Monosynaptic circuit tracing in vivo through Cre-dependent targeting and complementation of modified rabies virus (original) (raw)

We describe a powerful system for revealing the direct monosynaptic inputs to specific cell types in Cre-expressing transgenic mice through the use of Cre-dependent helper virus and a modified rabies virus. We generated helper viruses that target gene expression to Cre-expressing cells, allowing us to control initial rabies virus infection and subsequent monosynaptic retrograde spread. Investigators can use this system to elucidate the connections onto a desired cell type in a high-throughput manner, limited only by the availability of Cre mouse lines. This method allows for identification of circuits that would be extremely tedious or impossible to study with other methods and can be used to build subcircuit maps of inputs onto many different types of cells within the same brain region. Furthermore, by expressing various transgenes from the rabies genome, this system also has the potential to allow manipulation of targeted neuronal circuits without perturbing neighboring cells. transsynaptic | pseudotyped virus | adeno-associated virus | EnvA | TVA O ne of the most intractable problems in systems neuroscience has been the systematic description of neural connectivity in the intact mammalian brain. Many different types of neurons, each with distinct connectivity and function, can inhabit the same brain region. Even within a single neocortical column, dozens of types of projection neurons and local interneurons perform the computations that ultimately lead to the spiking output of that column. Through painstaking studies using molecular and cell biology techniques, electron microscopy, and electrophysiology, we are beginning to understand how a neuron's connectivity contributes to its function in the circuit in which it is embedded, but we lack efficient means for performing circuit-level analyses in vivo. Especially in brain regions with considerable neuronal heterogeneity, we are still greatly limited in our ability to study how groups of cells form their fine-scale connections, how these connections change over time, and how this plasticity affects a cell type's computational role in a dynamic circuit.