Vagal input to the enteric nervous system

Background The enteric nervous system (ENS) of the gastrointestinal tract has traditionally been viewed as a system of ganglia that operates largely independently of the brain and spinal cord. Because of this postulated autonomy, the ENS has even been characterised as the "little brain" or the "second brain." Methods To directly examine the connections between CNS outflow and the ENS, we injected anterograde neural tracers, includingPhaseolus vulgaris-leucoagglutinin, 4 DiI, 5 6 cholera toxin B subunit-horseradish peroxidase (unpublished), wheat germ agglutinin-horseradish peroxidase, 7 and conjugated dextrans 8 into brain stem pools of vagal motor neurones and prepared the stomach and duodenum as wholemounts. 9 In some series, limited injections were used to label only a few neurones thus making it possible to trace the course in individual axons; in other series larger injections were used to label the entire population of neurones innervating visceral targets.