Measuring CaMKII concentration in dendritic spines

► We developed a method for measuring the endogenous concentration of a protein in small cellular compartments in brain tissue. ► The method involves overexpression of the protein of interest which is fused with a fluorescent protein such as GFP. ► Overexpression of a soluble fluorescent protein with shifted emission (RFP) is also needed for demarcating the cell volume. ► It also requires immunostaining and high-resolution fluorescence confocal or two-photon imaging. ► The method was applied for measuring the endogenous concentration of CaMKII in cell soma, dendrites, and dendritic spines.