Projections of the dorsal motor nucleus of the vagus to cardiac ganglia ofrat atria: An anterograde tracing study

We injected the anterograde fluorescent tracer 1,1'-dioleyl-3,3,3',3 '-tetr amethylindocarbocyanine methanesulfonate (DiI) into the dorsal motor nucleu s of the vagus (DmnX), counterstained the cardiac ganglia with Fluorogold ( FG), and used confocal microscopy to examine the distributions and differen t types of DmnX fibers in wholemounts of the atria. We also quantified the number of DmnX cardiac axons and the number of innervated cardiac principal neurons (PNs). Rats with unilateral DiI injections were used in three diff erent experiments, including unilateral FG soaking of cervical vagal trunks , intracranially rhizotomizing the vagal afferent roots, or contralaterally sectioning the cervical vagus. These manipulations indicated that DiI-labe led cardiac fibers were exclusively from the DmnX. Our observations establi shed that: (1) three major ganglionic plexuses were localized in the epicar dium; (2) both sides of the DmnX supplied significant fibers to each of the plexuses; (3) these cardiac efferents formed dense basket terminals around individual PNs; (4) collaterals of individual DmnX fibers diverged, produc ing calyx endings on multiple PNs; (5) small intensely fluorescent (SIF) ce lls in the cardiac plexuses were innervated pericellularly; (6) individual axons could innervate both PNs and SIF cells; (7) the total number of DmnX fibers were in the range of [68, 96; left] and [67, 115; right]; (8) these fibers innervated 709 (left) and 494 (right), or at least 18% and 12%, of t he PNs, respectively; and (9) vagal preganglionics exhibited a degree of la teralization: Significantly more PNs were contacted by fiber varicosities i n the sinoatrial plexus than in the atrioventricular plexus after right Dmn X injections. In summary, the present observations suggest that the DmnX pl ays a significant role(s) in controlling the heart. (C) 1999 Wiley-Liss. In c.