title: Neurosteroid Structure-Activity Relationships for Functional Activation of Extrasynaptic δGABA(A) Receptors.
abstract: Synaptic GABAA receptors are primary mediators of rapid inhibition in the brain and play a key role in the pathophysiology of epilepsy and other neurologic disorders. The δ-subunit GABAA receptors are expressed extrasynaptically in the dentate gyrus and contribute to tonic inhibition, promoting network shunting as well as reducing seizure susceptibility. However, the neurosteroid structure-function relationship at δGABA(A) receptors within the native hippocampus neurons remains unclear. Here we report a structure-activity relationship for neurosteroid modulation of extrasynaptic GABAA receptor-mediated tonic inhibition in the murine dentate gyrus granule cells. We recorded neurosteroid allosteric potentiation of GABA as well as direct activation of tonic currents using a wide array of natural and synthetic neurosteroids. Our results shows that, for all neurosteroids, the C3α-OH group remains obligatory for extrasynaptic receptor functional activity, as C3β-OH epimers were inactive in activating tonic currents. Allopregnanolone and related pregnane analogs exhibited the highest potency and maximal efficacy in promoting tonic currents. Alterations at the C17 or C20 region of the neurosteroid molecule drastically altered the transduction kinetics of tonic current activation. The androstane analogs had the weakest modulatory response among the analogs tested. Neurosteroid potentiation of tonic currents was completely (approximately 95%) diminished in granule cells from δ-knockout mice, suggesting that δ-subunit receptors are essential for neurosteroid activity. The neurosteroid sensitivity of δGABA(A) receptors was confirmed at the systems level using a 6-Hz seizure test. A consensus neurosteroid pharmacophore model at extrasynaptic δGABA(A) receptors is proposed based on a structure-activity relationship for activation of tonic current and seizure protection.
authors: Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas.
authors: Chase Matthew
authors: CM
authors: Carver
authors: Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M University Health Science Center, Bryan, Texas reddy@medicine.tamhsc.edu.
authors: Doodipala Samba
authors: DS
authors: Reddy
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology; D018891:Dentate Gyrus / Q000187:drug effects / Q000378:metabolism; D018755:GABA Agonists / Q000737:chemistry / Q000494:pharmacology*; D018757:GABA Modulators / Q000494:pharmacology; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008874:Midazolam / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects; D018377:Neurotransmitter Agents / Q000737:chemistry / Q000494:pharmacology*; D011278:Pregnanes / Q000494:pharmacology; D011280:Pregnanolone / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000235:genetics; D012640:Seizures / Q000517:prevention & control; D013329:Structure-Activity Relationship
chemical_list: D000927:Anticonvulsants; D018755:GABA Agonists; D018757:GABA Modulators; C583130:Gabrd protein, mouse; D018377:Neurotransmitter Agents; D011278:Pregnanes; D011963:Receptors, GABA-A; D011280:Pregnanolone; D008874:Midazolam