Abstract
In both rats and guinea pigs the colonic motility, especially concerned with the transport of the content through the pacemaker area as well as the pacemaker mechanism, were studied. The results obtained were summarized as follows:
1. At the turn of the ascending to the descending part of the colon there existed a pulsating ring of constriction, pacemaker area, sending contraction waves, antiperistalsis and peristalsis.
2. The content which was inspissated to become scybalum, was anally transported through the pacemaker area by antiperistalses. The underlying mechanism might be as follows: The mucosa is stretched by the scybalum to elicit the intrinsic mucosal reflex, resulting in a rise of the excitability at the part over and proximal to the scybalum which in turn reinforces the antiperistalses there to produce the shifting of the scybalum toward the anal direction.
3. Rhythmic contractions elicited in the pacemaker area both in vivo and in vitro were reduced in strength by administration of hexamethonium, whereas they were abolished by atropine or tetrodotoxin.
4. The pacemaker area contained acetylcholine in an amount larger than its adjacent areas.
5. The histological examinations revealed that the pacemaker area was a site where the networks of AUERBACH'S plexus were denser than those observed in the adjacent areas.
6. From the results described in 3, 4 and 5 it may be concluded that the pacemaker is a site where the cholinergic neurones are much more numerous than in any other areas of the colon.
