Viral Injection and GRIN Lens Implantation

A Gradient-Refractive Index (GRIN) lens and metal headcap were implanted following previously described procedures (Namboodiri et al., 2019 (link)) with the following modifications. In most mice, once the dura was removed from the craniotomy, we performed two injections of 0.5 $\mu L$ of virus (1 $\mu L$ total) containing the GCaMP gene construct (AAVDJ-CamKIIa-GCaMP6s, $5.3*{10}^{12}$ viral particles/mL from UNC Vector core lot AV6364) using a glass pipette microinjector (Nanoject II) at Bregma +1.94 mm AP, 0.3, and 1.2 mm ML, –2 mm DV. Ten minutes elapsed before the microinjector withdrawal to allow the virus to diffuse away from each infusion site. Then, mice were implanted with a 1 × 4 mm GRIN lens (Inscopix) aimed at +1.94 mm AP, 0.6 mm ML, and –1.8 mm DV. A subset of mice did not receive viral injections; instead, a lens with the imaging face coated 1 $\mu L$ of the GCaMP6s virus mixed with 5% aqueous silk fibroin solution (Jackman et al., 2018 (link)) was implanted at the same coordinate. GCaMP expression and transients were similar in both preparations. Mice were allowed to recover for at least 5 weeks before experiments began.