Involvement of Peripheral Purinoceptors in Sympathetic Modulation of Capsaicin-Induced Sensitization of Primary Afferent Fibers

• Published in: Journal of neurophysiology Vol. 96; no. 5; pp. 2207 - 2216
• Main Authors: Ren, Yong, Zou, Xiaoju, Fang, Li, Lin, Qing
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.11.2006
• Subjects: Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - pharmacology; Animals; Capsaicin - pharmacology; Male; Nerve Fibers - drug effects; Nerve Fibers, Myelinated - drug effects; Nerve Fibers, Myelinated - physiology; Nerve Fibers, Unmyelinated - drug effects; Nerve Fibers, Unmyelinated - physiology; Neurons, Afferent - drug effects; Purinergic Agonists; Purinergic Antagonists; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate - analogs & derivatives; Pyridoxal Phosphate - pharmacology; Rats; Rats, Sprague-Dawley; Receptors, Purinergic - physiology; Sympathectomy; Sympathetic Nervous System - drug effects; Sympathetic Nervous System - physiology; Uridine Triphosphate - pharmacology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00502.2006

1 Department of Neuroscience and Cell Biology and 2 Department of Surgery, Division of Neurosurgery, University of Texas Medical Branch, Galveston, Texas Submitted 10 May 2006; accepted in final form 26 July 2006 Purinoceptors are distributed in primary afferent terminals, where transmission of nociceptive information is modulated by these receptors. In the present study, we evaluated whether the activation or blockade of purinoceptors of subtypes P2X and P2Y in the periphery affected the sensitization of primary afferents induced by intradermal injection of capsaicin (CAP) and examined their role in sympathetic modulation of sensitization of primary nociceptive afferents. Afferent activity was recorded from single A - and C-primary afferent fibers in the tibial nerve in anesthetized rats. Peripheral pretreatment with , -methylene adenosine 5'-triphosphate ( , -meATP), a P2X-selective receptor agonist, could potentiate the CAP-induced enhancement of responses of A - and C-primary afferent nociceptive fibers to mechanical stimuli in sympathetically intact rats. After sympathetic denervation, the enhanced responses of both A - and C-fibers after CAP injection were dramatically reduced. However, this reduction could be restored when P2X receptors were activated by , -meATP. A blockade of P2X receptors by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid could significantly reduce the CAP-induced sensitization of A - and C-fibers. Pretreatment with uridine 5'-triphosphate, a P2Y-selective receptor agonist, did not significantly affect or restore the CAP-induced sensitization of A - and C-fibers under sympathetically intact or sympathectomized conditions. Our study supports the view that ATP plays a role in modulation of primary afferent nociceptor sensitivity mainly by P2X receptors. Combined with our previous study, our data also provide further evidence that the sensitization of primary afferent nociceptors is subject to sympathetic modulation by activation of P2X as well as 1 -adrenergic receptors. Address for reprint requests and other correspondence: Q. Lin, Department of Neuroscience and Cell Biology, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-1069 (E-mail: qilin{at}utmb.edu )