁺] transients (arbitrary units; black traces, 1 mm Fluo-5F; gray traces, no added buffer, scaled down in amplitude by a factor of 15) using the NMDA-R uEPSC (bottom) as an input. Δ[Ca²⁺] time courses for extreme values of τ_FRAP are shown (200 ms, solid line; 20 ms, dotted line).