Fig. 1. Development of retino-geniculate connectivity. Representative coronal sections through dLGN of P4 (A-D, n=3) and P9 (E-H, n=3) rats. Fibers from the ipsilateral projecting eye are labeled with CTB-Alexa Fluor 488 (green), whereas the projections from contralateral eye are labeled with CTB-Alexa Fluor 594 (red). (I,J,K) Quantification of relative contralateral (I), ipsilateral (J) and overlap (K) areas of P4 (n=3) and P9 (n=3) rats. The areas occupied by ipsilateral and contralateral projections are significantly different between P4 and P9 groups (Student's t-test, P<0.05 for contralateral and ipsilateral areas). Note that the overlap area decreases from 20% in P4 to 2% in P9 dLGN (K). At P4, high magnification of the area of overlap shows that fibers from both eyes are largely intermixed (D), whereas by P9, high magnification of the border between the two projections shows that these fibers terminate in distinct regions (H). (L-O) pERK expression in the dLGN is developmentally regulated. pERK immunohistochemistry in the dLGN at different postnatal stages reveals an increasing expression of pERK from P0 (L, n=3) to P5 (M, n=4). Note the reduced staining at P8 (N, n=3) and P11 (O, n=3). pERK-positive cells (green) co-express the neuronal marker NeuN (red), (P5 rats, n=4, P). Error bars depict the s.d. Scale bars: 200 µm for A-C,E-G; 10 µm for D,H; 100 µm for L-O; 50 µm for the insets; 25 µm for P.