EVIDENCE FOR DIVERGENT PROJECTIONS TO THE BRAIN NORADRENERGIC SYSTEM AND THE SPINAL PARASYMPATHETIC SYSTEM FROM BARRINGTONS NUCLEUS

The present study was designed to determine whether Barrington's nucle us, which lies ventromedial to the locus coeruleus (LC) and projects t o the sacral parasympathetic nucleus, is a source of afferent projecti ons to the LC. Restricted injections of the anterograde tracer, biocyt in, into Barrington's nucleus labeled varicose fibers that extended fr om the injection site into the LC. Consistent with this, injections of the retro,grade tracers, wheatgerm agglutinin conjuated to horseradis h peroxidase coupled to gold particles (WGA-Au-HRP) or fluorescein-con jugated latex beads, into the LC labeled numerous (approximately 10%) Barrington's neurons that were also retrogradely labeled by Fluoro-Gol d (FG) injections in the spinal cord. Retrograde tracing from the LC c ombined with corticotropin-releasing hormone (CRH) immunohistochemistr y revealed that at least one third of the retrogradely labeled neurons in Barrington's nucleus were CRH-immunoreactive (CRH-IR). Finally, in triple labeling studies, CRH-Barrington's neurons were consistently o bserved that were retrogradely labeled from both the LC and spinal cor d. These findings implicate Barrington's nucleus as an LC afferent and a source of CRH-IR fibers in the LC. Additionally, the results sugges t that some Barrington's neurons diverge to innervate both the spinal cord and the LC. This divergent innervation may serve to coregulate th e sacral parasympathetic nervous system and brain noradrenergic system , thus providing a mechanism for coordinating pelvic visceral function s with forebrain activity.