These canine tissues (esophagus, stomach and part of the duodenum) have been collected from a series of experiments (N=7) conducted by a colleague who was interested in collecting the brain. The stomachs have been filled and distended with infusion of a 4%PFA solution and are now stored at 4C. I'd like to map the vagal innervation (both motor and sensory) to the stomach, so we preserved a good portion of the subdiaphragmatic vagi when we removed the specimen. Any suggestions on which tracers are best to use for anterograde or retrograde mapping? Any particular suggestion on how to do it? References are more than appreciated.