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Technical Report

Nature Neuroscience 10, 523–530 (1 April 2007) | doi:10.1038/nn1862

Anticonvulsant and anesthetic effects of a fluorescent neurosteroid analog activated by visible light

Lawrence N Eisenman , Hong-Jin Shu , Gustav Akk , Cunde Wang , Brad D Manion , Geraldine J Kress , Alex S Evers , Joe Henry Steinbach , Douglas F Covey , Charles F Zorumski & Steven Mennerick

Most photoactivatable compounds suffer from the limitations of the ultraviolet wavelengths that are required for activation. We synthesized a neuroactive steroid analog with a fluorescent (7-nitro-2,1,3-benzoxadiazol-4-yl) amino (NBD) group in the β configuration at the C2 position of (3α,5α)-3-hydroxypregnan-20-one (allopregnanolone, 3α5αP). Light wavelengths (480 nm) that excite compound fluorescence strongly potentiate GABAA receptor function. Potentiation is limited by photodepletion of the receptor-active species. Photopotentiation is long-lived and stereoselective and shows single-channel hallmarks similar to steroid potentiation. Other NBD-conjugated compounds also generate photopotentiation, albeit with lower potency. Thus, photopotentiation does not require a known ligand for neurosteroid potentiating sites on the GABAA receptor. Photoactivation of a membrane-impermeant, fluorescent steroid analog demonstrates that membrane localization is critical for activity. The photoactivatable steroid silences pathological spiking in cultured rat hippocampal neurons and anesthetizes tadpoles. Fluorescent steroids photoactivated by visible light may be useful for modulating GABAA receptor function in a spatiotemporally defined manner.