Early enucleation alters ephrin A5 expression in the neocortex. All panels are high magnification views of 100 μm sagittal sections of P10 brain hemispheres following in situ RNA hybridization with probes directed against (A1-C1; A2-C2) ephrin A5, (D1-D2) Id2, (E1-E2) Cad8 and (F1-F2) RZRß. (G1-G2) Sagittal sections of 40 μm stained for Nissl substance. Sections shown in A1-C1 and A2-C2 are at a medial location close to the midline, panels D1-D2 are mid-sagittal, and panels E1-E2 and F1-F2 show lateral sections. Ephrin A5 expression in the medial parietal cortex of controls was observed in one uninterrupted band of expression within layers 4 and 5 (below left arrows in A1-C1), and no transcripts were detected in the superficial layers (left arrows in A1-C1). In brains from enucleated animals, the expression of ephrin A5 was observed in the superficial layers (left arrows in A2-C2) in addition to the band of expression in lower layers (below left arrows in A2-C2). An ectopic expression is also present in caudal layer 4 (right arrows in A2-C2) and not present in the controls (right arrows in A1-C1). Expression patterns of Id2, Cad8 and RZRß in enucleated brains (D2-F2) show no significant differences from that of controls (D1-F1). Arrows in E1-E2 and F1-F2 denote the location of the barrel field. Cortical layers are labeled by roman numerals in G1-G2. Asterisks indicate the presumptive S-V boundary. All sections are oriented with dorsal (D) up and rostral (R) to the left. Scale bar = 1,000 μm. Cad8: Cadherin-8; Id2: inhibitor of DNA binding 2; P: postnatal day; RZRß: retinoic acid receptor related orphan receptor beta; S-V: somatosensory-visual.