17-β estradiol down regulates ganglionic microglial cells via nitric oxide release: Presence of an estrogen receptor β transcript

OBJECTIVES: In earlier studies we have demonstrated that 17-β-estradiol and an estrogen cell surface receptor can be found on various human cells where they are coupled to nitric oxide release. We also demonstrated the presence of estrogen signaling in Mytilus edulis ganglia. In the present report, we sought to determine a function for these ganglionic estrogen receptors, transcending a reproductive role for estrogen. MATERIAL & METHODS: Ganglionic microglial egress from excised pedal ganglia was examined microscopically following pharmacological treatments designed to determine a role for 17-β-estradiol in microglial regulation via nitric oxide. Additionally, we examined the tissue by RT-PCR and sequence analysis for the estrogen receptor β gene. RESULTS: In ganglia incubated with varying concentrations of 17-β-estradiolBSA there is a signifi cant drop in microglial egress at the 24 hour observation period (58.7 ± 7.4 vs. 17-β-estradiol-BSA exposed = 14.7 ± 1.5; P<0.01), which can be antagonized by tamoxifen and signifi cantly diminished by L-NAME, a nitric oxide synthase inhibitor. By RT-PCR and sequence analysis Mytilus edulis pedal ganglia was found to express a 266 bp fragment of the estrogen receptor-β gene, which exhibits 100% sequence identity with the human counterpart. CONCLUSION: These data suggest that 17-β-estradiol-BSA is working on estrogen cell surface receptors since 17-β-estradiol-BSA does not enter the cytoplasm and that these receptors are coupled to constitutive nitric oxide release. This study demonstrates that 17-β-estradiol can down regulate microglial fMLP induced activation and activation following ganglionic excision.