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.     

Development of regional specificity of spinal and medullary dorsal horn neurons

Extensive studies have focused on the development and regionalization of neurons in the central nervous system(CNS). Many genes, which play crucial roles in the development of CNS neurons, have been identified. By using the technique "direct reprogramming", neurons can be produced from multiple cell sources such as fibroblasts. However, understanding the region-specific regulation of neurons in the CNS is still one of the biggest challenges in the research field of neuroscience. Neurons located in the trigeminal subnucleus caudalis(Vc) and in the spinal dorsal horn(SDH) play crucial roles in pain and sensorimotor functions in the orofacial and other somatic body regions, respectively. Anatomically, Vc represents the most caudal component of the trigeminal system, and is contiguous with SDH. This review is focused on recent data dealing with the regional specificity involved in the development of neurons in Vc and SDH.     

Characterization of traumatic spinal cord injury model in relation to neuropathic pain in the rat

Purpose/aim: Neuropathic pain following spinal cord injury (SCI) has a tremendous impact on patient’s quality of life, and frequently is the most limiting aspect of the disease. In view of the severity of this condition and the absence of effective treatments, the establishment of a reliable animal model that reproduces neuropathic pain after injury is crucial for a better understanding of the pathophysiology and for the development of new therapeutic strategies. Thus, the objective of the present study was to standardize the traumatic SCI model in relation to neuropathic pain.

Materials and methods: Wistar rats were submitted to SCI of mild intensity (pendulum height 12.5?mm) or moderate intensity (pendulum height 25?mm) using the New York University Impactor equipment. Behavioural assessment was performed during 8 weeks. Thereafter, spinal cords were processed for immunohistochemistry.

Results: The animals of the moderate injury group in comparison with mild injury had a greater motor function deficit, worse mechanical allodynia, and latter bladder recovery; moreover, histological analysis revealed more extensive lesions with lower neuronal population.

Conclusions: Our study suggests that moderate SCI causes a progressive and long-lasting painful condition (at least 8 weeks), in addition to motor impairment, and thus represents a reliable animal model for the study of chronic neuropathic pain after SCI.     

Proteome of synaptosome‐associated proteins in spinal cord dorsal horn after peripheral nerve injury

Peripheral nerve injury may lead to neuroadaptive changes of cellular signals in spinal cord that are thought to contribute to central mechanisms underlying neuropathic pain. Here we used a 2‐DE‐based proteomic technique to determine the global expression changes of synaptosome‐associated proteins in spinal cord dorsal horn after unilateral fifth spinal nerve injury (SNI). The fifth lumbar dorsal horns ipsilateral to SNI or sham surgery were harvested on day 14 post‐surgery, and the total soluble and synaptosomal fractions were isolated. The proteins derived from the synaptosomal fraction were resolved by 2‐DE. We identified 27 proteins that displayed different expression levels after SNI, including proteins involved in transmission and modulation of noxious information, cellular metabolism, membrane receptor trafficking, oxidative stress, apoptosis, and degeneration. Six of the 27 proteins were chosen randomly and further validated in the synaptosomal fraction by Western blot analysis. Unexpectedly, Western blot analysis showed that only one protein in the total soluble fraction exhibited a significant expression change after SNI. The data indicate that peripheral nerve injury changes not only protein expression but also protein subcellular distribution in dorsal horn cells. These changes might participate in the central mechanism that underlies the maintenance of neuropathic pain.     

Estrogen alleviates neuropathic pain induced after spinal cord injury by inhibiting microglia and astrocyte activation

Neuropathic pain after spinal cord injury (SCI) is developed in about 80% of SCI patients and there is no efficient therapeutic drug to alleviate SCI-induced neuropathic pain. Here we examined the effect of estrogen on SCI-induced neuropathic pain at below-level and its effect on neuroinflammation as underlying mechanisms. Neuropathic pain is developed at late phase after SCI and a single dose of 17β-estradiol (100, 300?μg/kg) were administered to rats with neuropathic pain after SCI through intravenous injection. As results, both mechanical allodynia and thermal hyperalgesia were significantly reduced by 17β-estradiol compared to vehicle control. Both microglia and astrocyte activation in the lamina I and II of L4-5 dorsal horn was also inhibited by 17β-estradiol. In addition, the levels of p-p38MAPK and p-ERK known to be activated in microglia and p-JNK known to be activated in astrocyte were significantly decreased by 17β-estradiol. Furthermore, the mRNA expression of inflammatory mediators such as Il-1β, Il-6, iNos, and Cox-2 was more attenuated in 17β-estradiol-treated group than in vehicle-treated group. Particularly, we found that the analgesic effect by 17β-estradiol was mediated via estrogen receptors, which are expressed in dorsal horn neurons. These results suggest that 17β-estradiol may attenuate SCI-induced neuropathic pain by inhibiting microglia and astrocyte activation followed inflammation.     

Fractalkine and minocycline alter neuronal activity in the spinal cord dorsal horn

Fractalkine (FKN) evokes nociceptive behavior in nai ve rats, whereas minocycline attenuates pain acutely after neuronal injury. We show that, in nai ve rats, FKN causes hyperresponsiveness of lumbar wide dynamic range neurons to brush, pressure and pinch applied to the hindpaw. One day after spinal nerve ligation (SNL), minocycline attenuates after-discharge and responses to brush and pressure. In contrast, minocycline does not alter evoked neuronal responses 10 days after SNL or sciatic constriction, but increases spontaneous discharge. We speculate that microglia rapidly alter sensory neuronal activity in nai ve and neuropathic rats acutely, but not chronically, after injury.     

Fine structure of growth cones in the upper dorsal horn of the adult primate spinal cord in the course of reactive synapto-neogenesis

Summary Following transganglionic degenerative atrophy of primary afferent terminals induced by a crush-injury of the sciatic nerve, a regenerative process takes places in the upper dorsal horn of the lumbar spinal cord in the primate Macacus rhesus. Axonal growth cones are characterized by cisterns of axoplasmic reticulum; filopodia emanating from growth cones are electron-optically translucent sheet-like expansions, often containing growth-cone vesicles. Axoplasmic reticulum appears also in preterminal portions of regenerating axons. Dendritic growth cones contain a fine, filamentous matrix; electron-dense membrane specializations can be seen in well-defined areas of their surfaces. Immature synapses are formed between filopodia of axonal growth cones and dendritic growth cones. Electron-microscopic structures of this unique CNS regeneration are similar to those seen in the course of embryonic development of the spinal cord.     

甲醛炎性痛及痛过敏诱导大鼠脊髓后角环氧化酶-2表达的变化

目的:观察甲醛炎性痛及痛过敏过程中脊髓后角环氧化酶-2 (COX-2)表达的变化及其时间特征.方法:采用大鼠甲醛疼痛模型,用免疫组化法观察脊髓COX-2表达的变化.结果:与对照组相比,注射甲醛后4 h,1 d及3 d组脊髓后角Ⅰ-Ⅵ板层COX-2免疫反应阳性细胞的数目及染色深度均显著增加,以1 d组增加最为明显.结论:脊髓后角COX-2参与甲醛炎性痛及痛过敏.     

Numerical characteristics of synaptic vesicular apparatus structure in the dorsal horn of the cat spinal cord

Statistical parameters characterizing the structure of the vesicular apparatus of presynaptic endings (PE) were determined from the findings of ultrastructural morphometric analysis of 135 synapses in the dorsal horn of the cat spinal cord. Quantitative estimates of vesicles in the PE (averaging about 470) were obtained, based on stereometric principles. The bimodal pattern of distribution of distances from the center of each vesicle to the nearest portion of the active zone was demonstrated — viewed as the structural correlate of the two-pool model of transmitter storage. The possibility of classifying PE according to the sign of vesicle spatial distribution is discussed as well as the relationship between this distribution and parameters of transmitter mobilization and synaptic release.Dnepropetrovsk State University. A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 597–605, September–October, 1989.     

Altered gene expression of NIDD in dorsal root ganglia and spinal cord of rats with neuropathic or inflammatory pain

Nitric oxide and nitric oxide synthases are key players in synaptic plasticity events in spinal cord (SC), which underlies the chronic pain states. To date, little is known about the molecular mechanisms regulating the activity of nitric oxide synthases in nociceptive systems. The present study was aimed at the determination of the gene expression of nNOS-interacting DHHC domain-containing protein with dendritic mRNA (NIDD), a recently identified protein regulating nNOS enzyme activity, in rat SC and dorsal root ganglia (DRG) and studying its regulation in states of nociceptive hypersensitivity in a rat model of neuropathic or inflammatory pain. It was found that NIDD mRNA was predominantly expressed in nociceptive primary neurons and in neurons of the spinal dorsal horn (DH) and the number of NIDD-positive neurons in the corresponding DRG or SC increased significantly following induction of chronic hyperalgesia. Meanwhile, remarkable changes of nNOS were detected under such pain conditions. Our data suggest a potential role for NIDD in the maintenance of thermal pain hypersensitivity possibly via regulating the nNOS activity. Meng-Ling Chen and Chun Cheng are contributed equally to this work.     

去甲肾上腺素在脊髓背角的镇痛机制

疹髓背角浅层是传递和调制外周伤害性信息的关键部位。起源于脑干的去甲肾上腺素（NA）能纤维终止脊髓背角,它们释放的NA具有抑制初级传入末梢释放谷氨酸和P物质、增加Ⅱ层（胶状质）抑制性神经活性物质释放的作用。此外,形态学研究提示NA可能直接抑制Ⅰ/Ⅲ层向丘脑传递伤害性信息的投射神经元。NA可能通过以上途径,实现对外周伤害性信息传递的调制而发挥镇痛作用。     

Sensory function above lesion level in spinal cord injury patients with and without pain

Patients with spinal cord injury (SCI) may or may not develop central neuropathic pain despite having cord lesions of apparently the same site, extension and nature. The consequences of the cord lesion in the central nervous system and the mechanisms underlying pain are unclear. In this study, we examined sensory detection and pain thresholds above injury level in 17 SCI patients with central neuropathic pain, in 18 SCI patients without neuropathic pain, and in 20 control subjects without injury and pain. The SCI pain group had significantly higher cold and warm detection thresholds compared with the SCI pain free group and controls and higher tactile detection thresholds compared with the SCI pain free group. No difference in pain or pain tolerance thresholds was seen among pain and pain free SCI patients. These data suggest changes in somatosensory function in dermatomes rostral to the segmental injury level linked to the presence of central neuropathic pain in SCI patients. The results are discussed in relation to current concepts of pain inhibitory and facilitating systems.     

Gas7在成年大鼠脊髓和脊神经节的表达

目的 研究生长休止蛋白7（Gas7）在成年大鼠脊髓和脊神经节的表达.方法 成年SD大鼠12只,采用逆转录聚合酶链反应（RT-PCR）方法、焦油紫染色以及免疫组织化学方法来观察Gas7基因核酸和蛋白在成年SD大鼠脊髓和脊神经节的表达.结果 RT-PCR结果显示,脊髓和脊神经节有较丰富的Gas7 mRNA表达.免疫组化结果显示：与焦油紫染色相对照,脊髓灰质各板层神经元均表达Gas7蛋白,与其它版层相比较,后角Ⅱ版层胶状质的小细胞和前角Ⅸ版层的运动神经元显色较深且数量较多.脊髓白质Gas7免疫阳性反应较弱且分布均匀.脊神经节内大型感觉神经元呈Gas7免疫强阳性反应,中、小型感觉神经元为弱阳性反应.结论 本文首次描述了Gas7在成年大鼠脊髓和脊神经节的表达,为进一步研究Gas7在成年神经系统再生和修复过程中的功能提供形态学基础.     

Effect of repetitive ischemic preconditioning on spinal cord ischemia in a rabbit model

A completely randomized controlled study based on a rabbit model was designed to study the effect of repetitive ischemic preconditioning (IPC) on a spinal cord ischemic reperfusion injury. Twenty four white adult Japanese rabbits were randomly assigned to one of the 3 groups (n = 8 per group): Group I: sham-operation group, Group II: ischemic reperfusion group, and, Group III: IPC group. Spinal cord ischemia was induced by infra-renal aortic cross-clamp for 45 min in Group II. Before 45 min ischemia, the rabbits in Group III underwent four cycles of IPC (5 min of ischemia followed by 5 min of reperfusion). Post-operative neurological function, electromyography (EMG) of rear limbs, and spinal cord histopathological changes were measured. The concentrations of calcium, magnesium, copper, and zinc in spinal cord were measured in the 7th day. The neurological function and histopathological changes in Group II were significantly different from those in Group I or Group III (P < 0.05 or 0.01). There was a more significant change of EMG in Group II than that in Group III (P < 0.05). The concentrations of calcium and copper in Group II were significantly higher (P < 0.05 or 0.01), but magnesium and zinc were significantly lower (P < 0.05) than those in Group I. Calcium and copper in Group II were significantly higher (P < 0.05), but zinc was significantly lower (P < 0.01) than those in Group III. In conclusion, repetitive IPC can protect rabbit spinal cord from ischemic reperfusion injury in a timely manner, which is associated with corrections of imbalance of calcium, magnesium, copper, and zinc in the ischemic region.     

P2X receptor-mediated purinergic sensory pathways to the spinal cord dorsal horn

P2X receptors are expressed on different functional groups of primary afferent fibers. P2X receptor-mediated sensory inputs can be either innocuous or nociceptive, depending on which dorsal horn regions receive these inputs. We provide a brief review of P2X receptor-mediated purinergic sensory pathways to different regions in the dorsal horn. These P2X purinergic pathways are identified in normal animals, which provides insights into their physiological functions. Future studies on P2X purinergic pathways in animal models of pathological conditions may provide insights on how P2X receptors play a role in pathological pain states.