SOM-TD mice (P34, Supplementary Fig. 6f) were anesthetized with 4% isoflurane and perfused transcardially with saline followed by chilled 4 % paraformaldehyde in 0.1 M PBS. The brains were then postfixed in 4 % paraformaldehyde in 0.1 M PBS (<4°C) overnight. The fixed brains were sectioned into 50 μm visual cortical slices with a vibratome and then blocked in 10% normal goat serum with 1% triton in PBS (1 hour, room temperature) before being stained with rabbit anti-M1 and anti-M2 (1:200, Millipore, AB5164, AB5166) or rabbit anti-nAChR alpha4 and rabbit anti-nAChR beta2 or rabbit anti-nAChR alpha7 (1:200, Abcam, ab41172, ab55980, ab23832)67 (link) overnight (< 4 °C). This was followed by a 3 hour incubation in Alexa Fluor 488 goat anti-rabbit (1:200, Invitrogen, A11034) before being mounted on a glass slide with the Vectashield Hardset mounting media (Vector Labs). The slides were imaged using a confocal microscope (Zeiss LSM 5 Pascal Exciter) and the images were analyzed for co-localization of tdTomato positive SOM neurons and the respective cholinergic receptors stains.