VAGAL INNERVATION OF THE RAT PYLORUS - AN ANTEROGRADE TRACING STUDY USING CARBOCYANINE DYES AND LASER-SCANNING CONFOCAL MICROSCOPY

In an attempt to identify the distribution and structure of vagal fibe rs and terminals in the gastroduodenal junction, vagal efferents were labeled in vivo by multiple injections of the fluorescent carbocyanine dye DiA into the dorsal motor nucleus (dmnX), and vagal afferents wer e anterogradely labeled by injections of DiI into the nodose ganglia o f the same or separate rats. Thick frontal cryostat sections were anal ysed either with conventional or laser scanning confocal microscopy, u sing appropriate filter combinations and/or different wavelength laser excitation to distinguish the fluorescent tracers. Vagal efferent ter minal-like structures were present in small ganglia within the circula r sphincter muscle, which, in the absence of a well-developed, true my enteric plexus at this level, represent the myenteric ganglia. Further more, vagal efferent terminals were also present in submucosal ganglia , but were absent from mucosa, Brunner's glands and circular muscle fi bers. Vagal afferent fibers and terminal-like structures were more abu ndant than efferents. The most prominent afferent terminals were profu sely branching, large net-like aggregates of varicose fibers running w ithin the connective tissue matrix predominantly parallel to the circu lar sphincter muscle bundles. Profusely arborizing, highly varicose en dings were also present in large myenteric ganglia of the antrum and d uodenum, in the modified intramuscular ganglia, and in submucosal gang lia. Additionally, afferent fibers and terminals were present througho ut the mucosal lining of the gastroduodenal junction. The branching pa tterns of some vagal afferents suggested that individual axons produce d multiple collaterals in different compartments. NADPH-diaphorase pos itive, possibly nitroxergic neurons were present in myenteric ganglia of the immediately adjacent antrum and duodenum, and fine varicose fib ers entered the sphincter muscle from both sides, delineating the pote ntial vagal inhibitory postganglionic innervation. These morphological results support the view of a rich and differentiated extrinsic neura l control of this important gut region as suggested by functional stud ies.