Genetically targeted reporter imaging of deep neuronal network in the mammalian brain

Positron Emission Tomography (PET) allows biomolecular tracking, while PET monitoring of brain networks has been hampered by the lack of a suitable reporter. Here, we describe in-vivo brain reporters utilizing bacterial dihydrofolate reductase, ecDHFR, and its antagonist, TMP. In mice, peripheral administration of radiofluorinated and fluorescent TMP analogs enabled PET and intravital microscopy, respectively, of neuronal ecDHFR expressions. This technique was applicable to the visualization of chemogenetically provoked neuronal ensemble activities in the hippocampus. Notably, ecDHFR-PET captured neuronal projections in non-human primate brains, indicating the availability of ecDHFR-based techniques for network monitoring. Finally, we demonstrated PET assays of turnover and self-assembly of proteins tagged with ecDHFR mutants. Collectively, the current reporter technology offers diverse in-vivo molecular analyses of a brain circuit.