title: Preferential Inhibition of Tonically over Phasically Activated NMDA Receptors by Pregnane Derivatives.
abstract: Postsynaptic N-methyl-d-aspartate receptors (NMDARs) phasically activated by presynaptically released glutamate are critical for synaptic transmission and plasticity. However, under pathological conditions, excessive activation of NMDARs by tonically increased ambient glutamate contributes to excitotoxicity associated with various acute and chronic neurological disorders. Here, using heterologously expressed GluN1/GluN2A and GluN1/GluN2B receptors and rat autaptic hippocampal microisland cultures, we show that pregnanolone sulfate inhibits NMDAR currents induced by a prolonged glutamate application with a higher potency than the NMDAR component of EPSCs. For synthetic pregnanolone derivatives substituted with a carboxylic acid moiety at the end of an aliphatic chain of varying length and attached to the steroid skeleton at C3, the difference in potency between tonic and phasic inhibition increased with the length of the residue. The steroid with the longest substituent, pregnanolone hemipimelate, had no effect on phasically activated receptors while inhibiting tonically activated receptors. In behavioral tests, pregnanolone hemipimelate showed neuroprotective activity without psychomimetic symptoms. These results provide insight into the influence of steroids on neuronal function and stress their potential use in the development of novel therapeutics with neuroprotective action.
  
  
  CONCLUSIONS
  Synaptic activation of N-methyl-d-aspartate receptors (NMDARs) plays a key role in synaptic plasticity, but excessive tonic NMDAR activation mediates excitotoxicity associated with many neurological disorders. Therefore, there is much interest in pharmacological agents capable of selectively blocking tonically activated NMDARs while leaving synaptically activated NMDARs intact. Here, we show that an endogenous neurosteroid pregnanolone sulfate is more potent at inhibiting tonically than synaptically activated NMDARs. Further, we report that a novel synthetic analog of pregnanolone sulfate, pregnanolone hemipimelate, inhibits tonic NMDAR currents without inhibiting the NMDAR component of the EPSC and shows neuroprotective activity in vivo without inducing psychomimetic side effects. These results suggest steroids may have a clinical advantage over other known classes of NMDAR inhibitors.
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Vojtech
authors.identifier: http://orcid.org/0000-0002-7763-850X
authors.initials: V
authors.lastname: Vyklicky
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Tereza
authors.initials: T
authors.lastname: Smejkalova
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Barbora
authors.initials: B
authors.lastname: Krausova
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Ales
authors.initials: A
authors.lastname: Balik
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Miloslav
authors.initials: M
authors.lastname: Korinek
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Jirina
authors.initials: J
authors.lastname: Borovska
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Martin
authors.initials: M
authors.lastname: Horak
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Marketa
authors.initials: M
authors.lastname: Chvojkova
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Kleteckova
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Karel
authors.initials: K
authors.lastname: Vales
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic.
authors.forename: Jiri
authors.identifier: http://orcid.org/0000-0002-1969-9304
authors.initials: J
authors.lastname: Cerny
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 166 10 Prague 2, Czech Republic, and Faculty of Mathematics and Physics, Charles University in Prague, 121 16 Prague 2, Czech Republic.
authors.forename: Michaela
authors.initials: M
authors.lastname: Nekardova
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 166 10 Prague 2, Czech Republic, and.
authors.forename: Hana
authors.initials: H
authors.lastname: Chodounska
authors.affiliation: Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 166 10 Prague 2, Czech Republic, and.
authors.forename: Eva
authors.initials: E
authors.lastname: Kudova
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 142 20 Prague 4, Czech Republic, vyklicky@biomed.cas.cz.
authors.forename: Ladislav
authors.initials: L
authors.lastname: Vyklicky
mesh_terms: D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D057809:HEK293 Cells; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D018696:Neuroprotective Agents / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011278:Pregnanes / Q000737:chemistry / Q000494:pharmacology*; D011280:Pregnanolone / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000235:genetics; D013329:Structure-Activity Relationship; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D018696:Neuroprotective Agents; D011278:Pregnanes; D011280:Pregnanolone; D016194:Receptors, N-Methyl-D-Aspartate; C121001:NR2B NMDA receptor
keywords: NMDA receptor; memantine; neuroprotection; neurosteroid; pregnanolone sulfate; synaptic transmission