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Tsytsarev V, Plachez C, Zhao S, O'Connor DH, Erzurumlu RS. Bilateral Whisker Representations in the Primary Somatosensory Cortex in Robo3cKO Mice Are Reflected in the Primary Motor Cortex. Neuroscience 2024; 544:128-137. [PMID: 38447690 PMCID: PMC11146016 DOI: 10.1016/j.neuroscience.2024.02.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Revised: 02/09/2024] [Accepted: 02/28/2024] [Indexed: 03/08/2024]
Abstract
In Robo3cKO mice, midline crossing defects of the trigeminothalamic projections from the trigeminal principal sensory nucleus result in bilateral whisker maps in the somatosensory thalamus and consequently in the face representation area of the primary somatosensory (S1) cortex (Renier et al., 2017; Tsytsarev et al., 2017). We investigated whether this bilateral sensory representation in the whisker-barrel cortex is also reflected in the downstream projections from the S1 to the primary motor (M1) cortex. To label these projections, we injected anterograde viral axonal tracer in S1 cortex. Corticocortical projections from the S1 distribute to similar areas across the ipsilateral hemisphere in control and Robo3cKO mice. Namely, in both genotypes they extend to the M1, premotor/prefrontal cortex (PMPF), secondary somatosensory (S2) cortex. Next, we performed voltage-sensitive dye imaging (VSDi) in the left hemisphere following ipsilateral and contralateral single whisker stimulation. While controls showed only activation in the contralateral whisker barrel cortex and M1 cortex, the Robo3cKO mouse left hemisphere was activated bilaterally in both the barrel cortex and the M1 cortex. We conclude that the midline crossing defect of the trigeminothalamic projections leads to bilateral whisker representations not only in the thalamus and the S1 cortex but also downstream from the S1, in the M1 cortex.
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Affiliation(s)
- Vassiliy Tsytsarev
- Department of Neurobiology, University of Maryland School of Medicine, 20 Penn St, HSF-2, Baltimore, MD 21201, USA.
| | - Céline Plachez
- Department of Neurobiology, University of Maryland School of Medicine, 20 Penn St, HSF-2, Baltimore, MD 21201, USA.
| | - Shuxin Zhao
- Department of Neurobiology, University of Maryland School of Medicine, 20 Penn St, HSF-2, Baltimore, MD 21201, USA.
| | - Daniel H O'Connor
- The Zanvyl Krieger Mind/Brain Institute, The Johns Hopkins University, 3400 N. Charles Street, 338 Krieger Hall, Baltimore, MD 21218, USA.
| | - Reha S Erzurumlu
- Department of Neurobiology, University of Maryland School of Medicine, 20 Penn St, HSF-2, Baltimore, MD 21201, USA.
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2
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Drinovac Vlah V, Bach-Rojecky L. Mirror-Image Pain Update: Complex Interactions Between Central and Peripheral Mechanisms. Mol Neurobiol 2024:10.1007/s12035-024-04102-x. [PMID: 38602655 DOI: 10.1007/s12035-024-04102-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Accepted: 03/06/2024] [Indexed: 04/12/2024]
Abstract
The appearance of contralateral effects after unilateral injury has been shown in various experimental pain models, as well as in clinics. They consist of a diversity of phenomena in contralateral peripheral nerves, sensory ganglia, or spinal cord: from structural changes and altered gene or protein expression to functional consequences such as the development of mirror-image pain (MP). Although MP is a well-documented phenomenon, the exact molecular mechanism underlying the induction and maintenance of mirror-like spread of pain is still an unresolved challenge. MP has generally been explained by central sensitization mechanisms leading to facilitation of pain impulse transfer through neural connections between the two sides of the central nervous system. On the contrary, the peripheral nervous system (PNS) was usually regarded unlikely to evoke such a symmetrical phenomenon. However, recent findings provided evidence that events in the PNS could play a significant role in MP induction. This manuscript provides an updated and comprehensive synthesis of the MP phenomenon and summarizes the available data on the mechanisms. A more detailed focus is placed on reported evidence for peripheral mechanisms behind the MP phenomenon, which were not reviewed up to now.
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Affiliation(s)
- Višnja Drinovac Vlah
- Department of Pharmacology, University of Zagreb Faculty of Pharmacy and Biochemistry, Domagojeva 2, 10000, Zagreb, Croatia
| | - Lidija Bach-Rojecky
- Department of Pharmacology, University of Zagreb Faculty of Pharmacy and Biochemistry, Domagojeva 2, 10000, Zagreb, Croatia.
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3
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Li S, Brimmers A, van Boekel RL, Vissers KC, Coenen MJ. A systematic review of genome-wide association studies for pain, nociception, neuropathy, and pain treatment responses. Pain 2023; 164:1891-1911. [PMID: 37144689 PMCID: PMC10436363 DOI: 10.1097/j.pain.0000000000002910] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 02/07/2023] [Accepted: 02/10/2023] [Indexed: 05/06/2023]
Abstract
ABSTRACT Pain is the leading cause of disability worldwide, imposing an enormous burden on personal health and society. Pain is a multifactorial and multidimensional problem. Currently, there is (some) evidence that genetic factors could partially explain individual susceptibility to pain and interpersonal differences in pain treatment response. To better understand the underlying genetic mechanisms of pain, we systematically reviewed and summarized genome-wide association studies (GWASes) investigating the associations between genetic variants and pain/pain-related phenotypes in humans. We reviewed 57 full-text articles and identified 30 loci reported in more than 1 study. To check whether genes described in this review are associated with (other) pain phenotypes, we searched 2 pain genetic databases, Human Pain Genetics Database and Mouse Pain Genetics Database. Six GWAS-identified genes/loci were also reported in those databases, mainly involved in neurological functions and inflammation. These findings demonstrate an important contribution of genetic factors to the risk of pain and pain-related phenotypes. However, replication studies with consistent phenotype definitions and sufficient statistical power are required to validate these pain-associated genes further. Our review also highlights the need for bioinformatic tools to elucidate the function of identified genes/loci. We believe that a better understanding of the genetic background of pain will shed light on the underlying biological mechanisms of pain and benefit patients by improving the clinical management of pain.
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Affiliation(s)
- Song Li
- Department of Human Genetics, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, the Netherlands. Coenen is now with the Department of Clinical Chemistry, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Annika Brimmers
- Department of Human Genetics, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, the Netherlands. Coenen is now with the Department of Clinical Chemistry, Erasmus Medical Center, Rotterdam, the Netherlands
| | - Regina L.M. van Boekel
- Department of Anesthesiology, Pain and Palliative Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Kris C.P. Vissers
- Department of Anesthesiology, Pain and Palliative Medicine, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Marieke J.H. Coenen
- Department of Human Genetics, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, the Netherlands. Coenen is now with the Department of Clinical Chemistry, Erasmus Medical Center, Rotterdam, the Netherlands
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4
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Herrera A, Menendez A, Ochoa A, Bardia L, Colombelli J, Pons S. Neurogenesis redirects β-catenin from adherens junctions to the nucleus to promote axonal growth. Development 2023; 150:dev201651. [PMID: 37519286 PMCID: PMC10482005 DOI: 10.1242/dev.201651] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Accepted: 07/26/2023] [Indexed: 08/01/2023]
Abstract
Here, we show that, in the developing spinal cord, after the early Wnt-mediated Tcf transcription activation that confers dorsal identity to neural stem cells, neurogenesis redirects β-catenin from the adherens junctions to the nucleus to stimulate Tcf-dependent transcription in a Wnt-independent manner. This new β-catenin activity regulates genes implicated in several aspects of contralateral axon growth, including axon guidance and adhesion. Using live imaging of ex-vivo chick neural tube, we showed that the nuclear accumulation of β-catenin and the rise in Tcf-dependent transcription both initiate before the dismantling of the adherens junctions and remain during the axon elongation process. Notably, we demonstrated that β-catenin activity in post-mitotic cells depends on TCF7L2 and is central to spinal commissural axon growth. Together, our results reveal Wnt-independent Tcf/β-catenin regulation of genes that control the growth and guidance of commissural axons in chick spinal cord.
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Affiliation(s)
- Antonio Herrera
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC), Parc Científic de Barcelona, Baldiri Reixac 10-12, Barcelona 08028, Spain
| | - Anghara Menendez
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC), Parc Científic de Barcelona, Baldiri Reixac 10-12, Barcelona 08028, Spain
| | - Andrea Ochoa
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC), Parc Científic de Barcelona, Baldiri Reixac 10-12, Barcelona 08028, Spain
| | - Lídia Bardia
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10, Barcelona 08028, Spain
| | - Julien Colombelli
- Institute for Research in Biomedicine (IRB Barcelona), Barcelona Institute of Science and Technology (BIST), Baldiri Reixac 10, Barcelona 08028, Spain
| | - Sebastian Pons
- Instituto de Biología Molecular de Barcelona (IBMB-CSIC), Parc Científic de Barcelona, Baldiri Reixac 10-12, Barcelona 08028, Spain
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5
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Lv X, Gao F, Cao X. Skeletal interoception in bone homeostasis and pain. Cell Metab 2022; 34:1914-1931. [PMID: 36257317 PMCID: PMC9742337 DOI: 10.1016/j.cmet.2022.09.025] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2022] [Revised: 09/07/2022] [Accepted: 09/26/2022] [Indexed: 01/24/2023]
Abstract
Accumulating evidence indicates that interoception maintains proper physiological status and orchestrates metabolic homeostasis by regulating feeding behaviors, glucose balance, and lipid metabolism. Continuous skeletal remodeling consumes a tremendous amount of energy to provide skeletal scaffolding, support muscle movement, store vital minerals, and maintain a niche for hematopoiesis, which are processes that also contribute to overall metabolic balance. Although skeletal innervation has been described for centuries, recent work has shown that skeletal metabolism is tightly regulated by the nervous system and that skeletal interoception regulates bone homeostasis. Here, we provide a general discussion of interoception and its effects on the skeleton and whole-body metabolism. We also discuss skeletal interoception-mediated regulation in the context of pathological conditions and skeletal pain as well as future challenges to our understanding of these process and how they can be leveraged for more effective therapy.
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Affiliation(s)
- Xiao Lv
- Center for Musculoskeletal Research, Department of Orthopaedic Surgery and Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21205, USA
| | - Feng Gao
- Center for Musculoskeletal Research, Department of Orthopaedic Surgery and Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21205, USA
| | - Xu Cao
- Center for Musculoskeletal Research, Department of Orthopaedic Surgery and Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD 21205, USA.
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6
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Rastegar-Pouyani S, Kennedy TE, Kania A. Somatotopy of Mouse Spinothalamic Innervation and the Localization of a Noxious Stimulus Requires Deleted in Colorectal Carcinoma Expression by Phox2a Neurons. J Neurosci 2022; 42:7885-7899. [PMID: 36028316 PMCID: PMC9617615 DOI: 10.1523/jneurosci.1164-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 08/07/2022] [Accepted: 08/09/2022] [Indexed: 11/21/2022] Open
Abstract
Anterolateral system (AS) neurons transmit pain signals from the spinal cord to the brain. Their morphology, anatomy, and physiological properties have been extensively characterized and suggest that specific AS neurons and their brain targets are concerned with the discriminatory aspects of noxious stimuli, such as their location or intensity, and their motivational/emotive dimension. Among the recently unraveled molecular markers of AS neurons is the developmentally expressed transcription factor Phox2a, providing us with the opportunity to selectively disrupt the embryonic wiring of AS neurons to gain insights into the logic of their adult function. As mice with a spinal-cord-specific loss of the netrin-1 receptor deleted in colorectal carcinoma (DCC) have increased AS neuron innervation of ipsilateral brain targets and defective noxious stimulus localization or topognosis, we generated mice of either sex carrying a deletion of Dcc in Phox2a neurons. Such DccPhox2a mice displayed impaired topognosis along the rostrocaudal axis but with little effect on left-right discrimination and normal aversive responses. Anatomical tracing experiments in DccPhox2a mice revealed defective targeting of cervical and lumbar AS axons within the thalamus. Furthermore, genetic labeling of AS axons revealed their expression of DCC on their arrival in the brain, at a time when many of their target neurons are being born and express Ntn1 Our experiments suggest a postcommissural crossing function for netrin-1:DCC signaling during the formation of somatotopically ordered maps and are consistent with a discriminatory function of some of the Phox2a AS neurons.SIGNIFICANCE STATEMENT How nociceptive (pain) signals are relayed from the body to the brain remains an important question relevant to our understanding of the basic physiology of pain perception. Previous studies have demonstrated that the AS is a main effector of this function. It is composed of AS neurons located in the spinal cord that receive signals from nociceptive sensory neurons that detect noxious stimuli. In this study, we generate a genetic miswiring of mouse AS neurons that results in a decreased ability to perceive the location of a painful stimulus. The precise nature of this defect sheds light on the function of different kinds of AS neurons and how pain information may be organized.
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Affiliation(s)
- Shima Rastegar-Pouyani
- Institut de Recherches Cliniques de Montréal, Montréal Québec H2W 1R7, Canada
- Integrated Program in Neuroscience, McGill University, Montréal Québec H3A 2B4, Canada
| | - Timothy E Kennedy
- Integrated Program in Neuroscience, McGill University, Montréal Québec H3A 2B4, Canada
- Department of Neurology & Neurosurgery, Montreal Neurological Institute, McGill University, Montréal Quebéc H3A 2B4, Canada
| | - Artur Kania
- Institut de Recherches Cliniques de Montréal, Montréal Québec H2W 1R7, Canada
- Integrated Program in Neuroscience, McGill University, Montréal Québec H3A 2B4, Canada
- Division of Experimental Medicine, McGill University, Montréal Québec H3A 2B2, Canada
- Department of Anatomy and Cell Biology, McGill University, Montréal QC H3A 0C7, Canada
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7
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Wang J, Duan G, Zhan T, Dong Z, Zhang Y, Chen Y, Sun H, Xu S. Upregulation of Netrin-1 in the hippocampus mediates the formation of visceral hypersensitivity induced by maternal separation. Front Mol Neurosci 2022; 15:908911. [PMID: 35966013 PMCID: PMC9366914 DOI: 10.3389/fnmol.2022.908911] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 06/24/2022] [Indexed: 11/13/2022] Open
Abstract
Early adverse life events (EALs), such as maternal separation (MS), can cause visceral hypersensitivity, which is thought to be a key pathophysiological mechanism of irritable bowel syndrome (IBS). Previous studies mainly focused on EALs-induced visceral hypersensitivity in adulthood but did not consider that it may have occurred in the preadult period. We previously found that rats who experienced MS suffered from visceral hypersensitivity starting from the post-weaning period. Moreover, the hippocampus is considered to be critical in regulating the formation of visceral hypersensitivity induced by MS. But the underlying mechanisms throughout different life periods are unclear. In this study, behavioral tests, RNA-seq, lentiviral interference, and molecular biology techniques were applied to investigate the molecular mechanism in the hippocampus underlying MS-induced long-lasting visceral hypersensitivity. It was found that both visceral sensitivity and anxiety-like behaviors were significantly increased in MS rats in post-weaning, prepubertal, and adult periods, especially in the prepubertal period. Subsequently, RNA-seq targeting the hippocampus identified that the expression level of Netrin-1 was significantly increased in all periods, which was further confirmed by quantitative real-time PCR and Western blot. Knocking-down hippocampal Netrin-1 in the post-weaning period by lentivirus interference alleviated visceral hypersensitivity and anxiety-like behaviors of MS rats in the later phase of life. In addition, deleted in colorectal cancer (DCC), instead of neogenin-1(Neo-1) or uncoordinated (UNC5), was proved to be the specific functional receptor of Netrin-1 in regulating visceral hypersensitivity, whose upregulation may result in the most severe symptoms in the prepubertal period. Furthermore, the activation of the Netrin-1/DCC pathway could enhance long-term potentiation (LTP) in the hippocampus, probably via recruitment of the AMPA receptor subunit GluA1, which finally resulted in the formation of visceral hypersensitivity. These novel findings suggest that long-lasting over-expression of Netrin-1 can mediate visceral hypersensitivity and anxiety disorder from the post-weaning period to adulthood by activating DCC/GluA1 pathway in the hippocampus. Moreover, early intervention of Netrin-1 in the post-weaning period could lead to significant symptom relief afterward, which provides evidence that the Netrin-1/DCC/GluA1 signaling pathway may be a potential therapeutic target for the treatment of visceral hypersensitivity in clinics.
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8
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Tsytsarev V, Kwon SE, Plachez C, Zhao S, O'Connor DH, Erzurumlu RS. Layers 3 and 4 Neurons of the Bilateral Whisker-Barrel Cortex. Neuroscience 2022; 494:140-151. [PMID: 35598701 PMCID: PMC9884091 DOI: 10.1016/j.neuroscience.2022.05.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 05/11/2022] [Accepted: 05/13/2022] [Indexed: 01/31/2023]
Abstract
In Robo3R3-5cKO mouse brain, rhombomere 3-derived trigeminal principal nucleus (PrV) neurons project bilaterally to the somatosensory thalamus. As a consequence, whisker-specific neural modules (barreloids and barrels) representing whiskers on both sides of the face develop in the sensory thalamus and the primary somatosensory cortex. We examined the morphological complexity of layer 4 barrel cells, their postsynaptic partners in layer 3, and functional specificity of layer 3 pyramidal cells. Layer 4 spiny stellate cells form much smaller barrels and their dendritic fields are more focalized and less complex compared to controls, while layer 3 pyramidal cells did not show notable differences. Using in vivo 2-photon imaging of a genetically encoded fluorescent [Ca2+] sensor, we visualized neural activity in the normal and Robo3R3-5cKO barrel cortex in response to ipsi- and contralateral single whisker stimulation. Layer 3 neurons in control animals responded only to their contralateral whiskers, while in the mutant cortex layer 3 pyramidal neurons showed both ipsi- and contralateral whisker responses. These results indicate that bilateral whisker map inputs stimulate different but neighboring groups of layer 3 neurons which normally relay contralateral whisker-specific information to other cortical areas.
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Affiliation(s)
- Vassiliy Tsytsarev
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore 20 Penn St, HSF-2, 21201 MD, Baltimore, United States.
| | - Sung E Kwon
- Department of Neuroscience, John Hopkins School of Medicine, 855 N. Wolfe Street, Rangos 295, Baltimore, MD 21205, United States.
| | - Celine Plachez
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore 20 Penn St, HSF-2, 21201 MD, Baltimore, United States.
| | - Shuxin Zhao
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore 20 Penn St, HSF-2, 21201 MD, Baltimore, United States.
| | - Daniel H O'Connor
- Department of Neuroscience and Krieger Mind/Brain Institute Johns Hopkins University, 3400 N Charles St, 338 Krieger Hall, Baltimore, MD 21218, United States.
| | - Reha S Erzurumlu
- Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore 20 Penn St, HSF-2, 21201 MD, Baltimore, United States.
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9
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Heterozygous Dcc Mutant Mice Have a Subtle Locomotor Phenotype. eNeuro 2022; 9:ENEURO.0216-18.2021. [PMID: 35115383 PMCID: PMC8906791 DOI: 10.1523/eneuro.0216-18.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 12/18/2021] [Accepted: 12/20/2021] [Indexed: 11/30/2022] Open
Abstract
Axon guidance receptors such as deleted in colorectal cancer (DCC) contribute to the normal formation of neural circuits, and their mutations can be associated with neural defects. In humans, heterozygous mutations in DCC have been linked to congenital mirror movements, which are involuntary movements on one side of the body that mirror voluntary movements of the opposite side. In mice, obvious hopping phenotypes have been reported for bi-allelic Dcc mutations, while heterozygous mutants have not been closely examined. We hypothesized that a detailed characterization of Dcc heterozygous mice may reveal impaired corticospinal and spinal functions. Anterograde tracing of the Dcc+/− motor cortex revealed a normally projecting corticospinal tract, intracortical microstimulation (ICMS) evoked normal contralateral motor responses, and behavioral tests showed normal skilled forelimb coordination. Gait analyses also showed a normal locomotor pattern and rhythm in adult Dcc+/− mice during treadmill locomotion, except for a decreased occurrence of out-of-phase walk and an increased duty cycle of the stance phase at slow walking speed. Neonatal isolated Dcc+/− spinal cords had normal left-right and flexor-extensor coupling, along with normal locomotor pattern and rhythm, except for an increase in the flexor-related motoneuronal output. Although Dcc+/− mice do not exhibit any obvious bilateral impairments like those in humans, they exhibit subtle motor deficits during neonatal and adult locomotion.
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10
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Khoury S, Parisien M, Thompson SJ, Vachon-Presseau E, Roy M, Martinsen AE, Winsvold BS, Mundal IP, Zwart JA, Kania A, Mogil JS, Diatchenko L. Genome-wide analysis identifies impaired axonogenesis in chronic overlapping pain conditions. Brain 2021; 145:1111-1123. [PMID: 34788396 DOI: 10.1093/brain/awab359] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 07/08/2021] [Accepted: 08/20/2021] [Indexed: 11/12/2022] Open
Abstract
Chronic pain is often present at more than one anatomical location, leading to chronic overlapping pain conditions (COPC). Whether COPC represents a distinct pathophysiology from the occurrence of pain at only one site is unknown. Using genome-wide approaches, we compared genetic determinants of chronic single-site vs. multisite pain in the UK Biobank. We found that different genetic signals underlie chronic single-site and multisite pain with much stronger genetic contributions for the latter. Among 23 loci associated with multisite pain, 9 loci replicated in the HUNT cohort, with the DCC netrin-1 receptor (DCC) as the top gene. Functional genomics identified axonogenesis in brain tissues as the major contributing pathway to chronic multisite pain. Finally, multimodal structural brain imaging analysis showed that DCC is most strongly expressed in subcortical limbic regions and is associated with alterations in the uncinate fasciculus microstructure, suggesting that DCC-dependent axonogenesis may contribute to COPC via cortico-limbic circuits.
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Affiliation(s)
- Samar Khoury
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Anesthesia, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Marc Parisien
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Anesthesia, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Scott J Thompson
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Department of Anesthesiology, University of Minnesota, Minneapolis, MN, USA
| | - Etienne Vachon-Presseau
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Anesthesia, Faculty of Medicine, McGill University, Montreal, QC, Canada
| | - Mathieu Roy
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Department of Psychology, McGill University, Montreal, QC, Canada
| | - Amy E Martinsen
- K. G. Jebsen Center for Genetic Epidemiology, Department of Public Health and Nursing, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway.,Department of Research, Innovation and Education, Division of Clinical Neuroscience, Oslo University Hospital, Oslo, Norway.,Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway
| | - Bendik S Winsvold
- K. G. Jebsen Center for Genetic Epidemiology, Department of Public Health and Nursing, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway.,Department of Research, Innovation and Education, Division of Clinical Neuroscience, Oslo University Hospital, Oslo, Norway.,Department of Neurology, Oslo University Hospital, Oslo, Norway
| | | | - Ingunn P Mundal
- Department of Health Science, Molde University College, Molde, Norway
| | - John-Anker Zwart
- K. G. Jebsen Center for Genetic Epidemiology, Department of Public Health and Nursing, Faculty of Medicine and Health Sciences, Norwegian University of Science and Technology, Trondheim, Norway.,Department of Research, Innovation and Education, Division of Clinical Neuroscience, Oslo University Hospital, Oslo, Norway.,Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway
| | - Artur Kania
- Institut de recherches cliniques de Montreal (IRCM), Montreal, QC, Canada.,Department of Cell Biology and Anatomy, and Experimental Medicine, McGill University, Montreal, QC, Canada
| | - Jeffrey S Mogil
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Department of Psychology, McGill University, Montreal, QC, Canada
| | - Luda Diatchenko
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC, Canada.,Faculty of Dentistry, McGill University, Montreal, QC, Canada.,Department of Anesthesia, Faculty of Medicine, McGill University, Montreal, QC, Canada
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11
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Chisholm KI, Lo Re L, Polgár E, Gutierrez-Mecinas M, Todd AJ, McMahon SB. Encoding of cutaneous stimuli by lamina I projection neurons. Pain 2021; 162:2405-2417. [PMID: 33769365 PMCID: PMC8374708 DOI: 10.1097/j.pain.0000000000002226] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 12/11/2020] [Accepted: 01/04/2021] [Indexed: 11/26/2022]
Abstract
ABSTRACT Lamina I of the dorsal horn, together with its main output pathway, lamina I projection neurons, has long been implicated in the processing of nociceptive stimuli, as well as the development of chronic pain conditions. However, the study of lamina I projection neurons is hampered by technical challenges, including the low throughput and selection biases of traditional electrophysiological techniques. Here we report on a technique that uses anatomical labelling strategies and in vivo imaging to simultaneously study a network of lamina I projection neurons in response to electrical and natural stimuli. Although we were able to confirm the nociceptive involvement of this group of cells, we also describe an unexpected preference for innocuous cooling stimuli. We were able to characterize the thermal responsiveness of these cells in detail and found cooling responses decline when exposed to stable cold temperatures maintained for more than a few seconds, as well as to encode the intensity of the end temperature, while heating responses showed an unexpected reliance on adaptation temperatures.
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Affiliation(s)
- Kim I. Chisholm
- Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom
| | - Laure Lo Re
- Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom
| | - Erika Polgár
- Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Maria Gutierrez-Mecinas
- Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Andrew J. Todd
- Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Stephen B. McMahon
- Neurorestoration Group, Wolfson Centre for Age-Related Diseases, King's College London, London, United Kingdom
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Netrin1 and reelin signaling are required for the migration of anterolateral system neurons in the embryonic spinal cord. Pain 2021; 163:e527-e539. [PMID: 34471084 DOI: 10.1097/j.pain.0000000000002444] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/04/2021] [Indexed: 11/26/2022]
Abstract
ABSTRACT Projection neurons of the spinal cord dorsal horn which transmit pain, itch, and temperature information to the brain comprise the anterolateral system (AS). A recent molecular and genetic study showed that many developing AS neurons express the transcription factor Phox2a and provided insights into the mechanisms of their ontogeny and wiring of nociceptive neuronal circuits. Here, we show that the loss of the axonal guidance and neuronal migration signal netrin1 results in impaired migration of mouse Phox2a+ AS neurons into the spinal lamina I. Furthermore, we show that in the absence of Dab1, an intracellular transducer of the neuronal migration signal reelin, the migration of spinal lamina V and lateral spinal nucleus Phox2a+ AS neurons is impaired, in line with deficits in nociception seen in mice with a loss of reelin signaling. Together, these results provide evidence that netrin1 and reelin control the development of spinal nociceptive projection neurons, suggesting a mechanistic explanation for studies that link sequence variations in human genes encoding these neurodevelopmental signals and abnormal pain sensation.
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Sensational developments in somatosensory development? Curr Opin Neurobiol 2021; 66:212-223. [PMID: 33454646 DOI: 10.1016/j.conb.2020.12.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 12/10/2020] [Accepted: 12/12/2020] [Indexed: 12/25/2022]
Abstract
This is an overview of the most recent advances pertaining to the development of the cardinal components of the somatosensory system: the peripheral sensory neurons that perceive somatosensory stimuli, the first line central nervous system circuits that modulate them, and the higher structures such as the somatosensory cortex that eventually compute a motor response to them. Here, I also review the most recent findings concerning the role of neuronal activity in somatosensory development, formation of somatotopic maps, insights into human somatosensory development and the link between aberrant somatosensation and neurodevelopmental disorders.
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Bourojeni FB, Zeilhofer HU, Kania A. Netrin-1 receptor DCC is required for the contralateral topography of lamina I anterolateral system neurons. Pain 2021; 162:161-175. [PMID: 32701653 PMCID: PMC7737868 DOI: 10.1097/j.pain.0000000000002012] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 07/08/2020] [Accepted: 07/13/2020] [Indexed: 12/30/2022]
Abstract
Anterolateral system (AS) neurons relay nociceptive information from the spinal cord to the brain, protecting the body from harm by evoking a variety of behaviours and autonomic responses. The developmental programs that guide the connectivity of AS neurons remain poorly understood. Spinofugal axons cross the spinal midline in response to Netrin-1 signalling through its receptor deleted in colorectal carcinoma (DCC); however, the relevance of this canonical pathway to AS neuron development has only been demonstrated recently. Here, we disrupted Netrin-1:DCC signalling developmentally in AS neurons and assessed the consequences on the path finding of the different classes of spinofugal neurons. Many lamina I AS neurons normally innervate the lateral parabrachial nucleus and periaqueductal gray on the contralateral side. The loss of DCC in the developing spinal cord resulted in increased frequency of ipsilateral projection of spinoparabrachial and spinoperiaqueductal gray neurons. Given that contralateral spinofugal projections are largely associated with somatotopic representation of the body, changes in the laterality of AS spinofugal projections may contribute to reduced precision in pain localization observed in mice and humans carrying Dcc mutations.
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Affiliation(s)
- Farin B. Bourojeni
- Research Unit in Neural Circuit Development, Institut de Recherches Cliniques de Montréal (IRCM), Montréal, QC, Canada
- Integrated Program in Neuroscience, McGill University, Montréal, QC, Canada
| | - Hanns Ulrich Zeilhofer
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
- Institute of Pharmaceutical Sciences, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland
| | - Artur Kania
- Research Unit in Neural Circuit Development, Institut de Recherches Cliniques de Montréal (IRCM), Montréal, QC, Canada
- Integrated Program in Neuroscience, McGill University, Montréal, QC, Canada
- Division of Experimental Medicine, Department of Anatomy and Cell Biology, McGill University, Montréal, QC, Canada
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Thams S, Islam M, Lindefeldt M, Nordgren A, Granberg T, Tesi B, Barbany G, Nilsson D, Paucar M. Heterozygous variants in DCC: Beyond congenital mirror movements. NEUROLOGY-GENETICS 2020; 6:e526. [PMID: 33209984 PMCID: PMC7670573 DOI: 10.1212/nxg.0000000000000526] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 08/31/2020] [Indexed: 11/18/2022]
Abstract
Objective To perform a comprehensive characterization of a cohort of patients with congenital mirror movements (CMMs) in Sweden. Methods Clinical examination with the Woods and Teuber scale for mirror movements (MMs), neuroimaging, navigated transcranial magnetic stimulation (nTMS), and massive parallel sequencing (MPS) were applied. Results The cohort is ethnically diverse and includes a total of 7 patients distributed in 2 families and 2 sporadic cases. The degree of MMs was variable in this cohort. MPS revealed 2 novel heterozygous frameshift variants in DCC netrin 1 receptor (DCC). Two siblings harboring the pathogenic variant in c.1466_1476del display a complex syndrome featuring MMs and in 1 case receptive-expressive language disorder, chorea, epilepsy, and agenesis of the corpus callosum. The second DCC variant, c.1729delG, was associated with a typical benign CMM phenotype. No variants in DCC, NTN1, RAD51, or DNAL4 were found for the 2 sporadic CMM cases. However, one of these sporadic cases had concomitant high-risk myelodysplastic syndrome and a homozygous variant in ERCC excision repair like 2 (ERCC6L2). Reorganized corticospinal projection patterns to upper extremities were demonstrated with nTMS. Conclusions The presence of chorea expands the clinical spectrum of syndromes associated with variants in DCC. Biallelic pathogenic variants in ERCC6L2 cause bone marrow failure, but a potential association with CMM remains to be studied in larger cohorts.
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Affiliation(s)
- Sebastian Thams
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Mominul Islam
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Marie Lindefeldt
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Ann Nordgren
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Tobias Granberg
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Bianca Tesi
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Gisela Barbany
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Daniel Nilsson
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
| | - Martin Paucar
- Department of Clinical Neuroscience (S.T., T.G., M.P.), Karolinska Institutet; Department of Neurology (S.T., M.P.), Karolinska University Hospital; Department of Neurophysiology (M.I.), Karolinska University Hospital; Department of Pediatric Neurology (M.L.), Astrid Lindgren's Hospital; Department of Clinical Genetics (A.N., B.T., G.B.), Karolinska University Hospital; Department of Molecular Medicine and Surgery (A.N., B.T., G.B., D.N.), Karolinska Institutet; and Department of Neuroradiology (T.G.), Karolinska University Hospital, Stockholm, Sweden
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Abstract
The spinal cord receives, relays and processes sensory information from the periphery and integrates this information with descending inputs from supraspinal centres to elicit precise and appropriate behavioural responses and orchestrate body movements. Understanding how the spinal cord circuits that achieve this integration are wired during development is the focus of much research interest. Several families of proteins have well-established roles in guiding developing spinal cord axons, and recent findings have identified new axon guidance molecules. Nevertheless, an integrated view of spinal cord network development is lacking, and many current models have neglected the cellular and functional diversity of spinal cord circuits. Recent advances challenge the existing spinal cord axon guidance dogmas and have provided a more complex, but more faithful, picture of the ontogenesis of vertebrate spinal cord circuits.
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Vigouroux RJ, Cesar Q, Chédotal A, Nguyen-Ba-Charvet KT. Revisiting the role of Dcc in visual system development with a novel eye clearing method. eLife 2020; 9:51275. [PMID: 32096760 PMCID: PMC7062470 DOI: 10.7554/elife.51275] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2019] [Accepted: 02/24/2020] [Indexed: 12/22/2022] Open
Abstract
The Deleted in Colorectal Carcinoma (Dcc) receptor plays a critical role in optic nerve development. Whilst Dcc is expressed postnatally in the eye, its function remains unknown as Dcc knockouts die at birth. To circumvent this drawback, we generated an eye-specific Dcc mutant. To study the organization of the retina and visual projections in these mice, we also established EyeDISCO, a novel tissue clearing protocol that removes melanin allowing 3D imaging of whole eyes and visual pathways. We show that in the absence of Dcc, some ganglion cell axons stalled at the optic disc, whereas others perforated the retina, separating photoreceptors from the retinal pigment epithelium. A subset of visual axons entered the CNS, but these projections are perturbed. Moreover, Dcc-deficient retinas displayed a massive postnatal loss of retinal ganglion cells and a large fraction of photoreceptors. Thus, Dcc is essential for the development and maintenance of the retina.
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Affiliation(s)
- Robin J Vigouroux
- Institut de la Vision, Sorbonne Université, INSERM, CNRS, Paris, France
| | - Quénol Cesar
- Institut de la Vision, Sorbonne Université, INSERM, CNRS, Paris, France
| | - Alain Chédotal
- Institut de la Vision, Sorbonne Université, INSERM, CNRS, Paris, France
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Moon PD, Han NR, Kim HM, Jeong HJ. High-Fat Diet Exacerbates Dermatitis through Up-Regulation of TSLP. J Invest Dermatol 2019; 139:1198-1201. [DOI: 10.1016/j.jid.2018.11.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2017] [Revised: 10/25/2018] [Accepted: 11/06/2018] [Indexed: 10/27/2022]
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Abstract
Substance P (SP) is a highly conserved member of the tachykinin peptide family that is widely expressed throughout the animal kingdom. The numerous members of the tachykinin peptide family are involved in a multitude of neuronal signaling pathways, mediating sensations and emotional responses (Steinhoff et al. in Physiol Rev 94:265–301, 2014). In contrast to receptors for classical transmitters, such as glutamate (Parsons et al. in Handb Exp Pharmacol 249–303, 2005), only a minority of neurons in certain brain areas express neurokinin receptors (NKRs) (Mantyh in J Clin Psychiatry 63:6–10, 2002). SP is also expressed by a variety of non-neuronal cell types such as microglia, as well as immune cells (Mashaghi et al. in Cell Mol Life Sci 73:4249–4264, 2016). SP is an 11-amino acid neuropeptide that preferentially activates the neurokinin-1 receptor (NK1R). It transmits nociceptive signals via primary afferent fibers to spinal and brainstem second-order neurons (Cao et al. in Nature 392:390–394, 1998). Compounds that inhibit SP’s action are being investigated as potential drugs to relieve pain. More recently, SP and NKR have gained attention for their role in complex psychiatric processes. It is a key goal in the field of pain research to understand mechanisms involved in the transition between acute pain and chronic pain. The influence of emotional and cognitive inputs and feedbacks from different brain areas makes pain not only a perception but an experience (Zieglgänsberger et al. in CNS Spectr 10:298–308, 2005; Trenkwaldner et al. Sleep Med 31:78–85, 2017). This review focuses on functional neuronal plasticity in spinal dorsal horn neurons as a major relay for nociceptive information.
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Iwasato T, Erzurumlu RS. Development of tactile sensory circuits in the CNS. Curr Opin Neurobiol 2018; 53:66-75. [PMID: 29908482 DOI: 10.1016/j.conb.2018.06.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/30/2018] [Accepted: 06/01/2018] [Indexed: 12/13/2022]
Abstract
Molecular identification of neuronal types and genetic and imaging approaches to characterize their properties reveal morphological, physiological and dynamic aspects of sensory circuit development. Here we focus on the mouse tactile sensory circuitry, with particular emphasis on the main trigeminal pathway that connects the whiskers, the major tactile organ in rodents, to the neocortex. At each level of this pathway, neurogenesis, axonal elongation, pathfinding, target recognition and circuit reorganization including dendritic refinement of cortical layer 4 neurons occur contemporaneously and a multitude of molecular signals are used in differing combinations. We highlight recent advances in development of tactile circuitry and note gaps in our understanding.
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Affiliation(s)
- Takuji Iwasato
- National Institute of Genetics, Mishima, Japan; Department of Genetics, SOKENDAI, Mishima, Japan
| | - Reha S Erzurumlu
- Department of Anatomy and Neurobiology, School of Medicine, University of Maryland, Baltimore, MD, USA.
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