Imaging Cells and Pipettes in Subiculum

To visualize cells and glass pipettes in the distal subiculum (Fig. 3C, 3D), we used a 2-photon microscope (Bergamo II Series, ThorLabs) equipped with a Ti:Sapphire laser (920 nm; Chameleon Ultra, Coherent) to enable excitation of fluorescent markers through a 20x, NA 0.95 objective lens (Olympus). To detect fluorescence from intracellular tdTomato and Alexa 488 in the pipette, we used two photo-multiplier tubes (Hamamatsu) that receive either red or green optically filtered emission, respectively. Transgenic mice were generated by crossing CaMKIIa- or PV-Cre promoter mice (Jackson Labs, stock # 005359 or 008069) with the loxP-flanked tdTomato reporter mice (Jackson Labs, stock # 007914)(Madisen et al., 2010 (link)). The CamkIIa-promoter is specific for expression in principal cells (Tsien et al., 1996 (link)), while the PV-promoter targets interneurons expressing parvalbumin (Hippenmeyer et al., 2005 (link)).