Pain and Analgesic Mechanisms Section Editors: Martin Angst/Jianren Mao Resveratrol Regulates N-Methyl-D-Aspartate Receptor Expression and Suppresses Neuroinflammation in Morphine-Tolerant Rats Ru-Yin Tsai, PhD,*† Kuang-Yi Chou, PhD,† Ching-Hui Shen, MD, PhD,‡ Chih-Cheng Chien, MD, PhD,* Wei-Yuan Tsai, MS,§ Ya-Ni Huang, PhD, Pao-Luh Tao, PhD,¶ Yaoh-Shiang Lin, MD,# and Chih-Shung Wong, MD, PhD** BACKGROUND: In the present study, we examined the effects and mechanisms of the Chinese herb resveratrol on attenuation of morphine tolerance in rats. METHODS: Male Wistar rats were implanted with 2 intrathecal catheters; one catheter was connected to a mini-osmotic pump, used for either morphine (15 g/h) or saline (1 L/h) infusion for 5 days. On day 5, resveratrol (7.5, 15, 30, or 60 g), dimethyl sulfoxide (5 L), or saline (5 L) was injected via the other catheter immediately after the discontinued morphine infusion. Three hours later, intrathecal morphine (15 g in 5 L saline) was given. All rats received the nociceptive tail-flick test every 30 minutes for 120 minutes after the morphine challenge. RESULTS: Long-term morphine infusion induced antinociceptive tolerance and up-regulated N-methyl-D-aspartate receptor (NMDAR) subunit NR1 and NR2B expression in the synaptosome fraction of the tolerant spinal cord dorsal horn. Resveratrol pretreatment provided a significant antinociceptive effect of morphine in morphine-tolerant rats, and it was associated with reversal of the up-regulated NR1 and NR2B subunits in the synaptosome fraction of morphine-tolerant rat spinal cords. NR1/NR2B-specific antagonist ifenprodil treatment produced a similar effect as that of resveratrol. Furthermore, an increase of postsynaptic density-95/NR1/NR2B complex immunoprecipitation in morphine-tolerant rat spinal cord was also inhibited by resveratrol pretreatment. Moreover, chronic morphine infusion activated glial cells with an increase of proinflammatory cytokine tumor necrosis factor-, interleukin-1, and interleukin-6 mRNA expression in morphine-tolerant rat spinal cords and these effects were suppressed by resveratrol pretreatment before the morphine challenge. CONCLUSIONS: Resveratrol attenuates morphine tolerance by inhibiting neuroinflammation and down-regulating NMDAR NR1 and NR2B subunit expression. Resveratrol regulates the NMDAR expression, which might be involved in a loss of scaffolding postsynaptic density-95 protein. (Anesth Analg 2012;115:944 –52) M orphine is a powerful analgesic for treating mod- erate to severe pain. However, long-term mor- phine administration induces tolerance, which hampers its clinical use. Morphine tolerance is a complex physiological response, which includes opioid receptor uncoupling, 1 and endocytosis/desensitization, 2 increased binding of -arrestin to opioid receptor, 3 glutamatergic receptor activation, 4 and neuroinflammation. 5,6 The glutama- tergic receptor system, especially the N-methyl-d-aspartate receptor (NMDAR), is tetrameric hetero-oligomers consist- ing of the essential NR1 subunit and 1 modulatory NR2A–D and NR3 subunit. Activation of spinal NMDARs has a crucial role in the development of morphine toler- ance 7,8 and neuropathic pain. 9 Pharmacological blockade of NMDARs or disruption of the NR1 subunit gene signifi- cantly attenuates morphine tolerance. 10,11 The postsynaptic density (PSD) protein family, particularly PSD-95, is critical for anchoring NMDAR NR2 subunits in the postsynaptic membrane, which triggers many physiological and patho- logical responses. 12,13 Resveratrol (trans-3,4',5-trihydroxystilbene) is a natural polyphenolic compound found in a large number of plants as components of the human diet, including peanuts, mulberries, grapes, and red wine. Evidence suggests that resveratrol has several beneficial biological effects such as antioxidation, 14 neuroprotection, 15,16 anticancer, antiin- flammation, and cardioprotection. 17 It has no known toxic side effects. 18 Resveratrol suppresses synthesis of proin- flammatory mediators by inhibiting cyclooxygenase and lipoxygenase pathways, which implies that resveratrol may have analgesic activity. 19 –21 Moreover, in a carrageenan- induced inflammatory model, resveratrol reversed thermal Author affiliations are provided at the end of the article. Accepted for publication April 20, 2012. Supported by a grant from the National Science Council (NSC-98-2314-B- 281-002-MT3) and the Cathay General Hospital, Taipei, Taiwan (CGH-MR- 10010). The authors declare no conflicts of interest. Chih-Shung Wong, MD, PhD, is currently affiliated with the Department of Anesthesiology, Cathay General Hospital, Taipei, Taiwan. Reprints will not be available from the authors. Address correspondence to Chih-Shung Wong, MD, PhD, Department of Anesthesiology, Cathy General Hospital, 280, Renai Rd., Section 4, Taipei, Taiwan. Address e-mail to w82556@gmail.com. Copyright © 2012 International Anesthesia Research Society DOI: 10.1213/ANE.0b013e31825da0fb 944 www.anesthesia-analgesia.org October 2012 • Volume 115 • Number 4