Protocol to visualize three distinct neuronal ensembles encoding different events in the mouse brain using genetic and viral approaches

Activity tagging of neuronal ensembles has become an important tool in neuroscience. Here, we present a protocol for visualizing separate neuronal ensembles active during three distinct phases of a memory in transgenic mice. We describe steps to label active neurons using viral microinjection, inducing GFP expression under the robust activity marker (RAM) promoter, and transgenic mice, inducing tdTomato (TdT) expression, and immunohistochemical (IHC) visualization of endogenous cFos expression. We then detail procedures for preparation of tissue, imaging, and quantification of memory events. For complete details on the use and execution of this protocol, please refer to Lesuis et al.1.