The influence of capsaicin receptors in the locus coeruleus on morphine-induced analgesia in diabetic neuropathy: A comparison between morphine-dependent and non-dependent rats

Document Type : Original Research

Authors
A. Naderi Farjam 1
M. Sharifi 2
A. Komaki 2
A. Sarihi 3
1 Department of Biology, Faculty of Basic Sciences, Islamic Azad University of Hamadan, Iran
2 Neurophysiology Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
3 Department of Neuroscience, School of Sciences and Advanced Technology in Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
Abstract
Introduction: Diabetic neuropathies (DN) are neuropathic disorders associated with diabetes mellitus. Peripheral neuropathy, characterized by hyperalgesia, can occur in all types of diabetes. Morphine inhibits the activity of locus coeruleus (LC) neurons, which are involved in pain modulation. The capsaicin receptor (TRPV1) is expressed in several brain nuclei involved in pain perception, including the LC nucleus. This study was conducted to examine the role of TRPV1 in the LC on morphine-induced analgesia in morphine-dependent and non-dependent rats affected by DN.

Methods: This study was conducted on male Wistar rats. Diabetic neuropathy (DN) was induced by a single dose of STZ. Morphine sulfate was injected intraperitoneally (3 mg/kg) once daily for 3 days. Finally, we investigated the role of TRPV1 receptors (10 nmol) in the locus coeruleus (LC) in morphine analgesia in both normal and neuropathic rats.

Results: Our results indicated that activating TRPV1 receptors in the locus coeruleus (LC) has no effect on morphine analgesia in normal, non-dependent rats. However, in morphine-dependent animals, it can potentiate morphine analgesia 45 minutes after the injection of a TRPV1 agonist. In diabetic neuropathy (DN) and non-dependent rats, TRPV1 activation increased morphine analgesia 30 minutes after injection but had no effect on dependent rats.

Conclusion: The results of this study suggest that activating the capsaicinoid system could be a useful approach in pharmacological therapy for patients with peripheral neuropathy.

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Pathobiology Reserach
Volume 27, Issue 1
May 2024
Pages 53-58