Long-term effects of neonatal recurrent seizures on γ-aminobutyric acid A receptor α1 and γ2 subunit expressions in the rat brain

Objective: To investigate the long-term effects of flurothyl-induced neonatal recurrent seizures on GABA A receptor(GABA_AR) α1 and γ2 subunit expressions in adult rat brain,and discuss the relationship between these alterations of GABA_AR subunits in mature brain and the changes of spatial memory and seizure susceptibility in adult rats.Methods: Thirty-two of 7-day-old(P7) Sprague-Dawley rats were divided randomly into two groups: the control group and the seizure group.Seizures were induced by inhalant flurothyl daily for six consecutive days.Rats were tested for spatial memory by using the Morris water maze task from postnatal 61 d(P61) to P65.Seizure threshold was examined by intraperitoneal injection of pentylenetetrazol,and then the brains were sampled on P75.The expressions of GABA_AR α1 and γ2 subunits mRNA and protein in cerebral cortex and hippocampus were detected by reverse transcription-polymerase chain reaction(RT-PCR) and immunohistochemistry method.Results: On P64,the escape latencies in water maze for the rats in the seizure group were significantly longer than those of the control rats [(82 424±35 622)ms vs(40 712±29 468)ms,P=0.001].On P65,the frequency of crossing target within 120 s in water maze for the rats in the seizure group were significantly less than those of the control rats [(1.2±0.9) vs(3.1±1.3),P0.001]. There was no difference in seizure threshold between the two groups on P75 [(1 487±662)s vs(1 841±648)s,P=0.137].Compared to the control rats,the accumulated optical density(AOD) of GABA_AR α1 subunit immunoreactivity in seizure rats decreased significantly in the parietal cortex,CA1-2 and CA4 region(P0.05).The AOD of α1 subunit protein immunoreactivity in the frontal cortex,CA3 and dentate gyrus(DG) were of no significant difference between the two groups on P75(P0.05).There were also no differences in the AOD of γ2 subunit protein immunoreactivity in the parietal lobe,DG,and CA1-3 region between the two groups(P0.05).The AOD of γ2 subunit protein immunoreactivity in the frontal lobe and CA4 region decreased significantly in the seizure group than those in the control group(P0.05).The expressions of α1 subunits mRNA in the cerebral cortex and γ2 subunit mRNA in the hippocampus were similar between the two groups (P0.05),but the expressions of α1 subunits mRNA in the hippocampus and γ2 subunit mRNA in the cerebral cortex in the seizure group decreased significantly as compared with those in the control group(P0.05).Conclusion: Recurrent seizures in neonatal rats modify GABA_A receptor α1 and γ2 subunits expression in the cerebral cortex and hippocampus of adult rats,and cause long-term cognitive deficit,Which suggests that abnormal GABA_A receptor expression might play an important role in long-term cognitive deficit induced by early life recurrent seizures.