Visualizing the neuronal circuits underlying specific behaviors is a formidable technical challenge in mammalian brains. Indeed, in vivo measurements are often limited to brain surface, or – in the case of electrodes or optical fibers – to small volumes. An alternative strategy is to map neuronal activity by observing the expression of immediate early genes (IEGs). These genes, like Arc or c-Fos, are involved in neuronal plasticity and are expressed after sustained electrical activity. Thus, identifying the neurons expressing IEGs gives a good grasp of the neuronal networks that are activated during a selected task.
We combine behavioral testing on a transgenic reporter of c-Fos expression (TRAP mice) with cutting-edge imaging and image analysis. Whole mouse brains are cleared and then imaged with light-sheet microscopy. Finally, automatic cell detection and spatial registration to a reference atlas allow quantifying neuronal activation in different brain districts.
Our main focus is currently the dissection of brain circuits involved in the formation and consolidation of fear memory. In this context, we want to decipher the role of the histaminergic system in modulating different fear-related brain networks. To this aim, we couple our imaging pipeline with pharmacological and pharmacogenetics approach, and with anatomical tracing of brain-wide histaminergic pathways.
Ludovico Silvestri, Group Leader