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.