Pronociceptive and Antinociceptive Effects of Buprenorphine in the Spinal Cord Dorsal Horn Cover a Dose Range of Four Orders of Magnitude

• Published in: The Journal of neuroscience Vol. 35; no. 26; pp. 9580 - 9594
• Main Authors: Gerhold, K. J., Drdla-Schutting, R., Honsek, S. D., Forsthuber, L., Sandkuhler, J.
• Format: Journal Article
• Language: English
• Published: United States Society for Neuroscience 01.07.2015
• Subjects: Analgesics, Opioid - pharmacology; Animals; Animals, Newborn; Astrocytes - drug effects; Buprenorphine - pharmacology; Dose-Response Relationship, Drug; Hyperalgesia - drug therapy; In Vitro Techniques; Male; Naloxone - analogs & derivatives; Naloxone - pharmacology; Nerve Fibers, Unmyelinated - drug effects; Nerve Fibers, Unmyelinated - metabolism; Pain Measurement - drug effects; Pain Threshold - drug effects; Phosphopyruvate Hydratase - metabolism; Rats; Rats, Sprague-Dawley; Signal Transduction - drug effects; Spinal Cord - cytology; Spinal Nerve Roots - cytology; Synapses - drug effects; Time Factors; descending facilitation; pain; buprenorphine; spinal cord; synapse; opioid
• ISSN: 0270-6474; 1529-2401; 1529-2401
• DOI: 10.1523/JNEUROSCI.0731-14.2015

Due to its distinct pharmacological profile and lower incidence of adverse events compared with other opioids, buprenorphine is considered a safe option for pain and substitution therapy. However, despite its wide clinical use, little is known about the synaptic effects of buprenorphine in nociceptive pathways. Here, we demonstrate dose-dependent, bimodal effects of buprenorphine on transmission at C-fiber synapses in rat spinal cord dorsal horn in vivo. At an analgesically active dose of 1500 μg·kg(-1), buprenorphine reduced the strength of spinal C-fiber synapses. This depression required activation of spinal opioid receptors, putatively μ1-opioid receptors, as indicated by its sensitivity to spinal naloxone and to the selective μ1-opioid receptor antagonist naloxonazine. In contrast, a 15,000-fold lower dose of buprenorphine (0.1 μg·kg(-1)), which caused thermal and mechanical hyperalgesia in behaving animals, induced an enhancement of transmission at spinal C-fiber synapses. The ultra-low-dose buprenorphine-induced synaptic facilitation was mediated by supraspinal naloxonazine-insensitive, but CTOP-sensitive μ-opioid receptors, descending serotonergic pathways, and activation of spinal glial cells. Selective inhibition of spinal 5-hydroxytryptamine-2 receptors (5-HT2Rs), putatively located on spinal astrocytes, abolished both the induction of synaptic facilitation and the hyperalgesia elicited by ultra-low-dose buprenorphine. Our study revealed that buprenorphine mediates its modulatory effects on transmission at spinal C-fiber synapses by dose dependently acting on distinct μ-opioid receptor subtypes located at different levels of the neuraxis.