Brain Research 963 (2003) 121–131 www.elsevier.com / locate / brainres Research report V estibular nucleus projections to the Edinger–Westphal and anteromedian nuclei of rabbits * Carey D. Balaban Departments of Otolaryngology, Neurobiology and Communication Disorders, University of Pittsburgh, Eye and Ear Institute, 203 Lothrop Street, Pittsburgh, PA 15213, USA Accepted 8 November 2002 Abstract The Edinger–Westphal nucleus (EW), anteromedian nucleus (AM) and adjacent neurons in the ventral tegmental area (VTA) are sources of preganglionic parasympathetic innervation of intraocular smooth muscle, including blood vessels, pupillary muscle and the ciliary body in mammals. They also have central connections that are believed to affect parasympathetic outflow indirectly. This study utilized anterograde transport of biotinylated dextran amine and Phaseolus vulgaris leucoagglutinin to demonstrate direct projections from the vestibular nuclei to the Edinger–Westphal and anteromedian nuclei in rabbits. The rabbit AM and adjacent VTA contain moderate to intensely choline acetyltransferase (ChAT)-immunopositive neurons. The rabbit EW, by contrast, is nearly devoid of ChAT-immuno- positive neurons. Vestibular nucleus projections to these regions originate from all levels of the superior, medial and lateral vestibular nuclei, but do show topographic organization. The densest terminations were observed in AM and the ventral and central aspects of EW. The projections to AM terminate in both ipsilaterally and in a narrow paramedian region. Predominantly ipsilateral terminations were observed in VTA. Terminations on ChAT-positive cells in AM and VTA were verified in three rabbits. It is suggested that projections to some intensely ChAT-positive AM and VTA neurons may be a substrate for vestibular influences on lens accommodation, pupillary constriction and regulation of intraocular circulation during changes in posture and gravitoinertial challenges. The projections to ChAT-negative (and weakly immunoreactive) cells in AM,VTA and EW, on the other hand, are likely to contribute vestibular signals to a variety of motor responses via descending pathways.  2002 Elsevier Science B.V. All rights reserved. Theme: Motor systems and sensorimotor integration Topic: Vestibular system Keywords: Vestibular nucleus; Parasympathetic nervous system; Intraocular innervation; Edinger–Westphal nucleus; Anteromedian nucleus 1. Introduction [7,9,40,44,53,54]. The caudal medial vestibular nucleus and the inferior vestibular nucleus can influence postcra- Recent anatomic and physiologic studies have demon- nial parasympathetic and sympathetic outflow, either di- strated direct connections between the vestibular nuclei rectly or indirectly, via descending projections to the and brain stem regions that influence sympathetic and nucleus of the solitary tract, dorsal motor vagal nucleus, parasympathetic outflow (for a review, see Ref. [11]). nucleus ambiguus and the rostral ventrolateral medullary These so-called ‘vestibulo-autonomic pathways’ originate reticular formation. An ascending pathway also originates from an extensive region within the vestibular nuclei, from the dorsal aspect of the superior vestibular nucleus, which includes the dorsal aspect of the superior vestibular pars alpha (or caudoventral aspect) of the lateral vestibular nucleus, pars alpha (or caudoventral aspect) of the lateral nucleus, and the caudal half of the medial vestibular vestibular nucleus, and the caudal half of the medial nucleus and the inferior vestibular nucleus. This ascending vestibular nucleus and the inferior vestibular nucleus projection terminates densely in the parabrachial nucleus, which has both ascending projections to the amygdala, hypothalamus and prefrontal cortex, and descending con- *Tel.: 11-412-647-2298; fax: 11-412-647-0108. E-mail address: cbalaban@pitt.edu (C.D. Balaban). nections to medullary regions that control sympathetic and 0006-8993 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0006-8993(02)03955-0