Retrograde approach to dissect the mouse connectome and generation of new Rabies Virus tools for functional analysis of synaptically connected neurons

Connectomics research is putting in action a comprehensive analysis to dissect the anatomy of brain circuits and axonal architecture to better understand the neural functioning. Since the dawn of neuroanatomy research, viral tracers have been useful tools to investigate the neural connections. An excellent viral tracer is Rabies Virus (RV), that, thanks to its properties to specifically infect at pre-synaptic terminal can univocally link a target brain area to the relative synaptically connected neurons. However, to take a step forward in understanding neural functions, directly manipulation of the neural genome is required. Here, I describe different projects I worked on during my PhD course that took advantage of RV. First, I joined a project that resulted in drawing a map of serotonergic innervation to the rostral brain. We identified a serotonergic subpopulation characterized by the wiring transmission modality. Second, in collaboration with the Italian Institute of Technology of Rovereto, we analysed the cortical connectivity in the Cntnap2 autism spectrum disorder mouse model. The rsfMRI analysis highlighted an asynchronous activity in the cingulate cortex (CG) that could be ascribed to a reduced PFC-projecting subpopulation in CG identified by means of RV-based retrograde tracing. Third, in order to allow the direct manipulation of the genome of retrograded neurons I developed RV variants expressing iCre and Flpe recombinase enzymes which mediate somatic DNA recombination in presence of specific sites. Fourth, I generated a new non-cytotoxic recombinase-expressing RV tools that allow to manipulate the genome of infected subpopulation and to overcome the time limits of RV allowing long-term experiments.