The catFISH (cellular Compartment Analysis of Temporal activity by Fluorescence In Situ Hybridization) method allows us to trace back when a specific neuron has been activated. By using labeling for the RNA of the immediate early gene (IEG) zif268 for example, we know that when we detect its RNA in 2 punctae in the nucleus, zif268 gene transcription was initiated 5min ago. Is the zif268 RNA signal located in the cytoplasm, the transcription has been initiated approximately 30min ago.
By exposing an animal to two different experiences for 5min, spaced 25min apart and looking at the brain directly after the second context, we can differentiate by the location of the zif268 RNA, which cell has been active in which of the two, or maybe in both contexts.
This method will allow us to identify specific brain regions or cell populations that participate in certain behavioral functions. By combining this technique with BrdU birth-dating of newborn neurons, we can determine how old cells are that have been activated.
Here some pictures of initial tests, cell nuclei are stained with DAPI in blue, zif268 is shown in green and BrdU in red.