NMDA receptor antagonists sustain LTP and spatial memory: active processes mediate LTP decay

Administration of pediatric anesthetics with N-methyl D-aspartate (NMDA)-receptor antagonist and/or γ-aminobutyric acid (GABA) agonist activities may result in neuronal degeneration and/or neuronal cell death in neonatal rats. Evaluating pediatric drug candidates for this potential neurotoxicity is often part of overall preclinical new drug development strategy. This specialized assessment may require dosing neonatal rats at postnatal day 7 at the peak of the brain growth spurt and evaluating brain tissue 24 to 48 hours following dosing. The need to identify methods to aid in the accurate and reproducible detection of lesions associated with this type of neurotoxic profile is paramount for meeting the changing needs of neuropathology assessment and addressing emerging challenges in the neuroscience field. We document the use of Fluoro-Jade B (FJB) staining, to be used in conjunction with standard hematoxylin and eosin staining, to detect acute neurodegeneration and neuronal cell death that can be caused by some NMDA-receptor antagonists and/or GABA agonists in the neonatal rat brain. The FJB staining is simple, specific, and sensitive and can be performed on brain specimens from the same cohort of animals utilized for standard neurotoxicity assessment, thus satisfying animal welfare recommendations with no effect on achievement of scientific and regulatory goals.

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Structural basis of subunit selectivity for competitive NMDA receptor antagonists with preference for GluN2A over GluN2B subunits

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1707752114 ◽

2017 ◽

Vol 114 (33) ◽

pp. E6942-E6951 ◽

Cited By ~ 18

Author(s):

Genevieve E. Lind ◽

Tung-Chung Mou ◽

Lucia Tamborini ◽

Martin G. Pomper ◽

Carlo De Micheli ◽

...

Keyword(s):

Nmda Receptor ◽

Binding Affinity ◽

Binding Mode ◽

Structural Basis ◽

Nmda Receptor Antagonists ◽

Receptor Antagonists ◽

Glutamate Binding ◽

Subunit Interface ◽

The Central Nervous System ◽

Contact Residues

NMDA-type glutamate receptors are ligand-gated ion channels that contribute to excitatory neurotransmission in the central nervous system (CNS). Most NMDA receptors comprise two glycine-binding GluN1 and two glutamate-binding GluN2 subunits (GluN2A–D). We describe highly potent (S)-5-[(R)-2-amino-2-carboxyethyl]-4,5-dihydro-1H-pyrazole-3-carboxylic acid (ACEPC) competitive GluN2 antagonists, of which ST3 has a binding affinity of 52 nM at GluN1/2A and 782 nM at GluN1/2B receptors. This 15-fold preference of ST3 for GluN1/2A over GluN1/2B is improved compared with NVP-AAM077, a widely used GluN2A-selective antagonist, which we show has 11-fold preference for GluN1/2A over GluN1/2B. Crystal structures of the GluN1/2A agonist binding domain (ABD) heterodimer with bound ACEPC antagonists reveal a binding mode in which the ligands occupy a cavity that extends toward the subunit interface between GluN1 and GluN2A ABDs. Mutational analyses show that the GluN2A preference of ST3 is primarily mediated by four nonconserved residues that are not directly contacting the ligand, but positioned within 12 Å of the glutamate binding site. Two of these residues influence the cavity occupied by ST3 in a manner that results in favorable binding to GluN2A, but occludes binding to GluN2B. Thus, we reveal opportunities for the design of subunit-selective competitive NMDA receptor antagonists by identifying a cavity for ligand binding in which variations exist between GluN2A and GluN2B subunits. This structural insight suggests that subunit selectivity of glutamate-site antagonists can be mediated by mechanisms in addition to direct contributions of contact residues to binding affinity.

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