Ionotropic Glutamate Receptors in Spinal Nociceptive Processing

Glutamate is the predominant excitatory transmitter used by primary afferent synapses and intrinsic neurons in the spinal cord dorsal horn. Accordingly, ionotropic glutamate receptors mediate basal spinal transmission of sensory, including nociceptive, information that is relayed to supraspinal centers. However, it has become gradually more evident that these receptors are also crucially involved in short- and long-term plasticity of spinal nociceptive transmission, and that such plasticity have an important role in the pain hypersensitivity that may result from tissue or nerve injury. This review will cover recent findings on pre- and postsynaptic regulation of synaptic function by ionotropic glutamate receptors in the dorsal horn and how such mechanisms contribute to acute and chronic pain.     

miR-9 Mediates CALHM1-Activated ATP-P2X7R Signal in Painful Diabetic Neuropathy Rats

In this study, we planned to illuminate the mechanisms of the expression and function of CALHM1 in painful diabetic neuropathy (PDN). PDN rat model was constructed. The expression of CALHM1 and miR-9 in rat spinal dorsal horn neurons was detected. The correlation between the level of CALHM1 mRNA and 50 % PWT and the relationship between the expression of CALHM1 and miR-9 in rat spinal dorsal horn neurons were statistically analyzed. The effect of miR-9 and CALHM1 on each other’s expression in PDN rat spinal dorsal horn neurons were tested by qRT-PCR or Western blot. The co-culture system of neurons and glias from PDN rat spinal dorsal horn was constructed. The concentration of calcium and ATP as well as the expression of P2X7 receptor regulated by CALHM1 and miR-9 in PDN rat spinal dorsal horn neurons was measured. The results showed that the expression of CALHM1 was increased in PDN rat compared with controls, while its mRNA level was negatively correlated with 50 % PWT. miR-9, which was also upregulated in the spinal dorsal horn neurons of PDN rats, was positively correlated with the expression of CALHM1. The concentration of calcium and ATP as well as the expression of P2X7 receptor in glias was also increased in PDN rats. These increases could be reverted by inhibiting CALHM1 and/or miR-9. CALHM1 is involved in miR-9-mediated ATP-P2X7 pathway between neurons and glias in PDN rat.     

针刺对鼠部分背根切断模型的背根神经节和脊髓背角内生长相关蛋白GAP43表达的影响

制备大鼠备用根模型 （切断单侧腰骶背根Ｌ２, ３, ４, ６, 及Ｓ１, ２, 保留Ｌ５ 背根）, 用免疫组织化学和原位杂交方法研究生长相关蛋白ＧＡＰ４３ 在相应节段背根神经节和脊髓背角表达的变化及针刺对其表达的影响。结果发现, 切断一侧Ｌ２, ３, ４, ６, 及Ｓ１, ２ 背根后, 它们对应的背根神经节内ＧＡＰ４３ 表达与正常对照组和假手术组相比无显著性差别, 而备用根神经节Ｌ５ 的ＧＡＰ４３ 表达较正常对照组和假手术组明显增强; 手术侧Ｌ５ 水平脊髓背角与正常对照组相比ＧＡＰ４３ 阳性信号加强。针刺后可促进手术侧Ｌ５ 神经节内ＧＡＰ４３ 表达增加; Ｌ５ 水平脊髓背角ＧＡＰ４３ 阳性信号也进一步加强这表明在一定条件下, 神经系统损伤可诱发中枢神经系统ＧＡＰ４３ 介导的可塑性变化, 针刺可通过ＧＡＰ４３ 对神经的可塑性起调节作用。     

Long-term Therapeutic Effects of Extracorporeal Shock Wave-Assisted Melatonin Therapy on Mononeuropathic Pain in Rats

We evaluated the ability of extracorporeal shock wave (ECSW)-assisted melatonin (Mel) therapy to offer an additional benefit for alleviating the neuropathic pain (NP) in rats. Left sciatic nerve was subjected to chronic constriction injury (CCI) to induce NP. Animals (n?=?30) were randomized into group 1 (sham-operated control), group 2 (CCI only), group 3 (CCI?+?ECSW), group 4 (CCI?+?Mel) and group 5 (CCI?+?ECSW?+?Mel). By days 15, 22 and 29 after CCI, the thermal paw withdrawal latency (TPWL) and mechanical paw withdrawal threshold (MPWT) were highest in group 1, lowest in group 2, significantly higher in group 5 than in groups 3 and 4, but they showed no difference between the later two groups (all p?<?0.0001). The protein expressions of inflammatory (TNF-α, NF-κB, MMP-9, IL-1ß), oxidative-stress (NOXs-1, -2, -4, oxidized protein), apoptotic (cleaved-caspase3, cleaved-PARP), DNA/mitochondrial-damaged (γ-H2AX/cytosolic-cytochrome C), microglia/astrocyte activation (ox42/GFAP), and MAPKs [phosphorylated (p)-p38, p-JNK, p-ERK] biomarkers in dorsal root ganglia neurons (DRGs) and in spinal dorsal horn were exhibited an opposite pattern of TPWL among the five groups (all p?<?0.0001). Additionally, protein expressions of Nav.1.3, Nav.1.8 and Nav.1.9 in sciatic nerve exhibited an identical pattern to inflammation among the five groups (all p?<?0.0001). The numbers of cellular expressions of MAPKs (p-ERK1/2+/peripherin?+?cells, p-ERK1/2+/NF200?+?cells and p-JNK+/peripherin?+?cells, p-JNK+/NF200?+?cells) and voltage-gated sodium channels (Nav.1.8+/peripherin?+?cells, Nav.1.8+/NF200?+?cells, Nav.1.9+/peripherin?+?cells, Nav.1.9+/NF200?+?cells) in small and large DRGs displayed an identical pattern to inflammation among the five groups (all p?<?0.0001). In conclusion, the synergistic effect of combined ECSW-Mel therapy is superior to either one alone for long-term improvement of mononeuropathic pain-induced by CCI in rats.

     

Regulation of Wnt signaling by nociceptive input in animal models

ABSTRACT: BACKGROUND: Central sensitization-associated synaptic plasticity in the spinal cord dorsal horn (SCDH) critically contributes to the development of chronic pain, but understanding of the underlying molecular pathways is still incomplete. Emerging evidence suggests that Wnt signaling plays a crucial role in regulation of synaptic plasticity. Little is known about the potential function of the Wnt signaling cascades in chronic pain development. RESULTS: Fluorescent immunostaining results indicate that ?-catenin, an essential protein in the canonical Wnt signaling pathway, is expressed in the superficial layers of the mouse SCDH with enrichment at synapses in lamina II. In addition, Wnt3a, a prototypic Wnt ligand that activates the canonical pathway, is also enriched in the superficial layers. Immunoblotting analysis indicates that both Wnt3a and ?-catenin are up-regulated in the SCDH of various mouse pain models created by hind-paw injection of capsaicin, intrathecal (i.t.) injection of HIV-gp120 protein or spinal nerve ligation (SNL). Furthermore, Wnt5a, the prototypic Wnt ligand for non-canonical pathways, and its receptor Ror2 are also up-regulated in the SCDH of these models. CONCLUSION: Our results suggest that Wnt signaling pathways are regulated by nociceptive input. The activation of Wnt signaling may regulate the expression of spinal central sensitization during the development of acute and chronic pain.     

可视膜片钳法记录初级传入纤维介导的脊髓背角神经元突触后电流

本文描述了用明胶半包埋法制备带背根脊髓薄片的实验步骤,和在脊髓背角记录由初级传入纤维介导的突触后电流的可视膜片钳法。手术制备一段带背根的脊髓标本,并用20％的明胶包埋在琼脂块上,再用振动切片机切片获得带背根的脊髓薄片。通过红外线可视的引导,在脊髓背角神经元上建立全细胞封接模式。在钳制电压为-70mV条件下,记录自发的和背根刺激引起的兴奋性突触后电流。以传入纤维的传导速度与刺激阈值为指标,可以区分A样纤维与C样纤维兴奋性突触后电流。在钳制电压为0mV条件下,记录自发的和背根刺激引起的抑制性突触后电流。用5μmol／L的士宁或20μmol／L的荷包牡丹碱分离出γ-氨基丁酸能或甘氨酸能的抑制性突触后电流。用可视膜片钳方法可以准确测量脊髓背角神经元的突触后电流,从而研究初级传入突触的传递过程。更重要的是,在红外线可视观察的帮助下,建立膜片钳封接的成功率显著提高,同时也使记录研究脊髓背角深层神经元变得更加容易。本研究为探索初级传入突触传递过程提供了一个有效的方法。     

Regulation of Zinc Transporter 1 Expression in Dorsal Horn of Spinal Cord After Acute Spinal Cord Injury of Rats by Dietary Zinc

Zinc concentrations in the dorsal horn of spinal cord are important for wound healing, neurological function, and reproduction. However, the response of the spinal cord to alterations in dietary zinc is unknown in rats after spinal cord injury (SCI). The current study explored cellular zinc levels and zinc transporter 1 (ZnT1) expression in the dorsal horn of spinal cord with different dietary zinc after SCI. A hundred and forty-four male Wistar rats were randomly divided into four groups: sham-operated group (30?mg Zn/kg), zinc-high dietary SCI model group (ZH, 180?mg Zn/kg), zinc-adequate dietary SCI model group (30?mg Zn/kg), and marginal zinc-deficient dietary SCI model group (MZD, 5?mg Zn/kg). To test the hypothesis that dietary zinc may regulate role of ZnT1 expression in dorsal horn after acute SCI, we traced ZnT1 proteins and zinc ions with immunohistochemistry, western blot, and autometallography. Zinc and ZnT1 levels of the dorsal horn in ZH significantly increased after surgery (P?<?0.05), reached peak level (P?<?0.05) on the seventh day, and subsequently levels of their expression began to decrease. But zinc levels and ZnT1 expression of spinal cord in MZD dietary groups decreased (P?<?0.05) in SCI. There was a positive correlation between ZnT1 protein and zinc content in spinal cord (R?=?0.49880, P?=?0.0492). We found that both zinc and ZnT1 expressions in spinal cord are regulated by dietary zinc. These results indicate that dietary zinc may regulate the expression of ZnT1 in the dorsal horn of spinal cord after SCI. ZnT1 may, at the same time, play a significant role in the maintenance of zinc homeostasis in SCI.     

Short-term plasticity at primary afferent synapse in rat spinal dorsal horn and its biological function

Short-term plasticity (STP) is an important element of information processing in neuronal networks. As the first synaptic relay between primary afferent fibers (PAFs) and central neurons, primary afferent synapses in spinal dorsal horn (DH) are essential to the initial processing of somatosensory information. In this research, we examined the STP between Adelta-PAFs and spinal DH neurons by patch-clamp recording. Our results showed that depression dominated the STP at primary afferent synapses. The curves of STP had no significant changes in the presence of bicuculline, CTZ or AP-5. Lowering extracellular Ca(2+) concentration ([Ca(2+)](o)) from 2.4 to 0.8 mM reduced the depression of synaptic responses at all stimulus rates, while raising [Ca(2+)](o) from 2.4 to 4.0 mM increased the synaptic depression. Increasing the bath temperature from 24 to 32 degrees C clearly reduced the depression of all responses. These results indicate that the observed STP is of presynaptic origin and depends on transmitter release. By fitting the experimental data recorded under different conditions, a model of STP was used to quantitatively characterize the observed STP and to analyze the possible mechanisms underlying the effects of [Ca(2+)](o) and temperature. Furthermore, using a model neuron receiving synaptic inputs, we found that with this form of STP, postsynaptic DH neurons could detect rate changes in both rapidly- and slowly-firing afferents with equal sensitivity. The present study links the intrinsic STP properties of primary afferent synapses with their role in processing neural information, and provides a basis for further research on the STP in spinal DH and its biological function under in vivo conditions.     

Regulation of increased glutamatergic input to spinal dorsal horn neurons by mGluR5 in diabetic neuropathic pain

Diabetic neuropathic pain is associated with increased glutamatergic input in the spinal dorsal horn. Group I metabotropic glutamate receptors (mGluRs) are involved in the control of neuronal excitability, but their role in the regulation of synaptic transmission in diabetic neuropathy remains poorly understood. Here we studied the role of spinal mGluR5 and mGluR1 in controlling glutamatergic input in a rat model of painful diabetic neuropathy induced by streptozotocin. Whole-cell patch-clamp recordings of lamina II neurons were performed in spinal cord slices. The amplitude of excitatory post-synaptic currents (EPSCs) evoked from the dorsal root and the frequency of spontaneous EPSCs (sEPSCs) were significantly higher in diabetic than in control rats. The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) inhibited evoked EPSCs and sEPSCs more in diabetic than in control rats. Also, the percentage of neurons in which sEPSCs and evoked EPSCs were affected by MPEP or the group I mGluR agonist was significantly higher in diabetic than in control rats. However, blocking mGluR1 had no significant effect on evoked EPSCs and sEPSCs in either groups. The mGluR5 protein level in the dorsal root ganglion, but not in the dorsal spinal cord, was significantly increased in diabetic rats compared with that in control rats. Furthermore, intrathecal administration of MPEP significantly increased the nociceptive pressure threshold only in diabetic rats. These findings suggest that increased mGluR5 expression on primary afferent neurons contributes to increased glutamatergic input to spinal dorsal horn neurons and nociceptive transmission in diabetic neuropathic pain.     

甲醛炎性痛对大鼠脊髓HO-1表达的影响

目的:观察足底注射甲醛引起的外周组织炎性疼痛是否可诱导大鼠脊髓血红素氧合酶-1(HO-1)表达发生改变以及变化的时程特征。方法:健康雄性SD大鼠随机分为7组(n=6):对照组(control组)、甲醛6 h组(F6 h组)、甲醛12 h(F12 h组)、甲醛1 d组(F1 d组)、甲醛2 d组(F2 d组)、甲醛3 d组(F3 d组)和甲醛7 d组(F7 d组)。采用足底注射甲醛溶液复制炎性痛模型,采用免疫组织化学方法检测左、右两侧脊髓后角以及中央管周围灰质HO-1蛋白的表达。结果:Control组大鼠HO-1免疫反应阳性细胞在脊髓后角及中央管周围灰质仅有少量分布,且这些细胞染色较浅。足底注射甲醛后6 h,L5节段双侧脊髓后角和中央管周围灰质HO-1免疫反应阳性细胞数目即有所增多,足底注射甲醛后12 h时,双侧脊髓后角和中央管周围灰质HO-1免疫反应阳性细胞数目进一步增多,阳性细胞染色明显加深,1 d时阳性细胞数目和染色深度均达到高峰,7 d时仍高于control组水平。各时间点双侧脊髓后角比较,阳性细胞数目和阳性细胞染色深度均无明显差异。结论:大鼠足底注射甲醛引起的炎性痛可诱导双侧脊髓后角和中央管周围灰质HO-1表达增多,以注射甲醛后1 d时增多最为明显。     

Estrogen Facilitates Spinal Cord Synaptic Transmission via Membrane-bound Estrogen Receptors: IMPLICATIONS FOR PAIN HYPERSENSITIVITY*

Recent evidence suggests that estrogen is synthesized in the spinal dorsal horn and plays a role in nociceptive processes. However, the cellular and molecular mechanisms underlying these effects remain unclear. Using electrophysiological, biochemical, and morphological techniques, we here demonstrate that 17β-estradiol (E2), a major form of estrogen, can directly modulate spinal cord synaptic transmission by 1) enhancing NMDA receptor-mediated synaptic transmission in dorsal horn neurons, 2) increasing glutamate release from primary afferent terminals, 3) increasing dendritic spine density in cultured spinal cord dorsal horn neurons, and 4) potentiating spinal cord long term potentiation (LTP) evoked by high frequency stimulation (HFS) of Lissauer''s tract. Notably, E2-BSA, a ligand that acts only on membrane estrogen receptors, can mimic E2-induced facilitation of HFS-LTP, suggesting a nongenomic action of this neurosteroid. Consistently, cell surface biotinylation demonstrated that three types of ERs (ERα, ERβ, and GPER1) are localized on the plasma membrane of dorsal horn neurons. Furthermore, the ERα and ERβ antagonist ICI 182,780 completely abrogates the E2-induced facilitation of LTP. ERβ (but not ERα) activation can recapitulate E2-induced persistent increases in synaptic transmission (NMDA-dependent) and dendritic spine density, indicating a critical role of ERβ in spinal synaptic plasticity. E2 also increases the phosphorylation of ERK, PKA, and NR2B, and spinal HFS-LTP is prevented by blockade of PKA, ERK, or NR2B activation. Finally, HFS increases E2 release in spinal cord slices, which can be prevented by aromatase inhibitor androstatrienedione, suggesting activity-dependent local synthesis and release of endogenous E2.     

AMPA receptor regulation during synaptic plasticity in hippocampus and neocortex

Discovery of long-term potentiation (LTP) in the dentate gyrus of the rabbit hippocampus by Bliss and L?mo opened up a whole new field to study activity-dependent long-term synaptic modifications in the brain. Since then hippocampal synapses have been a key model system to study the mechanisms of different forms of synaptic plasticity. At least for the postsynaptic forms of LTP and long-term depression (LTD), regulation of AMPA receptors (AMPARs) has emerged as a key mechanism. While many of the synaptic plasticity mechanisms uncovered in at the hippocampal synapses apply to synapses across diverse brain regions, there are differences in the mechanisms that often reveal the specific functional requirements of the brain area under study. Here we will review AMPAR regulation underlying synaptic plasticity in hippocampus and neocortex. The main focus of this review will be placed on postsynaptic forms of synaptic plasticity that impinge on the regulation of AMPARs using hippocampal CA1 and primary sensory cortices as examples. And through the comparison, we will highlight the key similarities and functional differences between the two synapses.     

磷酸化钙/钙调蛋白依赖性蛋白激酶Ⅱ在大鼠脊髓背角C-纤维诱发电位长时程增强的诱导和维持中的作用

实验旨在探讨钙/钙调蛋白依赖性蛋白激酶II(calcium／calmodulin-dependent protein kinase Ⅱ,CaMKⅡ)在脊髓背角C-纤维诱发电位长时程增强(long—term potentiation,LTP)的诱导和维持中的作用。用Western blot技术分别检测LTP形成30min和3h脊髓背角(L4-L6)CaMKⅡ的含量及其磷酸化水平。同时观察脊髓局部给予CAMKⅡ选择性抑制剂KN-93后对脊髓背角LTP和CaMKII磷酸化的影响。观察结果如下：(1)诱导LTP后30min,CaMK Ⅱ的磷酸化水平明显高于对照组,而CaMKⅡ的总量无变化;诱导LTP后3h CaMKⅡ的磷酸化水平进一步升高。而且CaMKⅡ的总量也明显增加(n=4);(2)强直刺激前30min于脊髓局部给予CaMKⅡ的特异性抑制剂KN-93(100μmol/L),可阻断LTP的诱导,同时明显抑制CaMKⅡ的磷酸化水平;(3)诱导LTP后30min给予KN-93,可显著抑制LTP的维持,同时CaMKⅡ的磷酸化水平与未用药组相比也明显降低（n=3);(4)LTP3h后给予KN-93,LTP的幅值不受影响,磷酸化的CaMKⅡ的含量与用药前相比也无差别（n=3)。根据上述实验结果可以认为,CaMKⅡ的激活参与脊髓背角C-纤维诱发电位LTP的诱导和早期维持过程。     

Ultrastructure of orexin-1 receptor immunoreactivities in the spinal cord dorsal horn

The ultrastructural properties of orexin 1-receptor-like immunoreactive (OX1R-LI) neurons in the dorsal horn of the rat spinal cord were examined using light and electron microscopy techniques. At the light microscopy level, the most heavily immunostained OX1R-LI neurons were found in the ventral horn of the spinal cord, while some immunostained profiles, including nerve fibers and small neurons, were also found in the dorsal horn. At the electron microscopy level, OX1R-LI perikarya were identified containing numerous dense-cored vesicles which were more heavily immunostained than any other organelles. Similar vesicles were also found within the axon terminals of the OX1R-LI neurons. The perikarya and dendrites of some of the OX1R-LI neurons could be seen receiving synapses from immunonegative axon terminals. These synapses were found mostly asymmetric in shape. Occasionally, some OX1R-LI axon terminals were found making synapses on dendrites that were OX1R-LI in some cases and immunonegative in others. The synapses made by OX1R-LI axon terminals were found both asymmetric and symmetric in appearance. The results provide solid morphological evidence that OX1R is transported in the dense-cored vesicles from the perikarya to axon terminals and that OX1R-LI neurons in the dorsal horn of the spinal cord have complex synaptic relationships both with other OX1R-LI neurons as well as other neuron types.     

Time Course of Immediate Early Gene Protein Expression in the Spinal Cord following Conditioning Stimulation of the Sciatic Nerve in Rats

Long-term potentiation induced by conditioning electrical stimulation of afferent fibers is a widely studied form of synaptic plasticity in the brain and the spinal cord. In the spinal cord dorsal horn, long-term potentiation is induced by a series of high-frequency trains applied to primary afferent fibers. Conditioning stimulation (CS) of sciatic nerve primary afferent fibers also induces expression of immediate early gene proteins in the lumbar spinal cord. However, the time course of immediate early gene expression and the rostral-caudal distribution of expression in the spinal cord have not been systematically studied. Here, we examined the effects of sciatic nerve conditioning stimulation (10 stimulus trains, 0.5 ms stimuli, 7.2 mA, 100 Hz, train duration 2 s, 8 s intervals between trains) on cellular expression of immediate early genes, Arc, c-Fos and Zif268, in anesthetized rats. Immunohistochemical analysis was performed on sagittal sections obtained from Th13- L5 segments of the spinal cord at 1, 2, 3, 6 and 12 h post-CS. Strikingly, all immediate early genes exhibited a monophasic increase in expression with peak increases detected in dorsal horn neurons at 2 hours post-CS. Regional analysis showed peak increases at the location between the L3 and L4 spinal segments. Both Arc, c-Fos and Zif268 remained significantly elevated at 2 hours, followed by a sharp decrease in immediate early gene expression between 2 and 3 hours post-CS. Colocalization analysis performed at 2 hours post-CS showed that all c-Fos and Zif268 neurons were positive for Arc, while 30% and 43% of Arc positive neurons were positive for c-Fos and Zif268, respectively. The present study identifies the spinal cord level and time course of immediate early gene (IEGP) expression of relevance for analysis of IEGPs function in neuronal plasticity and nociception.     

Dorsal horn administration of muscimol abolishes the muscle pressor reflex.

The purpose of this study was to determine the effect of blocking synaptic transmission in the dorsal horn on the cardiovascular responses produced by activation of muscle afferent neurons. Synaptic transmission was blocked by applying the GABA(A) agonist muscimol to the dorsal surface of the spinal cord. Cats were anesthetized with alpha-chloralose and urethane, and a laminectomy was performed. With the exception of the L(7) dorsal root, the dorsal and ventral roots from L(5) to S(2) were sectioned on one side, and static contraction of the ipsilateral triceps surae muscle was evoked by electrically stimulating the peripheral ends of the L(7) and S(1) ventral roots. The dorsal surface of the L(4)--S(3) segments of the spinal cord were enclosed within a "well" created by applying layers of vinyl polysiloxane. Administration of a 1 mM solution of muscimol (based on dose-response data) into this well abolished the reflex pressor response to contraction (change in mean arterial blood pressure before was 47 +/- 7 mmHg and after muscimol was 3 +/- 2 mmHg). Muscle stretch increased mean arterial blood pressure by 30 +/- 8 mmHg before muscimol, but after drug application stretch increased MAP by only 3 +/- 2 mmHg. Limiting muscimol to the L(7) segment attenuated the pressor responses to contraction (37 +/- 7 to 24 +/- 11 mmHg) and stretch (28 +/- 2 to 16 +/- 8 mmHg). These data suggest that the dorsal horn of the spinal cord contains an obligatory synapse for the pressor reflex. Furthermore, these data support the hypothesis that branches of primary afferent neurons, not intraspinal pathways, are responsible for the multisegmental integration of the pressor reflex.     

Differential Changes in Neuronal Excitability in the Spinal Dorsal Horn After Spinal Nerve Ligation in Rats

Previous studies demonstrated that peripheral nerve injury induced excessive neuronal response and glial activation in the spinal cord dorsal horn, and such change has been proposed to reflect the development and maintenance of neuropathic pain states. The aim of this study was to examine neuronal excitability and glial activation in the spinal dorsal horn after peripheral nerve injury. We examined noxious heat stimulation-induced c-Fos protein-like immunoreactivity (Fos-LI) neuron profiles in fourth-to-sixth lumbar (L4–L6) level spinal dorsal horn neurons after fifth lumbar spinal nerve ligation (L5 SNL). Immunofluorescence labeling of OX-42 and GFAP was also performed in histological sections of the spinal cord. A significant increase in the number of Fos-LI neuron profiles in the spinal dorsal horn at the L4 level was found at 3 days after SNL, but returned to a level similar to that in sham-operated controls by 14 days after injury. As expected, a decrease in the number of Fos-LI neuron profiles in the spinal dorsal horn at the L5 level was found at 3 days after SNL. However, these profiles had reappeared in large numbers by 14 and 21 days after injury. Immunofluorescence labeling of OX-42 and GFAP indicated sequential activation of microglia and astrocytes in the spinal dorsal horn. We conclude that nerve injury causes differential changes in neuronal excitability in the spinal dorsal horn, which may coincide with glial activation. These changes may play a substantial role in the pathogenesis of neuropathic pain after peripheral nerve injury.     

MK-801抑制福尔马林实验引起的大鼠脊髓背角环氧合酶-2的表达

应用免疫组织化学方法,观察鞘内注射N-methyl—D—aspartate(NMDA)受体拮抗剂MK-801对福尔马林实验引起的大鼠脊髓背角环氧合酶-2(cyclooxygenase-2,COX-2)表达的影响。结果表明：MK-801对福尔马林实验引起的第1相缩足反射仅有一定抑制作用,但对第2相缩足反射有显著的抑制作用,且呈剂量依赖性。与这种行为学的变化相对应,MK-801可显著抑制福尔马林实验引起的脊髓背角COX-2表达的增加,并且这种抑制作用与MK-801的剂量呈正相关。这些结果表明,在福尔马林实验中,NMDA受体的活动是引起脊髓背角COX-2表达增加的原因之一。     

Speaking out of turn: a role for silent synapses in pain

Severe tissue or nerve injury can result in a chronic and inappropriate sensation of pain, mediated in part by the sensitization of spinal dorsal horn neurons to input from primary afferent fibers. Synaptic transmission at primary afferent synapses is mainly glutamatergic. Although a functioning excitatory synapse contains both alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors in the postsynaptic membrane, recent evidence suggests that dorsal horn neurons contain some "silent" synapses, which exhibit purely NMDA receptor-mediated evoked postsynaptic currents and do not conduct signals at resting membrane potential. Serotonin, which is released onto dorsal horn neurons by descending fibers from the rostroventral medulla, potentiates sensory transmission by activating silent synapses on those neurons, i.e., by recruiting functional AMPA receptors to the postsynaptic membrane. This phenomenon may contribute to the hyperexcitability of dorsal horn neurons seen in chronic pain conditions.