ABSTRACT
Activity of the enteric nervous system (ENS) is controlled by the autonomic nerves under the normal physiological condition, even though ENS has been regarded to be independent from the central nervous system. However, the relation between myenteric neurons and vagus nerves has not been fully clarified. For the defining of topographical and functional relationship between these two nervous systems, we analyzed how many myenteric neurons are activated after electrical vagal stimulation in the rat. Bilateral cervical vagi were electrically stimulated (10 V, 5 msec, 40 Hz) for a duration of 30 minutes, and then each part of the small intestine was obtained. Fos, as a functional marker for neuronal activation, immunohistochemistry was used for the detection of vagally activated myenteric neurons. Total number of myenteric neurons was obtained using cuprolinic blue stained samples, and was calculated as 12,819+/-1,514, 14,261+/-1,452, 15,411+/-2,380 per unit area (1 cm2) in duodenum, jejunum and ileum, respectively. Fos-positive myenteric neurons were scarcely observed in the normal control group. After the electrical vagal stimulation, Fos-immunoreactive (IR) neurons were detected as 31+/-17%, 17+/-9%, 16+/-10% of total number of myenteric neurons in duodenum, jejunum and ileum, respectively. These data demonstrate that only some (16~31%) of myenteric neurons are regulated by vagal efferent input, and the duodenum receives much more vagal input functionally than other distal regions. Furthermore, these findings can be applied to trials defining the functional circuit of the myenteric nervous system linked to the vagus nerves, since Fos-positive nuclei can be easily double-labeled with various neurotransmitters existing in the myenteric neurons.