Related Experiment Video
Updated: Aug 14, 2026
The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice
Published on: July 16, 2014
Intrathecal minocycline attenuates peripheral inflammation-induced hyperalgesia by inhibiting p38 MAPK in spinal
Xiao-Ying Hua1, Camilla I Svensson, Tomohiro Matsui
1Department of Anaesthesiology, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0818, USA. xyhua@ucsd.edu
Abstract:
Activation of p38 mitogen-activated protein kinase (p38) in spinal microglia is implicated in spinal nociceptive processing. Minocycline, a tetracycline derivative, displays selective inhibition of microglial activation, a function that is distinct from its antibiotic activity. In the present study we examined antinociceptive effects of intrathecal (IT) administration of minocycline in experimental models of inflammation-evoked hyperalgesia in addition to the effect of minocycline on stimulation-induced activation of p38 in spinal microglia. Intrathecal minocycline produced a dose-dependent reduction of formalin-evoked second-phase flinching behaviour in rats, and prevented thermal hyperalgesia induced by carrageenan injection into the paw. In contrast, systemic delivery (intraperitoneally) of minocycline inhibited the first but not the second phase of formalin-induced flinching, and it had no effect on carrageenan-induced hyperalgesia. Centrally mediated hyperalgesia induced by IT delivery of N-methyl-d-aspartate was completely blocked by IT minocycline. An increase in phosphorylation (activation) of p38 (P-p38) was observed in the dorsal spinal cord after carrageenan paw injection, assessed by both Western blotting and immunohistochemistry. The increased P-p38 immunoreactivity was seen primarily in microglia but also in a small population of neurons. Minocycline, at the IT dose that blocked carrageenan-induced hyperalgesia, also attenuated the increased P-p38 in microglia. In addition, minocycline suppressed lipopolysaccharide-evoked P-p38 in cultured spinal microglial cells. Taken together, these findings show that minocycline given IT produces a potent and consistent antinociception in models of tissue injury and inflammation-evoked pain, and they provide strong support for the idea that this effect is mediated by direct inhibition of spinal microglia and subsequent activation of p38 in these cells.
Insights
Minocycline administered intrathecally effectively reduces pain and inflammation by inhibiting spinal microglia activation and p38 kinase activity. This study highlights minocycline
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- Spinal microglia activation, particularly p38 mitogen-activated protein kinase (p38) signaling, plays a crucial role in processing pain signals.
- Minocycline, a tetracycline derivative, is known to inhibit microglial activation, independent of its antibiotic properties.
Purpose of the Study:
- To investigate the antinociceptive effects of intrathecal (IT) minocycline in experimental models of inflammation-evoked hyperalgesia.
- To determine the impact of minocycline on the activation of p38 in spinal microglia.
Main Methods:
- Intrathecal and intraperitoneal administration of minocycline in rat models of formalin-induced pain and carrageenan-induced hyperalgesia.
- Assessment of N-methyl-d-aspartate (NMDA)-induced central hyperalgesia.
- Western blotting and immunohistochemistry to evaluate p38 activation (P-p38) in spinal cord tissue and cultured microglial cells.
Main Results:
- Intrathecal minocycline dose-dependently reduced formalin-evoked pain and prevented carrageenan-induced thermal hyperalgesia.
- Systemic minocycline showed limited efficacy, affecting only the early phase of formalin pain and not carrageenan hyperalgesia.
- IT minocycline blocked NMDA-induced central hyperalgesia and attenuated carrageenan-induced p38 activation in spinal microglia.
Conclusions:
- Intrathecal minocycline demonstrates potent and consistent antinociception in models of tissue injury and inflammation-evoked pain.
- The antinociceptive effect of IT minocycline is mediated by direct inhibition of spinal microglia and subsequent p38 activation.
- Minocycline's efficacy is dependent on central administration for targeting spinal pain pathways.
