Generation and Application of Engineered Rabies Viral Vectors for Neural Circuit Research

Abstract

To understand how the brain functions, it is essential to reveal how neural circuits in the brain give rise to perception, cognition, and behavior. Neural circuits in the brain operate over a vast range of spatiotemporal and computational scales, from high-level circuits that integrate information across multiple regions of the brain to microcircuits that perform simple input/output transformations within a specialized brain structure. Because naturally occurring rabies viruses (RABV) have a unique property in their ability to spread trans-synaptically between neurons in the retrograde direction, they are extremely valuable for elucidating neural circuits. Genetic modifications of RABV restrict target cell types and control trans-synaptic viral spread, allowing cell-type-specific monosynaptic circuit tracing in the brain. The monosynaptic circuit tracing system is based on the conditional expression of EnvA/TVA-targeting systems for directing the initial infection of G-deleted RABV vectors (RABVΔG) to particular cell types and complementation of RABV glycoprotein (RABV-G) in trans for trans-synaptically labeling directly connected, presynaptic neurons with RABVΔG. Herein, we introduce a step-by-step protocol for generating RABVΔG to study the circuit structure and function of normal and diseased brains.