) mice were purchased from the Jackson Laboratory. C57BL/6 mice were obtained from the National Institute on Aging at the NIH. Hemizygous Chat-Cre mice were crossed with tdTomato mice to generate Chat-Cre;tdTomato mice, and with RiboTag mice to generate Chat-Cre;RiboTag mice. All mice were maintained on a mixed genetic background. Male and female mice were included in experiments, as described in the results. A COchamber was used to sacrifice mice for tissue collection, following NIH guidelines.
Rhesus monkey spinal cord samples were obtained from the National Institutes of Health Animal Center. Samples were collected from males following euthanasia for unrelated clinical or experimental purposes; collection occurred within 2 hours of death. Once harvested, samples were immersed in ice-cold 4% paraformaldehyde for 24–48 hours and then kept in cold 0.1 M PBS. Sectioning and IHC of nonhuman primate tissue was performed identically to C57BL/6 mouse spinal cord tissue, as described below.