Li Z S, Furness J B
Department of Anatomy & Cell Biology, University of Melbourne, Parkville, VIC, Australia.
Cell Tissue Res. 2000 Jan;299(1):1-8. doi: 10.1007/s004419900125.
Nitric oxide synthase (NOS) immunoreactivity occurs in two groups of neurons in the guinea pig small intestine: descending interneurons that are also immunoreactive for choline acetyltransferase (ChAT), and inhibitory motor neurons that lack ChAT immunoreactivity. Interneurons that are involved in local reflexes would be expected to have inputs from intrinsic primary afferent (sensory) neurons, most of which are calbindin-immunoreactive. We examined this possibility using triple staining for NOS, ChAT and calbindin immunoreactivity and investigated the relationships between calbindin-immunoreactive varicosities and the cell bodies of NOS-immunoreactive neurons, using high-resolution confocal microscopy and electron microscopy. By confocal microscopy, we found that the cell bodies of ChAT/NOS interneurons received 84 +/- 23 (mean +/- SD) direct appositions from calbindin-immunoreactive varicosities and that the cell bodies of NOS-inhibitory motor neurons received 82 +/- 20 appositions. Electron-microscopic examination of the relations of 265-calbindin-immunoreactive varicosities, at distances within the resolution of the confocal microscope (300 nm), to 30 NOS-immunoreactive nerve cells indicated that 84% formed close contacts or synapses and 16% were separated from neurons by thin glial cell processes. Thus, each NOS-immunoreactive nerve cell receives about 70 synaptic inputs or close contacts from the calbindin-immunoreactive varicosities of intrinsic primary afferent neurons. It is concluded that there are monosynaptic reflex connections in which intrinsic primary afferent neurons synapse directly with motor neurons and di- or poly-synaptic reflexes in which ChAT- and NOS-immunoreactive neurons are interneurons, interposed between intrinsic primary afferent neurons and NOS-inhibitory neurons.
一氧化氮合酶（NOS）免疫反应性存在于豚鼠小肠的两组神经元中：下行中间神经元，其对胆碱乙酰转移酶（ChAT）也有免疫反应性；以及缺乏ChAT免疫反应性的抑制性运动神经元。参与局部反射的中间神经元预计会接受来自内在初级传入（感觉）神经元的输入，其中大多数是钙结合蛋白免疫反应性的。我们使用NOS、ChAT和钙结合蛋白免疫反应性的三重染色来研究这种可能性，并使用高分辨率共聚焦显微镜和电子显微镜研究了钙结合蛋白免疫反应性曲张体与NOS免疫反应性神经元细胞体之间的关系。通过共聚焦显微镜，我们发现ChAT/NOS中间神经元的细胞体接受了来自钙结合蛋白免疫反应性曲张体的84±23（平均值±标准差）个直接贴附，而NOS抑制性运动神经元的细胞体接受了82±20个贴附。对265个钙结合蛋白免疫反应性曲张体（在共聚焦显微镜分辨率范围内，即300nm内）与30个NOS免疫反应性神经细胞之间关系的电子显微镜检查表明，84%形成了紧密接触或突触，16%被薄的神经胶质细胞突起与神经元隔开。因此，每个NOS免疫反应性神经细胞从内在初级传入神经元的钙结合蛋白免疫反应性曲张体接收约70个突触输入或紧密接触。得出的结论是，存在单突触反射连接，其中内在初级传入神经元直接与运动神经元形成突触，以及双突触或多突触反射，其中ChAT和NOS免疫反应性神经元是中间神经元，介于内在初级传入神经元和NOS抑制性神经元之间。
