Regular physical activity reduces the percentage of spinally projecting neurons that express mu-opioid receptors from the rostral ventromedial medulla in mice

Kathleen A Sluka; Jessica Danielson; Lynn Rasmussen; Sandra J Kolker

doi:10.1097/PR9.0000000000000857

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Regular physical activity reduces the percentage of spinally projecting neurons that express mu-opioid receptors from the rostral ventromedial medulla in mice

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Regular physical activity reduces the percentage of spinally projecting neurons that express mu-opioid receptors from the rostral ventromedial medulla in mice

Kathleen A Sluka, Jessica Danielson, Lynn Rasmussen and Sandra J Kolker

Pain reports, Vol.5(6), pp.e857-e857

11/2020

DOI: 10.1097/PR9.0000000000000857

PMCID: PMC7717783

PMID: 33294758

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Abstract

Regular physical activity/exercise is an effective nonpharmacological treatment for individuals with chronic pain. Central inhibitory mechanisms, involving serotonin and opioids, are critical to analgesia produced by regular physical activity. The rostral ventromedial medulla (RVM) sends projections to the spinal cord to inhibit or facilitate nociceptive neurons and plays a key role in exercise-induced analgesia. The goal of these studies was to examine if regular physical activity modifies RVM-spinal cord circuitry. Male and female mice received Fluoro-Gold placed on the spinal cord to identify spinally projecting neurons from the RVM and the nucleus raphe obscurus/nucleus raphe pallidus, dermorphin-488 into caudal medulla to identify mu-opioid receptors, and were immunohistochemically stained for either phosphorylated-N-methyl-d-aspartate subunit NR1 (p-NR1) to identify excitatory neurons or tryptophan hydroxylase (TPH) to identify serotonin neurons. The percentage of dermorphin-488-positive cells that stained for p-NR1 (or TPH), and the percentage of dermorphin-488-positive cells that stained for p-NR1 (or TPH) and Fluoro-Gold was calculated. Physically active animals were provided running wheels in their cages for 8 weeks and compared to sedentary animals without running wheels. Animals with chronic muscle pain, induced by 2 intramuscular injections of pH 4.0, were compared to sham controls (pH 7.2). Physically active animals had less mu-opioid-expressing neurons projecting to the spinal cord when compared to sedentary animals in the RVM, but not the nucleus raphe obscurus/nucleus raphe pallidus. No changes were observed for TPH. These data suggest that regular exercise alters central facilitation so that there is less descending facilitation to result in a net increase in inhibition.

Opioid

Muscle

Exercise

Pain

Physical activity

Serotonin

Details

Title: Subtitle: Regular physical activity reduces the percentage of spinally projecting neurons that express mu-opioid receptors from the rostral ventromedial medulla in mice
Creators: Kathleen A Sluka - Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
Jessica Danielson - Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
Lynn Rasmussen - Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
Sandra J Kolker - Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA, USA
Resource Type: Journal article
Publication Details: Pain reports, Vol.5(6), pp.e857-e857
DOI: 10.1097/PR9.0000000000000857
PMID: 33294758
PMCID: PMC7717783
NLM abbreviation: Pain Rep
ISSN: 2471-2531
eISSN: 2471-2531
Publisher: United States
Grant note: R01 AR061371 / NIAMS NIH HHS
Language: English
Date published: 11/2020
Academic Unit: Iowa Neuroscience Institute; Nursing; Anesthesia; Physical Therapy and Rehabilitation Science; Neuroscience and Pharmacology
Record Identifier: 9984071943802771

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