LIMITED EXCITATORY LOCAL EFFECTOR FUNCTION OF GASTRIC VAGAL AFFERENT INTRAGANGLIONIC TERMINALS IN RATS

Intraganglionic laminar endings (IGLEs) are complex terminal structure s of vagal afferent origin, distributed throughout the myenteric plexu s of the esophagus and gastrointestinal tract and without a known func tion. They may serve local effector function by means of peripheral ax on reflexes, analogously to dorsal root afferents. To test this possib ility, vagal afferent fibers were antidromically activated by suprathr eshold electrical stimulation of the cervical vagus nerve in anestheti zed rats that underwent prior supranodose vagotomy, and responses of m yenteric neurons were monitored with Fos immunocytochemistry. Stimulat ion of vagal afferents produced Fos expression in a slightly, but sign ificantly, higher proportion of myenteric plexus neurons of the gastri c corpus (1.02 +/- 0.21%, P < 0.05) and esophagus (1.59 +/- 0.46%, P < 0.05) than in control animals with sham-stimulation (corpus, 0.12 +/- 0.05%; esophagus, 0.18 +/- 0.18%). Stimulation of vagal efferents pro duced widespread Fos induction in myenteric neurons. Given the many en teric neurons in close anatomic contact with IGLEs and the low proport ion of Fos activated neurons after selective afferent stimulation, the results do not support a widespread excitatory local effector functio n of IGLEs. However, inhibitory effects and/or weak excitatory synapti c inputs that do not engage Fos expression cannot be ruled out.