The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in 1 NPY / AgRP neurons : Role in mediating the anorexigenic effects of 17 β - estradiol

26 Besides its quintessential role in reproduction, 17β-estradiol (E2) is a potent anorexigenic 27 hormone. E2 and the selective Gq-coupled membrane estrogen receptor (Gq-mER) ligand, 28 STX, rapidly increase membrane excitability in proopiomelanocortin (POMC) neurons by 29 desensitizing the coupling of GABAB receptors to G protein-coupled inwardly rectifying K 30 channels (GIRKs), which upon activation elicit a hyperpolarizing outward current. However, it is 31 unknown whether E2 and STX can modulate GABAB signaling in neuropeptide Y (NPY)/agouti32 related peptide (AgRP) neurons. We used single-cell RT-PCR and whole-cell patch clamping 33 with selective pharmacological reagents to show that NPY/AgRP cells of mice express the 34 GABAB-R1 and -R2 receptors and are hyperpolarized by the GABAB agonist baclofen in an E235 dependent manner. In males, E2 rapidly attenuated the coupling of GABAB receptors to GIRKs, 36 which was blocked by the general PI3K inhibitors wortmannin and LY294002 or the selective 37 p110β subunit inhibitor TGX-221. The ERα selective agonist PPT mimicked the effects of E2. 38 STX, in contrast, enhanced the GABAB response in males, which was abrogated by the ER 39 antagonist ICI 182, 780. In gonadectomized mice of both sexes, E2 enhanced or attenuated the 40 GABAB response in different NPY/AgRP cells. Co-perfusing wortmannin with E2 or simply 41 applying STX always enhanced the GABAB response. Thus, in NPY/AgRP neurons, activation 42 of the Gq-mER by E2 or STX enhances the GABAergic postsynaptic response, whereas 43 activation of ERα by E2 attenuates it. These findings demonstrate a clear functional dichotomy 44 of rapid E2 membrane-initiated signaling via ERα versus Gq-mER in a CNS neuron vital for 45 regulating energy homeostasis. 46