VAGAL PREGANGLIONIC PROJECTIONS TO THE ENTERIC NERVOUS-SYSTEM CHARACTERIZED WITH PHASEOLUS-VULGARIS-LEUKOAGGLUTININ

The patterns and extent of vagal preganglionic divergence and converge nce within the gastrointestinal tract of the rat were characterized wi th the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Three weeks after tracer was iontophoretically injected into two to fo ur sites within the dorsal motor nucleus of the vagus, wholemounts of perfused gut organs (stomach, duodenum, cecum) were prepared, counters tained with Cuprolinic blue, and processed for PHA-L using the avidin biotin complex with diaminobenzidine. Controls included animals inject ed with PHA-L after intracranial deafferentations. Well-positioned inj ections labeled an extremely dense and intricate network of varicose e fferent axons throughout the gastric myenteric plexus (including that of the fundus). Individual fibers collateralized extensively, forming a variety of pericellular arborizations and terminal complexes made up of both en passant and end swellings. Single axons frequently innerva ted subsets of neurons within ganglia. Most enteric neurons were conta cted by varicosities of more than one vagal fiber. The patterns of vag al preganglionic fibers in the duodenal and cecal myenteric plexuses r esembled the organization in the stomach in many aspects, but the proj ections in each organ had distinctive characteristics, and label was l ess dense in the intestines than in the stomach. Vagal preganglionic f ibers directly innervated submucosal ganglia, although sparsely. Brain stem injections of PHA-L retrogradely labeled a few myenteric neurons in the corpus, fundus, and duodenum: These ''gastrobulbar'' and ''duod enobulbar'' neurons received reciprocal vagal preganglionic innervatio n. Finally, the PHA-L that spread to the nucleus of the solitary tract occasionally produced transganglionic labeling of afferent intramuscu lar arrays (gastric fundus). The results of this paper provide strong evidence that the traditional ''command neuron'' or ''mother cell'' hy potheses of vagal-enteric organization should be abandoned for an inte grative neural network, model. (C) 1997 Wiley-Liss, Inc.