Cre Activated and Inactivated Recombinant Adeno‐Associated Viral Vectors for Neuronal Anatomical Tracing or Activity Manipulation

Recombinant adeno‐associated viruses (rAAVs) transcriptionally activated by Cre recombinase (Cre‐On) are powerful tools for determining the anatomy and function of genetically defined neuronal types in transgenic Cre driver mice. Here we describe how rAAVs transcriptionally inactivated by Cre (Cre‐Off) can be used in conjunction with Cre‐On rAAVs or genomic Cre‐reporter alleles to study brain circuits. Intracranial injection of Cre‐On/Cre‐Off rAAVs into spatially intermingled Cre + and Cre ‐ neurons allows these populations to be differentially labeled or manipulated within individual animals. This comparison helps define the unique properties of Cre + neurons, highlighting the specialized role they play in their constituent brain circuits. This protocol touches on the conceptual and experimental background of Cre‐Off rAAV systems, including caveats and methods of validation. © 2015 by John Wiley & Sons, Inc.