Figure 1.

Intraspinal delivery of viral vectors presents a powerful approach for addressing basic questions regarding the organization and function of spinal circuits

Genetically-defined groups of spinal neurons and the circuits that they are embedded in can be manipulated using two different groups of AAVs – anterogradely transporting (A and B) and retrogradely transporting AAVs (C). By injecting recombinant anterogradely transporting AAVs into different segments of the spinal cord in wildtype mice or genetic reporter lines, it is possible to acutely manipulate select spatially defined populations of spinal neurons, specifically in adulthood (Dougherty et al., 2013; Fink et al., 2014; Bourane et al., 2015; Foster et al., 2015; Ruder, Takeoka and Arber, 2016; Choi et al., 2020; Sheahan et al., 2020; Barik et al., 2021; Gatto et al., 2021) (A). By combining spinal injections of anterogradely transporting AAVs with stereotactic injections of retrogradely transporting AAVs in brain regions that are targeted by ascending spinal neurons, and/or by the placement of optic fibers or drug cannulae in specific brain regions, it is possible to manipulate ascending pathways in a circuit-specific manner (Conner et al., 2021; Fink et al., 2014; Bouvier et al., 2015; François et al., 2017; Sheahan et al., 2020) (B). Spinal injections of retrogradely transporting AAV (AAVretro) (Tervo et al. 2016) combined with stereotactic injections of anterogradely transporting viral vectors in the brain enables the targeting of functionally and somatotopically distinct groups of supraspinal neurons that communicate with specific segments of the spinal cord (Esposito, Capelli and Arber, 2014; Basaldella et al., 2015; Murray et al., 2018; Sathyamurthy et al., 2020; Usseglio et al., 2020).