Capsaicin-evoked substance P release in rat dorsal horn increases after peripheral inflammation: a microdialysis study

• Published in: Neuroscience letters Vol. 368; no. 2; pp. 226 - 230
• Main Authors: Warsame Afrah, Abdullahi, Gustafsson, Henrik, Olgart, Leif, Brodin, Ernst, Stiller, Carl-Olav, Taylor, Bradley K.
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 23.09.2004; Elsevier
• Subjects: Animals; Biological and medical sciences; Capsaicin; Capsaicin - pharmacology; Dose-Response Relationship, Drug; Drug Interactions; Excitatory Amino Acid Agonists - pharmacology; Freund's Adjuvant; Fundamental and applied biological sciences. Psychology; Inflammation; Male; Medicin och hälsovetenskap; Microdialysis; Microdialysis - methods; Neurogenic Inflammation - chemically induced; Neurogenic Inflammation - metabolism; NMDA; Pain; Posterior Horn Cells - drug effects; Posterior Horn Cells - metabolism; Radioimmunoassay - methods; Rats; Rats, Sprague-Dawley; Spinal cord; Spinal Cord - cytology; Substance P; Substance P - metabolism; Time Factors; Valine - analogs & derivatives; Valine - pharmacology; Vertebrates: nervous system and sense organs; Spinal cord; Pain; Microdialysis; Substance P; Capsaicin; NMDA; Inflammation; Rat; Rodentia; Central nervous system; Posterior spinal horn; Neuropeptide; Vertebrata; Mammalia; Animal; Tachykinin; Release
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/j.neulet.2004.07.041

Numerous in vitro studies suggest that inflammation is associated with enhanced release of substance P (SP) in the dorsal horn. To test the hypothesis that inflammation increases the evoked concentration of SP in the intact animal, we used in vivo microdialysis with a highly sensitive radioimmunoassay to monitor SP-like immunoreactivity (SP-LI) in the dorsal horn. Seven days after the induction of persistent unilateral inflammation with hindpaw injection of complete Freund’s adjuvant, perfusion of the microdialysis probe with 10 μM capsaicin (a concentration which failed to induce SP-LI release in rats without inflammation) induced a significant increase of microdialysate SP-LI. Inclusion of an NMDA antagonist in the perfusion fluid completely blocked this capsaicin-evoked SP release. Administration of a five-fold higher dose of capsaicin did not further increase SP release. These results in a rat model of chronic arthritis suggest that persistent inflammatory signaling facilitates capsaicin-evoked SP release in the dorsal horn in vivo.