VAGAL AFFERENT INNERVATION OF THE ATRIA OF THE RAT-HEART RECONSTRUCTED WITH CONFOCAL MICROSCOPY

We have used confocal microscopy to analyze the vagal afferent innerva tion of the rat heart. Afferents were labeled by injecting 1,1'-dioley l-3,3,3',3'-tetramethylindocarbocyanine methanesulfonate (DiI) into th e nodose ganglia of animals with prior supranodose de-efferentations, autonomic ganglia were stained with Fluoro-gold, and tissues were exam ined in whole mounts. Distinctively different fiber specializations we re observed in the epi-, myo-, and endocardium: Afferents to the epica rdium formed complexes associated with cardiac ganglia. These ganglia consisted of four major ganglionated plexuses, two on each atrium, at junctions of the major vessels with the atria. Ganglionic locations an d sizes (left > right) were consistent across animals. In addition to principal neurons (PNs), significant numbers of small intensely fluore scent (SIF) cells were located in each of these plexuses, and vagal af ferents provided dense pericellular varicose endings around the SIF ce lls in each ganglionic plexus, with few if any terminations on PNs. In the myocardium, vagal afferents formed close contacts with cardiac mu scles, including conduction fibers. In the endocardium, vagal fibers f ormed ''flower-spray'' and ''end-net'' terminals in connective tissue. With three-dimensional reconstruction of confocal optical sections, a novel polymorphism was seen: Some fibers had one or more collaterals ending as endocardial flower sprays and other collaterals ending as my ocardial intramuscular endings. Some unipolar or pseudounipolar neuron s within each cardiac ganglionic plexus were retrogradely labeled from the nodose ganglia. In conclusion, vagal afferents form a heterogenei ty of differentiated endings in the heart, including structured elemen ts which may mediate chemoreceptor function, stretch reception, and lo cal cardiac reflexes. (C) 1997 Wiley-Liss, Inc.