Adult gerbils were stereotactically injected with 50-100nl of rAAV-mDlx-ChR2-mCherry in auditory cortex (A1) and sectioned for optogenetics and electrophysiological recording after 5 weeks (n=6 animals). (a) Infrared and fluorescence images showing the cells targeted for electrophysiological recording. Dashed lines highlight the edges of the recording pipet. Note that the cell in (c) does not express mCherry but is surrounded by mCherry-expressing cells. (b) Left panel: Membrane potential of a mCherry+ cell in response current pulses corresponding to twice the rheobase. Baseline membrane potential is -60 to -70 mV. Right panel: intensity-dependent increase of firing upon 1ms pulse of blue light for both FS and LTS interneurons. (c) Left panel: Membrane potential of a cell mCherry- in response current pulses corresponding to twice the rheobase. Baseline membrane potential is -60 to -70 mV. Right panel: the firing of pyramidal neurons is interrupted by a 1ms pulse of blue light suggesting activation of interneurons produces such inhibitory postsynaptic response. Scale bars represent 5μm.