Bound amount of GFP-CaMKIIα strongly correlates with spine volume but bound fraction does not. A, Merged image of a dendritic segment of neuron expressing mGFP-CaMKIIα and infused with Alexa 594 dye. B, A map of the bound mGFP-CaMKIIα in spines in pseudocolor coding; warmer colors correspond to larger bound amount. Red outline shows the dendrite morphology. BA was calculated only in clearly identified spines. Scale, 1 μm. C, D, Plots of data obtained from the dendrite shown in A and B. Each symbol shows the value for an individual spine. Dashed line, Linear fit of data. E, F, Summary data for the correlations of spine BA or BF of GFP-CaMKIIα and spine volume. Each data point is a result of comparison of two spines from the same dendrite. E, Fold change in BA versus fold change in spine size. F, Fold change in BF versus fold change in spine size. G, H, Measuring BA using PAGFP-CaMKIIα. Merged image of a dendritic segment of neuron expressing PAGFP-CaMKIIα and mRFP(Cherry) before (G) and 2 min after (I) the photoactivation of PAGFP. H, Summary graph, showing fold change in spine size versus fold change in BA of PAGFP-CaMKIIα, reveals strong correlation between these parameters.