Limited excitatory local effector function of gastric vagal afferent intraganglionic terminals in rats

Intraganglionic laminar endings (IGLEs) are complex terminal structures of vagal afferent origin, distributed throughout the myenteric plexus of the esophagus and gastrointestinal tract and without a known function. They may serve local effector function by means of peripheral axon reflexes, analogously to dorsal root afferents. To test this possibility, vagal afferent fibers were antidromically activated by suprathreshold electrical stimulation of the cervical vagus nerve in anesthetized rats that underwent prior supranodose vagotomy, and responses of myenteric neurons were monitored with Fos immunocytochemistry. Stimulation of vagal afferents produced Fos expression in a slightly, but significantly, higher proportion of myenteric plexus neurons of the gastric 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 produced widespread Fos induction in myenteric neurons. Given the many enteric neurons in close anatomic contact with IGLEs and the low proportion of Fos activated neurons after selective afferent stimulation, the results do not support a widespread excitatory local effector function of IGLEs. However, inhibitory effects and/or weak excitatory synaptic inputs that do not engage Fos expression cannot be ruled out.