DISTRIBUTION AND STRUCTURE OF VAGAL AFFERENT INTRAGANGLIONIC LAMINAR ENDINGS (IGLES) IN THE RAT GASTROINTESTINAL-TRACT

Intraganglionic laminar endings (IGLEs) are special terminal structure s of vagal afferent fibers and have been demonstrated in the myenteric plexus of esophagus and stomach. In order to quantitatively map their presence and distribution over the entire gastrointestinal tract, inc luding the small and large intestines, vagal afferents were anterograd ely labeled in vivo by microinjections of the fluorescent carbocyanine dye DiI into the left or right nodose ganglion of adult male rats. In the most successfully labeled cases the highest density of IGLEs was found in the stomach, with about half to one-third of the myenteric ga nglia receiving at least one IGLE. The proportion of myenteric ganglia innervated by IGLEs decreased in the small intestine; however,because of its large surface area this gut segment was estimated to contain t he highest total number of IGLEs. Both the cecum and colon also contai ned significant numbers of IGLEs. In the stomach, this vagal afferent innervation by IGLEs was more or less lateralized, with less than 20% of labeled IGLEs found on the contralateral side with respect to the i njection. The left/ventral vagus contributed a larger proportion of IG LEs to the proximal duodenum, while the right/dorsal vagus contributed a larger proportion of IGLEs to the distal duodenum and jejunum. Lase r scanning confocal microscopy on select specimens revealed further st ructural details. The parent axon typically formed two or more branche s that flanked the ganglia laterally, and in turn produced numerous hi ghly arborizing laminar terminal branches that covered one or both fla t sides of the ganglion in a dome-like fashion. The similar distributi on patterns and structural details suggest a uniform function for the IGLEs throughout the gastrointestinal tract, but there is as yet no cl ear proof for any of the hypothesized roles as specialized mechanosens ors or local effector terminals.