Protein Kinase C Signaling in the Hypothalamic Arcuate Nucleus Regulates Sexual Receptivity in Female Rats

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Abstract
Rapid membrane-mediated estradiol signaling regulating sexual receptivity requires the interaction of the estrogen receptor (ER)-α and the metabotropic glutamate receptor 1a (mGluR1a). A cell signaling antibody microarray revealed that estradiol activated 42 proteins in the arcuate nucleus of the hypothalamus (ARH). To begin an analysis of various signaling pathways, protein kinase A and protein kinase C (PKC)-θ, whose signaling pathways have been implicated in the estradiol regulation of sexual receptivity, were examined. In the ARH sample, the increase in phospho-protein kinase A could not be confirmed by Western blotting, in either cytosolic or membrane fractions. However, the increase in phosphorylated PKCθ seen with the pathway array was verified by Western blotting. To study whether rapid estradiol activation of PKC regulates the ARH-medial preoptic nucleus pathway regulating lordosis, μ-opioid receptor (MOR) internalization and lordosis reflex were tested. Blocking PKC in ARH with 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]3-(1H-indol-3-yl) maleimide significantly attenuated estradiol-induced MOR internalization. Furthermore, disruption of PKC signaling within the ARH at the time of estradiol treatment significantly diminished the lordosis reflex. Moreover, blocking PKC prevented MOR internalization when the circuit was activated by the mGluR1a agonist, (RS)-3,5-dihydroxyphenylglycine. Activation of PKC with phorbol 12, 13-dibutyrate induced MOR internalization, indicating that PKC was a critical step for membrane ERα-initiated mGluR1a-mediated cell signaling and phorbol 12, 13-dibutyrate significantly facilitated the lordosis reflex. Together these findings indicate that rapid membrane ERα-mGluR1a interactions activate PKCθ cell signaling, which regulates female sexual receptivity.

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