Visualization of Selective Neural Pathways by Double Viral Infection Method

Application of viral vector technology for neural tracing enabled the visualization of neural pathways in a manner that had been impossible by classic techniques. The development of highly efficient retrograde vector played a pivotal role in its success. This chapter explains the strategy, protocol, and the expected results for visualization of selective neural pathways by double viral vector infection method. This method utilizes the combination of lentiviral vector showing retrograde gene transfer and adeno-associated viral (AAV) vector to split the TET-Off/TET-On system to these vectors. By co-injection of these vectors at the target and the origins of the pathway, it is possible to label a specific population of neurons that connect the two injection sites. The enhancement of transgene expression by TET system results in Golgi-like visualization of the cells from their dendrites to axon terminals. Using this technique, the corticothalamic cells are specifically labeled in their entirety including their collateral axons.