Axons labeled in Po by BDA injections in GABAergic projection structures. Microiontophoretic deposits in a dorsal (a) and ventral (c) portion of the thalamic reticular nucleus (TRN), the anterior pretectal nuclei (g) and in the dorsal (ZId; j) and ventral (ZIv; m) zona incerta. Axonal arborizations in the ipsilateral Po are represented in panels b, e, h, k, n, respectively. Cytochrome oxidase histochemistry counterstain. c, f, i, l, o, Location of axonal varicosities in Po and adjacent thalamic nuclei, plotted from the respective anterograde axonal labeling. Individual axonal varicosities in Po are represented in red ink; those outside Po are drawn in gray. Eth: Ethmoid thalamic nucleus; LD: laterodorsal thalamic nucleus; VPL: Ventral posterolateral nucleus; ZId, ZIv: dorsal and ventral divisions of the Zona Incerta. Scale bars: 250 µm (a, c, d, f, g, i, j, l, m, o), 100 µm (b, e, h, k, n), and 25 µm (insets).