A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds
A: Schematic overview of anatomical features according to cresylviolet staining (shown in B, C and D) and tracing patterns in the thalamus. Each input source (retina, red; medial wulst, blue; Cluster N, green) and their overlapping tracing patterns are color-coded separately. Retinofugal fibers show a high degree of overlap with neurons projecting upon Cluster N (shown in yellow) in ventral parts of the DLL, the SpRt and the LdOPT, whereas neurons projecting upon the medial wulst exclusively co-localize with retinofugal fibers only in dorsal DLL regions and the DLAmc (shown in magenta). Lateral parts of the DLL, which receive afferents from the retina, project upon the medial wulst and Cluster N (shown in white). B: Retrograde tracing pattern from the medial visual wulst, ipsilateral side. Neurons are mainly located in lateral parts of the DLL and LdOPT with few single neurons positioned in lateral parts of the DLAmc. C: Retrograde tracing pattern from Cluster N, ipsilateral side. Labeled neurons cover lateral and ventral parts of the DLL and are found in the SpRT and LdOPT (compare Fig. 1C). D: Contralaterally projecting retinofugal fibers innervate the LdOPT, SpRt and lateral/ventral parts of the DLL, the nMOT and a small band along the lateral DLL reaching parts of the DLAmc (compare Fig. 1C). E: Retrograde tracing pattern from Cluster N, contralateral side. Few scattered neurons are found in DLL and LdOPT. Scale bar (for B–E): 100 µm; scale bar in insert (for insert in B–E): 50 µm. Abbreviations: AL, Ansa lenticularis; DLAmc, Nucleus dorsolateralis anterior thalami, pars magnocellularis: DLL, Nucleus dorsolateralis anterior thalami, pars lateralis; FPL, Fasciculus prosencephali lateralis; LdOPT, Nucleus lateralis dorsalis nuclei optici principalis thalami; nMOT, Nucleus marginalis tractus optici; OM, Tractus occipitomesencephalicus; Rt, Nucleus rotundus; SPC, Nervus superficialis parvocellularis; SpRt, nucleus suprarotundus; Tel, Telencephalon; TrO, Tractus opticus; TSM, Tractus septomesencephalicus.