Maduka U P, Hamity M V, Walder R Y, White S R, Li Y, Hammond D L
Departments of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, United States.
Department of Anesthesia, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, United States.
Neuroscience. 2016 Mar 11;317:1-11. doi: 10.1016/j.neuroscience.2015.12.054. Epub 2016 Jan 4.
This study examined whether peripheral inflammatory injury increases the levels or changes the disposition of substance P (SubP) in the rostral ventromedial medulla (RVM), which serves as a central relay in bulbospinal pathways of pain modulation. Enzyme immunoassay and reverse transcriptase quantitative polymerase chain reaction were used to measure SubP protein and transcript, respectively, in tissue homogenates prepared from the RVM and the periaqueductal gray (PAG) and cuneiform nuclei of rats that had received an intraplantar injection of saline or complete Freund's adjuvant (CFA). Matrix-Assisted Laser Desorption/Ionization Time of Flight analysis confirmed that the RVM does not contain hemokinin-1 (HK-1), which can confound measurements of SubP because it is recognized equally well by commercial antibodies for SubP. Levels of SubP protein in the RVM were unchanged four hours, four days and two weeks after injection of CFA. Tac1 transcripts were similarly unchanged in the RVM four days or two weeks after CFA. In contrast, the density of SubP immunoreactive processes in the RVM increased 2-fold within four hours and 2.7-fold four days after CFA injection; it was unchanged at two weeks. SubP-immunoreactive processes in the RVM include axon terminals of neurons located in the PAG and cuneiform nucleus. SubP content in homogenates of the PAG and cuneiform nucleus was significantly increased four days after CFA, but not at four hours or two weeks. Tac1 transcripts in homogenates of these nuclei were unchanged four days and two weeks after CFA. These findings suggest that there is an increased mobilization of SubP within processes in the RVM shortly after injury accompanied by an increased synthesis of SubP in neurons that project to the RVM. These findings are consonant with the hypothesis that an increase in SubP release in the RVM contributes to the hyperalgesia that develops after peripheral inflammatory injury.
本研究探讨了外周炎性损伤是否会增加延髓头端腹内侧区（RVM）中P物质（SubP）的水平或改变其分布，RVM是痛觉调制延髓脊髓通路的中枢中继站。采用酶免疫测定法和逆转录定量聚合酶链反应分别测量接受足底注射生理盐水或完全弗氏佐剂（CFA）的大鼠RVM、导水管周围灰质（PAG）和楔状核组织匀浆中的SubP蛋白和转录本。基质辅助激光解吸/电离飞行时间分析证实RVM中不含有hemokinin-1（HK-1），HK-1会干扰SubP的测量，因为它与SubP的商业抗体具有相同的识别能力。注射CFA后4小时、4天和2周，RVM中SubP蛋白水平未发生变化。CFA注射后4天或2周，RVM中Tac1转录本同样未发生变化。相比之下，CFA注射后4小时内，RVM中SubP免疫反应性过程的密度增加了2倍，4天后增加了2.7倍；2周时未发生变化。RVM中SubP免疫反应性过程包括位于PAG和楔状核的神经元的轴突终末。CFA注射后4天，PAG和楔状核匀浆中的SubP含量显著增加，但4小时或2周时未增加。这些核匀浆中的Tac1转录本在CFA注射后4天和2周未发生变化。这些发现表明，损伤后不久RVM内SubP在其过程中的动员增加，同时投射到RVM的神经元中SubP的合成增加。这些发现与以下假设一致，即RVM中SubP释放的增加导致外周炎性损伤后出现的痛觉过敏。
