“ACUTE HYPOXIA DIFFERENTIALLY AFFECTS THE NMDA RECEPTOR NR1, NR2A AND NR2B SUBUNIT mRNA LEVELS IN DEVELOPING CNS: STAGE-DEPENDENT SENSITIVITY”.

FISZER DE PAZAS, S., RAPACIOLI,M., RODRIGUEZ GIL, D., VACOTTO, M., FLORES, V.

Washington, USA

Congreso; Society for Neuroscience; 2008

Society for Neuroscience

Hypoxic injury is associated to an increase in the release of excitatory aminoacids and then to CNS pathologies ranging from apoptotic cell death to loss of specific neural projections and neurodegeneration. The NMDA receptor, one of the three ionotropic receptors for glutamate, has been implicated in excitotoxicity induced by hypoxia. Changes in its subunit mRNA levels could affect the receptor complex subunit composition and could affect synaptic transmission. The aim of the present work was to analyze the effect of an acute hypoxic treatment on the level of three (NR1, NR2A and NR2B) subunit mRNAs of the NMDA receptor in the layer “i” of the developing chick optic tectum. For this purpose, 12 and 18 days old (E) chick embryos were submitted to severe hypoxia (8% O2, for 60 min). After 1hr under normobaric hypoxic treatment, embryos were immediately processed for in situ hybridization analysis.  The control group was maintained under normoxic conditions. Two parameters were computed to test the hypoxia effect: Percentage of labeled cells and number of grains/cell (ng/c). The higher percentage of labeled cells corresponded to the NR1 mRNA-expressing cells. This percentage increased during normal development. In this case, hypoxia produced a significant increase in the percentages of cells both at E12 and E18. The percentage of cells expressing the others two mRNA subunits remained approximately unchanged during normal development and hypoxia did not produce significant changes in this parameter. With regards to the ng/c, there was a remarkable increase (100%) in this parameter in the NR1-expressing cell population between E12 – E18 during normal development. The NR2B-expressing population underwent a lesser increase (30%), and in the NR2A-expressing cell population this parameter did not change at all. The level of NR1 mRNA expression (in terms of ng/c) significantly changed under hypoxia. At E12 the level of this mRNA subunit was very sensitive and the ng/c almost duplicated under hypoxia and by E18 the sensitivity decreased. The level of NRB2 mRNA expression also changed under hypoxia but in this case only at E12. This increase was lower (38%) than that underwent by the NR1 mRNA subunit. By E18 the expression of the NR2B mRNA subunit was not modify by hypoxia. Interestingly, the level of the NR2A mRNA subunit which did not change during the normal development was completely insensitive to hypoxia. In conclusion, hypoxia does not produce a simple effect: on one hand, hypoxia differentially affects the expression of different receptor mRNA subunits and, on the other, the window of sensitivity to hypoxia differentially changes as a function of the developmental stage.