INTERACTION BETWEEN PARASYMPATHETIC AND SYMPATHETIC-NERVES IN PREVERTEBRAL GANGLIA - MORPHOLOGICAL EVIDENCE FOR VAGAL EFFERENT INNERVATION OF GANGLION-CELLS IN THE RAT

Vagal efferent preganglionic neurons were anterogradely labeled by inj ecting either DiI or DiA, fluorescent lipophilic carbocyanine dyes, in to the dorsal motor nucleus of the vagus of the rat. All neurons of th e peripheral nervous system (outside the blood-brain barrier) were the n fluorescently counterstained in vivo by injecting Fluorogold (Fluoro chrome, Inc., Englewood, CO) intraperitoneally. The upper abdominal pr evertebral ganglia, including the numerous microganglia associated wit h the periarterial plexuses of the celiac and superior mesenteric arte ries, were identified and dissected in formalin-fixed tissue under ult raviolet light and stereomicroscopic guidance. In 14 of 15 animals ana lyzed (93%), labeled vagal efferent fibers were found to penetrate int o both the left and right celiac ganglia and the superior mesenteric g anglion, as well as into some of the associated microganglia. These pr ojections formed varicose terminal-like structures, highly suggestive of synaptic contacts surrounding individual ganglion cells. In about h alf the animals, such vagal innervation was also seen in the left and right suprarenal ganglia. The specificity of vagal efferent labeling w as confirmed by control experiments, which included injections in vago tomized animals and direct selective labeling of vagal afferents from the nodose ganglia. It is concluded that vagal efferent preganglionics innervate principal ganglion cells of prevertebral ganglia. These vag al contacts may either directly modulate the postganglionic outflow or else gate some or all of the potential modulatory inputs to these pos tganglionic neurons, thus allowing the vagal system to exert a more se lective influence on sympathetic outflow. Finally, the use of laser sc anning confocal microscopy and the in tote Fluorogold staining method for investigations of the peripheral nervous system are discussed. (C) 1996 Wiley-Liss, Inc.