Neural regulation of the interrelation between haustral and taenial motility in the rabbit proximal colon

Neural regulation of the motility between the haustra and taenia coli was studied in the isolated rabbit proximal colon. Four types of haustral and taenial preparations were used: the haustral strip without the taenia coli (type 1), the haustral strip including the taenia coli (type 2), the L-shaped (taenia-haustra) preparations for recording the haustral (circular) response to taenial stimulation (type 3) and the L-shaped (haustra-taenia) preparation for recording the taenial (longitudinal) response to haustral stimulation (type 4). Field electrical stimulation induced a contractile response in the haustra and taenia coli. Hexamethonium reduced the contraction in type 2, 3 and 4 preparations. The desensitization to serotonin reduced the response in type 2 and 3 preparations. After atropinization, the response in types 1 and 4 was reversed to relaxation, and the response in types 2 and 3 was reversed to relaxation followed by contraction which was reduced or abolished by indomethacin. The responses remaining after atropinization in all types of preparations were not affected by other blocking agents tested or desensitization to neuropeptides. Tetrodotoxin abolished all relaxation and contractile responses in all types of preparations. These results suggest that the indirect contractile response to field stimulation is induced mainly via cholinergic and serotonergic neurons, and that the relaxation is mainly mediated by nonadrenergic noncholinergic neurons. The late haustral contractions after atropine may be caused by endogenous prostaglandin.