IN-VITRO CHARACTERIZATION 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 th e duodenum and sphincter of Oddi are intramural, activated by duodenal electrical field stimulation (EFS) in vitro, and contain capsaicin-se nsitive primary afferents. The possible involvement of cholinergic (mu scarinic 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 (ii = 3). Excitatory res ponses from duodenal circular muscle were also evident. Tetrodotoxin ( 1 mu M; n = 7) pretreatment abolished both sphincter of Oddi and duode nal responses to duodenal EFS. Crushing the duodenum between the site of stimulation and the sphincter of Oddi-duodenal junction also abolis hed sphincter of Oddi response. The sphincter of Oddi responses to duo denal EFS at the oral and anal sites were reduced by pretreatment with (i) atropine (100 nM; it = 7) to 19 +/- 6% (P < 0.05) and 22 +/- 8% ( P < 0.05) of control respectively, (ii) hexamethonium (100 mu M; n = 9 ) to 10 +/- 2% (P < 0.01) and 6.0 +/- 2.5% (P < 0.01) of control respe ctively and (iii) guanethidine (1 mu M; n = 6) to 75 +/- 6% (P < 0.05) and 78 +/- 10% (P < 0.05) of control, respectively. Combined pretreat ment with phentolamine and propranolol (both 1 mu M; it = 7) was witho ut effect, as was capsaicin (1 mu M; it = 12) pretreatment. Excitatory intramural pathways between the sphincter of Oddi and the duodenum ar e primarily cholinergic in nature and contain an adrenergic component. Capsaicin-sensitive primary afferents are not involved.