Long-term Effects of Seizures in Neonatal Rats on Spatial Learning Ability and N-methyl-D-aspartate Receptor Expression in the Brain

For the purpose of investigating the long-term effects of seizures in neonatal rats on spatial learning ability and N-methyl-D-aspartate (NMDA) receptor expression in adult rat brain, a seizure was induced by inhalant flurothyl daily in neonatal Wistar rats from postnatal day 6 (P6). The authors assigned six rats each averagely into the single-seizure group, the recurrent-seizure group (seizures induced in six consecutive days), and the control group. During P60 to P65, the rats were tested for spatial learning ability with the Morris water maze task. On P75, the authors examined protein expression of the NMDA receptor (NR) subunits, NR1, 2A, 2B, 2C, and 2D, in the cerebral cortex and hippocampus by Western blotting analysis. On P65, the escape latencies from the water maze of the rats in the recurrent-seizure group were significantly longer than those of the control rats, but there was no difference between the single-seizure group and the control group. NR subunit expression in the cerebral cortex and hippocampus of the rats with single seizure was similar to those in the control rats. Compared with the control rats, the protein expressions of NR1, NR2A and NR2B in the cerebral cortex and NR2A in the hippocampus of the recurrent-seizure group was significantly decreased, but NR2C protein expression in the cerebral cortex and hippocampus significantly increased. Recurrent seizures induced in neonatal rats might cause long-term spatial learning ability deficit and modify NR expression in the cerebral cortex and hippocampus of adult rats. The results suggest that abnormal NR expression might play an important role in long-term spatial learning ability deficit induced by recurrent seizures in early life.