Anterograde mass labeling of some subcortical inputs to Po with viral vector-mediated transfection. Two-photon tomography image samples taken from experiments in which viral vectors able to drive the expression of high levels of fluorescent protein were injected in some of the structures that originate inputs to Po. Injections sites in the anterior pretectal nucleus (APT; a), the zona incerta (ZI; c), the interpolaris spinal trigeminal nucleus (SpVI; e), or the superior colliculus (SC; g). Coronal section images showing fluorescently labeled axons in Po are shown in b, d, f, h. Images from the Mouse Connectivity Projection datasets can be found in http://connectivity.brain-map.org/projection/experiment/278401778 (a, b), /301539438 (c, d), /272738620 (e, f), and /128001349 (g, h). AP: bregma level in mm. CL: central lateral nucleus; PC: paracentral nucleus; PF: parafascicular nucleus; VL: ventrolateral nucleus; VPM: ventral posteromedial nucleus; ZId: dorsal zona incerta; ZIv: ventral zona incerta; DpG: deep gray layer; InG: intermediate gray layer; InWh: intermediate white layer; Op: optic tract. Scale bars: 1000 µm (a, c, e, g) and 500 µm (b, d, f, h).