Optogenetic Activation of Oxytocin Neurons

To identify channelrhodopsin 2-expressing PVN oxytocin neurons in Oxytocin:Cre × Ai32 dams through channelrhodopsin 2-assisted patching during each recording session^{52 (link),53 (link)}, we used a Fiber-Optic Light Stimulating Device with a 465-nm blue LED (A-M Systems, 726500) connected to a Fiber-Optic Light Guide (A-M Systems, 726527). The optic fibre was inserted into the patch pipette using a 1.5-mm outer-diameter Continuous Optopatcher Holder (A-M Systems, 663943). Pulses of blue light were delivered through the optic fibre by a Digidata 1440A system (Molecular Devices) while recording in cell-attached or whole-cell configuration the responses of channelrhodopsin 2-positive oxytocin neurons (ChR2⁺, OT⁺) or other channelrhodopsin 2-negative PVN neurons (ChR2⁻, OT⁻). Different steps of light pulses (50 or 200 ms duration) were delivered with increasing intensity from 20 to 100% of the full LED power (3 mW at the tip of the fibre). ChR2⁺ (OT⁺) neurons responded to light pulses by an increase in their firing rate and spiking probability, whereas ChR2⁻ (OT⁻) neurons were not modulated by blue light.