Mapping the connectivity of neural circuits is essential for understanding their function in health and disease. However, our ability to map connectivity in polysynaptic circuits, i.e. between neurons separated by more than a single synaptic connection, remains limited in mammalian brains. Approaches such as electron microscopy and brain slice recordings can determine connectivity in microcircuits or small samples but cannot be used in live animals. Conversely, viral and non-viral trans-neuronal tracers can trace connections between brain areas, but either only cross a single synaptic connection or many in a poorly controlled way. To overcome these limitations, we propose to develop a viral approach that allows for tracing of polysynaptic circuits with control over the number and location of crossed synapses, as well as functional access to traced neurons in vivo. Our method will use a modified rabies virus that expresses an orthogonal receptor, which allows for selective re-delivery of the G-protein to presynaptic neurons. This will allow us to gain access to higher-order inputs to a specific neuronal population. If successful, we will apply this approach to analyse chemosensory inputs into hypothalamic neurons that regulate parental behaviour. This tracing approach has the potential to provide unprecedented access to polysynaptic circuits defined by connectivity and gene expression and could significantly advance our understanding of brain function.