Acute Hypoxia Differentially Affects the NMDA Receptor NR1, NR2A and NR2B Subunit mRNA Levels in the Developing Chick Optic Tectum: Stage-Dependent Plasticity in the 2B–2A Ratio

It is known that the NMDA-R NR1 subunit is needed for the receptor activity and that under hypoxia the evolution toward apoptosis or neuronal survival depends on the balance NR2A/NR2B subunits. This paper analyzes the effect of acute hypoxia on the above mentioned subunits mRNAs during development. The mean percentage of NR1+ neurons displayed the higher plasticity during development while the NR2A+ neurons the higher stability. Acute hypoxia increased the mean percentage of NR1+ and NR2B+ neurons at ED12 but only that of NR1+ neurons at ED18. Acute hypoxia increased the levels of expression of NR1 and NR2B mRNAs at ED12 without changes in the NR2A mRNA. During early stages there is a higher sensitivity to change the subunits mRNA levels under a hypoxic treatment. At ED12 acute hypoxia increased the probability of co-expression of the NR1–NR2A and NR1–NR2B subunits combinations, the level of NR1 and NR2B and the ratio NR2B/NR2A. These conditions facilitate the evolution towards apoptosis.