Smid S D, Blackshaw L A
Nerve-Gut Research Laboratory, Level 1 Hanson Centre, Frome Rd, Adelaide, SA 5000, Australia.
Auton Neurosci. 2000 Dec 28;86(1-2):30-6. doi: 10.1016/S1566-0702(00)00210-1.
In the present study we aimed to discretely characterise ganglionic and neuroeffector transmission to the ferret lower oesophageal sphincter (LOS) using a novel preparation of LOS muscle with intact vagal innervation in conjunction with isolated LOS muscle strips. In this way we could compare vagally mediated LOS relaxation with that of enteric inhibitory motorneurones which were directly stimulated. Preparations of LOS muscle, with or without attached vagus nerves, were dissected from adult ferrets and maintained under preload in organ baths, where LOS muscle developed spontaneous tone. LOS relaxations in response to vagal stimulation (0.5-5 Hz, 30 V) were recorded, alone and following pretreatment with tetrodotoxin (TTX), hexamethonium (Hex), Hex and atropine and NG-nitro-L-arginine (L-NNA). Direct activation of enteric inhibitory motorneurones was performed via electrical field stimulation (EFS). Vagal stimulation elicited frequency-dependent relaxations of the LOS that were abolished by tetrodotoxin (1 microM) and markedly reduced following L-NNA pretreatment (100 microM), but unaltered following pretreatment with the selective VIP or PACAP receptor antagonists VIP (10-28) or PACAP (6-38), respectively (each at 5 microM). The potent NOS inhibitor S-methyl-L-thiocitrulline (100 microM) inhibited LOS relaxation to the same degree at 5 Hz. Hex alone (500 microM) reduced maximal relaxation by 50%; in combination with atropine (2 microM), 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 relax the LOS. Moreover, LOS relaxation due to direct activation of inhibitory motorneurones also utilises primarily nitric oxide and other as yet undefined neurotransmitters. Neither VIP nor PACAP are involved in vagally mediated or direct enteric neuronally stimulated LOS relaxation in the ferret.
在本研究中，我们旨在使用一种具有完整迷走神经支配的新型食管下括约肌（LOS）肌肉制剂，并结合分离的LOS肌条，来分别表征向雪貂食管下括约肌的神经节和神经效应器传递。通过这种方式，我们可以将迷走神经介导的LOS松弛与直接刺激的肠抑制运动神经元的松弛进行比较。从成年雪貂身上解剖出带有或不带有迷走神经的LOS肌肉制剂，并在器官浴槽中以预负荷状态维持，LOS肌肉在其中产生自发张力。记录单独以及在用河豚毒素（TTX）、六甲铵（Hex）、Hex与阿托品以及NG-硝基-L-精氨酸（L-NNA）预处理后，迷走神经刺激（0.5 - 5Hz，30V）引起的LOS松弛。通过电场刺激（EFS）直接激活肠抑制运动神经元。迷走神经刺激引起LOS频率依赖性松弛，这种松弛被河豚毒素（1μM）消除，并且在L-NNA预处理（100μM）后显著降低，但在用选择性VIP或PACAP受体拮抗剂VIP（10 - 28）或PACAP（6 - 38）（各5μM）预处理后未改变。强效一氧化氮合酶抑制剂S-甲基-L-硫代瓜氨酸（100μM）在5Hz时对LOS松弛的抑制程度相同。单独使用Hex（500μM）可使最大松弛降低50%；与阿托品（2μM）联合使用时，松弛几乎完全被消除。在分离的LOS肌条中，VIP（10 - 28）和PACAP（6 - 38）均未改变EFS诱导的松弛。综上所述，这些结果表明，向雪貂LOS的神经节神经传递主要通过烟碱样和毒蕈碱样受体的组合发生，并利用含一氧化氮的肠抑制运动神经元来松弛LOS。此外，由于抑制性运动神经元的直接激活引起的LOS松弛也主要利用一氧化氮和其他尚未明确的神经递质。在雪貂中，VIP和PACAP均不参与迷走神经介导的或直接由肠神经元刺激引起的LOS松弛。
