Effects of NMDA receptor antagonists with different subtype selectivities on retinal spreading depression

Abstract

BACKGROUND AND PURPOSE Spreading depression (SD) is a local, temporary disruption of cellular ionic homeostasis that propagates slowly across the cerebral cortex and other neural tissues such as the retina. Spreading depolarization associated with SD occurs in different types of stroke, and this phenomenon correlates also with the initiation of classical migraine aura. The aim of this study was to investigate how NMDA receptor antagonists with different subtype selectivity alter SD. EXPERIMENTAL APPROACH Immunoblotting was applied to the chick retina for NMDA receptor subunit protein analysis, and an efficient in vitro chick retinal model used with SD imaging for NMDA receptor pharmacology. KEY RESULTS The prominent NMDA receptor subtypes GluN1, GluN2A and GluN2B were found highly expressed in the chick retina. Nanomolar concentrations of NVP‐AAM077 (GluN2A‐preferring receptor antagonist) markedly suppressed high K+‐induced SD; that is, ∼30 times more effectively than MK801. At sub‐micromolar concentrations, Ro 25‐6981 (GluN2B‐preferring receptor antagonist) produced a moderate SD inhibition, whereas CP‐101,606 (also GluN2B‐preferring receptor antagonist) and UBP141 (GluN2C/2D‐preferring receptor antagonist) had no effect. CONCLUSIONS AND IMPLICATIONS The expression of major NMDA receptor subtypes, GluN1, GluN2A and GluN2B in the chick retina makes them pertinent targets for pharmacological inhibition of SD. The high efficacy of NVP‐AAM077 on SD inhibition suggests a critical role of GluN2A‐containing receptors in SD genesis. Such high anti‐SD potency suggests that NVP‐AAM077, and other GluN2A‐selective drug‐like candidates, could be potential anti‐migraine agents.

Synergistic Suppression of Cortical Spreading Depression under NR2A and NR2B Inhibition

“…The main finding of this work was that co-application of NVP-AAM077 and Ro 25-6981 showed synergistic inhibitory effects on CSD magnitude and propagation rate, suggesting simultaneous inhibition of NR2A-and NR2B-containing NMDA receptors is a useful strategy for migraine prophylaxis with improved efficacy. The additional inhibitory effect by Ro 25-6981 to NVP-AAM077 on tissue excitability and CSD magnitude in chick retina (Figure 3(a) and Figure 3(b)) is in consistent with previous findings that NR2B contributes to CSD propagation both in rats using electrophysiology recording [13], fMRI [21] and intrinsic optical imaging in chick retina [8]. Additionally, this study extended previous findings that inhibition of NR2A alone suppresses tissue excitability to CSD propagation in the same tissue [8].…”

“…As reported previously [8], for each 360-frame sequence, an area of interest (AOI) parallel to each CSD wave front was delineated manually (Figure 2). For each picture within the sequence, the gray levels of the pixels constituting the AOI were averaged and plotted against the time as an indicator to characterize the excitation phase of CSD (Figure 2).…”

“…CSD is implicated in migraine with aura [1] and may lead to sensitization of migraine pain pathway [2] [3] via both central [4] and peripheral modulations [5] [6]. CSD is accompanied with massive release of neurotransmitters, peptides and cerebral blood flow changes and can also be mediated by key neurotransmitter receptors [7] [8] or neuropeptides [9] [10], pointing them possible therapeutic targets in migraine prophylaxis. Consequently, CSD has been regarded as a useful tool for testing current and novel prophylactic anti-migraine agents [11].…”

“…NMDA receptors are heteromeric tetramer consisting of two NR1 and two of four NR2 (A-D) and/or one of NR3 (A-B) subunits [14]. Previous studies showed that NR2A-or NR2B-selective NMDA antagonists can partially suppresses CSD both in vitro [8] or in vivo [13], however with lower efficacy than MK801 [8] [13]. Interestingly, memantine, an non-competitive lowaffinity NMDA receptor channel blocker, first synthesized by Eli Lilly and Company in 1968, which targets both NR2A and NR2B subunits, is clinically well tolerated for treating moderate to severe migraine [15]- [17] and the drug was shown to have anti-CSD effect in rats [13].…”

Involvement of NMDA receptor subtypes in cortical spreading depression in rats assessed by fMRI

“…Previously, in vitro studies have shown that NR2A selective antagonists were effective in blocking CSD in chick retinas (Wang et al, 2012). However, in brain slices of mouse entorhinal cortex, the NR2B specific antagonist ifenprodil prevented CSDs from occurring (Faria and Mody, 2004).…”