PROJECTIONS OF THE NUCLEUS OF THE BASAL OPTIC ROOT IN PIGEONS (COLUMBA-LIVIA) REVEALED WITH BIOTINYLATED DEXTRAN-AMINE

The nucleus of the basal optic root (nBOR) of the accessory optic syst em is known to be involved in the analysis of the visual consequences of self-motion. Previous studies have shown that the nBOR in pigeons p rojects bilaterally to the vestibulocerebellum, the inferior olive, th e interstitial nucleus of Cajal, and the oculomotor complex and projec ts unilaterally to the ipsilateral pretectal nucleus lentiformis mesen cephali and the contralateral nBOR. By using the anterograde tracer bi otinylated dextran amine, we confirmed these projections and found (pr eviously unreported) projections to the nucleus Darkshewitsch, the nuc leus ruber, the mesencephalic reticular formation, and the area ventra lis of Tsai as well as ipsilateral projections to the central gray, th e pontine nuclei, the cerebellar nuclei, the vestibular nuclei, the pr ocessus cerebellovestibularis, and the dorsolateral thalamus. In addit ion to previous studies, which showed a projection to the dorsomedial subdivision of the contralateral oculomotor complex, we found terminal labelling in the ventral and dorsolateral subdivisions. Individual fi bers were reconstructed from serial sections, and collaterals to vario us nuclei were demonstrated. For example, collaterals of fibers projec ting to the vestibulocerebellum terminated in the vestibular or cerebe llar nuclei; collaterals of fibers to the inferior olive terminated in the pontine nuclei; many individual neurons projected to the intersti tial nucleus of Cajal, the nucleus Darkshewitsch, and the central gray and also projected to the nucleus ruber and the mesencephalic reticul ar formation; collaterals of fibers to the contralateral nucleus of th e basal optic root terminated in the mesencephalic reticular formation and/or the area ventralis of Tsai; neurons projecting to the nucleus lentiformis mesencephali also terminated in the dorsolateral thalamus. The consequences of these data for understanding the visual control o f eye movements, neck movements, posture, locomotion, and visual perce ption are discussed. (C) 1997 Wiley-Liss, Inc.