Presence of cholinergic neurons in the vagal afferent system: involvement in a heterogenous reinnervation.

As is now well established, the anastomosis of the central cut end of the vagus with the peripheral stump of the accessory spinal nerve results in a functional reinnervation of the muscular fibers of the sterno-cleido-mastoïd muscle in various species. In chronically anastomosed animals this heterogenous crossed nerve anastomosis allows the electrophysiological characterization of peripheral enteroceptors mainly located in the larynx, oesophagus and stomach. Pharmacological treatments indicate that the reinnervation is supplied by cholinergic afferent fibers of the vagus nerve. 4 months after the anastomosis, when functional responses are recorded in the sterno-cleido-mastoïd muscle, choline acetyl transferase activity is still present in sutured ganglia of rabbit and cat, but is decreased by 88% and 60%, respectively. A decrease of 39% of choline acetyl transferase activity was also observed in the lower brain stem of the rabbit, but no significant change was detected in the nucleus of the solitary tract after 3 months in sutured cats. A kinetic study of the nodose endogenous acetylcholine content of rabbits with vagus-spinal accessory anastomosis shows a decrease of up to 4 months, followed by an increase during the 5th month. On the contrary, a significant decrease of acetylcholine content is observed in the contralateral nodose ganglion after 4 months, suggesting the involvement of central and/or peripheral compensatory mechanisms.