Effects of subtype-selective NMDA receptor antagonists on retinal spreading depression

Minyan Wang1, Sura Ali1, Stevens Duckett1, Rachel Stevens1, Tiho Obrenovitch2. 1School of Pharmacy and Biomedical Sciences, University of Central Lancashire, United Kingdom, 2School of Pharmacy, University of Bradford, United Kingdom

Spreading depression (SD) is a temporary disruption of local ionic homeostasis that propagates slowly across the cortex. SD contributes to the initiation of migraine attack and lesion progression in experimental stroke. NMDA receptor (NMDAR) antagonists are known to be the most effective drugs to suppress SD (Gill et al., 1992). So far, NMDAR antagonists are still perceived as unlikely candidates as anti-SD drug in humans because of their unacceptable side effects, but the NMDAR antagonist, memantine is now used chronically in elderly for Alzheimer’s and epilepsy patients and some subtype selective receptor antagonists may well be effective with reduced side effects. The aim of this study was to determine whether NMDAR antagonists, with different subtype selectivity, suppress SD in the chicken retina preparation (Farkas et al., 2008; Wang et al., BJP under submission) in comparison with the non-competitive NMDAR antagonist, MK801.

Fifteen SD episodes were elicited by ejection of 0.1M KCl in each experiment. Image acquisition was started as each SD was initiated, and carried out for 3 minutes. Three separate SD were elicited for each of the different tests: (i) initial Ringer’s control; (ii) low concentration; (iii) medium concentration; and (vi) high concentration of vehicle or drug; (v) post-treatment Ringer’s control. A recovery of 15 min followed each SD elicitation, and the drug-syringe was changed immediately after the third recording of each test to ensure adequate perfusion of a drug or Ringer’s condition for the following test. Kruskal-Wallis test was used for comparison of magnitude and propagation rate of SD wave between the drug and respective vehicle group.

MK801 significantly suppressed the magnitude of SD wave to 24.3% of initial levels at 10 µM. Both NR2B preferring (CP,101-606) and NR2C/NR2D preferring receptor antagonists (UBP141), did not alter retinal SD, whereas a reduced magnitude of SD to 59.3% was observed with Ro25-6981 (NR1/NR2A/2B and NR1/NR2B preferring) at 3 µM (p<0.05, n = 8). Surprisingly, the NR2A preferring receptor antagonist, NVP-AAM077 (gift from Dr Yves Auberson, Novartis, Basel, Switzerland), markedly reduced both magnitude and propagation rate of SD in a concentration dependent manner. At 0.3 µM, the magnitude and propagation rate of SD reduced to 31.5 % and 52.5% respectively (p<0.01, n = 7). Unlike that of MK801, the effect of NVP-AAM077 on SD is reversible after the drug withdrawal (p<0.05, the 5th test versus the 4th test, paired-t-test). Our results suggested NR2A is key in SD elicitation and propagation, indicating potential therapeutic benefit for NVP-AAM077 to treat SD-related neurological diseases, e.g. migraine.