Organization of the coeruleo-vestibular pathway in rats, rabbits, and monkeys

Inputs from locus coeruleus (LC) appear to be important for altering sensor imotor responses in situations requiring increase vigilance or alertness. T his study documents the organization of coeruleo-vestibular pathways in rat s, rabbits and monkeys. A lateral descending noradrenergic bundle (LDB) pro jects from LC to the superior vestibular nucleus (SVN) and rostral lateral vestibular nucleus (LVN). A medial descending noradrenergic bundle (MDB) pr ojects from LC to LVN, the medial vestibular nucleus (MVN), group y and ros tral nucleus prepositus hypoglossi (rNPH). There is a characteristic, speci fic pattern of innervation of vestibular nuclear regions across the three s pecies. A quantitative analysis revealed four distinct innervation density levels (minimal, low, intermediate and high) across the vestibular nuclei. The densest plexuses of noradrenergic fibers were observed in the SVN and L VN. Less dense innervation was observed in the MVN, and minimal innervation was observed in the inferior vestibular nucleus (IVN). In monkeys and rabb its, rostral MVN contained a higher innervation density than the rat MVN. I n monkeys, the rNPH also contained a dense plexus of fibers. Selective dest ruction of terminal LC projections (distal axons and terminals) by the neur otoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) resulted in a d ramatic reduction of immunoreactive fibers within the vestibular nuclear co mplex of rats, suggesting that the source of these immunoreactive fibers is LC. Retrograde tracer injections into the vestibular nuclei resulted in la beled cells in the ipsilateral, caudal LC and adjacent nucleus subcoeruleus . It is hypothesized that the regional differences in noradrenergic innerva tion are a substrate for differentially altering vestibule-ocular and vesti bule-spinal responses during changes in alertness or vigilance. (C) 1999 El sevier Science B.V. All rights reserved.