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

• Published in: Nature neuroscience Vol. 10; no. 4; pp. 523 - 530
• Main Authors: Mennerick, Steven, Manion, Brad D, Akk, Gustav, Zorumski, Charles F, Wang, Cunde, Covey, Douglas F, Shu, Hong-Jin, Steinbach, Joe Henry, Eisenman, Lawrence N, Evers, Alex S, Kress, Geraldine J
• Format: Journal Article
• Language: English
• Published: United States Nature Publishing Group 01.04.2007
• Subjects: Anesthetics - pharmacology; Animals; Animals, Newborn; Anticonvulsants; Anticonvulsants - pharmacology; Cell Line, Transformed; Dosage and administration; Fluorescein; GABA; gamma-Aminobutyric Acid - pharmacology; Hippocampus - cytology; Humans; Larva - drug effects; Light; Membrane Potentials - drug effects; Membrane Potentials - physiology; Membrane Potentials - radiation effects; Neurons - drug effects; Neurosciences; Patch-Clamp Techniques; Physiological aspects; Pregnanolone - analogs & derivatives; Pregnanolone - chemical synthesis; Pregnanolone - pharmacology; Protein Subunits - genetics; Rats; Rats, Sprague-Dawley; Receptors; Receptors, GABA-A - drug effects; Receptors, GABA-A - metabolism; Spectrophotometer; Steroids; Structure-Activity Relationship; Swimming; Transfection; United States
• ISSN: 1097-6256; 1546-1726
• DOI: 10.1038/nn1862

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 beta configuration at the C2 position of (3alpha,5alpha)-3-hydroxypregnan-20-one (allopregnanolone, 3alpha5alphaP). 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.