title: Norepinephrine depresses the capsaicin-evoked miniature excitatory postsynaptic currents in substantia gelatinosa of the rat spinal cord.
abstract: Capsaicin selectively excites nociceptive primary afferent fibers and increases the frequency of glutaminergic miniature excitatory postsynaptic currents (mEPSCs) in the substantia gelatinosa of the spinal dorsal horn. The whole-cell voltage-clamp recording technique was used to examine the effect of norepinephrine (NE) on the capsaicin-induced increase in the frequency of mEPSCs. In the presence of tetrodotoxin, bath application of capsaicin (1 microM) remarkably enhanced the frequency of mEPSCs (295+/-52% of control). Following pretreatment with NE (10 microM), the capsaicin-induced frequency facilitation of mEPSCs was significantly depressed to 151+/-17% of the control. NE-induced depression in capsaicin action was blocked by yohimbine, a selective alpha(2)-adrenergic receptor antagonist, indicating that NE exerts depression by activating the alpha(2)-adrenergic receptor. As the postsynaptic action of NE has been precluded in the present study, the results suggest that NE inhibits nociceptive input at a presynaptic site, the primary afferent terminal, during the nociceptive transmission in the spinal dorsal horn.
authors.affiliation: Department of Anatomy and K. K. Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, People's Republic of China.
authors.forename: Yu-Peng
authors.initials: YP
authors.lastname: Feng
authors.forename: Kun
authors.initials: K
authors.lastname: Yang
authors.forename: Yun-Qing
authors.initials: YQ
authors.lastname: Li
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013376:Substantia Gelatinosa / Q000187:drug effects* / Q000502:physiology
chemical_list: D000316:Adrenergic alpha-Agonists; D002211:Capsaicin; D009638:Norepinephrine