Ca2+ Imaging in Brain Slices Using Bioluminescent Reporters

Imaging of Ca²⁺ indicators is widely used to record transient intracellular Ca²⁺ increases associated with bioelectrical activity. The natural bioluminescent Ca²⁺ sensor aequorin has been historically the first Ca²⁺ indicator used to address biological questions. Aequorin is generally superseded today by fluorescent Ca²⁺ indicators for imaging applications that require high spatial and temporal resolution. Nonetheless, aequorin imaging offers several advantages over fluorescent reporters: it is virtually devoid of background signal; it does not require light excitation and interferes little with intracellular processes. In this chapter, we describe protocols allowing the expression of a GFP-aequorin fusion protein in acute brain slices and the bioluminescence recording of Ca²⁺ transients in single neurons, or multiple neurons simultaneously.