Distinct Function of Estrogen Receptors in the Rodent Anterior Cingulate Cortex in Pain-related Aversion

Background: Brain-derived estrogen is implicated in pain-related aversion; however, which estrogen receptors mediate this effect remains unclear. This study hypothesized that the different estrogen receptors in the rostral anterior cingulate cortex play distinct roles in pain-related aversion. Methods: Formalin-induced conditioned place avoidance and place escape/avoidance paradigms were used to evaluate pain-related aversion in rodents. Immunohistochemistry and Western blotting were used to detect estrogen receptor expression. Patch-clamp recordings were used to examineN-methyl-d-aspartate-mediated excitatory postsynaptic currents in rostral anterior cingulate cortex slices. Results: The administration of the estrogen receptor-beta antagonist 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP) or the G protein-coupled estrogen receptor-1 antagonist (3aS*,4R*,9bR*)-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15) but not the estrogen receptor-alpha antagonist 1,3-bis (4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy) phenol]-1H-pyrazole dihydrochloride (MPP) into the rostral anterior cingulate cortex blocked pain-related aversion in rats (avoidance score, mean +/- SD: 1,3-bis [4-hydroxyphenyl]-4-methyl-5-(4-[2-piperidinylethoxy] phenol)-1H-pyrazole dihydrochloride (MPP): 47.0 +/- 18.9%, 4-(2-phenyl-5,7-bis [trifluoromethyl] pyrazolo [1,5-a] pyrimidin-3-yl) phenol (PHTPP): -7.4 +/- 20.6%, and [3aS*,4R*,9bR*]-4-[6-bromo-1,3-benzodioxol-5-yl]-3a,4,5,9b-3H-cyclopenta [c] quinolone (G15): -4.6 +/- 17.0%vs.vehicle: 46.5 +/- 12.2%; n = 7 to 9;P< 0.0001). Consistently, estrogen receptor-beta knockdown but not estrogen receptor-alpha knockdown by short-hairpin RNA also inhibited pain-related aversion in mice (avoidance score, mean +/- SD: estrogen receptor-alpha-short-hairpin RNA: 26.0 +/- 7.1% and estrogen receptor-beta-short-hairpin RNA: 6.3 +/- 13.4%vs.control short-hairpin RNA: 29.1 +/- 9.1%; n = 7 to 10;P< 0.0001). Furthermore, the direct administration of the estrogen receptor-beta agonist 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN) or the G protein-coupled estrogen receptor-1 agonist (+/-)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1) into the rostral anterior cingulate cortex resulted in conditioned place avoidance (avoidance score, mean +/- SD: 2,3-bis (4-hydroxyphenyl)-propionitrile (DPN): 35.3 +/- 9.5% and (+/-)-1-([3aR*,4S*,9bS*]-4-(6-bromo-1,3-benzodioxol-5-yl)-3a,4,5,9b-tetrahydro-3H-cyclopenta [c]quinolin-8-yl)-ethanone (G1): 43.5 +/- 22.8%vs.vehicle: 0.3 +/- 14.9%; n = 8;P< 0.0001) but did not affect mechanical or thermal sensitivity. The activation of the estrogen receptor-beta/protein kinase A or G protein-coupled estrogen receptor-1/protein kinase B pathway elicited the long-term potentiation ofN-methyl-d-aspartate-mediated excitatory postsynaptic currents. Conclusions: These findings indicate that estrogen receptor-beta and G protein-coupled estrogen receptor-1 but not estrogen receptor-alpha in the rostral anterior cingulate cortex contribute to pain-related aversion by modulatingN-methyl-d-aspartate receptor-mediated excitatory synaptic transmission.