Activation of p38 mitogen-activated protein kinase in spinal microglia mediates morphine antinociceptive tolerance.
ABSTRACT Compelling evidence has suggested that spinal glial cells were activated by chronic morphine treatment and involved in the development of morphine tolerance. However, the mechanisms of glial activation were still largely unknown in morphine tolerance. In present study, we investigated the role of p38 mitogen-activated protein kinase (p38 MAPK) in the spinal cord in the development of chronic morphine antinociceptive tolerance. We found that intrathecal administration of morphine (15 microg) daily for 7 consecutive days significantly induced an increase in number of phospho-p38 (p-p38) immunoreactive cells in the spinal cord compared with chronic saline or acute morphine treated rats. Double immunofluorescence staining revealed that p-p38 immunoreactivity was exclusively restricted in the activated spinal microglia, not in astrocytes or neurons. Repeated intrathecal administration of 4-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580) (10 microg or 2 microg), a specific p38 inhibitor, 30 min before each morphine injection for 7 consecutive days significantly attenuated tolerance to morphine analgesia assessed by tail flick test. However, a single intrathecal administration of SB203580 (10 microg) did not antagonize the established tolerance to morphine analgesia. Taken together, these findings suggested that p38 MAPK activation in the spinal microglia was involved in the development of morphine antinociceptive tolerance. Inhibition of p38 MAPK by SB203580 in the spinal cord attenuated but not reversed the tolerance to morphine analgesia. The present study provides the first evidence that p38 activation in spinal microglia played an important role in the development of tolerance to morphine analgesia.
SourceAvailable from: Peter Michael Grace[Show abstract] [Hide abstract]
ABSTRACT: Despite being the mainstay of pain management, opioids are limited in their clinical utility by adverse effects, such as tolerance and paradoxical hyperalgesia. Research of the past 15 years has extended beyond neurons, to implicate central nervous system immune signaling in these adverse effects. This article will provide an overview of these central immune mechanisms in opioid tolerance and paradoxical hyperalgesia, including those mediated by Toll-like receptor 4, purinergic, ceramide, and chemokine signaling. Challenges for the future, as well as new lines of investigation will be highlighted. © 2015 American Headache Society.Headache The Journal of Head and Face Pain 04/2015; DOI:10.1111/head.12552 · 3.19 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: In spite of the potency and efficacy of morphine, its clinical application for chronic persistent pain is limited by the development of tolerance to the antinociceptive effect. The cellular and molecular mechanisms underlying morphine tolerance are complex and still unclear. Recently, the activation of glial cells and the release of glia-derived proinflammatory mediators have been suggested to play a role in the phenomenon. N-Palmitoylethanolamine (PEA) is an endogenous compound with antinociceptive effects able to reduce the glial activation. On this basis, 30 mg kg(-1) PEA was subcutaneously daily administered in morphine treated rats (10 mg kg(-1) intraperitoneally, daily). PEA treatment significantly attenuated the development of tolerance doubling the number of days of morphine antinociceptive efficacy in comparison to the vehicle + morphine group. PEA prevented both microglia and astrocyte cell number increase induced by morphine in the dorsal horn; on the contrary, the morphine-dependent increase of spinal TNF-α levels was not modified by PEA. Nevertheless, the immunohistochemical analysis revealed significantly higher TNF-α immunoreactivity in astrocytes of PEA-protected rats suggesting a PEA-mediated decrease of cytokine release from astrocyte. PEA intervenes in the nervous alterations that lead to the lack of morphine antinociceptive effects; a possible application of this endogenous compound in opioid-based therapies is suggested.01/2015; 2015:894732. DOI:10.1155/2015/894732
[Show abstract] [Hide abstract]
ABSTRACT: Recent studies suggested that statins have anti-inflammatory effects beyond their lipid-lowering properties. Since inflammation in the central nervous system was highly related to morphine tolerance, we sought to investigate whether statins could affect morphine tolerance by mediating glia-derived proinflammatory cytokines secretion. We have undertaken two separate studies: Firstly, we determined the effect of rosuvastatin on naïve rats during induction of morphine tolerance. Secondly, we investigated whether rosuvastation could attenuate the morphine analgesic tolerance in rats that the morphine tolerance established previously. Results demonstrated that peroral rosuvastatin not only delays, but also partially reverses the tolerance to morphine analgesia in rats. The administration of rosuvastatin during induction of morphine tolerance attenuated the activation of ERK and the release of proinflammatory cytokines in the lumbar spinal cord. Similar outcomes were observed in rats were morphine tolerance was established previously. Moreover, our study also found that repeated administration of morphine could activate the astrocytes in the spinal cord while rosuvastation succeeds in suppressing the activation of astrocytes. Our results support the idea that targeting glia-derived proinflammatory effects during morphine treatment is a novel and clinically promising method for enhancing analgesic effects of morphine. We identify a potential new application of statins in the treatment of morphine analgesic tolerance.Inflammation 09/2014; 38(1). DOI:10.1007/s10753-014-0015-y · 1.92 Impact Factor