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Neural projections from midbrain optic flow nuclei to the inferior olive and vestibulocerebellum of zebra finches (Taeniopygia guttata) Wu, Pei-Hsuan


Global visual motion across the retina due to self-motion is called optic flow. Optic flow is an important idiothetic cue for locomotion control. In birds, the lentiformis mesencephali (LM) and the nucleus of the basal optic root (nBOR) of the midbrain process optic flow and transmit it to the cerebellum for integration with other sensory inputs. The vestibulocerebellum (VbC), composed of folium IXcd and X, is important for visuomotor control and has been divided into several functional sagittal compartments, defined by multiple factors. Purkinje cells in the VbC differentially express a molecular marker, zebrin II, generating parasagittal zebrin immuno-positive bands alternating with zebrin immuno-negative bands. Both the LM and the nBOR project directly to the VbC as mossy fibers and are co-localized within immuno-positive bands. The LM and nBOR also project indirectly to the VbC via the medial column of the inferior olive (mcIO). The mcIO cells project as climbing fibers to the VbC. In pigeons, the LM projects to the caudal mcIO and the nBOR project to the rostral mcIO. These pathways have not been explored to the same detail in other avian species. I dual-injected anterograde tracers of different fluorescence in the LM and the nBOR of zebra finches and traced the projections to the mcIO and VbC. Folium IXcd was also immunolabeled for zebrin II. I show that the zebra finch inferior olive has a more complex structure than previously reported in other birds. The nBOR axon terminals can be found in most of the mcIO subdivisions, whereas the LM terminals are mostly in the dorsal divisions. The zebrin expression and the mossy fiber distribution patterns are in general similar between zebra finches and pigeons. However, further analysis revealed that LM has more projections to per unit area of the immuno-positive bands, whereas more nBOR mossy fiber terminals were found in the area-corrected immuno-negative bands. The present study suggests that species differences in visuomotor pathways exist and zebra finches may serve as an important species to understand the evolution of the neuroanatomy that supports birds to perform different flight behaviors.

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