CAG-Cre-GFP AAV (Serotype Retrograde)

Retrograde pathway-selective optogenetics or chemogenetics involves the injection of a virus that is preferentially internalized at axon terminals at the injection site and then retrogradely transported to upstream cell bodies, allowing optical or ligand-mediated pathway manipulation. Retrograde pathway-selective manipulation provides a powerful ability to compare the contribution of multiple inputs to a single brain region. Senova and colleagues combined retrograde pathway-selective optogenetics with diffusion-weighted MRI tractography to characterize the motor cortico-subthalamic pathway. They injected retrogradely transported opsin-encoding viral constructs into the subthalamic nucleus and then optically stimulated the cell bodies of cortico-subthalamic neurons. Retrogradely transported viruses include canine adenovirus type 2, adeno-associated virus (AAV), herpes simplex virus, rabies virus, and pseudotyped lentiviral vectors such as HiRet and EIAV. In contrast, recombinant adeno-associated virus (rAAV) is relatively safe and commonly used in gene therapy and research. AAV is a non-enveloped, single-stranded DNA virus. rAAV is produced by removing viral DNA from wild-type AAV and replacing coding and noncoding DNA regions with expression cassettes encoding the transgenic protein of interest. These modifications render rAAV replication-defective. rAAV are particularly well suited for delivering transgenes to the brain because they can transduce post-mitotic tissues and their genome remains episomal. Furthermore, they can produce long-term, stable transgene expression with minimal immunogenicity. As a result, rAAV has been used to deliver a range of transgenes in clinical trials for neurological disorders. In NHP optogenetics and chemogenetics studies, AAV has been primarily used to manipulate neural activity at the injection site.