OBJECTIVE: The activation of N-methyl-D-aspartate(NMDA) receptors plays critical roles in the pathogenesis of diseases of the brain. This study aimed to examine the expression of phosphor-NR1 S897 in the cerebral cortex after NMDA microinjection in vivo. METHODS: Forty seven-day-old Sprague-Dawley rats were randomly assigned into normal control and NMDA injection groups. The rats from the NMDA injection group were injected with 10 mmol of NMDA and were sacrificed 1 hr after injection. 2, 3, 5-triphenyltetrazolium chloride (TTC) and fluorescent immunohistochemical stainings were conducted and the fluorescence intensity OD value between the two groups was compared. RESULTS: TTC staining from the two groups was normal. Expression of phosphor-NR1 S897 in the cerebral cortex of the ipsilateral hemisphere to injection in the NMDA injection group decreased significantly compared with the normal control group, with OD values of 0.366±0.087 vs 1.364±0.268 (P<0.01). CONCLUSIONS: NMDA microinjection, as a hypoxia-ischemia (HI) insult, significantly decreased the expression of phosphor-NR1 S897. This indicates the importance of the HI-NMDA-phospho-NR1 S897 dephosphorylation-cell damage pathway in HI brain damage.［Chin J Contemp Pediatr, 2007, 9(1):51-53］