A direct neuronal connection between the telencephalic nucleus robustus arcopallialis and the nucleus nervi hypoglossi, pars tracheosyringealis in Bengalese finches (Lonchura striata var. domestica)

Bird species with vocal learning possess a projection from the telencephalic nucleus to the nucleus nervi hypoglossi, pars tracheosyringealis (XIIts) in the medulla, where a final common pathway that controls the vocal organ, i.e., the synrinx, originates. The anatomical basis of this projection has not been well investigated in one species of songbird, the Bengalese finch (Lonchura striata var. domestica). The present study used anterograde and retrograde tracing experiments to examine and describe this projection in Bengalese finches. Following iontophoretic injections of biotinylated dextran amine into the telencephalic nucleus robustus arcopallialis (RA), we detected anterograde-labeled terminations in the XIIts. In addition, labeled terminals were seen in other vocal-respiratory-related nuclei, such as the dorsomedial nucleus of the nucleus intercollicularis, nucleus infraolivaris superior, nucleus of the rostral ventrolateral medulla, nucleus parambigualis, nucleus ambiguous, and nucleus retroambigualis. Furthermore, following injections into the XIIts, we detected retrograde-labeled cell bodies scattered throughout the ipsilateral RA. The present results revealed that the direct projections of the RA to the XIIts in male Bengalese finches are similar to those in other songbirds with vocal learning abilities.