Ferrets aged P27-P30 were injected with rAAV-mDlx-GCaMP6f in primary visual cortex and then imaged at P50 (n=4 animals). (a) rAAV-mDlx-GCaMP6f labeled large numbers of inhibitory neurons, allowing for in vivo two-photon calcium imaging of inhibitory neurons. (b) Representative recording of calcium fluorescence of individual neurons upon presentation of visual stimulus. Labeled neurons show robust calcium fluorescence changes to visual stimuli during functional imaging. Black traces represent mean over 8 trials and grey represent ± s.e.m. Blue bars above responses indicate period of stimulus presentation. PS: preferred stimulus. NPS: non preferred stimulus. Scale bar represents 100 μm.