Fig. 3. In vivo electroporation of embryonic chicken midbrain. a, Epifluorescence photography of a chicken embryo at E7, i.e., at 24 hr after electroporation with an expression plasmid for GFP showing expression in the dorsocaudal region of the tectum. Arrows point to the transgenic GFP expression domain; note that the yellowish dots are merely reflections of light, and two examples of these artifacts are marked by open arrowheads.b, Confocal laser scanning image of double transgenic tectal neurons showing cytoplasmic localization of GFP in their cell somata and transgenic R-cadherin labeling on their surface. Scale bar, 10 μm. c, Laser scanning image of an immunostained frontal section of a transgenic tectal hemisphere at 5 d after electroporation (E11). Transgenic neurons are identified by their expression of GFP. Axonal projections of labeled stratum griseum centrale (SGC) neurons can be followed (arrows) via the stratum album centrale (SAC) to the brachium of the superior colliculus (BCS), in which the tectoefferent fascicles segregate into the tectothalamic tract (tt), tectobulbar tract (tb), and tectoisthmic tract (ti). Tectal layering is revealed by nuclear staining (in blue). Cadherin staining (Rcad, in red) marks the tectoisthmic projection to the nuclus isthmi, pars parvocellularis (IPC). SO, Stratum opticum;SGFS, stratum griseum et fibrosum superficiale. Scale bar, 100 μm. d–p, Coelectroporation of different expression plasmids for GFP and a cadherin leads to respective overexpression of GFP (d, f,g, i, k, m,n, p) and the cadherin (Ncad ind and e, cad7 in g andh, cad6B in k and l, and Rcad in n and o) by tectal neurons (d, g, k,n; yellow indicates costaining) and their axonal growth cones (e, f,h, i, l, m,o, p; red andgreen scans are shown separately). Arrowsin e and f point to matching areas of the red and the green scan. Scale bars: (in d)d, g, k, n, 20 μm ; (in e) e, d,l, m and (in h)h, i, o, p, 5 μm.