Long-term actions of BDNF on inhibitory synaptic transmission in identified neurons of the rat substantia gelatinosa

2012 ◽  
Vol 108 (2) ◽  
pp. 441-452 ◽  
Author(s):  
Van B. Lu ◽  
William F. Colmers ◽  
Peter A. Smith

Peripheral nerve injury promotes the release of brain-derived neurotrophic factor (BDNF) from spinal microglial cells and primary afferent terminals. This induces an increase in dorsal horn excitability that contributes to “central sensitization” and to the onset of neuropathic pain. Although it is accepted that impairment of GABAergic and/or glycinergic inhibition contributes to this process, certain lines of evidence suggest that GABA release in the dorsal horn may increase after nerve injury. To resolve these contradictory findings, we exposed rat spinal cord neurons in defined-medium organotypic culture to 200 ng/ml BDNF for 6 days to mimic the change in spinal BDNF levels that accompanies peripheral nerve injury. Morphological and electrophysiological criteria and glutamic acid decarboxylase (GAD) immunohistochemistry were used to distinguish putative inhibitory tonic-islet-central neurons from putative excitatory delay-radial neurons. Whole cell recording in the presence of 1 μM tetrodotoxin showed that BDNF increased the amplitude of GABAergic and glycinergic miniature inhibitory postsynaptic currents (mIPSCs) in both cell types. It also increased the amplitude and frequency of spontaneous, action potential-dependent IPSCs (sIPSCs) in putative excitatory neurons. By contrast, BDNF reduced sIPSC amplitude in inhibitory neurons but frequency was unchanged. This increase in inhibitory drive to excitatory neurons and decreased inhibitory drive to inhibitory neurons seems inconsistent with the observation that BDNF increases overall dorsal horn excitability. One of several explanations for this discrepancy is that the action of BDNF in the substantia gelatinosa is dominated by previously documented increases in excitatory synaptic transmission rather than by impediment of inhibitory transmission.

2021 ◽  
Vol 17 ◽  
pp. 174480692110066
Author(s):  
Orest Tsymbalyuk ◽  
Volodymyr Gerzanich ◽  
Aaida Mumtaz ◽  
Sanketh Andhavarapu ◽  
Svetlana Ivanova ◽  
...  

Background Neuropathic pain following peripheral nerve injury (PNI) is linked to neuroinflammation in the spinal cord marked by astrocyte activation and upregulation of interleukin 6 (IL -6 ), chemokine (C-C motif) ligand 2 (CCL2) and chemokine (C-X-C motif) ligand 1 (CXCL1), with inhibition of each individually being beneficial in pain models. Methods Wild type (WT) mice and mice with global or pGfap-cre- or pGFAP-cre/ERT2-driven Abcc8/SUR1 deletion or global Trpm4 deletion underwent unilateral sciatic nerve cuffing. WT mice received prophylactic (starting on post-operative day [pod]-0) or therapeutic (starting on pod-21) administration of the SUR1 antagonist, glibenclamide (10 µg IP) daily. We measured mechanical and thermal sensitivity using von Frey filaments and an automated Hargreaves method. Spinal cord tissues were evaluated for SUR1-TRPM4, IL-6, CCL2 and CXCL1. Results Sciatic nerve cuffing in WT mice resulted in pain behaviors (mechanical allodynia, thermal hyperalgesia) and newly upregulated SUR1-TRPM4 in dorsal horn astrocytes. Global and pGfap-cre-driven Abcc8 deletion and global Trpm4 deletion prevented development of pain behaviors. In mice with Abcc8 deletion regulated by pGFAP-cre/ERT2, after pain behaviors were established, delayed silencing of Abcc8 by tamoxifen resulted in gradual improvement over the next 14 days. After PNI, leakage of the blood-spinal barrier allowed entry of glibenclamide into the affected dorsal horn. Daily repeated administration of glibenclamide, both prophylactically and after allodynia was established, prevented or reduced allodynia. The salutary effects of glibenclamide on pain behaviors correlated with reduced expression of IL-6, CCL2 and CXCL1 by dorsal horn astrocytes. Conclusion SUR1-TRPM4 may represent a novel non-addicting target for neuropathic pain.


2019 ◽  
Vol 20 (1) ◽  
pp. 33-37 ◽  
Author(s):  
Marzia Malcangio

AbstractBackgroundAcute pain is a warning mechanism that exists to prevent tissue damage, however pain can outlast its protective purpose and persist beyond injury, becoming chronic. Chronic Pain is maladaptive and needs addressing as available medicines are only partially effective and cause severe side effects. There are profound differences between acute and chronic pain. Dramatic changes occur in both peripheral and central pathways resulting in the pain system being sensitised, thereby leading to exaggerated responses to noxious stimuli (hyperalgesia) and responses to non-noxious stimuli (allodynia).Critical role for immune system cells in chronic painPreclinical models of neuropathic pain provide evidence for a critical mechanistic role for immune cells in the chronicity of pain. Importantly, human imaging studies are consistent with preclinical findings, with glial activation evident in the brain of patients experiencing chronic pain. Indeed, immune cells are no longer considered to be passive bystanders in the nervous system; a consensus is emerging that, through their communication with neurons, they can both propagate and maintain disease states, including neuropathic pain. The focus of this review is on the plastic changes that occur under neuropathic pain conditions at the site of nerve injury, the dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. At these sites both endothelial damage and increased neuronal activity result in recruitment of monocytes/macrophages (peripherally) and activation of microglia (centrally), which release mediators that lead to sensitisation of neurons thereby enabling positive feedback that sustains chronic pain.Immune system reactions to peripheral nerve injuriesAt the site of peripheral nerve injury following chemotherapy treatment for cancer for example, the occurrence of endothelial activation results in recruitment of CX3C chemokine receptor 1 (CX3CR1)-expressing monocytes/macrophages, which sensitise nociceptive neurons through the release of reactive oxygen species (ROS) that activate transient receptor potential ankyrin 1 (TRPA1) channels to evoke a pain response. In the DRG, neuro-immune cross talk following peripheral nerve injury is accomplished through the release of extracellular vesicles by neurons, which are engulfed by nearby macrophages. These vesicles deliver several determinants including microRNAs (miRs), with the potential to afford long-term alterations in macrophages that impact pain mechanisms. On one hand the delivery of neuron-derived miR-21 to macrophages for example, polarises these cells towards a pro-inflammatory/pro-nociceptive phenotype; on the other hand, silencing miR-21 expression in sensory neurons prevents both development of neuropathic allodynia and recruitment of macrophages in the DRG.Immune system mechanisms in the central nervous systemIn the dorsal horn of the spinal cord, growing evidence over the last two decades has delineated signalling pathways that mediate neuron-microglia communication such as P2X4/BDNF/GABAA, P2X7/Cathepsin S/Fractalkine/CX3CR1, and CSF-1/CSF-1R/DAP12 pathway-dependent mechanisms.Conclusions and implicationsDefinition of the modalities by which neuron and immune cells communicate at different locations of the pain pathway under neuropathic pain states constitutes innovative biology that takes the pain field in a different direction and provides opportunities for novel approaches for the treatment of chronic pain.


2012 ◽  
Vol 90 (6) ◽  
pp. 783-790
Author(s):  
Van B. Lu ◽  
Peter A. Smith ◽  
Saifee Rashiq

Changes in central neural processing are thought to contribute to the development of chronic osteoarthritis pain. This may be reflected as the presence of inflammatory mediators in the cerebral spinal fluid (CSF). We therefore exposed organotypically cultured slices of rat spinal cord to CSF from human subjects with osteoarthritis (OACSF) at a ratio of 1 part CSF in 9 parts culture medium for 5–6 days, and measured changes in neuronal electrophysiological properties by means of whole-cell recording. Although OACSF had no effect on the membrane properties and excitability of neurons in the substantia gelatinosa, synaptic transmission was clearly altered. The frequency of spontaneous excitatory postsynaptic currents (sEPSC) in delay-firing putative excitatory neurons was increased, as was sEPSC amplitude and frequency in tonic-firing inhibitory neurons. These changes could affect sensory processing in the dorsal horn, and may affect the transfer of nociceptive information. Although OACSF also affected inhibitory synaptic transmission (frequency of spontaneous inhibitory synaptic currents; sIPSC), this may have little bearing on sensory processing by substantia gelatinosa neurons, as sEPSC frequency is >3× greater than sIPSC frequency in this predominantly excitatory network. These results support the clinical notion that changes in nociceptive processing at the spinal level contribute to the generation of chronic osteoarthritis pain.


Author(s):  
Ivett Dorina Szeredi ◽  
Gábor Jancsó ◽  
Orsolya Oszlács ◽  
Péter Sántha

Abstract Peripheral nerve injury is associated with spinal microgliosis which plays a pivotal role in the development of neuropathic pain behavior. Several agents of primary afferent origin causing the microglial reaction have been identified, but the type(s) of primary afferents that release these mediators are still unclear. In this study, specific labeling of C-fiber spinal afferents by lectin histochemistry and selective chemodenervation by capsaicin were applied to identify the type(s) of primary afferents involved in the microglial response. Comparative quantitative morphometric evaluation of the microglial reaction in central projection territories of intact and injured peripheral nerves in the superficial (laminae I and II) and deep (laminae III and IV) spinal dorsal horn revealed a significant, about three-fold increase in microglial density after transection of the sciatic or the saphenous nerve. Prior perineural treatment of these nerves with capsaicin, resulting in a selective defunctionalization of C-fiber afferent fibers failed to affect spinal microgliosis. Similarly, peripheral nerve injury-induced increase in microglial density was unaffected in rats treated neonatally with capsaicin known to result in a near-total loss of C-fiber dorsal root fibers. Perineural treatment with capsaicin per se did not evoke a significant increase in microglial density. These observations indicate that injury-induced spinal microgliosis may be attributed to phenotypic changes in injured myelinated primary afferent neurons, whereas the contribution of C-fiber primary sensory neurons to this neuroimmune response is negligible. Spinal myelinated primary afferents may play a hitherto unrecognized role in regulation of neuroimmune and perisynaptic microenvironments of the spinal dorsal horn.


PROTEOMICS ◽  
2009 ◽  
Vol 9 (5) ◽  
pp. 1241-1253 ◽  
Author(s):  
Om V. Singh ◽  
Myron Yaster ◽  
Ji-Tian Xu ◽  
Yun Guan ◽  
Xiaowei Guan ◽  
...  

2014 ◽  
Vol 40 (3) ◽  
pp. 438-445 ◽  
Author(s):  
Ryuji Terayama ◽  
Noriko Kishimoto ◽  
Yuya Yamamoto ◽  
Kotaro Maruhama ◽  
Hiroki Tsuchiya ◽  
...  

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