Paradoxical effect of minocycline on established neuropathic pain in rat
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Date
2017-03-08
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Abstract
Neuropathic pain occurs after peripheral nerve damage, inflammation or infection. In this
situation, microglial cells become activated and play a key role in producing pain. Minocycline
(microglia inhibitor), was reported to reduce pain when used preventively. However, it seems that,
when used after nerve injury, results in its pain reducing effects are different. In this regard,
to assess the pain reducing differences of minocycline, neuropathic pain was induced by the
ligation of the sciatic nerve in the rat which is recognized as chronic constriction injury (CCI)
and minocycline was administered before and after sciatic nerve injury. Wistar male rats (200-250
g, n=6) were used in these experiments. Rats were distributed in various groups: vehicle-treated
CCI (control), sham- operated and minocycline-treated CCI groups. In the first part of the
experiment (pre-injury study), minocycline (10, 20, 30 and 40 mg/kg,) was injected one hour before
surgery and then daily for two weeks. In the second part (post injury study), minocycline was
administered: 1: at day one after nerve damage once a day to day 14, 2: at day seven after surgery
and continued daily until day 14. Analgesimeter for thermal hyperalgesia and von Frey hairs for
mechanical allodynia were used to evaluate pain behavior. Thermal hyperalgesia and mechanical allo-
dynia were attenuated significantly, when minocycline used before surgery, while it was not able to
reduce pain behavior administered after surgery. It seems that, in spite of what some previous
studies have reported, here, minocycline is not able to attenuate established neuropathic pain.
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Keywords
minocycline, neuropathic pain, microglia, allodynia, hyperalgesia, rat