ESTROGEN RECEPTORS BETA AND ALPHA HAVE SPECIFIC PRO- AND ANTI-NOCICEPTIVE ACTIONS M.-A. COULOMBE, a M.-F. SPOONER, a I. GAUMOND, a J. C. CARRIER b AND S. MARCHAND a * a Département de Neurochirurgie, Faculté de Médecine et des Sci- ences de la Santé, Université de Sherbrooke, 3001, 12e Avenue Nord, Sherbrooke, QC, Canada J1H 5N4 b Département de Médecine et Département d’Anatomie et Biologie Cellulaire, Faculté de Médecine et des Sciences de la Santé, Univer- sité de Sherbrooke, 3001, 12e Avenue Nord, Sherbrooke, QC, Can- ada J1H 5N4 Abstract—It is strongly suggested that estrogen plays a key role in pain modulation. Estrogen’s effects are mediated mainly by two receptors, ER and ER. However, the specific role of these receptors is still not clear. In this study, the involvement of both receptors on nociceptive responses was measured in ER and ER knockout (KO) C57BL/6j mice and their respective wild type (WT) littermate (male and female). It was also measured in four groups of ovariectomized mice injected for 7 days with either (1) vehicle, (2) 17-estradiol, (3) ER-selective agonist propylpyrazoletriol (PPT) or (4) ER- selective agonist diarylpropionitril (DPN). As previously de- scribed, ER KO females showed lower nociceptive re- sponses compared to WT female mice during the interphase and early tonic phase 2 of the formalin test. The observed pronociceptive nature of ER was confirmed using ER- selective agonist DPN injections in ovariectomized mice. Moreover, we found that ER KO male and female mice pre- sented a small increase in nociceptive behaviors during phase 1 of the formalin test, suggesting an anti-nociceptive effect of ER. These results were confirmed by the injection of ER-selective agonist PPT in ovariectomized mice. Inter- estingly, both ER agonists reduced nociceptive responses during late phase 2, suggesting an anti-inflammatory action of estrogen. Results were supported by spinal c-Fos immu- nohistochemistry. In conclusion, both ER and ER appear to be involved in pain transmission and modulation but may be acting at distinct levels of the pain pathways. © 2011 IBRO. Published by Elsevier Ltd. All rights reserved. Key words: formalin test, pain, nociception, estrogen recep- tor, c-Fos, mice. Women have a lower pain threshold and a higher inci- dence of chronic pain syndromes than men (Riley et al., 1998; Wolfe et al., 1995; LeResche et al., 2003). More- over, several studies have observed sex differences in pain perception and analgesia in both clinical and animal models (Fillingim and Gear, 2004; Fillingim, 2000; Craft, 2003). Previous studies demonstrated that sex hormones are involved in this variation of sensitivity to painful stimu- lations (Forman et al., 1989; Gaumond et al., 2002, 2005). More specifically, in a previous study manipulating sex hormone levels in gonadectomized rats, we found that estrogen and progesterone are hyperalgesic through a reduction of pain inhibition mechanisms while testosterone is hypoalgesic by reducing excitatory mechanisms as- sessed by the formalin test in rat’s population (Gaumond et al., 2005). Estrogens predominantly, but not exclusively, bind to two nuclear receptors, ER and ER, to regulate gene transcription (McEwen, 1991; Levin, 2009; Moss et al., 1997; Kelly and Levin, 2001; Kato et al., 2005; Deroo and Korach, 2006). Both of these receptors are present throughout the CNS, but have different distribution (Mitra et al., 2003; Nomura et al., 2003; Shughrue et al., 1997). They are genetically and functionally distinct and have dichotomous actions (Kuiper et al., 1998; Lund et al., 2005). ER plays a predominant role in sexual behavior and reproductive functions, but it is also involved in brain macrophage reactivity and in synaptic connectivity (Hewitt and Korach, 2003; Vegeto et al., 2003; McEwen and Alves, 1999; Mong and McCarthy, 1999). In counterpart, ER does not seem to be essential for the reproductive func- tion, but appears to be involved in non-reproductive be- haviors such as brain development (Lund et al., 2005; Hewitt and Korach, 2003; Nomura et al., 2003; Krezel et al., 2001). Both ER and ER are present in brain areas involved in pain transmission and pain inhibition (Lu et al., 2001; Alves et al., 1998a,b; Papka et al., 2002; Vander- horst et al., 2002; Mitra et al., 2003). Physiological and anatomical studies suggest that es- trogens might exert a great influence on ascending and descending inhibitory tones (Blurton-Jones and Tuszynski, 2002; Papka et al., 2001). In fact, estradiol acts on several neurotransmitters involved in pain transmission and pain inhibition (Aloisi, 2003; Aloisi and Bonifazi, 2006; Murphy et al., 1998, Foy et al., 1999). It is known to modulate opioid peptides expression and opioid receptor levels (Priest et al., 1995; Micevych et al., 1997; Amandusson et al., 1999; Micevych and Sinchak, 2001), but it also binds to receptors in the dorsal root ganglion neurons to modulate Ca 2+ signaling of nociceptive information (Chaban et al., 2003). Estrogens seem to play a key role in pain modulation but the specific role of ER and ER in pain perception is *Corresponding author. Tel: +1-819-346-111015889; fax: +1-819- 564-5424. E-mail address: Serge.Marchand@USherbrooke.ca (S. Marchand). Abbreviations: AVP, arginine vasopressin; DPN, diarylpropionitril; DRG, dorsal root ganglia; ER, estrogen receptor; ETOH, ethanol; E2, 17-estradiol; KO, knockout; MOR, -opioid receptor; NGS, normal goat serum; OT, oxytocin; OVX, ovariectomy(ovariectomized); PAG, periaqueductal gray; PBS, phosphate-buffered saline; PPT, propy- lpyrazoletriol; PR, progestin hormone-receptor; PVN, paraventricular nucleus; RVM, rostroventral medulla; SON, supraoptic nucleus; WT, wild type. Neuroscience 184 (2011) 172–182 0306-4522/11 $ - see front matter © 2011 IBRO. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.neuroscience.2011.02.057 172