Fig. 3
From: Rodent models for psychiatric disorders: problems and promises
Calcium imaging workflow. GCaMP is a fusion protein composed of green fluorescent protein (GFP), calmodulin (CaM), and a peptide sequence from myosin light chain kinase (M13). In the presence of calcium, CaM undergoes a conformational change, and binds to the M13 protein, resulting in detectable fluorescence from the GFP (A). Cell-type specific expression of the calcium indicator, GCaMP can be achieved utilizing a cre-lox system (B). LoxP sites flank a stop codon, which inhibits transcription of GCaMP. In the presence of cre-recombinase, recombination removes the stop codon, permitting expression of GCaMP. This system can be achieved by crossing transgenic mice expressing cre-recombinase in a certain cell type with mice expressing cre-dependent GCaMP. Alternatively, cre-dependent GCaMP can be virally packaged and injected in vivo into mice expressing cell type-specific cre-recombinase (C). In fiber photometry, the fiber optic cable is utilized to deliver blue light to excite GFP, as well as detect and amplify the fluorescent signal produced in the presence of calcium (D). Microendoscopes (not shown) use a similar setup, but with the laser, photodetector, and amplifier mounted on top of the rodents head in addition to the imaging lenses