A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds
A: Schematic side view of the bird's brain indicating the locations of tracer application. Retrograde tracer (BDA, shown in green) was iontophoretically applied into Cluster N (shown in magenta). Anterograde tracer (CtB, shown in red) was injected into the vitreous of the contralateral eye. B: Double-labeling of ZENK and the retrograde tracer BDA in sagittal brain sections at the level of Cluster N proves the correct placement of tracer into Cluster N: arrows point to examples of neurons displaying ZENK-immunoreactivity (shown in magenta) in the nucleus together with BDA (shown in green) in the somata. Scale bar: 25 µm. C: Tracer distribution in frontal brain sections at the level of the thalamic Gld. Anterogradely labeled fibers from the retina (shown in red) project upon all substructures of the Gld, i.e. LdOPT, SpRt and lateral/ventral parts of the DLL. Retrogradely labeled neurons projecting upon Cluster N (visualised green) mainly originate within the DLL, with few additional connections from the LdOPT and SpRt. Scale bar: 50 µm. D: Confocal 3D-stacks in the thalamic Gld at high magnification indicate direct contact (arrows) between retinofugal fibers (shown in red) and somata/proximal dendrites retrogradely labeled from Cluster N (shown in green). Scale bar: 4 µm. Abbreviations: DLL, Nucleus dorsolateralis anterior thalami, pars lateralis; Gld, dorsolateral geniculate complex; LdOPT, Nucleus lateralis dorsalis nuclei optici principalis thalami; Rt, Nucleus rotundus; SPC, Nervus superficialis parvocellularis; SpRt, Nucleus suprarotundus; TSM, Tractus septomesencephalicus.