Meng X W, Budra B, Skinner K, Ohara P T, Fields H L
Department of Anatomy, University of California at San Francisco 94143, USA.
J Comp Neurol. 1997 Jan 20;377(3):381-91.
Within the rostral ventromedial medulla (RVM), there are two classes of putative pain modulation neurons: ON cells and OFF cells, which respectively burst or pause prior to withdrawal reflexes elicited by noxious stimulation. Alpha-adrenergic agonists injected into the RVM produce changes in the latency of spinal nocifensive reflexes and, when iontophoretically applied, alter the firing of RVM ON but not OFF cells. To provide further information about the contribution of norepinephrine to RVM neuron function, we analyzed the distribution of tyrosine hydroxylase immunoreactive (TH-ir) appositions upon RVM ON and OFF cells. In the lightly anesthetized rat, seven ON and five OFF cells were identified by changes in their discharge rate in relation to nociceptive withdrawal reflexes and were labeled by intracellular injection of neurobiotin. Sections containing labeled cells were visualized by using avidin conjugated to a Texas Red fluorophore. Tissue with labeled cells was subsequently processed for TH-ir by using a Bodipy fluorophore conjugated secondary antibody. The distribution of the Bodipy-labeled fibers and terminals upon the Texas Red-labeled neurons was mapped using a confocal laser-scanning microscope. All the labeled neurons exhibited close TH-ir appositions. Appositions were of two types: swellings and fibers. Although the numbers and density of appositions varied among the cells, there were no consistent differences that correlated with physiological properties. Thus the overall density of appositions for ON cells (29.0 +/- 22.2 x 10(4) microns2) did not differ significantly from that for OFF cells (25.4 +/- 22.2 x 10(4) microns2). Tyrosine hydroxylase immunoreactive (TH-ir) appositions upon ON and OFF cells varied with their location along the dorso-ventral axis with more ventral neurons having a greater density of TH-ir swelling-type appositions. In a separate study, TH-ir and dopamine-beta-hydroxylase-like immunoreactivity (DBH-ir) were mapped in the same sections by using confocal microscopy. Nearly 97% of the TH-ir profiles co-localized with DBH-ir. These observations provide evidence that both ON and OFF cells in the RVM are targeted by noradrenergic inputs.
在延髓头端腹内侧区（RVM）内，存在两类假定的疼痛调节神经元：ON细胞和OFF细胞，它们分别在有害刺激引发的退缩反射之前爆发或暂停发放。向RVM内注射α-肾上腺素能激动剂会改变脊髓伤害性防御反射的潜伏期，当通过离子电泳施加时，则会改变RVM中ON细胞而非OFF细胞的放电。为了进一步了解去甲肾上腺素对RVM神经元功能的作用，我们分析了酪氨酸羟化酶免疫反应性（TH-ir）与RVM的ON细胞和OFF细胞形成的突触联系的分布情况。在轻度麻醉的大鼠中，根据与伤害性退缩反射相关的放电率变化，鉴定出7个ON细胞和5个OFF细胞，并通过细胞内注射神经生物素进行标记。使用与德克萨斯红荧光团偶联的抗生物素蛋白使含有标记细胞的切片可视化。随后，使用与Bodipy荧光团偶联的二抗对含有标记细胞的组织进行TH-ir处理。使用共聚焦激光扫描显微镜绘制Bodipy标记的纤维和终末在德克萨斯红标记神经元上的分布。所有标记的神经元都显示出紧密的TH-ir突触联系。突触联系有两种类型：膨体和纤维。尽管不同细胞之间突触联系的数量和密度有所不同，但与生理特性没有一致的相关性。因此，ON细胞的突触联系总体密度（29.0±22.2×10⁴平方微米）与OFF细胞（25.4±22.2×10⁴平方微米）相比，差异不显著。ON细胞和OFF细胞上的酪氨酸羟化酶免疫反应性（TH-ir）突触联系沿背腹轴的位置不同，腹侧神经元的TH-ir膨体型突触联系密度更高。在另一项研究中，使用共聚焦显微镜在同一切片上绘制TH-ir和多巴胺-β-羟化酶样免疫反应性（DBH-ir）。近97%的TH-ir图像与DBH-ir共定位。这些观察结果提供了证据，表明RVM中的ON细胞和OFF细胞都接受去甲肾上腺素能输入的靶向作用。
