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Halina Machelska, Charité-Universitätsmedizin Berlin
This is an interesting study
This is an interesting study confirming analgesic effects mediated by peripheral kappa opioid receptors (KOR). One of the authors’ findings is that peripherally-restricted KOR agonists attenuate paw incision-induced mechanical, but not heat sensitivity. That peripherally-acting opioids are particularly effective against mechanical pain has been observed previously. For example, we found that activation of peripheral KOR (as well as mu- and delta-opioid receptors) in injured nerves was more effective in amelioration of mechanical than heat sensitivity in the chronic constriction injury-induced neuropathic pain model in mice. Nevertheless, heat sensitivity was also diminished, providing that opioids were injected at higher, but still peripherally-acting doses (Labuz and Machelska, 2013). Thus, the conclusion that peripherally-restricted KOR agonists fail to influence heat sensitivity, based on testing the agonists at only one dose, appears premature. Dose-response experiments and verification of the peripheral action site would be required to make a definitive conclusion.