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Modulatory effects of [Met5]-enkephalin on interleukin-1 beta secretion from microglia in mixed brain cell cultures
K P Das1, M K McMillian, G Bing
1Section of Neuropharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
Abstract:
In the present study, functional interactions between [Met5]-enkephalin (ME), naloxone and lipopolysaccharide (LPS) on interleukin-1 beta (IL-1 beta) immunostaining and secretion have been assessed in mixed brain cell cultures from embryonic day 17 mice. Adding ME alone or together with LPS to the culture increased the release of IL-1 beta after 48 h in a concentration-dependent fashion. In situ hybridization studies showed that LPS, but not ME, increased the abundance of IL-1 beta mRNA. The enhanced release of IL-1 beta caused by ME or LPS was partially blocked by naloxone. LPS induced concentration-dependent morphological changes in microglia in mixed brain cell cultures, identified by a monoclonal antibody F4/80 which is specific for macrophages/microglia. Despite increasing IL-1 beta release into the media, ME (10(-8) M) did not induce morphological changes in microglia. Naloxone alone also had no effect on glial morphology; however, the LPS-induced morphological changes were blocked by naloxone. Our data indicate that both exogenous and endogenous opioids regulate IL-1 beta production by microglial cells in the mixed brain cell cultures.
Insights
Opioids like [Met5]-enkephalin (ME) and naloxone, along with lipopolysaccharide (LPS), influence interleukin-1 beta (IL-1 beta) in brain cells. Opioids and LPS increase IL-1 beta release, with naloxone partially blocking these effects.
Area of Science:
- Neuroscience
- Immunology
- Pharmacology
Background:
- Interleukin-1 beta (IL-1 beta) is a key inflammatory cytokine in the central nervous system.
- Opioid peptides and their antagonists play roles in neuroinflammation.
- Microglia are the primary immune cells in the brain and are implicated in inflammatory responses.
Purpose of the Study:
- To investigate the functional interactions between [Met5]-enkephalin (ME), naloxone, and lipopolysaccharide (LPS) on IL-1 beta production and microglial activation.
- To determine the effects of ME and LPS on IL-1 beta secretion and mRNA expression.
- To examine the impact of these substances on microglial morphology.
Main Methods:
- Mixed brain cell cultures from embryonic day 17 mice were used.
- Cells were treated with varying concentrations of ME, LPS, and naloxone.
- IL-1 beta levels were assessed via immunostaining and secretion assays.
- IL-1 beta mRNA abundance was measured using in situ hybridization.
- Microglial morphology was analyzed using F4/80 antibody staining.
Main Results:
- Both ME and LPS increased IL-1 beta release in a concentration-dependent manner.
- LPS, but not ME, significantly increased IL-1 beta mRNA levels.
- Naloxone partially inhibited the enhanced IL-1 beta release induced by ME and LPS.
- LPS induced concentration-dependent morphological changes in microglia, which were blocked by naloxone.
- ME did not induce microglial morphological changes, despite increasing IL-1 beta release.
Conclusions:
- Exogenous and endogenous opioids modulate IL-1 beta production by microglial cells.
- Naloxone acts as an antagonist, partially reversing the effects of ME and LPS on IL-1 beta release and microglial activation.
- Opioid signaling pathways are involved in the regulation of neuroinflammation mediated by microglia.