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Priming of adult incision response by early life injury: neonatal microglial inhibition has persistent but sexually dimorphic effects in adult rats

Moriarty, O; Tu, Y; Sengar, AS; Salter, MW; Beggs, S; Walker, SM; (2019) Priming of adult incision response by early life injury: neonatal microglial inhibition has persistent but sexually dimorphic effects in adult rats. Journal of Neuroscience 10.1523/JNEUROSCI.1786-18.2019. (In press). Green open access

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Abstract

Neonatal hindpaw incision primes developing spinal nociceptive circuitry, resulting in enhanced hyperalgesia following re-injury in adulthood. Spinal microglia contribute to this persistent effect and microglial inhibition at the time of adult re-incision blocks the enhanced hyperalgesia. Here, we pharmacologically inhibited microglial function with systemic minocycline or intrathecal SB203580 at the time of neonatal incision and evaluated sex-dependent differences following adult re-incision. Incision in adult male and female rats induced equivalent hyperalgesia and spinal dorsal horn expression of genes associated with microglial proliferation (Emr1) and transformation to a reactive phenotype (Irf8). In control adults with prior neonatal incision, the enhanced degree and duration of incision-induced hyperalgesia and spinal microglial responses to re-incision were equivalent in males and females. However, microglial inhibition at the time of the neonatal incision revealed sex-dependent effects: the persistent mechanical and thermal hyperalgesia following re-incision in adulthood was prevented in males but unaffected in females. Similarly, re-incision induced Emr1 and Irf8 gene expression was downregulated in males, but not in females following neonatal incision with minocycline. To evaluate the distribution of re-incision hyperalgesia, prior neonatal incision was performed at different body sites. Hyperalgesia was maximal when the same paw was re-incised, and was increased following prior incision at ipsilateral, but not contralateral sites; supporting a segmentally restricted spinal mechanism. These data highlight the contribution of spinal microglial mechanisms to persistent effects of early-life injury in males, and sex-dependent differences in the ability of microglial inhibition to prevent the transition to a persistent pain state spans developmental stages.Significant Statement: Following the same surgery, some patients develop persistent pain. Contributory mechanisms are not fully understood, but early-life experience and sex/gender may influence the transition to chronic pain. Surgery and painful procedural interventions in vulnerable preterm neonates are associated with long-term alterations in somatosensory function and pain that differ in males and females. Surgical injury in neonatal rodents primes the developing nociceptive system and enhances re-injury response in adulthood. Neuroimmune interactions are critical mediators of persistent pain, but sex-dependent differences in spinal neuroglial signaling influence the efficacy of microglial inhibitors following adult injury. Neonatal microglial inhibition has beneficial long-term effects on re-injury response in adult males only, emphasizing the importance of evaluating sex-dependent differences at all ages in pre-clinical studies.

Type: Article
Title: Priming of adult incision response by early life injury: neonatal microglial inhibition has persistent but sexually dimorphic effects in adult rats
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1523/JNEUROSCI.1786-18.2019
Publisher version: https://doi.org/10.1523/JNEUROSCI.1786-18.2019
Language: English
Additional information: This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Pop Health Sciences > UCL GOS Institute of Child Health > ICH Developmental Neurosciences Prog
URI: http://discovery.ucl.ac.uk/id/eprint/10068868
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