In vitro characterisation of intramural neural pathways between the duodenum and the sphincter of Oddi of the brush-tailed possum.

The aims of this study were to determine if neural pathways between the duodenum and sphincter of Oddi are intramural, activated by duodenal electrical field stimulation (EFS) in vitro, and contain capsaicin-sensitive primary afferents. The possible involvement of cholinergic (muscarinic and/or nicotinic) and adrenergic receptors in these pathways were also investigated. Duodenal EFS (5-60 Hz, 70 V, 0.5 ms duration, 10 s train) at sites 2 cm oral and 2 cm anal to the sphincter of Oddi-duodenal junction produced frequency-dependent excitatory responses in the sphincter of Oddi, measured by manometry (n = 3). Excitatory responses from duodenal circular muscle were also evident. Tetrodotoxin (1 microM; n = 7) pretreatment abolished both sphincter of Oddi and duodenal responses to duodenal EFS. Crushing the duodenum between the site of stimulation and the sphincter of Oddi-duodenal junction also abolished sphincter of Oddi response. The sphincter of Oddi responses to duodenal EFS at the oral and anal sites were reduced by pretreatment with (i) atropine (100 nM: n = 7) to 19 +/- 6% (P < 0.05) and 22 +/- 8% (P < 0.05) of control respectively. (ii) hexamethonium (100 microM: n = 9) to 10 +/- 2% (P < 0.01) and 6.0 + 2.5% (P < 0.01) of control respectively and (iii) guanethidine (1 microM; n = 6) to 75 +/- 6% (P < 0.05) and 78 +/- 10% (P < 0.05) of control, respectively. Combined pretreatment with phentolamine and propranolol (both 1 microM; n = 7) was without effect, as was capsaicin (1 microM; n = 12) pretreatment. Excitatory intramural pathways between the sphincter of Oddi and the duodenum are primarily cholinergic in nature and contain an adrenergic component. Capsaicin-sensitive primary afferents are not involved.