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Hedley KE, Cuskelly A, Callister RJ, Horvat JC, Hodgson DM, Tadros MA. The medulla oblongata shows a sex-specific inflammatory response to systemic neonatal lipopolysaccharide. J Neuroimmunol 2024; 389:578316. [PMID: 38394966 DOI: 10.1016/j.jneuroim.2024.578316] [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: 10/19/2023] [Revised: 02/12/2024] [Accepted: 02/14/2024] [Indexed: 02/25/2024]
Abstract
Early life inflammation has been linked to long-term modulation of behavioural outcomes due to the central nervous system, but it is now becoming apparent it is also linked to dysfunction of visceral physiology. The medulla oblongata contains a number of nuclei critical for homeostasis, therefore we utilised the well-established model of neonatal lipopolysaccharide (LPS) exposure to examine the immediate and long-term impacts of systemic inflammation on the medulla oblongata. Wistar rats were injected with LPS or saline on postnatal days 3 and 5, with tissues collected on postnatal days 7 or 90 in order to assess expression of inflammatory mediators and microglial morphology in autonomic regions of the medulla oblongata. We observed a distinct sex-specific response of all measured inflammatory mediators at both ages, as well as significant neonatal sex differences in inflammatory mediators within saline groups. At both ages, microglial morphology had significant changes in branch length and soma size in a sex-specific manner in response to LPS exposure. This data not only highlights the strong sex-specific response of neonates to LPS administration, but also the significant life-long impact on the medulla oblongata and the potential altered control of visceral organs.
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Affiliation(s)
- Kateleen E Hedley
- School of Biomedical Sciences & Pharmacy, University of Newcastle, NSW, Australia; Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
| | - Annalisa Cuskelly
- Hunter Medical Research Institute, New Lambton Heights, NSW, Australia; School of Psychological Sciences, University of Newcastle, NSW, Australia; School of Education, University of Newcastle, NSW, Australia
| | - Robert J Callister
- School of Biomedical Sciences & Pharmacy, University of Newcastle, NSW, Australia; Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
| | - Jay C Horvat
- School of Biomedical Sciences & Pharmacy, University of Newcastle, NSW, Australia; Hunter Medical Research Institute, New Lambton Heights, NSW, Australia
| | - Deborah M Hodgson
- Hunter Medical Research Institute, New Lambton Heights, NSW, Australia; School of Psychological Sciences, University of Newcastle, NSW, Australia
| | - Melissa A Tadros
- School of Biomedical Sciences & Pharmacy, University of Newcastle, NSW, Australia; Hunter Medical Research Institute, New Lambton Heights, NSW, Australia.
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Ca 2+-Permeable AMPA Receptors Contribute to Changed Dorsal Horn Neuronal Firing and Inflammatory Pain. Int J Mol Sci 2023; 24:ijms24032341. [PMID: 36768663 PMCID: PMC9916706 DOI: 10.3390/ijms24032341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 01/20/2023] [Accepted: 01/23/2023] [Indexed: 01/26/2023] Open
Abstract
The dorsal horn (DH) neurons of the spinal cord play a critical role in nociceptive input integration and processing in the central nervous system. Engaged neuronal classes and cell-specific excitability shape nociceptive computation within the DH. The DH hyperexcitability (central sensitisation) has been considered a fundamental mechanism in mediating nociceptive hypersensitivity, with the proven role of Ca2+-permeable AMPA receptors (AMPARs). However, whether and how the DH hyperexcitability relates to changes in action potential (AP) parameters in DH neurons and if Ca2+-permeable AMPARs contribute to these changes remain unknown. We examined the cell-class heterogeneity of APs generated by DH neurons in inflammatory pain conditions to address these. Inflammatory-induced peripheral hypersensitivity increased DH neuronal excitability. We found changes in the AP threshold and amplitude but not kinetics (spike waveform) in DH neurons generating sustained or initial bursts of firing patterns. In contrast, there were no changes in AP parameters in the DH neurons displaying a single spike firing pattern. Genetic knockdown of the molecular mechanism responsible for the upregulation of Ca2+-permeable AMPARs allowed the recovery of cell-specific AP changes in peripheral inflammation. Selective inhibition of Ca2+-permeable AMPARs in the spinal cord alleviated nociceptive hypersensitivity, both thermal and mechanical modalities, in animals with peripheral inflammation. Thus, Ca2+-permeable AMPARs contribute to shaping APs in DH neurons and nociceptive hypersensitivity. This may represent a neuropathological mechanism in the DH circuits, leading to aberrant signal transfer to other nociceptive pathways.
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Early life inflammation is associated with spinal cord excitability and nociceptive sensitivity in human infants. Nat Commun 2022; 13:3943. [PMID: 35803920 PMCID: PMC9270448 DOI: 10.1038/s41467-022-31505-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 06/16/2022] [Indexed: 11/08/2022] Open
Abstract
Immune function and sensitivity to pain are closely related, but the association between early life inflammation and sensory nervous system development is poorly understood-especially in humans. Here, in term-born infants, we measure brain activity and reflex withdrawal activity (using EEG and EMG) and behavioural and physiological activity (using the PIPP-R score) to assess the impact of suspected early-onset neonatal infection on tactile- and noxious-evoked responses. We present evidence that neonatal inflammation (assessed by measuring C-reactive protein levels) is associated with increased spinal cord excitability and evoked brain activity following both tactile and noxious stimulation. There are early indications that this hyperalgesia could be maintained post-inflammation, supporting pre-clinical reports of early-life immune dysfunction influencing pain sensitivity in adults.
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Gomes CI, Barr GA. Local injury and systemic infection in infants alter later nociception and pain affect during early life and adulthood. Brain Behav Immun Health 2021; 9:100175. [PMID: 34589906 PMCID: PMC8474633 DOI: 10.1016/j.bbih.2020.100175] [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: 11/02/2020] [Accepted: 11/06/2020] [Indexed: 10/25/2022] Open
Abstract
Newborns in intensive care are regularly exposed to minor painful procedures at developmental time points when noxious stimulation would be normally absent. Pain from these interventions is inconsistently treated and often exists concurrently with systemic infection, a common comorbidity of prematurity. Our understanding of the independent and combined effects of early painful experiences and infection on pain response is incomplete. The main goals of this research therefore were to understand how pain and infection experienced early in life influence future nociceptive and affective responses to painful stimuli. Rat pups were infected with E-coli on postnatal day 2 (PN2) and had left hind paw injury with carrageenan on PN3. Standard thermal tests for acute pain, formalin tests for inflammatory pain, and conditioned place aversion testing were performed at different ages to assess the nociceptive and affective components of the pain response. Early E-coli infection and early inflammatory injury with carrageenan both independently increased pain scores following hind paw reinjury with formalin on PN8, with effects persisting into adulthood in the carrageenan exposed group. When experienced concurrently, early E-coli infection and carrageenan exposure also increased conditioned aversion to pain in adults. Effect of sex was significant only in formalin testing, with males showing higher pain scores in infancy and females showing higher pain scores as adults. These findings demonstrate that infection experienced early in life can alter both the nociceptive and affective components of the pain response and that there is a cumulative effect of local and systemic pro-inflammatory processes on the aversive component of pain.
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Affiliation(s)
- Carly I Gomes
- Department of Neonatology, Children's Hospital of Philadelphia, Philadelphia, PA, USA
| | - Gordon A Barr
- Department of Anesthesiology and Critical Care Medicine, Children's Hospital of Philadelphia and the Perelman School of Medicine at the University of Pennsylvania, 3615 Civic Center Boulevard, Philadelphia, PA, 19104, USA.,Department of Psychology, University of Pennsylvania, 425 S. University Avenue, Stephen A. Levin Building, Philadelphia, PA, USA
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Karshikoff B, Tadros MA, Mackey S, Zouikr I. Neuroimmune modulation of pain across the developmental spectrum. Curr Opin Behav Sci 2019; 28:85-92. [PMID: 32190717 DOI: 10.1016/j.cobeha.2019.01.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Today's treatment for chronic pain is inadequate, and novel targets need to be identified. This requires a better understanding of the mechanisms involved in pain sensitization and chronification. In this review, we discuss how peripheral inflammation, as occurs during an infection, modulates the central pain system. In rodents, neonatal inflammation leads to increased pain sensitivity in adulthood by priming immune components both peripherally and centrally. The excitability of neurons in the spinal cord is also altered by neonatal inflammation and may add to pain sensitization later in life. In adult humans, inflammation modulates pain sensitivity as well, partly by affecting the activity in brain areas that process and regulate pain signals. Low-grade inflammation is common in clinical populations both peripherally and centrally, and priming of the immune system has also been suggested in some pain populations. The nociceptive and immune systems are primed by infections and inflammation. The early life programming of nociceptive responses following exposure to infections or inflammation will define individual differences in adult pain perception. Immune-to-brain mechanisms and neuroimmune pathway need further investigation as they may serve both as predictors and therapeutic targets in chronic pain.
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Affiliation(s)
- Bianka Karshikoff
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Palo Alto, USA.,Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
| | - Melissa Anne Tadros
- Faculty of Health and Hunter Medical Research Institute, School of Biomedical Sciences and Pharmacy, The University of Newcastle, Callaghan, NSW, Australia
| | - Sean Mackey
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Palo Alto, USA
| | - Ihssane Zouikr
- School of Psychology, The University of Newcastle, Callaghan, NSW, Australia
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