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Updated: Aug 26, 2025
Identifying Microglia and Peripheral Infiltrating Macrophages in the Injured Spinal Cords Using Flow Cytometry
Published on: June 24, 2025
Morphine-induced changes in the function of microglia and macrophages after acute spinal cord injury
Mabel N Terminel1, Carla Bassil2, Josephina Rau2
1Department of Neuroscience and Experimental Therapeutics, Texas A&M Health Science Center, 8447 Riverside Parkway 47, Bryan, TX, 77807, USA. mabelt19@tamu.edu.
Background:
Opioids are among the most effective and commonly prescribed analgesics for the treatment of acute pain after spinal cord injury (SCI). However, morphine administration in the early phase of SCI undermines locomotor recovery, increases cell death, and decreases overall health in a rodent contusion model. Based on our previous studies we hypothesize that morphine acts on classic opioid receptors to alter the immune response. Indeed, we found that a single dose of intrathecal morphine increases the expression of activated microglia and macrophages at the injury site. Whether similar effects of morphine would be seen with repeated intravenous administration, more closely simulating clinical treatment, is not known.
Methods:
To address this, we used flow cytometry to examine changes in the temporal expression of microglia and macrophages after SCI and intravenous morphine. Next, we explored whether morphine changed the function of these cells through the engagement of cell-signaling pathways linked to neurotoxicity using Western blot analysis.
Results:
Our flow cytometry studies showed that 3 consecutive days of morphine administration after an SCI significantly increased the number of microglia and macrophages around the lesion. Using Western blot analysis, we also found that repeated administration of morphine increases β-arrestin, ERK-1 and dynorphin (an endogenous kappa opioid receptor agonist) production by microglia and macrophages.
Conclusions:
These results suggest that morphine administered immediately after an SCI changes the innate immune response by increasing the number of immune cells and altering neuropeptide synthesis by these cells.
Insights
Morphine given after spinal cord injury (SCI) increases immune cells like microglia and macrophages. This impacts the innate immune response and neuropeptide synthesis, potentially affecting recovery.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Opioids, like morphine, are common painkillers after spinal cord injury (SCI).
- Early morphine administration in SCI models impairs recovery and increases cell death.
- Previous studies suggest morphine alters the immune response via opioid receptors.
Purpose of the Study:
- To investigate the effects of repeated intravenous morphine on immune cells after SCI.
- To determine if morphine alters microglia and macrophage function and signaling pathways.
Main Methods:
- Flow cytometry was used to analyze microglia and macrophage populations post-SCI and morphine treatment.
- Western blot analysis examined cell-signaling pathways and neuropeptide production.
Main Results:
- Repeated intravenous morphine significantly increased microglia and macrophage numbers around the SCI lesion.
- Morphine administration elevated β-arrestin, ERK-1, and dynorphin production in these immune cells.
Conclusions:
- Morphine administered early after SCI alters the innate immune response.
- Increased immune cell infiltration and altered neuropeptide synthesis are key effects.
