Age-Specific Changes of the AMPA Receptor and ADAR Enzyme Expression Profile in the Neonatal Mouse Brain due to Pilocarpine-Induced Seizures

Background: Glutamate excitotoxicity during the acute seizure activity may initiate prolonged apoptosis in the neonatal brain increasing risks for developmental delay and epilepsy. Since calcium-permeable AMPA receptors have important implication in early maturational neuronal and glial programs, we analyzed acute effects of pilocarpine-induced neonatal seizures on age- and region-specific cerebral AMPA receptor and ADAR expression.

Methods: P10 C57BL6/NCrl mice were injected intraperitoneally with Methylscopolamine bromide (1 mg/kg) and Pilocarpine (400 mg/kg). Seizures were terminated by diazepam (5 mg/kg) 90 minutes after seizure onset. Thereafter, tissue preparation was performed after a regeneration period of 1, 24, and 72 hour. Cerebral expression of AMPA subunits and ADAR enzymes was analyzed by real-time RT-PCR. Degree of apoptotic cell death was quantified by TUNEL and caspase 3 staining.

Results: While absolute mRNA concentrations of AMPA receptor subunits GluR1, GluR2, GluR3, and GluR4 were unaffected, composition of the GluR1,2,3,4 mRNA pool changed within 1 hour in pilocarpine-treated mice compared with controls. The relative levels of GluR2 and GluR4 mRNA decreased significantly by 55% and 53%, respectively. Additionally, ADAR1 and ADAR2 mRNA expression was downregulated 24 hour post pilocarpine treatment correlating with significantly increased TUNEL-positive cells in the subventricular zone.

Conclusion: Considering functional role of RNA-edited GluR2 for calcium-permeability of AMPA receptors and based on the present observations, reduced expression of GluR2 and the GluR2-mRNA-editing enzymes ADAR1 and ADAR2 may explain enhanced and region specific activation of caspase 3-mediated apoptosis. Thus, AMPA receptor antagonists might be a promising target for age-specific prevention of excitotoxicity-induced neuronal loss in the developing brain.