title: Activation of a Gq-coupled membrane estrogen receptor rapidly attenuates α2-adrenoceptor-induced antinociception via an ERK I/II-dependent, non-genomic mechanism in the female rat.
abstract: Though sex differences in pain and analgesia are known, underlying mechanisms remain elusive. This study addresses the selective contribution of membrane estrogen receptors (mERs) and mER-initiated non-genomic signaling mechanisms in our previously reported estrogen-induced attenuation of α2-adrenoceptor-mediated antinociception. By selectively targeting spinal mERs in ovariectomized female rats using β-estradiol 6-(O-carboxy-methyl)oxime bovine serum albumin (E2BSA) (membrane impermeant estradiol analog), and ERα selective agonist 4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), ERβ selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN), G-protein-coupled estrogen receptor 30 (GPR30) agonist G1 and Gq-coupled mER (Gq-mER) agonist STX, we provide strong evidence that Gq-mER activation may solely contribute to suppressing clonidine (an α2-adrenoceptor agonist)-induced antinociception, using the nociceptive tail-flick test. Increased tail-flick latencies (TFLs) by intrathecal (i.t.) clonidine were not significantly altered by i.t. PPT, DPN, or G1. In contrast, E2BSA or STX rapidly and dose-dependently attenuated clonidine-induced increase in TFL. ICI 182,780, the ER antagonist, blocked this effect. Consistent with findings with the lack of effect of ERα and ERβ agonists that modulate receptor-regulated transcription, inhibition of de novo protein synthesis using anisomycin also failed to alter the effect of E2BSA or STX, arguing against a contribution of genomic mechanisms. Immunoblotting of spinal tissue revealed that mER activation increased levels of phosphorylated extracellular signal-regulated kinase (ERK) but not of protein kinase A (PKA) or C (PKC). In vivo inhibition of ERK with U0126 blocked the effect of STX and restored clonidine antinociception. Although estrogen-induced delayed genomic mechanisms may still exist, data presented here indicate that Gq-mER may solely mediate estradiol-induced attenuation of clonidine antinociception via a rapid, reversible, and ERK-dependent, non-genomic mechanism, suggesting that Gq-mER blockade might provide improved analgesia in females.
authors.affiliation: Department of Neuroscience and Pharmacology, Meharry Medical College, Nashville, TN 37208, United States. Electronic address: snag@mmc.edu.
authors.forename: S
authors.initials: S
authors.lastname: Nag
authors.affiliation: Department of Neuroscience and Pharmacology, Meharry Medical College, Nashville, TN 37208, United States.
authors.forename: S S
authors.initials: SS
authors.lastname: Mokha
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005260:Female; D059225:Nociception / Q000187:drug effects*; D010052:Ovariectomy; D010147:Pain Measurement / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects*; D013116:Spinal Cord; D013997:Time Factors
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D004791:Enzyme Inhibitors; D018341:Receptors, Adrenergic, alpha-2; C043090:estradiol-bovine serum albumin; D012710:Serum Albumin, Bovine; D004958:Estradiol; D048049:Extracellular Signal-Regulated MAP Kinases; D003000:Clonidine
keywords: analgesia; clonidine; estrogen; pain; sex-differences; spinal cord