Analgesic tolerance and cross-tolerance to i.c.v. endomorphin-1, endomorphin-2, and morphine in mice
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Acknowledgements
Supported by the University of New Orleans, the Veterans Affairs Administration (Merit Review and MIRECC) and the Louisiana State Board of Regents.
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2023, NeuropeptidesCitation Excerpt :The above findings of differences between the cross-tolerance of EN-9 and morphine suggest that chronic injection of EN-9 may lead to the downstream μ-mediated pathway participating, consistent with previous studies that κ- and μ-opioid receptors interact with each in chronic treatment (Yamada et al., 2006; Li et al., 2010). Additionally, the observation of symmetrical but not complete cross-tolerance between 60 nmol EM2 and 30 nmol morphine in this study was consistent with the findings of previous investigation (Soignier et al., 2004). Furthermore, previous studies demonstrated that co-injection of RF9 with EN-9 produced a stage-wise loss of analgesia and developed significant tolerance after repeated injections, and antinociception recovered after the removal of RF9, implying the important role of the activation of NPFF receptor in reducing the development of tolerance to EN-9 (Wang et al., 2016).
Morphological features of endomorphin-2-immunoreactive ultrastructures in the dorsal root ganglion and spinal dorsal horn of the rat
2022, Journal of Chemical NeuroanatomyCitation Excerpt :These EM2-ir fibers and terminals play important roles in modulating nociceptive information transmission by interacting with projection neurons and interneurons in the superficial laminae of the SDH. EM2 is a better pain killer than morphine due to its powerful analgesic effect and much weaker side effects (Zadina et al., 1997; Przewlocka et al., 1999; Labuz et al., 2003; Soignier et al., 2004; Fichna et al., 2007; Lazarus, Okada, 2012; Wu et al., 2012). As a highly selective and affinity endogenous agonist for the μ-opioid receptor (MOR), EM2 activates MORs in the SDH via two mechanisms.
Pharmacological characterization of EN-9, a novel chimeric peptide of endomorphin-2 and neuropeptide FF that produces potent antinociceptive activity and limited tolerance
2016, NeuropharmacologyCitation Excerpt :Antinocicptive tolerance is one of the major side-effects of opioid analgesics for pain treatment. Our results indicated that repeated administration of EM-2 could induce significant antinociceptive tolerance on day 4, which is consistent with the previous study (Soignier et al., 2004). It is worthy to note that EN-9 had the equivalent analgesic responses over the 6-day course of repeated i.c.v. administration, suggesting no tolerance developed to its central antinociception.
Melatonin attenuates the development of antinociceptive tolerance to delta-, but not to mu-opioid receptor agonist in mice
2007, Behavioural Brain ResearchDevelopment of antinociceptive tolerance and physical dependence following morphine i.c.v. infusion in mice
2005, European Journal of PharmacologyEndogenous opiates and behavior: 2004
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