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Deng Y, Tang S, Cheng J, Zhang X, Jing D, Lin Z, Zhou J. Integrated analysis reveals Atf3 promotes neuropathic pain via orchestrating JunB mediated release of inflammatory cytokines in DRG macrophage. Life Sci 2023; 329:121939. [PMID: 37451398 DOI: 10.1016/j.lfs.2023.121939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2023] [Revised: 06/08/2023] [Accepted: 07/11/2023] [Indexed: 07/18/2023]
Abstract
The dorsal root ganglion (DRG) is actively involved in the development of neuropathic pain (NP), serving as an intermediate station for pain signals from the peripheral nervous system to the central nervous system. The mechanism by which DRG is involved in NP regulation is not fully understood. The immune system plays a pivotal role in the physiological and pathological states of the human body. In recent years, the immune system has been thought to play an increasingly important role in the pathogenesis of NP. The immune system plays a key role in pain through specific immune cells and their immune-related genes (IRGs). However, the mechanism by which IRGs of DRG regulate NP action has not been fully elucidated. Here, we performed Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of IRGs in DRG bulk-RNA sequencing data from spared nerve injury (SNI) model mice and found that their IRGs were enriched in many pathways, especially in the immune response pathway. Subsequently, we analyzed single-cell RNA sequencing (scRNA-seq) data from DRGs extracted from the SNI model and identified eight cell populations. Among them, the highest IRG activity was presented in macrophages. Next, we analyzed the scRNA and bulk-sequencing data and deduced five common transcription factors (TFs) from differentially expressed genes (DEGs). The protein-protein interaction (PPI) network suggested that Atf3 and JunB are closely related. In vitro experiments, we verified that the protein and mRNA expressions of Atf3 and JunB were up-regulated in macrophages after lipopolysaccharide (LPS) stimulation. Moreover, the down-regulation of Atf3 reduced the release of inflammatory cytokines and decreased the protein and mRNA expression levels of JunB. The down-regulation of JunB also reduced the release of inflammatory cytokines. Furthermore, overexpression of JunB attenuated the effect of Atf3 down-regulation in reducing the release of inflammatory cytokines. Therefore, we speculated that Atf3 might promote NP through JunB-mediated release of inflammatory factors in DRG macrophages.
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Affiliation(s)
- Yingdong Deng
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China
| | - Simin Tang
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China
| | - Jiurong Cheng
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China
| | - Xiangsheng Zhang
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China
| | - Danqin Jing
- College of Anesthesiology, Shanxi Medical University, Taiyuan, Shanxi Province 030001, China
| | - Ziqiang Lin
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China
| | - Jun Zhou
- Department of Anesthesiology, The Third Affiliated Hospital of Southern Medical University, Guangzhou, Guangdong Province 510000, China.
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Kummer KK, Mitrić M, Kalpachidou T, Kress M. The Medial Prefrontal Cortex as a Central Hub for Mental Comorbidities Associated with Chronic Pain. Int J Mol Sci 2020; 21:E3440. [PMID: 32414089 PMCID: PMC7279227 DOI: 10.3390/ijms21103440] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 05/06/2020] [Accepted: 05/07/2020] [Indexed: 12/13/2022] Open
Abstract
Chronic pain patients frequently develop and suffer from mental comorbidities such as depressive mood, impaired cognition, and other significant constraints of daily life, which can only insufficiently be overcome by medication. The emotional and cognitive components of pain are processed by the medial prefrontal cortex, which comprises the anterior cingulate cortex, the prelimbic, and the infralimbic cortex. All three subregions are significantly affected by chronic pain: magnetic resonance imaging has revealed gray matter loss in all these areas in chronic pain conditions. While the anterior cingulate cortex appears hyperactive, prelimbic, and infralimbic regions show reduced activity. The medial prefrontal cortex receives ascending, nociceptive input, but also exerts important top-down control of pain sensation: its projections are the main cortical input of the periaqueductal gray, which is part of the descending inhibitory pain control system at the spinal level. A multitude of neurotransmitter systems contributes to the fine-tuning of the local circuitry, of which cholinergic and GABAergic signaling are particularly emerging as relevant components of affective pain processing within the prefrontal cortex. Accordingly, factors such as distraction, positive mood, and anticipation of pain relief such as placebo can ameliorate pain by affecting mPFC function, making this cortical area a promising target region for medical as well as psychosocial interventions for pain therapy.
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Affiliation(s)
| | | | | | - Michaela Kress
- Institute of Physiology, Medical University of Innsbruck, 6020 Innsbruck, Austria; (K.K.K.); (M.M.); (T.K.)
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Abstract
The anterior cingulate cortex (ACC) is activated in both acute and chronic pain. In this Review, we discuss increasing evidence from rodent studies that ACC activation contributes to chronic pain states and describe several forms of synaptic plasticity that may underlie this effect. In particular, one form of long-term potentiation (LTP) in the ACC, which is triggered by the activation of NMDA receptors and expressed by an increase in AMPA-receptor function, sustains the affective component of the pain state. Another form of LTP in the ACC, which is triggered by the activation of kainate receptors and expressed by an increase in glutamate release, may contribute to pain-related anxiety.
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Russo JF, Sheth SA. Deep brain stimulation of the dorsal anterior cingulate cortex for the treatment of chronic neuropathic pain. Neurosurg Focus 2016; 38:E11. [PMID: 26030699 DOI: 10.3171/2015.3.focus1543] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Chronic neuropathic pain is estimated to affect 3%-4.5% of the worldwide population. It is associated with significant loss of productive time, withdrawal from the workforce, development of mood disorders such as depression and anxiety, and disruption of family and social life. Current medical therapeutics often fail to adequately treat chronic neuropathic pain. Deep brain stimulation (DBS) targeting subcortical structures such as the periaqueductal gray, the ventral posterior lateral and medial thalamic nuclei, and the internal capsule has been investigated for the relief of refractory neuropathic pain over the past 3 decades. Recent work has identified the dorsal anterior cingulate cortex (dACC) as a new potential neuromodulation target given its central role in cognitive and affective processing. In this review, the authors briefly discuss the history of DBS for chronic neuropathic pain in the United States and present evidence supporting dACC DBS for this indication. They review existent literature on dACC DBS and summarize important findings from imaging and neurophysiological studies supporting a central role for the dACC in the processing of chronic neuropathic pain. The available neurophysiological and empirical clinical evidence suggests that dACC DBS is a viable therapeutic option for the treatment of chronic neuropathic pain and warrants further investigation.
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Affiliation(s)
- Jennifer F Russo
- 1Columbia University College of Physicians and Surgeons and.,2Department of Neurological Surgery, Columbia University Medical Center, New York, New York
| | - Sameer A Sheth
- 2Department of Neurological Surgery, Columbia University Medical Center, New York, New York
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Wang XQ, Zhong XL, Li ZB, Wang HT, Zhang J, Li F, Zhang JY, Dai RP, Xin-Fu Z, Li CQ, Li ZY, Bi FF. Differential roles of hippocampal glutamatergic receptors in neuropathic anxiety-like behavior after partial sciatic nerve ligation in rats. BMC Neurosci 2015; 16:14. [PMID: 25884414 PMCID: PMC4372276 DOI: 10.1186/s12868-015-0150-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 02/25/2015] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Neuropathic pain evoked by nerve injury is frequently accompanied by deterioration of emotional behaviors, but the underlying signaling mechanisms remain elusive. Glutamate (Glu) is the major mediator of excitatory synaptic transmission throughout the brain, and abnormal activity of the glutamatergic system has been implicated in the pathophysiology of pain and associated emotional comorbidities. In this study we used the partial sciatic nerve ligation (PSNL) model of neuropathic pain in rats to characterize the development of anxiety-like behavior, the expression of glutamatergic receptors, and the phosphorylation of extracellular signal-regulated kinase (ERK) in the hippocampus, the region that encodes memories related to emotions. RESULTS We found that the mechanical withdrawal threshold was significantly reduced and an anxiety-like behavior was increased as determined via open field tests and elevated plus-maze tests at 28 days after injury. No significant differences were found in the ratio of sucrose preference and immobility time detected by sucrose preference tests and forced swimming tests respectively, possibly due to the timing factor. The expression of N-methyl-D-aspartate (NMDA) receptor subtypes NR1 and NR2B, but not NR2A, GluR1, or GluR2 (the main subtype of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid [AMPA] receptor) in the hippocampus of injured rats was significantly reduced. Moreover, PSNL resulted in decreased phosphorylation of ERK1/2 in the hippocampus. Intriguingly, treatment with D-serine (a co-agonist of NMDA receptor, 1 g/kg intraperitoneally) reduced the anxiety-like behavior but not the mechanical hypersensitivity induced by PSNL. CONCLUSIONS PSNL can induce significant anxiety-like but not depression-like behavior, and trigger down-regulation of NMDA but not AMPA receptors in the hippocampus at 28 days after injury.
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Affiliation(s)
- Xue-Qin Wang
- Center for Experimental Medicine, the Third Xiangya Hospital, Central South University, Tongzipo Road 138, Changsha, Hunan, China. .,Department of Anesthesiology, the Third Xiangya Hospital, Central South University, Tongzipo Road 138, Changsha, Hunan, China. .,Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Xiao-Lin Zhong
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Zhi-Bin Li
- Department of Neurology, XiangYa Hospital, Central South University, XiangYa Road 88, Changsha, Hunan, China.
| | - Hong-Tao Wang
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Juan Zhang
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Fang Li
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Jian-Yi Zhang
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Ru-Ping Dai
- Department of Anesthesia, the Second XiangYa Hospital of Central South University, Ren-Min Road 86, Changsha, Hunan, China.
| | - Zhou Xin-Fu
- School of Pharmacy and Medical Sciences, Sansom Institute, University of South Australia, Adelaide, SA, 5000, Australia.
| | - Chang-Qi Li
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Zhi-Yuan Li
- Department of Anatomy and Neurobiology, School of Basic Medical Science, Central South University, Tongzipo Road 172, Changsha, Hunan, China.
| | - Fang-Fang Bi
- Department of Neurology, XiangYa Hospital, Central South University, XiangYa Road 88, Changsha, Hunan, China.
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Lin HC, Huang YH, Chao THH, Lin WY, Sun WZ, Yen CT. Gabapentin reverses central hypersensitivity and suppresses medial prefrontal cortical glucose metabolism in rats with neuropathic pain. Mol Pain 2014; 10:63. [PMID: 25253440 PMCID: PMC4182821 DOI: 10.1186/1744-8069-10-63] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 09/10/2014] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND Gabapentin (GBP) is known to suppress neuropathic hypersensitivity of primary afferents and the spinal cord dorsal horn. However, its supra-spinal action sites are unclear. We identify the brain regions where GBP changes the brain glucose metabolic rate at the effective dose that alleviates mechanical allodynia using 18 F-fluorodeoxyglucose-positron emission tomography (FDG-PET) scanning. RESULTS Comparing the PET imaging data before and after the GBP treatment, the spared nerve injury-induced increases of glucose metabolism in the thalamus and cerebellar vermis were reversed, and a significant decrease occurred in glucose metabolism in the medial prefrontal cortex (mPFC), including the anterior cingulate cortex. GBP treatment also reversed post-SNI connectivity increases between limbic cortices and thalamus. CONCLUSIONS Our results indicate that GBP analgesic effect may be mediated by reversing central hypersensitivity, and suppressing mPFC, a crucial part of the cortical representation of pain, in the brain.
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Affiliation(s)
- Hsiao-Chun Lin
- />Department of Life Science, National Taiwan University, No 1, Section 4, Roosevelt Road, Taipei, 10617 Taiwan
| | - Yu-Hsin Huang
- />Department of Anesthesiology, National Taiwan University Hospital, Taipei, 10002 Taiwan
| | - Tzu-Hao Harry Chao
- />Department of Life Science, National Taiwan University, No 1, Section 4, Roosevelt Road, Taipei, 10617 Taiwan
| | - Wen-Ying Lin
- />Department of Life Science, National Taiwan University, No 1, Section 4, Roosevelt Road, Taipei, 10617 Taiwan
- />Department of Anesthesiology, National Taiwan University Hospital, Taipei, 10002 Taiwan
| | - Wei-Zen Sun
- />Department of Anesthesiology, National Taiwan University Hospital, Taipei, 10002 Taiwan
| | - Chen-Tung Yen
- />Department of Life Science, National Taiwan University, No 1, Section 4, Roosevelt Road, Taipei, 10617 Taiwan
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Nakahara K, Fujiwara Y, Tsukahara T, Yamagami H, Tanigawa T, Shiba M, Tominaga K, Watanabe T, Urade Y, Arakawa T. Acid reflux directly causes sleep disturbances in rat with chronic esophagitis. PLoS One 2014; 9:e106969. [PMID: 25215524 PMCID: PMC4162547 DOI: 10.1371/journal.pone.0106969] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2014] [Accepted: 08/04/2014] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND & AIMS Gastroesophageal reflux disease (GERD) is strongly associated with sleep disturbances. Proton pump inhibitor (PPI) therapy improves subjective but not objective sleep parameters in patients with GERD. This study aimed to investigate the association between GERD and sleep, and the effect of PPI on sleep by using a rat model of chronic acid reflux esophagitis. METHODS Acid reflux esophagitis was induced by ligating the transitional region between the forestomach and the glandular portion and then wrapping the duodenum near the pylorus. Rats underwent surgery for implantation of electrodes for electroencephalogram and electromyogram recordings, and they were transferred to a soundproof recording chamber. Polygraphic recordings were scored by using 10-s epochs for wake, rapid eye movement sleep, and non-rapid eye movement (NREM) sleep. To examine the role of acid reflux, rats were subcutaneously administered a PPI, omeprazole, at a dose of 20 mg/kg once daily. RESULTS Rats with reflux esophagitis presented with several erosions, ulcers, and mucosal thickening with basal hyperplasia and marked inflammatory infiltration. The reflux esophagitis group showed a 34.0% increase in wake (232.2±11.4 min and 173.3±7.4 min in the reflux esophagitis and control groups, respectively; p<0.01) accompanied by a reduction in NREM sleep during light period, an increase in sleep fragmentation, and more frequent stage transitions. The use of omeprazole significantly improved sleep disturbances caused by reflux esophagitis, and this effect was not observed when the PPI was withdrawn. CONCLUSIONS Acid reflux directly causes sleep disturbances in rats with chronic esophagitis.
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Affiliation(s)
- Kenichi Nakahara
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Yasuhiro Fujiwara
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Takuya Tsukahara
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Hirokazu Yamagami
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Tetsuya Tanigawa
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Masatsugu Shiba
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Kazunari Tominaga
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Toshio Watanabe
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
| | - Yoshihiro Urade
- Department of Molecular Behavioral Biology, Osaka Bioscience Institute, Suita, Japan
- Molecular Sleep Biology Laboratory, International Institute for Integrative Sleep Medicine, World Premier International Research Center, Tsukuba University, Tsukuba, Japan
| | - Tetsuo Arakawa
- Department of Gastroenterology, Osaka City University Graduate School of Medicine, Osaka, Japan
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Yamashita A, Hamada A, Suhara Y, Kawabe R, Yanase M, Kuzumaki N, Narita M, Matsui R, Okano H, Narita M. Astrocytic activation in the anterior cingulate cortex is critical for sleep disorder under neuropathic pain. Synapse 2014; 68:235-47. [DOI: 10.1002/syn.21733] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Accepted: 01/09/2014] [Indexed: 01/21/2023]
Affiliation(s)
- Akira Yamashita
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Asami Hamada
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Yuki Suhara
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Rui Kawabe
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Makoto Yanase
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Naoko Kuzumaki
- Department of Physiology; Keio University School of Medicine; 35 Shinanomachi Shinjuku-ku Tokyo 160-8582 Japan
| | - Michiko Narita
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
| | - Ryosuke Matsui
- Department of Molecular and Systems Biology; Graduate School of Biostudies, Kyoto University; Yoshida Sakyo-ku Kyoto 606-8501 Japan
| | - Hideyuki Okano
- Department of Physiology; Keio University School of Medicine; 35 Shinanomachi Shinjuku-ku Tokyo 160-8582 Japan
| | - Minoru Narita
- Department of Pharmacology; Hoshi University School of Pharmacy and Pharmaceutical Sciences; 2-4-41 Ebara Shinagawa-ku Tokyo 142-8501 Japan
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Zhuo M. Cortical plasticity as a new endpoint measurement for chronic pain. Mol Pain 2011; 7:54. [PMID: 21798042 PMCID: PMC3157449 DOI: 10.1186/1744-8069-7-54] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Accepted: 07/28/2011] [Indexed: 02/03/2023] Open
Abstract
Animal models of chronic pain are widely used to investigate basic mechanisms of chronic pain and to evaluate potential novel drugs for treating chronic pain. Among the different criteria used to measure chronic pain, behavioral responses are commonly used as the end point measurements. However, not all chronic pain conditions can be easily measured by behavioral responses such as the headache, phantom pain and pain related to spinal cord injury. Here I propose that cortical indexes, that indicate neuronal plastic changes in pain-related cortical areas, can be used as endpoint measurements for chronic pain. Such cortical indexes are not only useful for those chronic pain conditions where a suitable animal model is lacking, but also serve as additional screening methods for potential drugs to treat chronic pain in humans. These cortical indexes are activity-dependent immediate early genes, electrophysiological identified plastic changes and biochemical assays of signaling proteins. It can be used to evaluate novel analgesic compounds that may act at peripheral or spinal sites. I hope that these new cortical endpoint measurements will facilitate our search for new, and more effective, pain medicines, and help to reduce false lead drug targets.
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Affiliation(s)
- Min Zhuo
- Center for Neuron and Disease, Frontier Institute for Science and Technology, Xian Jiaotong University, China.
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Functional interaction between medial thalamus and rostral anterior cingulate cortex in the suppression of pain affect. Neuroscience 2010; 172:460-73. [PMID: 21034797 DOI: 10.1016/j.neuroscience.2010.10.055] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 10/19/2010] [Accepted: 10/19/2010] [Indexed: 11/22/2022]
Abstract
The medial thalamic parafascicular nucleus (PF) and the rostral anterior cingulate cortex (rACC) are implicated in the processing and suppression of the affective dimension of pain. The present study evaluated the functional interaction between PF and rACC in mediating the suppression of pain affect in rats following administration of morphine or carbachol (acetylcholine agonist) into PF. Vocalizations that occur following a brief noxious tailshock (vocalization afterdischarges) are a validated rodent model of pain affect, and were preferentially suppressed by injection of morphine or carbachol into PF. Vocalizations that occur during tailshock were suppressed to a lesser degree, whereas, spinal motor reflexes (tail flick and hindlimb movements) were only slightly suppressed by injection of carbachol into PF and unaffected by injection of morphine into PF. Blocking glutamate receptors in rACC (NMDA and non-NMDA) by injecting D-2-amino-5-phosphonovalerate (AP-5) or 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX) produced dose-dependent antagonism of morphine-induced increases in vocalization thresholds. Carbachol-induced increases in vocalization thresholds were not affected by injection of either glutamate receptor antagonist into rACC. The results demonstrate that glutamate receptors in the rACC contribute to the suppression of pain affect produced by injection of morphine into PF, but not to the suppression of pain affect generated by intra-PF injection of carbachol.
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