Vagal ganglionic and nonadrenergic noncholinergic neurotransmission to theferret lower oesophageal sphincter

In the present study we aimed to discretely characterise ganglionic and neu roeffector transmission to the ferret lower oesophageal sphincter (LOS) usi ng a novel preparation of LOS muscle with intact vagal innervation in conju nction with isolated LOS muscle strips. In this way we could compare vagall y mediated LOS relaxation with that of enteric inhibitory motorneurones whi ch were directly stimulated. Preparations of LOS muscle, with or without at tached vagus nerves, were dissected from adult ferrets and maintained under preload in organ baths, where LOS muscle developed spontaneous tone. LOS r elaxations in response to vagal stimulation (0.5-5 Hz, 30 V) were recorded, alone and following pretreatment with tetrodotoxin (TTX), hexamethonium (H ex). Hex and atropine and N-G-nitro-L-arginine (L-NNA). Direct activation o f enteric inhibitory motorneurones was performed via electrical field stimu lation (EFS). Vagal stimulation elicited frequency-dependent relaxations of the LOS that were abolished by tetrodotoxin (1 muM) and markedly reduced f ollowing L-NNA pretreatment (100 muM), but unaltered following pretreatment with the selective VIP or PACAP receptor antagonists VIP (10-28) or PACAP (6-38), respectively (each at 5 muM) The potent NOS inhibitor S-methyl-L-th iocitrulline (100 muM) inhibited LOS relaxation to the same degree at 5 Hz. Hex alone (500 muM) reduced maximal relaxation by 50%; in combination with atropine (2 muM), relaxation was almost abolished. In isolated LOS muscle strips, neither VIP (10-28) nor PACAP (6-38) altered EFS-induced relaxation . Taken together, these results suggest ganglionic neurotransmission to the ferret LOS occurs mainly through a combination of nicotinic and muscarinic receptors and utilises nitroxidergic enteric inhibitory motorneurones to r elax the LOS. Moreover, LOS relaxation due to direct activation of inhibito ry motorneurones also utilises primarily nitric oxide and other as yet unde fined neurotransmitters. Neither VIP nor PACAP are involved in vagally medi ated or direct enteric neuronally stimulated LOS relaxation in the ferret. (C) 2000 Elsevier Science B.V. All rights reserved.