Ai9 reporter mice

All of the animal procedures were approved by the UConn Health Institutional Animal Care and Use Committee, and experiments were performed in accordance with its guidelines and regulations, and authors complied with the ARRIVE guidelines. We used αSMACreERT2 and Col2.3GFP mice that have been previously described in refs. ^{4 (link),44 (link)}. Ai9 reporter mice (007909), were purchased from Jackson Labs^{45 (link)}. We backcrossed PDGFRβ^fl/fl (129S4/SvJaeSor) generated by Dr. Phillipe Soriano^{46 (link)} for 8 generations to C57Bl/6J background. All strains were maintained on a C57Bl/6J background. Mice were housed in ventilated cages, maintained at 22 ± 2 °C, 55 ± 5% humidity, and 12-h light/dark cycle with ad libitum access to food and water. αSMACreERT2 mice were crossed with the Ai9 reporter mice (Jackson Labs) and Col2.3GFP mice, and triple transgenic male mice αSMACreERT2/Ai9/Col2.3GFP (termed SMA9/Col2.3GFP) were used at the age of 5–7 months for evaluation of growth factor efficiency. For fracture healing, αSMACreERT2/PDGFRβ^fl/fl Cre⁺ experimental animals and Cre⁻ littermates as controls at 8–10 weeks of age, were treated with tamoxifen (75 µg/g). We determined genotype for Cre, Pdgfrβ and DNA recombination by PCR (primer sequences in Supplementary Table 1).

Six weeks old male Sprague–Dawley rats weighing 167.8 ± 7.3 g (purchased from the Experimental Animal Center of the Fourth Military Medical University, Xi'an, Shaanxi, China) were used in the behavioral, immunohistochemistry, western blot, and ELISA experiments. Adult heterozygous male vGlut2-Cre mice (Jackson Laboratories) were crossed with Ai9 reporter mice (Jackson Laboratories) to generate vGlut2-tdTomato mice. Young adult (3–5 weeks old) male vGlut2-tdTomato mice were used for electrophysiological experiments. Animals were group-housed (4 per cage) at a temperature of 22-24°C, with a 12-hour light/dark cycle and free access to food and water. All rats were acclimatized to the laboratory conditions for at least 7 days before experimental manipulation in case their stress responses affected the experiment results. All animal experiments were approved by the Ethic Committee of the Fourth Military Medical University and followed the policies for the use of laboratory animals issued by the International Association for the Study of Pain. All efforts were made to minimize the number of animals used and their suffering.