2.7. In vivo recording
Single-unit recordings were conducted in a subset of animals
(n ¼ 3) under urethane anesthesia (1.5 g/kg, i.p.) 18e21 days postviral
injection. Simultaneous optical silencing and electrical
recording of IL pyramidal neurons transduced with AAV-NpHReYFP
were performed using an optrode consisting of a tungsten
electrode (1e1.5 MU; MicroProbes) attached to an optical fiber. The
optical fiber was coupled to a green diode laser (l ¼ 532 nm;
Shanghai Laser & Optics Century) and yielded a fiber tip irradiance
of approximately 150 mW/mm2 as determined by an optical power
meter (Newport) prior to insertion into brain. A small craniotomy
was made over the viral injection site in the IL and the optrode was
gradually lowered in 50 mm increments using a hydraulic micromanipulator
(Narishige) starting from the dorsal boundary of the IL.
Recorded signals were bandpass filtered at 300 Hz (low)/8 kHz
(high) for unit activity using an ExAmp-20K low-noise spike
amplifier (Kation Scientific).